## 1. Motivations


 There are many reasons for philosophical interest in nonhuman
animal (hereafter "animal") consciousness:


 First, if philosophy often begins with questions about the place
of humans in nature, one way humans have attempted to locate
themselves is by comparison and contrast with those things in nature
most similar to themselves, i.e., other animals. At least in the
West, the traditional -- and perhaps still intuitive to many
people -- way of thinking about consciousness is as primarily an
innate endowment of humans, which other animals may or may not share
in virtue of being sufficiently like us. Within the traditional
Biblical cosmology, while all animals were said to have arisen through
divine intentional creation, humans were the only ones created in the
likeness of the deity, and thus enjoyed a special, privileged role in
the intended workings of the cosmos -- including, for example,
access to an eternal afterlife not overpopulated with fleas, ants and
snails. (See Lewis, 2009 Ch 9 for an in-depth treatment of the problem
of animal consciousness in relation to Christian theology.) However,
within a modern biological worldview, while humans may be unique in
certain (perhaps quite important) respects, we are only one species of
animal among many -- one tip of one branch of the phylogenetic
tree of life, and enjoy no particular special status. 


From an evolutionary perspective, consciousness is a trait that
some animals have (at least humans have it). Salient questions
include: Is it a late evolved, narrowly distributed trait, or an older
more broadly shared trait? And, did it evolve only once, or a number
of times independently? From this view point, the question "Are
(non-human) animals conscious?" is rather strange, because, for
example, it implicitly groups bats together with rabbits (as
'nonhuman' animals) in contrast to humans. In reality,
rabbits are more closely related to humans than they are to bats
(Nishihara et al. 2006), so framing the question this way embeds a
false presupposition. Of course, it is consistent with an evolutionary
perspective that humans are the only conscious animals. This would
imply that consciousness was acquired through a recent evolutionary
event that occurred since the split of our ancestral lineage from that
of our closest non-human relatives, chimpanzees and bonobos (see
section 6 for discussion of such hypotheses). But such a view requires
support; though perhaps intuitive to some, its choice as a default
position is arbitrary.


 Second, there is a lot at stake morally in the question of whether
animals are conscious beings or "mindless automata". (See
article on the Moral Status of Animals.) Many billions of animals are
slaughtered every year for food, use in research, and other human
purposes. Moreover, before their deaths, many -- perhaps most
-- of these animals are subject to conditions of life that, if
they are in fact experienced by the animals in anything like the way a
human would experience them, amount to cruelty. Arguments that
non-human animals are not conscious therefore effectively double as
apologetics for our treatment of animals. When the question of animal
consciousness is under consideration, our guilt or innocence as a
civilization for an enormous body of cruelty may hang in the
balance. However, some philosophers have argued that consciousness per
se does not matter for the treatment of animals, and therefore either
that a) even if animals are not conscious, they may deserve moral
consideration, or b) even if animals are conscious, they may not
deserve moral consideration. (For more discussion of the ethical
issues, see Singer 1990 [1975]; Regan 1983; Rollin 1989; Varner 1998,
2012; Steiner 2008.)


Third, while theories of consciousness are frequently developed
without special regard to questions about animal consciousness, the
plausibility of such theories has sometimes been assessed against the
results of their application to animal consciousness (and, similarly,
to human infants). This raises questions about the relative epistemic
weight of theoretical considerations (e.g. philosophical arguments for
a given theory of consciousness) against particular case judgments or
intuitions about whether a given creature is conscious. For example,
Searle (1998) argues that our intuitive, commonsense attributions of
intentional and emotional states to dogs carries more epistemic weight
than philosophically motivated skeptical concerns. In contrast,
Carruthers (1989) asserts that his own arguments that nonhuman animals
(even dogs) lack consciousness are sufficiently weighty that we are
morally obligated to eradicate or ignore our sympathetic feelings
toward such creatures. Should our theories of consciousness be
constrained by our intuitive attributions of consciousness to animals
(or, e.g., babies), or should the former override the latter?




 Fourth, the problem of determining whether animals are conscious
 stretches the limits of knowledge and scientific methodology (beyond
 the breaking point, according to some).

The so-called "cognitive revolution" that took place
during the latter half of the 20th century has led to many innovative
experiments by comparative psychologists and ethologists probing the
cognitive capacities of animals. The philosophical issues surrounding
the interpretation of experiments to investigate perception, learning,
categorization, memory, spatial cognition, numerosity, communication,
language, social cognition, theory of mind, causal reasoning, and
metacognition in animals are discussed in the entry
on animal cognition. Despite this
work on cognition, the topic of consciousness per se in animals has
remained controversial, even taboo, among many scientists, while other
scientists from a variety of disciplinary backgrounds
(e.g. neuroscience, animal behavior, evolutionary biology) have
developed novel ways of approaching the subject (see Boly et al. 2013 for a review). The 2012
 Cambridge Declaration on Animal Consciousness 
indicates that many scientists agree that "the weight of evidence
indicates that humans are not unique in possessing the neurological
substrates that generate consciousness." However, other scientists,
including Marian Stamp Dawkins, who has been prominent in the science
of animal welfare (Dawkins 1985, 1993), are not ready to endorse the
claim, writing that, "The mystery of consciousness remains. The
explanatory gap is as wide as ever and all the wanting in the world
will not take us across it" (Dawkins 2012, pp. 171-172).




Many philosophers and scientists have either argued or assumed that
consciousness is inherently private, and hence that one's own
experience is unknowable to others. While language may allow humans to
cross this supposed gap by communicating their experience to others,
this is allegedly not possible for other animals. Despite the
controversy in philosophical and scientific circles, it remains a
matter of common sense to most people that some animals do have
conscious experiences. Most people, if asked why they think familiar
animals such as their pets are conscious, would point to similarities
between the behavior of those animals and human behavior -- for
example, animals seem to visibly express pleasure and displeasure and
a variety of emotions, their behavior seems to be motivated by seeking
food, comfort, social contact, etc., they seem aware of their
surroundings and able to learn from experience. Similarity arguments
for animal consciousness thus have roots in common sense
observations. But they may also be bolstered by scientific
investigations of behavior and the comparative study of brain anatomy
and physiology, as well as considerations of evolutionary continuity
between species. Neurological similarities between humans and other
animals have been taken to suggest commonality of conscious
experience; all mammals share the same basic brain anatomy, and much
is shared with vertebrates more generally. Even structurally different
brains may be neurodynamically similar in ways that enable inferences
about animal consciousness to be drawn (Seth *et
al*. 2005). 




As well as generic arguments about the connections among
consciousness, neural activity, and behavior, a considerable amount of
scientific research directed towards understanding particular
conscious states uses animals as proxies for humans.
The reactions of many animals, particularly other mammals, to bodily
events that humans would report as painful are easily and
automatically recognized by most people as pain
responses. High-pitched vocalizations, fear responses, nursing of
injuries, and learned avoidance are among the responses to noxious
stimuli that are all part of the common mammalian heritage, and
similar responses are also observable in organisms from a wide range
of taxonomic groups (see section 7.1 below).



Much of the research that is of direct relevance to the treatment of
human pain, including on the efficacy of analgesics and anesthetics,
is conducted on rats and other animals. The validity of this research
depends on the similar mechanisms
 involved[1]
 and to many it seems arbitrary to deny that injured rats, who respond
well to opiates for example, feel
 pain.[2] 
Likewise, much of the basic research that is of direct relevance to
understanding human visual consciousness has been conducted on the
very similar visual systems of monkeys. Monkeys whose primary visual
cortex is damaged even show impairments analogous to those of human
blindsight patients (Stoerig & Cowey 1997) suggesting that the
visual consciousness of intact monkeys is similar to that of intact
humans. Scientific demonstrations that members of
other species, even of other phyla, are susceptible to the same visual
illusions as we are (e.g., Fujita *et al*. 1991) suggesting
that their visual experiences are similar.


It is often argued that the use of animals to model
neuropsychiatric disorders presupposes convergence of emotional and
other conscious states and further refinements of those models may
strengthen the argument for attributing such states to animals. 
An interesting reversal of the modeling
relationship can be found in the work of Temple Grandin, Professor of
Animal Science at Colorado State University, who uses her experience
as a so-called "high-functioning autistic" as the basis
for her understanding of the nature of animal experience (Grandin
1995, 2004).




Such similarity arguments are, of course, inherently limited in that
it is always open to critics to exploit some *dis*analogy
between animals and humans to argue that the similarities don't entail
the conclusion that both are sentient. Even when bolstered by
evolutionary considerations of continuity between the species, the
arguments are vulnerable, for the mere fact that humans have a trait
does not entail that our closest relatives must have that trait too.
There is no inconsistency with evolutionary continuity to maintain
that only humans have the capacity to learn to play chess. Likewise
for consciousness. Povinelli & Giambrone (2000) also argue that
the argument from analogy fails because superficial observation of
quite similar behaviors even in closely related species does not
guarantee that the underlying cognitive principles are the same, a
point that Povinelli believes is demonstrated by his research into how
chimpanzees use cues to track visual attention (Povinelli 1996). 




Perhaps a combination of behavioral, physiological and morphological
similarities with evolutionary theory amounts to a stronger overall
case[3].
 However, a convincing argument will
likely also require motivation in terms of a well developed theory of
the structure and function of consciousness as a cognitive process
-- a route that many recent participants in the debate on animal
consciousness have pursued (see section 6).



## 2. Concepts of Consciousness


 The term "consciousness" is notoriously ambiguous and
difficult to define. Having origins in folk psychology,
"consciousness" has a multitude of uses that may not be
resolvable into a single, coherent concept (Wilkes
1984). Nevertheless, several useful distinctions among different
notions of consciousness have been made, and with the help of these
distinctions it is possible to gain some clarity on the important
questions that remain about animal consciousness.




Two ordinary senses of consciousness which are not in dispute when
applied to animals are the sense of consciousness involved when a
creature is awake rather than 
asleep[4],
 or in a coma, and the sense of
consciousness implicated in the basic ability of organisms to perceive
and thereby respond to selected features of their environments, thus
making them conscious or aware of those features. Consciousness in
both these senses is identifiable in organisms belonging to a wide
variety of taxonomic groups (see, e.g., Mather 2008).




A third, more technical notion of consciousness, access consciousness,
has been introduced by Block (1995) to capture the sense in which
mental representations may be poised for use in rational control of
action or speech. This "dispositional" account of access
consciousness -- the idea that the representational content is
available for other systems to use -- is amended by Block (2005)
to include an occurrent aspect in which the content is
"broadcast" in a "global workspace" (Baars
1997) which is then available for higher cognitive processing tasks
such as categorization, reasoning, planning, and voluntary direction
of attention. Block believes that many animals possess access
consciousness (speech is not a requirement). Indeed, some of the
neurological evidence cited by Block (2005) in support of the global
workspace is derived from monkeys. But clearly an author such as
Descartes, who, we will see, denied speech, language, *and*
rationality to animals, would also deny access consciousness to
them. Those who follow Davidson (1975) in denying intentional states
to animals would likely concur.




There are two remaining senses of consciousness that cause more
controversy when applied to animals: *phenomenal consciousness*
and *self-consciousness*.



*Phenomenal consciousness* refers to the qualitative,
subjective, experiential, or phenomenological aspects of conscious
experience, sometimes identified with qualia. (In this article we also
use the term "sentience" to refer to phenomenal
consciousness.) To contemplate animal consciousness in this sense is
to consider the possibility that, in Nagel's (1974) phrase, there
might be "something it is like" to be a member of another
species. Nagel disputes our capacity to know, imagine, or describe in
scientific (objective) terms *what* it is like to be a bat, but
he assumes that there *is* something it is like. 


 For many authors, Nagel's formulation of phenomenal consciousness
as "what it's like" serves as a reference point for what's at stake in
the debate on animal consciousness -- in investigating whether a
group of animals are conscious, the crucial question is whether
there is 'something it is like' to be those animals,
i.e. whether there is a subjective experience of life or being for
them, a proprietary perspective that individuals have on their own
perceptual, cognitive and emotive processes. 


Though some authors (including Nagel himself) have argued that the
very subjectivity of phenomenal consciousness makes it exceedingly
difficult or even impossible to investigate scientifically,
particularly in other species, others have proceeded by developing
structural and/or functional theories of consciousness, and using
these to argue for a particular hypothesis about the distribution of
consciousness among animals. Such theories will be discussed below, in
sections 5 and 6.



*Self-consciousness* refers to a subject's awareness of itself,
but is also a notoriously ambiguous term -- there are importantly
distinct senses in which a subject can be self-aware (see for example
the SEP article on Phenomenological Approaches to
Self-Consciousness). These include: an awareness of one's body as a
physical object, or as the medium of one's own perception and action
(i.e. bodily self-awareness); awareness of one's own mental states
(i.e. mental or experiential self-awareness); awareness of one-self as
perceived by others, or as a member of a social group such as a
family, team, or institution (i.e. social self-awareness); awareness
of one-self as a persistent character in the narratives told by
oneself and others (i.e. narrative self-awareness). This list is far
from exhaustive, and further, each listed notion is subject to
further disambiguation. Hence, although on many theories self-consciousness is
tightly related to phenomenal consciousness, proposals to this effect
can vary greatly in their meaning and their implications for which
animals might be conscious.




The remainder of this article deals primarily with the attribution of
consciousness in its phenomenal sense to animals, although there will
be some discussion of access consciousness, self-consciousness and
theory of mind in animals, especially where these have been related
theoretically to phenomenal consciousness -- as, for instance, in
Carruthers' (1998a,b, 2000) argument that a particular sort of mental
self-representation is required for phenomenal consciousness.


## 3. Historical Background


 Questions about animal consciousness in the Western tradition have
their roots in ancient discussions about the nature of human beings,
as filtered through the "modern" philosophy of
Descartes. It would be anachronistic to read ideas about
consciousness from today back into the ancient literature. Nevertheless, because
consciousness is sometimes thought to be a uniquely human mental
phenomenon, it is important to understand the origins of the idea that
humans are qualitatively (and "qualia-tatively") different
from animals.




Aristotle asserted that only humans had rational souls, while the
locomotive souls shared by all animals, human and nonhuman, endowed
animals with instincts suited to their successful reproduction and
survival. Sorabji (1993) argues that the denial of reason to animals
created a crisis for Greek thought, requiring a "wholesale
reanalysis" (p. 7) of the nature of mental capacities, and a
revision in thinking about "man and his place in nature above
the animals" (ibid.). The argument about what is reasoning, and
whether animals display it, remains with us 25 centuries later, as
evidenced by the volume *Rational Animals?* (Hurley & Nudds
2006). The Great Chain of Being derived from early Christian
interpretation of Aristotle's scale of nature (Lovejoy 1936) provides
another Aristotelian influence on the debate about animal minds.


 Two millennia after Aristotle, Descartes' mechanistic philosophy
introduced the idea of a reflex to explain the behavior of nonhuman
animals. Although his conception of animals treated them as
reflex-driven machines, with no intellectual capacities, it is
important to recognize that he took mechanistic explanation to be
perfectly adequate for explaining sensation and perception --
aspects of animal behavior that are nowadays often associated with
consciousness. He drew the line only at rational thought and
understanding. Given the Aristotelian division between instinct and
reason and the Cartesian distinction between mechanical reflex and
rational thought, it's tempting to map the one distinction onto the
other. Nevertheless, it may be
a mistake to assimilate the two. First, a number of authors before and
after Darwin have believed that conscious experience can accompany
instinctive and reflexive actions. Second, the dependence of
phenomenal consciousness on rational, self-reflective thought is a
particularly strong and contentious claim (although it has current
defenders, discussed below).


 Although the roots of careful observation and experimentation of
the natural world go back to ancient times, study of animal behavior
remained largely anecdotal until long after the scientific
revolution. Animals were, of course, widely used in pursuit of answers
to anatomical, physiological, and embryological questions. Vivisection
was carried out by such ancient luminaries as Galen and there was a
resurgence of the practice in early modern times (Bertoloni Meli
2012). Descartes himself practiced and advocated vivisection
(Descartes, Letter to Plempius, Feb 15 1638), and wrote in
correspondence that the mechanical understanding of animals absolved
people of any guilt for killing and eating animals. Mechanists who
followed him (e.g. Malebranche) used Descartes' denial of reason and a
soul to animals as a rationale for their belief that animals were
incapable of suffering or emotion, and did not deserve moral
consideration -- justifying vivisection and other brutal
treatment (see Olson 1990, p. 39-40, for support of this claim). The
idea that animal behavior is purely reflexive may also have served to
diminish interest in treating behavior as a target of careful study in
its own right.


 A few glimmers of experimental approaches to animal behavior can
be seen in the late 18th century (e.g., Barrington 1773; White 1789),
and soon thereafter Frederic Cuvier worked from 1804
until his death in 1838 on the development of sexual and social
behavior in captive mammals. By the mid 19th century Alfred Russel
Wallace (1867) was arguing explicitly for an experimental approach to
animal behavior, and Douglas Spalding's (1872) experiments on
instinctual feeding behaviors in chicks were seminal. Still, the
emergence of experimental approaches had very little to say about
consciousness per se, though Spalding's work can be seen as a
contribution to the discussion about instinct and reason.




In the same vein of instinct vs. reason, Darwin in the *Origin of
Species* wrote, "It is a significant fact, that the more the
habits of any particular animal are studied by a naturalist, the more
he attributes to reason, and the less to unlearnt instinct"
(1871, Book I, p.46). He devoted considerable attention in both the
*Origin* and in the *Descent of Man* to animal behavior,
with the obvious goal of demonstrating mental continuity among the
species. To make his case, Darwin relied heavily on anecdotes provided
by his correspondents -- a project infamously pursued after
Darwin's death by his protege George Romanes
(1882). Darwin also carried out experiments and was a keen observer,
however. In his final work he describes experiments on the flexibility
of earthworm behavior in manipulating leaves, which he took to show
considerable intelligence (Darwin 1881; see also Crist 2002).


 The idea of behavioral flexibility is central to discussions of
animal mind and consciousness. Descartes' conception of animals as
automata seems to make phenomenal consciousness superfluous at best
-- a connection whose philosophical development was traced by
T.H. Huxley (1874). Huxley reported a series of experiments on a
frog, showing very similar reflexive behavior even when its spinal
cord had been severed, or large portions of its brain removed. He
argued that without a brain, the frog could not be conscious, but
since it could still do the same sort of things that it could do
before, there is no need to assume consciousness even in the presence
of the entire brain, going on to argue that consciousness is
superfluous. (The argument is somewhat curious since it seems to show
too much by making the brain itself superfluous to the frog's
behavior!)




Still, for those (including Huxley) who became quickly convinced of
the correctness of Darwin's theory of evolution, understanding and
defending mental continuity between humans and animals loomed
large. In his *Principles of Psychology* (1890), William James
promoted the idea of differing intensities of conscious experience
across the animal kingdom, an idea that was echoed by the leading
British psychologist of his day, Conwy Lloyd Morgan in his 1894
textbook *An Introduction to Comparative Psychology*. Morgan
had been very skeptical and critical of the anecdotal approach favored
by Darwin and Romanes, but he came around to the Darwinian point of
view about mental continuity if not about methodology. To address the
methodological deficit he introduced his "double
inductive" method for understanding the mental states of animals
(Morgan 1894). The double induction consisted of inductive inferences
based on observation of animal behavior combined with introspective
knowledge of our own minds. At the same time, to counteract the
anthropomorphic bias in the double inductive method, Lloyd Morgan
introduced a principle now known as Morgan's canon: "in no case
may we interpret an action as the outcome of the exercise of a higher
psychical faculty, if it can be interpreted as the outcome of the
exercise of one which stands lower in the psychological scale"
(Lloyd Morgan 1894, p.53).



![double-induction](doubleinduction.jpg)
Lloyd Morgan's Double Induction Method from his 1894 textbook



 Even though the double inductive method is now mainly of
historical interest, Morgan's canon lives on. Questions about quite
what the canon means and how to justify it are active topics of
historical and philosophical investigation (e.g., Burghardt 1985;
Sober 1998, 2005, 2012; Radick 2000; Thomas 2001 (Other Internet
Resources), Fitzpatrick 2008). The questions include what Lloyd Morgan
means by 'higher' and 'lower', to what extent
the principle can or should be justified by evolutionary
considerations, and whether the canon collapses to a principle of
parsimony, a version of Ockham's razor, or some general principles of
empirical justification. Despite current uncertainty about what it
really means, Morgan's canon, interpreted (or, perhaps,
misinterpreted; Thomas 2001, Other Internet Resources) as a strong
parsimony principle, served a central rhetorical role for
behavioristic psychologists, who sought to eliminate any hint of
Cartesian dualism from comparative psychology.


 Behaviorism dominated American psychology in the early part of the
20th century, beginning with Thorndike's (1911) experiments on animals
learning by trial and error to escape from the "puzzle
boxes" that he had constructed. But even Thorndike's famous
"law of effect" refers to the animal's "satisfaction
or discomfort" (1911, p.244). It was with the radical
anti-mentalism of John B. Watson (1928) and B.F. Skinner (1953), both
of whom strongly rejected any attempts to explain animal behavior in
terms of unobservable mental states, that American psychology became
the science of behavior rather than, as the dictionary would have it,
the science of mind and behavior. 


 At the same time, things were progressing rather differently in
Europe, where ethological approaches to animal behavior were more
dominant. Ethology is part natural history with an emphasis on
fieldwork and part experimental science conducted on captive animals,
reflecting the different styles of its two seminal figures, Konrad
Lorenz and Niko Tinbergen (see Burkhardt 2005). Initially,
"innate" behaviors were the central focus of Lorenz's
work. According to Lorenz, it is the investigation of innate behaviors
in related species that puts the study of animal behavior on a par
with other branches of evolutionary biology, and he demonstrated that
it was possible to derive the phylogenetic relations among species by
comparing their instinctive behavioral repertoires (Lorenz 1971a). In
pursuing this direction, Lorenz and Tinbergen explicitly sought to
distance ethology from the purposive, mentalistic, animal psychology
of Bierens de Haan and the lack of biological concern they detected in
American comparative psychology (see Brigandt 2005). Like Lloyd
Morgan, the ethologists rejected Romanes anecdotal approach, but they
also criticized Lloyd Morgan's subjectivist approach.




In the 1970s, Donald Griffin, who made his reputation taking careful
physical measurements to prove that bats use echolocation, made a
considerable splash with his plea for a return to questions about
animal minds, especially animal consciousness. Griffin (1978) coined
the term "cognitive ethology" to describe this research
program, which is based in naturalistic observations of animal
behavior and the attempt to understand animal minds in the context of
evolution.

Fierce criticism of Griffin emerged both from psychologists
and classically trained ethologists. Griffin
emphasized behavioral flexibility and versatility as the chief source
of evidence for consciousness, which he defined as "the
subjective state of feeling or thinking about objects and
events" (Griffin & Speck 2004, p. 6). In seeing
subjectivity, at least in simple forms, as a widespread phenomenon in
the animal kingdom, Griffin's position also bears considerable
resemblance to Lloyd Morgan's. Burghardt reports that
"considerable discomfort with subjectivism" (Burghardt
1985, p. 907) arose during the Dahlem conference that Griffin convened
in an early discipline-building exercise (Griffin 1981). Griffin's
subjectivist position, and the suggestion that even insects such as
honeybees are conscious, seemed to many scientists to represent a
lamentable return to the anthropomorphic over-interpretation of
anecdotes seen in Darwin and Romanes. This criticism may be partly
unfair in that Griffin does not repeat the
"friend-of-a-farmer" kinds of story collected by Romanes,
but bases his interpretations on results from the more sophisticated
scientific literature that had accumulated more than a century after
Darwin (e.g., Giurfa *et al*. 2001). However, the charge of
over-interpretation of those results may be harder to avoid. It is
also important to note the role played by neurological evidence in his
argument, when he concludes that the intensive search for neural
correlates of consciousness has not revealed "any structure or
process necessary for consciousness that is found only in human
brains" (Griffin & Speck 2004). This view is widely although
not universally shared by neuroscientists.




Griffin's behavior-based methodology for studying animal consciousness
has also been dismissed as anthropomorphic (see Bekoff & Allen
1997 for a survey). But such criticisms may have overestimated the
dangers of anthropomorphism (Fisher 1990) and many of the critics
themselves rely on claims for which there are scant scientific data
(e.g., Kennedy 1992, who claims that the "sin" of
anthropomorphism may be programmed into humans genetically). At the
same time, other scientists, whether or not they have explicitly
endorsed Griffin's program, have sought to expand evolutionary
investigation of animal consciousness to include the neurosciences and
a broad range of functional considerations (e.g., Arhem *et
al*. 2002, and see section 6). Whatever the shortfalls of his
specific proposals, Griffin played a crucial role in reintroducing
explicit discussions of consciousness to the science of animal
behavior and cognition, hence paving the way for modern investigations
of the distribution and evolutionary origins of consciousness. 


## 4. Epistemological and Metaphysical Issues


The topic of consciousness in nonhuman animals has been primarily
of epistemological interest to philosophers of mind. Two central
questions are:


1. Can we know which animals beside humans are conscious? (The
Distribution
 Question)[5]
2. Can we know what, if anything, the experiences of animals are like?
(The Phenomenological Question)



In his seminal paper "What is it like to be a bat?" Thomas
Nagel (1974) simply assumes that there *is* something that it
is like to be a bat, and focuses his attention on what he argues is
the scientifically intractable problem of knowing what it is
like. Nagel's confidence in the existence of conscious bat experiences
would generally be held to be the commonsense view and, as the
preceding section illustrates, a view that is increasingly taken for
granted by many scientists too. But, as we shall see, it is subject to
challenge and there are those who would argue that the Distribution
Question is just as intractable as the Phenomenological Question.


### 4.1 The Problem of Other Minds


The two questions might be seen as special cases -- or,
alternatively, as generalized versions -- of the skeptical
"problem of other minds" -- how can one know that
others have mental states that are anything like one's own? Although
there is no generally accepted solution to this problem, it is
nevertheless generally ignored to good effect by psychologists, and
indeed by most people, who in practice are willing to take for granted
that others have mental states similar to theirs. However it is often
thought that knowledge of animal minds presents special methodological
difficulties. First of all, nonhuman animals cannot describe their
mental states using language. Although there have been attempts to
teach human-like languages to members of other species, none has
reached a level of conversational ability that would solve this
problem directly (see Anderson 2004 for a review). Furthermore, except
for some language-related work with parrots and dolphins, such
approaches are generally limited to those animals most like ourselves,
particularly the great apes. But there is great interest in possible
forms of consciousness in a much wider variety of species than are
suitable for such research. More generally, the problem of other
minds is more acute when applied to nonhuman animals because the
similarities between our behavior and bodies, and those of others
animals (which form the basis for 'analogical' solutions
to the problem of other minds) are less exact. As well, the perceptual
access to other minds that some have argued defuses the problem of
other minds is arguably weaker regarding the minds of other animals.
(Sober (2000) discusses of the problem of other minds within an
evolutionary framework, and Farah 2008 provides a neuroscientist's
perspective.)


### 4.2 The Epistemic Status of Intuitions and Perception of Mental States


 For many people it seems obvious that familiar animals such as
dogs and cats have conscious mental lives that include perceptual
states, motivational and hedonic states, basic emotions and social
attachments. David Hume, known for championing skepticism generally,
wrote that "no truth appears to me more evident, than that beasts are
endow'd with thought and reason as well as men" (1888 p 176,
reproduced in Jamieson 1998). Hume did not provide elaborate
philosophical or empirical arguments to this effect -- he thought
it was clear from observation. As Searle (1998) puts it,



> 
>  I do not infer that my dog is conscious, any more than, when I came
> into this room, I inferred that the people present are conscious. I
> simply respond to them as is appropriate to conscious beings. I just
> treat them as conscious beings and that is that.
>  



What is the epistemic status of such pretheoretical intuitions (if
that is indeed a fair way of describing them)?



 Defenders of theories that deny consciousness to such animals must
deny that such intuitions have any epistemic weight. For example
Dennett (who argues that consciousness is unique to humans), claims
that intuitive attributions of mental states are "untrustworthy", and
points out that "it is, in fact, ridiculously easy to induce powerful
intuitions of not just sentience but full-blown consciousness (ripe
with malevolence or curiosity) by exposing people to quite simple
robots  *made to move in familiar mammalian ways at mammalian speeds* (1995)." (Emphasis from the original.)


 Carruthers (1989) acknowledges that intuitive attributions of
consciousness to animals are widespread, and go hand in hand with
sympathetic attitudes toward animals (e.g. wanting to prevent
suffering). However, he argues that these attitudes are incorrect, and
we have a moral imperative to purge or at least override them:



> In the case of brutes: since their experiences, including
> their pains, are nonconscious ones, their pains are of no immediate
> moral concern... Neither the pain of the broken leg, itself, nor its
> further effects upon the life of the dog, have any rational claim upon
> our sympathy... Are we really capable of suppressing our sympathy when
> we see an animal (especially a cuddly one) in severe pain? Not only is
> it possible that this should occur -- after all, the history of
> mankind is replete with examples of those who have eradicated all
> feelings of sympathy even for members of other races, by telling
> themselves that they are not 'really human' -- but it
> is a moral imperative that it ought to. Much time and money is
> presently spent on alleviating the pains of brutes which ought
> properly to be directed toward human beings, and many are now
> campaigning to reduce the efficiency of modern farming methods because
> of the pain caused to the animals involved. If the arguments presented
> here have been sound, such activities are not only morally
> unsupportable but morally objectionable (Carruthers 1989,
> p. 268). 


It should be noted that while Carruthers continues to argue that
only humans have consciousness, he has more recently amended his
ethical view, holding that animals may deserve some moral concern
despite lacking consciousness (1999).



A crucial point here is how trustworthy these pretheoretic intuitions
about the minds of animals are. Call *Perceptualism* the view
that there is direct perception of (at least some) mental states of
others. What this means is that, at least sometimes, when we observe
another in a mental state (e.g. in joy, or in pain) their mental state
is part of the content of our perception -- we perceive the
mental states of others. In contrast, call *inferentialism* the
view that we perceive 'mere behavior' and must infer or
reason to conclusions about mental states. An alternative way of
framing the issues is in terms of whether or not behavior as we
perceive it is laden with mental properties. According to
perceptualism, we (at least sometimes) perceive states of mind
*in* behavior -- an action (e.g. walking across a room) can
be perceivably angry or sad, purposeful or eager or hesitant,
etc. Goals, desires, motivations, emotions, pain or pleasure, and many
other mental states are manifested in modes of action -- though
they cannot be reduced to patterns of disposition to behave (this
would amount to behaviorism), they are tightly linked to behavior by
conceptual, constitutive or causal connections that ground perceptual
access.


Jamieson (1998) argues for perceptualism, pointing out that our
everyday practices of attributing mental states to nonhuman animals
are deeply ingrained, automatic, conceptually unifying and empirically
powerful. Strands of the same point of view can also be found in
scientists writing about cognitive ethology and in
Wittgensteinian attitudes towards questions of animal mind (e.g.,
Gaita 2003). Perceptualism as a theory of social cognition
(e.g. empathy) in philosophy of psychology has recently been defended
by Zahavi (2011) and Gallagher (2008).


 The Perceptualism/Inferentialism question is critical for the
deciding the epistemic value of common sense attributions of mental
states to nonhuman animals. If inferentialism is true, then when I
see, e.g., a dog bounding around in front of me with a toy in its
mouth, wagging its tail and looking at me, then I may consider the
possibility that the dog *wants* my attention, that it is feeling
*happy* and *playful* -- but this is only a hypothesis,
for which I must provide a solid argument from justified premises if I
am to justifiably believe it. On a perceptualist account, by contrast,
I literally see (or at least, seem to see) that the dog *wants*
my attention and feels *happy* and *playful*.


 Perception is usually understood to ground defeasible epistemic
warrant for belief -- for example, if you look outside and it
appears to be raining, you have some grounds to believe that it is
raining. It is difficult to forgo this assumption without succumbing
to radical global skepticism, since we base so many of our beliefs on
perception. If seeming to perceive something to be the case provides
defeasible epistemic warrant for believing it to be the case, than the
fact the I seem to perceive a dog as being happy and playful warrants
my belief that the dog is happy and playful, i.e. warrants my
ascription of mental states to the dog. Given the prima facie
epistemic support of seeming to perceive mental states in familiar
animals like dogs, perceptualists would argue that only overwhelming
evidence should overturn the common-sense, intuitive attribution of
mental states to those animals. Whereas, as discussed above,
Carruthers (1989) argues that because his theory denies consciousness
to animals, we should strive to eradicate our intuitive attributions
of consciousness, a perceptualist would respond that the evidence
derived from our perceptual encounters with dogs is more convincing
than his arguments (which hang on the plausibility of his higher order
thought theory of consciousness; see section 6.1). 


 Nevertheless, even if we have perceptual access to the mental
states of other humans and familiar animals like our pet dogs, there
are sharp limitations to how far this will get us toward solving the
general problem of animal consciousness. First of all, our perceptual
access may be limited to animals that are familiar, comfortable
interacting with humans, and biologically very similar to humans
(i.e. mammals). It may be much harder to 'see' what (if
anything) a spider or a squid is thinking and feeling as she goes
about her business -- both because these animals may express
their mental states differently, and more radically because they may
have a very different repertoire of mental states.


 Second, as argued by Dennett, there are examples where our
perceptions of mental states can be deceived -- so Dennett seems
to embrace perceptualism, but to hold that perceptions of mental
states are particularly unreliable. However, Dennett's favored example
of the robot
 'Cog',
 unlike nonhuman animals, was
intentionally designed by human engineers to seem life-like, i.e., to
mimic the dynamical properties of motion that trigger the perception
of mindedness. Hence, there may be no more reason to fear that our
seeming perceptions of mind in others are undermined by such examples
than to fear that our perception of objects in space is undermined by
the existence of photography -- in both cases, human engineers
can be characterized as having figured out ways of creating perceptual
illusions. There are deep questions about how perception of bodies in
motion might disclose the mental states of others -- just as
there are deep questions about how visual perception of objects in
space is generally possible. But, *pace* Dennett, there is no
clear reason why the existence of carefully crafted illusions
undermines the general epistemic value of perception.



 Third, even among scientists who are sympathetic to the idea of
themselves as sensitive observers of animals with rich mental lives,
there is the recognition that the scientific context requires them to
provide a particular kind of empirical justification of mental state
attributions. This demand requires those who would say that a tiger
pacing in the zoo is "bored", or that the hooked fish is
in pain to define their terms, state empirical criteria for their
application, and provide experimental or observational evidence for
their claims. Even if perceptualism is a viable theory of folk
practice with respect to attributing animal consciousness, it seems
unlikely to make inroads against scientific epistemology. 


### 4.3 Cognition and Consciousness


Many scientists and philosophers remain convinced that even if some
questions about animal minds are empirically tractable, no amount of
experimentation can provide access to  *phenomenal consciousness* per se. This remains true even among those who are willing to
invoke cognitive explanations of animal behavior that advert to
internal representations. Opposition to dealing with consciousness can
be understood in part as a legacy of behavioristic psychology first
because of the behaviorists' rejection of terms for unobservables
unless they could be formally defined in terms of observables, or
otherwise operationalized experimentally, and second because of the
strong association in many behaviorists' minds between the use of
mentalistic terms and the twin bugaboos of Cartesian dualism and
introspectionist psychology. In some cases
these scientists are even dualists themselves, but they are strongly
committed to denying the possibility of scientifically investigating
consciousness, and remain skeptical of all attempts to bring it into
the scientific mainstream.


Also important has been a line of argumentation by philosophers
that the subjective nature of consciousness makes it inherently
difficult to study. Block's (1995) influential distinction between
phenomenal and access consciousness was framed as part of a critique of
treatments of consciousness in the psychological literature: by
failing to properly distinguish between consciousness as experience
(phenomenal consciousness) and consciousness as general availability
of information (access consciousness), scientists were equivocating
-- drawing conclusions about consciousness in the phenomenal
sense from premises about consciousness in the access sense. The
conceptual distinction between access consciousness and phenomenal
consciousness, and the difficulty of gaining empirical traction on the
latter, has been seen as a major hurdle to empirical consciousness
studies. Block himself has recently been more optimistic, even arguing
that certain experiments can empirically tease apart phenomenal and
access consciousness (Block 2011). But the distinction between access
and phenomenal consciousness does raise special methodological hurdles
for those who want to study the latter empirically.




Because consciousness is assumed to be private or subjective, it is
often taken to be beyond the reach of objective scientific methods
(e.g., Nagel 1974). This claim might be taken in either of two
ways. On the one hand it might be taken to bear on the possibility of
answering the Distribution Question, i.e., to reject the possibility
of knowledge that a member of another taxonomic group (e.g., a bat)
has conscious states. On the other hand it might be taken to bear on
the possibility of answering the Phenomenological Question, i.e., to
reject the possibility of knowledge of the phenomenological details of
the mental states of a member of another taxonomic group. The
difference between believing with justification *that* a bat is
conscious and knowing *what* it is like to be a bat is
important because, at best, the privacy of conscious experience
supports a negative conclusion only about the latter. To support a
negative conclusion about the former, one must also assume that
consciousness has absolutely no measurable effects on behavior, i.e.,
one must accept epiphenomenalism.
But if one rejects epiphenomenalism and maintains that consciousness
does have effects on behavior then a strategy of inference to the best
explanation may be used to support its attribution. Moreover, if
particular conscious states have particular effects on behavior, then
this strategy might be pursued to elucidate some specific features of
the conscious experience of other animals, even if some aspects must
remain out of reach because of our inability, as humans, to fully
grasp what it would be like to experience them. More will be said
about this in the next section.




If phenomenal consciousness is completely epiphenomenal, as some
philosophers believe, then a search for the functions of consciousness
is doomed to futility. In fact, if consciousness is completely
epiphenomenal then it cannot have evolved by natural selection. On the
assumption that phenomenal consciousness is an evolved characteristic
of human minds, at least, and therefore that epiphenomenalism is
false, then an attempt to understand the biological functions of
consciousness may provide the best chance of identifying its
occurrence in different species. (See Robinson 2007 for more
discussion of this issue.)


### 4.4 Dualism and Physicalism




While epistemological and related methodological issues have been at
the forefront of discussions about animal consciousness, philosophical
attention to consciousness in the analytic tradition over the last
several decades has focused on metaphysical questions about the nature
of phenomenal consciousness and its fit (or lack thereof) within a
naturalistic framework.


One might think that the question of what consciousness is
(metaphysically) should be settled prior to tackling the Distribution
Question -- that ontology should drive the epistemology.
However, the metaphysical questions that have occupied analytic
philosophers over the last few decades are largely orthogonal to the
distribution problem, which depends more on questions about the
*structure* and *function* of consciousness, discussed
below.


 The traditional 'Mind Body Problem' concerns the
metaphysical status of mind in relation to the physical world (see SEP
article on dualism). Dualists argue that the
mental and physical are fundamentally distinct, whereas physicalists
hold that the mind is physical -- and therefore not distinct,
despite supposed appearances to the contrary. A third alternative is
idealism, the view that the physical world is actually mental (and
therefore that the two are not really distinct).


Dualistic theories of consciousness typically deny that it can be
accounted for in the current terms of the natural
sciences. Traditional dualists may argue that the reduction of
consciousness to physically describable mechanisms is impossible on
any concept of the physical. Others may hold that consciousness is an
as-yet-undescribed fundamental constituent of the physical universe,
not reducible to any known physical principles. Such accounts of
consciousness (with the possible exception of those based in
anthropocentric theology) provide no principled reasons, however, for
doubting that animals are conscious.


 Cartesian dualism is, of course, traditionally associated with the
view that animals lack minds. Descartes' argument for this view was
not based, however, on any ontological principles, but upon what he
took to be the failure of animals to use language rationally, or to
reason generally. On this basis he claimed that nothing in animal
behavior requires a non-mechanistic, mental explanation; hence he saw
no reason to attribute possession of mind to animals. In a sense,
therefore, the Cartesian argument for the human-uniqueness of
consciousness rests on the premise that material processes are
insufficient to account for human capacities for language,
rationality, and self-awareness (i.e. the awareness of oneself as,
putatively, an essentially thinking thing) -- and hence a
non-material soul was posited to account for these phenomena. Few
today would hold that material processes are incapable of producing
complex phenomena such as language and rationality, and indeed our
understanding of 'the material' has changed dramatically
since Descartes' time. However, the subjective nature of consciousness
continues to motivate some authors to argue that mental phenomena
cannot be reduced to physical phenomena.



There is no conceptual reason why animal bodies are any less suitable
vehicles for embodying a Cartesian soul, or any other of the
putatively non-physical aspects of mind posited by proponents of
dualism, than are human bodies. Hence, dualism does not preclude
animal minds as a matter of conceptual necessity. The distribution of
consciousness is a matter of empirical contingency on dualist theories
as for physicalist theories. For some dualists, this may come down to
whether or not the animals in question possess specific cognitive
capacities, although others may argue that the non-physical nature of
the mental makes it difficult or impossible to investigate
empirically. 




Early physicalist accounts of consciousness explored the philosophical
consequences of identifying consciousness with unspecified physical or
physiological properties of neurons. In this generic form, such
theories do not provide any particular obstacles to attributing
consciousness to animals, given that animals and humans are built upon
the same biological, chemical, and physical principles. If it could
be determined that phenomenal consciousness was identical to (or at
least perfectly correlated with) some general property such as quantum
coherence in the microtubules of neurons, or brain waves of a specific
frequency, then settling the Distribution Question would be a
straightforward matter of establishing whether or not members of other
species possess the specified properties. Searle (1998) too, although
he rejects the physicalist/dualist dialectic, also suggests that
settling the Distribution Question for hard cases like insects will
become trivial once neuroscientists have carried out the non-trivial
task of determining the physiological basis of consciousness in
animals for which no reasonable doubt of their consciousness can be
entertained (i.e., mammals). 


### 4.5 Neurofunctional Accounts



Some philosophers have sought more specific grounding in the
neurosciences for their accounts of consciousness. Block (2005)
pursues a strategy of using tentative functional characterizations of
phenomenal and access consciousness to interpret evidence from the
search by neuroscientists for neural correlates of consciousness. He
argues, on the basis of evidence from both humans and monkeys, that
recurrent feedback activity in sensory cortex is the most plausible
candidate for being the neural correlate of phenomenal consciousness
in these species. Prinz (2005) also pursues a neurofunctional
account, but identifies phenomenal consciousness with a different
functional role than Block. He argues for identifying phenomenal
consciousness with brain processes that are involved in attention to
intermediate-level perceptual representations which feed into working
memory via higher level, perspective-invariant representations. Since
the evidence for such processes is at least partially derived from
animals, including other primates and rats, his view is supportive of
the idea that phenomenal consciousness is found in some nonhuman
species (presumably most mammals). Nevertheless, he maintains that it
may be impossible ever to answer the Distribution Question for more
distantly related species; he mentions octopus, pigeons, bees, and
slugs in this context.


### 4.6 Representationalist Accounts



Representational theories of consciousness
 link phenomenal consciousness with the
representational content of mental states, subject to some further
functional criteria. 



First-order representationalist accounts hold that if a particular
state of the visual system of an organism represents some property of
the world in a way that is functionally appropriate (e.g., not
conceptually mediated, and operating as part of a sensory system),
then the organism is phenomenally conscious of that
property. First-order accounts are generally quite friendly to
attributions of consciousness to animals, for it is relatively
uncontroversial that animals have internal states that have the
requisite functional and representational properties (insofar as
mental representation itself is uncontroversial, that is). Such a view
underlies Dretske's (1995) claim that phenomenal consciousness is
inseparable from a creature's capacity to perceive and respond to
features of its environment, i.e., one of the uncontroversial senses
of consciousness identified above. On Dretske's view, phenomenal
consciousness is therefore very widespread in the animal kingdom.
Likewise, Tye (2000) argues, based upon his first-order
representational account of phenomenal consciousness, that it extends
even to honeybees. 


 Driven by a variety of allegedly counter-intuitive consequences of
first-order theories of consciousness, including skepticism about the
range of organisms it spans, a number of philosophers have offered a
variety of higher-order accounts of phenomenal consciousness. Such
accounts invoke mental states directed towards other mental states to
explain phenomenal consciousness. Carruthers' "higher order
thought" (HOT) theory is that a mental state is phenomenally
conscious for a subject just in case it is available to be thought
about directly by that subject (Carruthers 1998a,b, 2000). The term
"available" here makes this a
"dispositionalist" account. The contrast is an
"actualist" account, which requires the actual occurrence
of the 2nd order thought for subject to be conscious in the relevant
sense. According to Carruthers, such higher-order thoughts are not
possible unless a creature has a "theory of mind" to
provide it with the concepts necessary for thought about mental
states. Carruthers' view is of particular interest in the current
context because he has used it explicitly to deny phenomenal
consciousness to (almost) all nonhuman animals. 



Carruthers argues, there is little, if any, scientific support for
theory of mind in nonhuman animals, even among the great apes --
with the possible exception of chimpanzees -- from which he
concludes that there is little support either for the view that any
animals possess phenomenological consciousness. Further evaluation of
this argument will be taken up further below, but it is worth noting
here that if (as experiments on the attribution of false beliefs
suggest) young children before the age of four years typically lack a
theory of mind, Carruthers' view entails that they are not sentient
either -- fear of needles notwithstanding! This is a bullet
Carruthers bites, although for many it constitutes a *reductio*
of his view (a response Carruthers would certainly regard as
question-begging).




In contrast to Carruthers' higher-order *thought* account of
sentience, other theorists such as Armstrong (1980), and Lycan (1996)
have preferred a higher-order *experience* account, where
consciousness is explained in terms of inner perception of mental
states, a view that can be traced back to Aristotle, and also to John
Locke. Because such models do not require the ability to conceptualize
mental states, proponents of higher-order experience theories have
been slightly more inclined than higher-order theorists to allow that
such abilities may be found in other 
animals[6].
 Gennaro (2004) argues, however, that a higher order *thought* theory is
compatible with consciousness in nonhuman animals, arguing that
Carruthers and others have overstated the requirements for the
necessary mental concepts and that reentrant pathways in animal brains
provide a structure in which higher- and lower-order representations
could actually be combined into a unified conscious state.


### 4.7 Is Consciousness Binary?


 One metaphysical question that is more directly relevant for the
question of the phylogenetic distribution and evolution of
consciousness is whether possessing it (i.e. being conscious) is
binary (i.e. on/off, all-or-nothing), or admits of degrees. Several
authors have, for quite different reasons, denied what they take to be
a common but problematic assumption -- that "Consciousness is an
on/off switch; a system is either conscious or not," as Searle --
who endorses the thesis puts it (quoted by Lycan 1996, who denies the
thesis).




Lycan argues that consciousness can come in a wide spectrum of degrees
of richness or fullness of consciousness, and that there is a
meaningful sense in which a system with a minimal degree of
consciousness is not "really" conscious (1996, p. 8). Admittedly, this
sounds a bit paradoxical, but the point seems to be that it is
counter-intuitive for us to consider very low degrees of
consciousness, as it is hard to imagine the contents of very simple
mental states. One reading of this is that Lycan is arguing that the
predicate 'conscious' is vague, without committing himself
to the view that consciousness is distributed according to a linear
scale.



Dennett (1995) also argues that consciousness is not binary. He does
so in the context of advocating a radically deflationary anti-realism
about consciousness overall, on which consciousness is essentially an
illusion created by language (1991/1995). On his view, "the very idea
of there being a dividing line between those creatures 'it is
like something to be' and those that are 'mere
automata' (is) an artifact of our traditional assumptions."
(1995, p. 706)



 Velmans (2012) distinguishes between 'discontinuity
theories', which claim that there was a particular point at
which consciousness originated, before which there was no
consciousness (this applies both the universe at large, and also
to any particular consciousness individual), and 'continuity
theories', which conceptualize the evolution of consciousness in
terms of "a gradual transition in consciousness from unrecognizable to
recognizable." He argues that continuity theories are more elegant, as
any discontinuity is based on arbitrary criteria, and that
discontinuity theories face "the hard problem" in a way that
continuity theories don't. Velmans takes these arguments to weigh in
favor of adopting, not just a continuity theory, but a form of
panpsychism.



The three authors described just above deny that consciousness is
binary for very different reasons, and each of their views is
controversial. Further, none of them offers much in the way of tools
or concepts for thinking about the putatively nonbinary nature of
consciousness. Following up on Lycan's suggestion of degrees of
richness or fullness, one might ask what graded dimensions or
qualitative thresholds might be available to distinguish different
kinds of minds? Various authors have distinguished between
'primary' and 'higher order' consciousness
(Seth et al. 2005); 'primary', 'secondary',
and 'tertiary' consciousness (Panksepp 2005); and
'core' and 'extended' consciousness (Damasio
1999). However, most of these authors seem to correlate phenomenal
consciousness, i.e. having any subjective experience at all, with
primary or core consciousness. The terms "secondary" and
"tertiary" are supposed to pick out elaborated forms of
consciousness. Hence it is not clear that any of these taxonomies are
at odds with the idea that phenomenal consciousness itself is binary
-- either wholly present or wholly absent for a given
system. However, the issue deserves more scrutiny, as it bears on the
problems of the distribution and evolutionary origins of
consciousness. If consciousness is non-binary, then the distribution
of consciousness will not be sharply bounded, but will include
gradations -- some animals may be partially or incompletely
conscious.



### 4.8 Limits of Philosophical Theories




Phenomenal consciousness is just one feature (some would say the
defining feature) of mental states or events. Any theory of animal
consciousness must be understood, however, in the context of a larger
investigation of animal cognition that (among philosophers) will also
be concerned with issues such as intentionality (in the sense
described by the 19th C. German psychologist Franz Brentano) and
mental content (Dennett 1983, 1987; Allen 1992a,b).




Philosophical opinion divides over the relation of consciousness to
intentionality with some philosophers maintaining that they are
strictly independent, others (particularly proponents of the
functionalist theories of consciousness described in this section)
arguing that intentionality is necessary for consciousness, and still
others arguing that consciousness is necessary for genuine
intentionality. Many behavioral
scientists accept cognitivist explanations of animal behavior that
attribute representational states to their subjects. Yet they remain
hesitant to attribute consciousness. If the representations invoked
within cognitive science are intentional in Brentano's sense, then
these scientists seem committed to denying that consciousness is
necessary for intentionality.



There remains great uncertainty about the metaphysics of phenomenal
consciousness and its precise relations to intentionality, to the
brain, to behavior, etc. It is beyond the scope of this article to
survey the strong attacks that have been mounted against the various
accounts of consciousness in these terms, but it is safe to say that
none of them seems secure enough to hang a decisive endorsement or
denial of animal consciousness upon it. Accounts of consciousness in
terms of basic neurophysiological properties, the quantum-mechanical
properties of neurons, or *sui generis* properties of the
universe are just as insecure as the various functionalist
accounts. And even those accounts that are compatible with animal in
their general outline, are not specific enough to permit ready answers
to the Distribution Question in its full generality. Hence no firm
conclusions about the distribution of consciousness can be drawn on
the basis of the philosophical theories of consciousness that have
been discussed so far.


 Where does this leave the epistemological questions about animal
consciousness? While it may seem natural to think that we must have a
theory of what consciousness is before we try to determine whether
other animals have it, this may in fact be putting the conceptual cart
before the empirical horse. In the early stages of the scientific
investigation of any phenomenon, putative samples must be identified
by rough rules of thumb (or working definitions) rather than complete
theories. Early scientists identified gold by contingent
characteristics rather than its atomic essence, knowledge of which had
to await thorough investigation of many putative examples -- some
of which turned out to be gold and some not. Likewise, at this stage
of the game, perhaps the study of animal consciousness would benefit
from the identification of animal traits worthy of further
investigation, with no firm commitment to idea that all these examples
will involve conscious experience. 


Recall the Cartesian argument that animals do not use language
conversationally or reason generally. This argument, based on the
alleged failure of animals to display certain intellectual capacities,
is illustrative of a general pattern of using certain
*dissimilarities* between animals and humans to argue that
animals lack consciousness.




A common refrain in response to such arguments is that, in situations
of partial information, "absence of evidence is not evidence of
absence". Descartes dismissed parrots vocalizing human words
because he thought it was merely meaningless repetition. This judgment
may have been appropriate for the few parrots he encountered, but it
was not based on a systematic, scientific investigation of the
capacities of parrots. Nowadays many would argue that Pepperberg's
study of the African Grey parrot "Alex" (Pepperberg 1999)
should lay the Cartesian prejudice to rest. This study, along with
several on the acquisition of a degree of communicative competence by
chimpanzees and bonobos (e.g., Gardner *et al*. 1989;
Savage-Rumbaugh 1996) would seem to undermine Descartes' assertions
about lack of meaningful communication and general reasoning abilities
in animals. (See, also, contributions to Hurley & Nudds 2006.)




Cartesians respond by pointing out the limitations shown by animals in
such studies (they can't play a good game of chess, after all, let
alone tell us what they are thinking about), and they join linguists
in protesting that the subjects of animal-language studies have not
fully mastered the recursive syntax of natural human
languages.[7]
 But this kind of post hoc raising of
the bar suggests to many scientists that the Cartesian position is not
being held as a scientific hypothesis, but as a dogma to be defended
by any means. Convinced by evidence of sophisticated cognitive
abilities, most philosophers these days agree with Block that
something like access consciousness is properly attributed to many
animals. Nevertheless, when it comes to phenomenal consciousness,
dissimilarity arguments are not entirely powerless to give some pause
to defenders of animal sentience, for surely most would agree that, at
some point, the dissimilarities between the capacities of humans and
the members of another species (the common earthworm *Lumbricus
terrestris*, for example) are so great that it is unlikely that
such creatures are sentient. A grey area arises precisely because no
one can say how much dissimilarity is enough to trigger the judgment
that sentience is absent.


The aim of picking out, in a principled way, behavioral or
neurophysiological characteristics that could serve as reliable
indicators for consciousness motivates the structure and function
oriented approach that many authors have pursued since the turn of the
21st century. Though sometimes pursued along with metaphysical
questions about consciousness, this project promises empirical
tractability even in the face of persistent uncertainty about the
metaphysical questions of consciousness.


## 5. The Structure and Function of Consciousness



One strategy for bringing consciousness into the scientific fold is to
try to articulate a theoretical basis for connecting the observable
characteristics of animals (behavioral or neurological) to
consciousness. What effects should consciousness have on behavior?
What capacities and dispositions should we expect a conscious creature
to have that might be absent in a nonconscious creature? What
neurophysiological structures and processes might realize the dynamics
or information processing required for consciousness?



 Such an approach is nascent in Griffin's attempts to force
ethologists to pay attention to questions about animal consciousness,
in all its senses -- including phenomenal consciousness. In a
series of books, Griffin (who made his scientific reputation by
carefully detailing the physical and physiological characteristics of
echolocation by bats) provides examples of communicative and
problem-solving behavior by animals, particularly under natural
conditions, and argues that these are prime places for ethologists to
begin their investigations of animal consciousness (Griffin 1976,
1984, 1992).


 Although he thinks that the intelligence displayed by these
examples suggests conscious thought, many critics have been
disappointed by the lack of systematic connection between Griffin's
examples and the attribution of consciousness (see, e.g., Alcock 1992).
Griffin's main positive
proposal in this respect has been the rather implausible suggestion
that consciousness might have the function of compensating for limited
neural machinery. Thus Griffin is motivated to suggest that
consciousness may be more important to honey bees than to humans.




If compensating for small sets of neurons is not a plausible function
for consciousness, what might be? The commonsensical answer would be
that consciousness "tells" the organism about events in
the environment, or, in the case of pain and other proprioceptive
sensations, about the state of the body. But this answer begs the
question against opponents of attributing conscious states to animals
for it fails to respect the distinction between phenomenal
consciousness and mere awareness (in the uncontroversial sense of
detection) of environmental or bodily events. Opponents of attributing
phenomenal consciousness to animals are not committed to denying the
more general kind of consciousness *of* various external and
bodily events, so there is no logical entailment from awareness of
things in the environment or the body to animal sentience.




Perhaps more sophisticated attempts to spell out the functions of
consciousness are similarly doomed. But Allen & Bekoff (1997, ch.
8) suggest that progress might be made by investigating the capacities
of animals to adjust to their own perceptual errors. Not all
adjustments to error provide grounds for suspecting that consciousness
is involved, but in cases where an organism can adjust to a perceptual
error while retaining the capacity to exploit the content of the
erroneous perception, then there may be a robust sense in which the
animal internally distinguishes its own appearance states from other
judgments about the world. (Humans, for instance, have conscious
visual experiences that they know are misleading -- i.e., visual
illusions -- yet they can exploit the erroneous content of these
experiences for various purposes, such as deceiving others or
answering questions about how things *appear* to them.) Given
that there are theoretical grounds for identifying conscious
experiences with "appearance states", attempts to discover
whether animals have such capacities might be a good place to start
looking for animal consciousness. It is important, however, to
emphasize that such capacities are not themselves intended to be
definitive or in any way criterial for consciousness.

Carruthers (2000) makes a similar suggestion about the function of
consciousness, relating it to the general capacity for making an
appearance-reality distinction; of course, he continues to maintain
that this capacity depends upon having conceptual resources that are
beyond the grasp of nonhuman animals.



The broad issue of function is closely related to questions about just
what sort of mental process consciousness is. As we shall see in the
next section, hypotheses in the modern literature on the distribution
and evolution of consciousness are therefore generally advanced
together with theories of its structure and function in the following
senses:




Structure: what are the contents of consciousness (what information,
representations, intentional contents, properties, processes,
etc. does it include)? What (possibly unconscious or subconscious)
information, representations, or other cognitive or intentional
processes, entities and relations, are required for consciousness?




Function: how does consciousness relate to other (nonconscious)
processes, in cognition, the body and the environment? How does
possessing consciousness contribute to an animal's ability to navigate
and respond adaptively to its environment, to survive and thrive?



 Different views about what consciousness is, qua cognitive
process, and how it relates to other biological processes such as
behavior, development and ecological interaction, largely determine
biologically oriented views about which animals have consciousness and
when, how, and why it evolved. To illustrate this, we can start with a
crude distinction between views that see consciousness as fundamental
to the basic perceptual and cognitive processes involved in
controlling an animal body, or as something that can be added on or
plugged in to a system that is already sufficient for basic control of
perception-guided action. The more fundamental consciousness is to
basic animal functioning, the more widely distributed and ancient
consciousness must be; if, however, consciousness is relatively
modular, functionally narrow, and conceptually high level, then it
should be narrowly distributed among animals and relatively recently
evolved. The views surveyed in the following section all exploit the
connections between function, structure, distribution and evolutionary
origin. 


 One further point worth noting is that structural models of
consciousness are usually justified in terms of phenomenological or
introspective observations -- i.e. observations about the nature
of consciousness as it is experienced by the subject. Though the use
of such first person methods is now and has been controversial in
psychology and philosophy throughout the 20th and 21st century, there
seems to now be a broad acknowledgement that it has an indispensable
role in the scientific study of consciousness, as many authors who
have published recent scientific theories of consciousness include
some appeal to phenomenological premises in justifying their views
(e.g. Seth, Edelman and Baars 2005; Merker 2005; Tononi 2008; Cabanac
et al. 2009).


## 6. Evolution and Distribution of Consciousness


 A variety of hypotheses have been put forward by scientists and
philosophers about which animals are conscious and which are
not. These views span a huge range of possibilities, from the
narrowest, which is that only humans are conscious, to some authors
arguing that almost all animals, even simple invertebrates, have a
basic capacity to experience the world. Some authors have even argued
that single-celled organisms (Margulis 2001) or plants (A. Nagel 1997)
are conscious, and some have given arguments for versions of
pan-psychism, the view that consciousness is a property of fundamental
physical entities, much in the same way that mass and charge are
(Chalmers 2015). It is worth noting that neither the attribution of
consciousness to single-celled organisms, nor to fundamental physical
entities, implies that all animals are conscious. In the former case,
it may be that the information processing complexity and integration
of relatively complex single-celled organisms outstrips that of the
simplest animals. In the latter case, while the version of panpsychism
developed by Chalmers attributes 'microexperience' to
'fundamental physical entities', this does not imply that
any particular macroscopic object (like an animal) has
'macroexperience' -- i.e. "the sort of conscious
experience had by human beings" (Chalmers 2015). This view is
compatible with the possibility that a given animal has no conscious
experience, although it is composed of microphysical entities which
possess conscious microexperience. These issues will not be discussed
further here, as they fall outside the scope of Animal
Consciousness. 


The question of which lineages (species, or more inclusive
groupings such as class or phylum) of animals are conscious,
inevitably goes hand-in-hand with considerations of the evolutionary
origin of consciousness. This is a logical implication of the broadly
Darwinian view of life, on which modern organisms have evolved through
descent, with modification, from a small number (perhaps one) of very
ancient ancestors. If a trait is characteristic of a given species,
it either arose in that species, or is derived from an ancestor
-- in which case, it will be present in other species derived
from that ancestor, unless it has been secondarily lost in those
species. Did consciousness first arise in humans, or in an earlier,
nonhuman ancestor? If the latter, then what was this ancestor? Another
possibility is that consciousness may have arisen multiple times, like
winged flight, which evolved independently in insects, birds, bats,
and pterosaurs. 


### 6.1 Humans


 As described above, the view that consciousness is unique to
humans has a long history. It coheres with a religious view of
humanity as the pinnacle of creation, and it also may be appealing
insofar as it absolves us of any guilt for our treatment of
animals. Religion aside, it may derive considerable intuitive support
because of the appeal of connecting consciousness to the problem of
human uniquenesss. If consciousness can be tied together with
language, abstract reasoning, or some other mental characteristic that
potentially could explain our apparent seperateness from the natural
world, this would solve two outstanding mysteries at once. 



Dennett (1991, 1995) has been an outspoken advocate of the
human-uniqueness of consciousness. Dennett argues for this position in
connection with his anti-realist theory of consciousness, the upshot
of which is that consciousness is a sort of "user
illusion" (1995) or "fiction" (1991, p. 365, p. 429)
constructed through people's narrative descriptions:




> What there is, really, is just various events of
> content-fixation occuring in various places at various times in the
> brain... Some of these content-fixations have further effects, which
> eventually lead to the utterance of sentences -- in a natural
> language -- either public or merely internal. And so a
> heterophenomenological text is created... What about the actual
> phenomenology? There is no such thing. (1991 p 365)



On Dennett's view, because consciousness is a sort of story telling,
which requires language, and only (adult, normally enculturated and
language-capable) humans have language, only these humans have
consciousness.




Carruthers has championed the view that only humans (with the possible
exception of chimpanzees) are conscious, although for different
reasons than Dennett. Carruthers (1998a,b, 2000) has argued to this
effect based on his 'higher-order thought' theory,
according to which, phenomenal consciousness requires the capacity to
think about, and therefore conceptualize, one's own 
 thoughts.[8] 
 Such conceptualization requires, according to Carruthers, a theory of mind.
And, Carruthers maintains, there is little basis for thinking that any
nonhuman animals have a theory of mind, with the possible exception of
chimpanzees (see Lurz 2011 and Andrews 2012 for in depth discussion of
theory of mind in nonhuman animals). This argument is, of course, no
stronger than the higher-order thought account of consciousness upon
which it is based. But setting that aside for the sake of argument,
this challenge by Carruthers deserves further attention as perhaps the
most empirically-detailed case against animal consciousness to have
been made in the philosophical literature.




Carruthers neither endorses nor outright rejects the conclusion that
chimpanzees are sentient. His suspicion that even chimpanzees might
lack theory of mind, and therefore (on his view) phenomenal
consciousness, is based on some ingenious laboratory studies by
Povinelli (1996) showing that in interactions with human food
providers, chimpanzees apparently fail to understand the role of eyes
in providing visual information to the humans, despite their outwardly
similar behavior to humans in attending to cues such as facial
orientation. The interpretation of Povinelli's work remains
controversial. Hare *et al*. (2000) conducted experiments in
which dominant and subordinate animals competed with each other for
food, and concluded that "at least in some situations
chimpanzees know what conspecifics do and do not see and, furthermore,
that they use this knowledge to formulate their behavioral strategies
in food competition situations." They suggest that Povinelli's
negative results may be due to the fact that his experiments involve
less natural chimp-human interactions. Given the uncertainty,
Carruthers is therefore well-advised in the tentative manner in which
he puts forward his claims about chimpanzee sentience.




A full discussion of the controversy over theory of mind (e.g., Heyes
1998; Lurz 2011; Andrews 2012) deserves an entry of its own, but it is
worth remarking here that the theory of mind debate has origins in the
hypothesis that primate intelligence in general, and human
intelligence in particular, is specially adapted for social cognition
(see Byrne & Whiten 1988, especially the first two chapters, by
Jolly and Humphrey). Consequently, it has been argued that evidence
for the ability to attribute mental states in a wide range of species
might be better sought in natural activities such as social play,
rather than in laboratory designed experiments which place the animals
in artificial situations (Allen & Bekoff 1997; see esp. chapter 6;
see also Hare *et al*. 2000, Hare *et al*. 2001, and
Hare & Wrangham 2002). Alternative approaches that have attempted
to provide strong evidence of theory of mind in nonhuman animals under
natural conditions have generally failed to produce such evidence
(see, e.g., the conclusions about theory of mind in vervet monkeys and
baboons by Cheney & Seyfarth 1990, 2007), although anecdotal
evidence tantalizingly suggests that researchers still have not
managed to devise the right experiments. Furthermore, theory of mind
-- and social cognition more broadly -- are active areas of
research, and it is quite possible that new research will reveal
evidence of theory of mind in nonhuman animals. 




On views such as Carruthers', consciousness is grounded in cognitive
processes that are highly specific and modular -- indeed,
irrelevant for the perceptual, motivational and cognitive processes
involved with all nonhuman animal behavior. Given that most of the
cognitive processes (and corresponding brain-systems) involved with
human activities are shared with nonhuman animals, this line of
thinking implies that much of human activity is nonconscious as
well. Thus, for example, Carruthers (1989, 1992) argued that
*all* animal behavior can be assimilated to the non-conscious
activities of humans, such as driving while distracted ("on
autopilot"), or to the capacities of "blindsight"
patients whose damage to visual cortex leaves them phenomenologically
blind in a portion of their visual fields (a "scotoma")
but nonetheless able to identify things presented to the scotoma. (He
refers to both of these as examples of "unconscious
experiences".)


 This comparison of animal behavior to the unconscious capacities
of humans can be criticized on the grounds that, like Descartes'
pronouncements on parrots, it is based only on unsystematic
observation of animal behavior. There are grounds for thinking that
careful investigation would reveal that there is not a very close
analogy between animal behavior and human behaviors associated with
these putative cases of unconscious experience. For instance, it is
notable that the unconscious experiences of automatic driving are not
remembered by their subjects, whereas there is no evidence that
animals are similarly unable to recall their allegedly unconscious
experiences. Likewise, blindsight subjects do not spontaneously
respond to things presented to their scotomas, but must be trained to
make responses using a forced-response paradigm. There is no evidence
that such limitations are normal for animals, or that animals behave
like blindsight victims with respect to their visual experiences
(Jamieson & Bekoff 1992).




Nevertheless, there are empirical grounds for concern that behavior
suggesting consciousness in animals may be the product of unconscious
processes. Allen *et al*. (2009) describe work on learning in
spinal cords of rats that shows phenomena analogous to latent
inhibition and overshadowing. In intact animals, these learning and
memory related phenomena have been argued to involve attention. But
their similarity to mechanisms in the spinal cord, assumed by most not
to involve consciousness, calls into question their status as evidence
for consciousness. There are, of course, differences between the
learning capacities of spinal cords and the learning capacities of
intact organisms, and there are prima facie reasons for thinking that
sophisticated forms of learning are related to consciousness (Clark
& Squire 1998; Allen 2004; Ginsburg & Jablonka 2007b). But 
the current point is similar to that made
about blindsight: a more fine-grained analysis of these similarities
and differences is needed before conclusions about consciousness can
be drawn.


### 6.2 Great Apes




Gallup (1970) developed an experimental test of mirror
self-recognition that has become widely used as a test of
self-awareness, although interpretation of the test remains
controversial (see the section on
 self-consciousness and metacognition
below). Gallup argues that the performance of chimpanzees in this test
indicates that they are self-aware, and that animals that fail the
test lack self-awareness. Further, foreshadowing Carruthers, Gallup
argues that self-awareness -- in the sense of being able to think
about one's own mental states -- is required for having a mind,
and therefore that animals that 'fail' the mirror test
have no minds (1982, 1985). Though there has been controversy over
just which animals 'pass' the validity of versions of the test modified for use with elephants, dolphins,and magpies has been challenged 
-- as of 2002, Gallup maintained that there was evidence that
humans, common chimpanzees, bonobos and orangutans consistently pass
the test, and strong evidence that a wide range of other primates fail
consistently fail. He took this to support the claim that
self-awareness is unique to great apes (Gallup et al. 2002). Combined
with his earlier arguments that consciousness requires the sort of
self-awareness measured by the mirror test, this would imply that
consciousness is unique to the great apes.



 Gallup's interpretation of the mirror results have not been
uncontroversial (Mitchell 2002). Rochat and Zahavi (2010) challenge
Gallup both on a) the interpretation of chimps' mirror-oriented
behavior as indicating a human-like experience of mirror
self-recognition, and b) the claim that mirror self-recognition is
implied by consciousness.


 As a side note, there has been a debate, ongoing since the early
1990s (Cavalieri and Singer 1994) about whether great apes deserve
special legal protection amounting to 'human rights'. The
crux of the debate is not whether the great apes have consciousness
per se (this seems to be assumed by most participants of the debate,
on both sides), but whether they have *personhood*. Personhood is
a vexed notion, but is generally thought to be related to certain
forms of agency and self awareness, and is often thought to be tightly
coupled to moral status, as reflected in this debate (DeGrazia 1997;
SEP article on Moral Status of Animals; Varner 2012). Though not
essential to phenomenal consciousness, personhood is often thought to
presuppose consciousness, and so perhaps is best thought of as a level
of elaboration or complexity of consciousness.


### 6.3 Mammals


A variety of theoretical and empirical arguments have been put
forward to the effect that consciousness is shared across all
mammals. Seth, Baars and Edelman (2005) argue that the neural
processes essential to human conscious -- widespread reentrant
activity in the thalamo-cortical complex -- involve anatomical
systems that are shared among all mammals (and perhaps more
widely). Panksepp (reviewed in 2005) takes a similar approach,
although focusing on the neurophysiological systems involved in the
'core emotions'. Although in both of the above proposals,
the authors acknowledge that consciousness may be more widespread than
just mammals, they argue that in the case of mammals, the weight of
evidence based on homology of relevant neurophysiological systems is
overwhelming, whereas outside of mammals, the inference is more
tenuous because of the biological differences in non-mammalian
animals. Further, it should be kept in mind that all of the following
proposals imply that consciousness is widely shared among
mammals. Hence, the position that all mammals are conscious is widely
agreed upon among scientists who express views on the distribution of
consciousness.


### 6.4 Amniotes (including birds and reptiles)



Questions about whether reptiles are conscious (and if so what their
mental lives might be like) are especially interesting because birds
are more closely related to them than they are to mammals, yet birds
display a variety of behaviors that tend to intuitively suggest
intelligence and emotion to human observers much more obviously than
the behavior of scaly, so-called 'cold-blooded' animals
like snakes and turtles. Do birds and mammals share mental features
(consciousness, intelligence, emotion, social attachment) that are
absent in reptiles? If so this would represent independent, convergent
evolution of these phenomena. Alternatively, are these features common
to all of these animals, but less obvious in some than others?


 Cabanac et al. (2009) argue that consciousness is unique to, and
shared by all *amniotes* -- the clade that includes all
descendants of the common ancestor of living birds and mammals,
including reptiles such as lizards, snakes, turtles and extinct
animals such as dinosaurs, pterosaurs and pleseiosaurs (see
http://tolweb.org/Amniota). On this hypothesis, only these animals,
and not amphibians, fish, or any invertebrates, possess
consciousness. Cabanac's argument is based on an explicit structural
and functional theory of consciousness as a unified representational
space, "an abstract private model of reality with four dimensions:
quality, intensity, hedonicity and duration" (2009, p.268). Possessing
this ability to model reality allows animals to simulate possible
courses of action, using hedonicity (pleasure or pain) as a
'common currency' to evaluate and choose between actions
based on expected consequences (which are based on prior
experience). 



Cabanac identifies a set of behavioral markers of consciousness, based
on this model structural and functional theory:


* the ability to make motivational tradeoffs;
* play;
* navigational detouring (which requires an animal to pursue a
series of nonrewarding intermediate goals in order to obtain an
ultimate reward);
* expression of emotion;
* expression of sensory pleasure;
* emotional fever (an increase in body temperature in response to a
supposedly stressful situation -- gentle handling, as
operationalized in Cabanac's experiments);
* taste aversion.


 Based on supposed evidence of these phenomena in amniotes but not
in non-amniotes, Cabanac argues that consciousness originated in the
common ancestor of amniotes, and hence is present in all living
amniotes but in no other animals. Cabanac and Cabanac (2009) also
argue that a qualitative difference in the role of dopamine in
motivational processes in the brains of amniotes compared to
non-amniotes supports this distribution/origin hypothesis. 


 Cabanac and colleagues have documented the presence of some of
these phenomena in amniotes, in contrast with their absence in at
least a small number of non-amniote species, such as emotional fever
(Cabanac and Bernieri 2000; Cabanac and Cabanac 2000; Cabanac and
Cabanac 2004) and taste aversion (Paradis and Cabanac 2004). 


 However, the assertion that these aspects of behavior and
cognition do not exist outside amniota is largely based on absence of
evidence (and hence, inherently limited). In particular, they do not
offer direct support for their claims that non-amniotes are incapable
of trading off punishments and rewards, play or detouring. Indeed,
some of these claims appear to be contradicted by existing studies
-- for example, documentation of detouring in jumping spiders
(Jackson and Wilcox 2003) and work by Elwood and Appel(2009) that
shows motivational trade-off behavior in hermit crabs. 


 Cabanac's structural and functional theory of consciousness can be
evaluated independently of the evidence that he marshals in support of
his view of the distribution and origins of consciousness. Indeed, one
might challenge his views on distribution and origins precisely by
accepting his structural and functional theory, and arguing that the
list of proposed indicators can actually by identified with a wider
distribution (i.e. if motivational trade-offs, play, and detouring are
present outside of amniotes). As we shall see, his structural and
functional views of consciousness have much in common with those of
other authors who argue for wider distributions of consciousness among
animals.


### 6.5 Vertebrates


'Fish' is a folk-biological term that does not correspond precisely
to any monophyletic taxonomic group. This can be appreciated by noted
that a coelacanth is more closely related to a human than to a tuna,
or that a tuna is more closely related to a human than it is to a
shark. I.e., some things that are intuitively fish are more closely
related to non-fish than to other fish. Basically, the folk term 'fish'
refers to all vertebrates other than tetrapods, although it is
somewhat ambiguous in regards to animals such as sea-horses, eels,
hagfish and sting-rays.


In any case, there has a lively debate over fish consciousness,
mostly focusing on the issue of whether fish can experience pain,
stress and suffering (see below, section 7.1; see also Rose (2002) and
Sneddon et al. (2003) for contrasting views of conscious pain in fish;
Allen 2013 and Brown 2015 for reviews of fish cognition and
consciousness as it may relate to pain; and Braithwaite 2010 for a
book-length treatment). This is of special relevance in the context of
welfare regulation in commercial aquaculture and recreational angling;
accordingly, the fish consciousness literature has focused
experimentally on salmonids (especially salmon and trout), a group of
high commercial and sport-fishing importance, but only a tiny
phylogenetic corner of the animals that colloquially count as
fish. 


 Merker (2005) has proposed that consciousness originated early in
vertebrate evolution, and is therefore both ancient and widespread. On
this proposal, not only mammals and birds, but amphibians and all
marine vertebrates are conscious. Merker begins his argument with the
phenomenological observation that the contents of conscious experience
are object- and goal-oriented, but exclude the fine-grained sensory
and motor details represented in peripheral and low-level neural
processing. Merker argues that consciousness is an integrated
representational platform -- what he refers to a
'synthesized reality space' -- that, for animals with
complex bodies with many degrees of freedom of movement and multiple
sensory modalities, solves a cluster of critical neural logistics
problems. This includes:


* maintaining the stability of perceptual contents against
interference from self-generated motion;
* integrating interoceptive information about the body's movements
and the body's self-regulative needs (e.g. temperature, thirst,
hunger);
* affording high-level decision making that abstracts away from the
irrelevant sensorimotor details of implementation.


 The neuroanatomical details of Merker's argument (2005) are beyond
the scope of this article to review, but his conclusion is that the
systems that solve the above problems -- giving rise to
consciousness -- arose in an early vertebrate ancestor. Hence,
consciousness is both ancient and widespread among living
vertebrates.


### 6.6 Invertebrates


There are additional daunting challenges to addressing questions of
consciousness outside the vertebrate lineage, given the radical
differences between vertebrates and invertebrates with respect to
anatomy and physiology. The strategy of identifying homologous and
functionally analogous structures and processes, which underlies the
confidence of researchers such as Cabanac (2009), Seth et al. (2005),
Merker (2005), and Panksepp (2005) that consciousness is shared with
other animals is much more difficult to apply (Seth et al. 2005).



The vertebrate lineage represents just one of approximately 34 known
phyla -- ancient lineages of animals characterized by differences
in fundamental anatomical organization and the developmental processes
that generate it. Each of these phyla is derived from a relatively
simple state (i.e. few tissue types and a minimal central nervous
system with limited sensory capacities). Hence, the invertebrates such
as cephalopod mollusks (e.g., octopi and squids) and arthropods
(e.g. crustaceans, insects and spiders), that are complex enough to
attract the attention of those interested in animal consciousness,
evolved their complexity independently from vertebrates, and in the
case of cephalopods and arthropods, independently from each other.




Today, only three of the phyla (vertebrates, arthropods, and mollusks)
include animals with complex active bodies (Trestman 2013a),
characterized by:


* articulated and differentiated appendages;
* many degrees of freedom of controlled motion;
* distal senses (e.g., ''true'' eyes);
* anatomical capability for active, distal-sense-guided mobility
(fins, legs, jet propulsion, etc.);
* anatomical capability for active object manipulation (e.g.,
chelipeds, hands, tentacles, mouth-parts with fine-motor
control).


Trestman (2013a) argues that the evolution of complex active bodies
requires a capacity for integrated, embodied spatial cognition, and
that this capacity evolved independently in each of the three phyla in
which it is currently found (vertebrates, arthropods and mollusks). If
Merker (2005) is right that consciousness represents a solution to the
neural-logistics problems posed by controlling a complex body in
space, it may be a good bet that these three lineages are likely
suspects for possessing consciousness. This line of reasoning can be
bolstered by considering the role of temporal integration of
perceptual information in consciousness and in action-selection and
object-oriented perception (Trestman 2013b). Perhaps each of these
three lineages evolved consciousness independently during the
transition from a relatively simple worm-like body morphology to
having complex active bodies.


 One group of invertebrate animals that has received attention in
the context of questions about consciousness is the coleoid
cephalopods -- octopuses, squids and cuttlefish. These are
large-brained, notoriously clever animals, well-known for their
remarkable abilities to camouflage th emselves, and for their flexible
hunting strategies. Mather (2008) argues that cephalopods exhibit many
behavioral indicators of consciousness, including complex learning and
spatial memory, as well as apparent play. Both Merker (2005) and Edelman et
al. (2005, 2009) argue that a strong provisional case can be made for
consciousness in cephalopods -- although these authors emphasize
the limitations on our understanding posed by the differences in
anatomy and physiology between cephalopods and vertebrates.



The other phylum that has received particular attention is the
arthropods, which includes insects, crustaceans, spiders, and many
other less familiar animals. This is an ancient and tremendously
diverse group of animals, so any generalizations should be made with
caution. Arthropods were among the earliest animals to evolve complex
active bodies -- and correlatively to evolve brains capable of
adaptively controlling complex adaptive bodies (Trestman 2013a), and
so if the function of consciousness is to solve problems raised by the
control of complex active bodies (cf. Merker 2005), it may have
evolved early on in the arthropod lineage, in a common ancestor of all
living arthropods.



 Few studies have aimed directly at answering questions about
consciousness in arthropods, but relevant empirical work includes:


* Work by Elwood and Appel (2009) that seems to show that hermit
crabs remember an aversive event (an electric shock), and can use that
memory in later context-sensitive decision-making. This seems to
satisfy Cabanac and Cabanac's (2009) definition of 'motivational
trade-off' behavior, which those authors argue is an indicator
of consciousness.
* Work by Jackson and colleagues (reviewed in Jackson and Wilcox
1998) documenting a variety of impressive behaviors in in jumping
spiders, including:
	+ detouring and other forms of apparent planning (noted as a
	 potential indicator of consciousness by Cabanac et al., 2009)
	+ flexible, context-sensitive adjustment of predatory behavior to prey behavior
	+ deception and smokescreen tactics
* Studies on bees, revealing pattern recognition, concepts of
'same' and 'different', navigation,
communication, and visual working memory (reviewed in Srinivasan
2010), and on mood and cognitive bias (Mendl et al. 2011).


Another possibility is that consciousness evolved even earlier in
animal history and is even more widely distributed among animals, and
hence has a function that is even more fundamental to animal
life. Ginsburg & Jablonka (2007a,b) attribute a primitive form of
"overall sensation" as a by-product of even the simplest
nerve nets in animals. They argue that as these states became
harnessed to learning and motivation that they acquired the functional
properties of "basic consciousness". If this is right,
than consciousness may have arisen not independently in arthropods,
mollusks and vertebrates, but only once in the common ancestor of
these ancient groups, very early in animal evolution.



## 7. Special Topics in the Study of Animal Consciousness


With the gradual loosening of behaviorist strictures in psychology
and ethology, and independent advances in neuroscience, there has been
a considerable increase in the number of animal studies that have some
bearing on animal consciousness. Some of these studies focus on
specific kinds of experience, such as pain, while others focus on
cognitive abilities such as self-awareness that seem to be strongly
correlated with human consciousness. This section contains brief
reviews of some of the main areas of investigation. The aim is to
provide some quick entry points into the scientific literature. 


### 7.1 Animal pain and suffering


Given the centrality of pain to most accounts of our ethical
obligations towards animals, as well as the importance of animal
models of pain in clinical medical research (see Mogil 2009 for a
review), it is hardly surprising that there is a substantial (albeit
controversial) scientific literature bearing on animal pain. Reports
by the Nuffield Council on Bioethics in the U.K. (Nuffield Council
2005; see esp. chapter 4) and the U.S. National Academy of the
Sciences Institute for Animal Laboratory Research (ILAR 2009) have
recently covered the definition of pain and the physiological,
neurological, and behavioral evidence for pain in nonhuman
animals. These reviews also distinguish pain from distress and
suffering (see also Bermond 2001), and the ILAR has divided what used
to be a single report on recognition and alleviation of pain and
distress into two separate reports, although the scientific
investigation of distress is relatively rudimentary (but see Dawkins
1985; Farah 2008). 


A proper understanding of neurological studies of animal pain
begins with the distinction between nociception and pain. Nociception
-- the capacity to sense noxious stimuli -- is one of the
most primitive sensory capacities. Neurons functionally specialized
for nociception have been described in invertebrates such as the
medical leech and the marine snail *Aplysia californica*
(Walters 1996). Because nociceptors are found in a very wide range of
species, and are functionally effective even in decerebrate or
spinally transected animals, their presence and activity
in a species provides little or no direct evidence for phenomenally
conscious pain experiences. The gate control theory of Melzack and
Wall (1965) describes a mechanism by which "top-down"
signals from the brain modulate "bottom-up" nociception,
providing space for the distinction between felt pain and
nociception.


 Smith & Boyd (1991) assess the evidence for the pain-sensing
capabilities of animals in the categories of whether nociceptors are
connected to the central nervous system, whether endogenous opioids
are present, whether analgesics affect responses, and whether the
ensuing behavioral responses are analogous to those of humans (see
table 2.3 in Varner 1998, p. 53, which updates the one presented by
Smith & Boyd). On the basis of these criteria, Varner follows
Smith & Boyd in concluding tentatively that the most obvious place
to draw a line between pain-conscious organisms and those not capable
of feeling pain consciously is between vertebrates and invertebrates.
However, Elwood & Appel (2009) conducted an experiment on hermit
crabs which they interpret as providing evidence that pain is
experienced and remembered by these crustaceans. Varner also expressed
some hesitation about the evidence for conscious pain in
"lower" vertebrates: fish, reptiles and amphibians. Allen
(2004) argues, however, that subsequent research indicates that the
direction of discovery seems uniformly towards identifying more
similarities among diverse species belonging to different taxonomic
classes, especially in the domains of anatomy and physiology of the
nociceptive and pain systems.


It is generally accepted that the mammalian pain system has both a
sensory and an affective pathway, and that these can be dissociated to
some degree both pharmacologically (with morphine, e.g.) and surgical
lesions. The anterior cingulate cortex (ACC) is a particularly
important structure of the mammalian brain in this regard (Price
2000). Allen *et al*. (2005) and Shriver (2006) argue that
this dissociability provides a route to empirical assessment of the
affective component of animal consciousness, and Farah (2008) uses it
to distinguish suffering from "mere pain".


Detailed analysis of other taxonomic groups may, however, indicate
important anatomical differences. Rose (2002) argues that because fish
lack an ACC they may not be bothered by pain. This is in contrast to
Sneddon *et al*. (2003) who argue that there is adequate
behavioral and physiological evidence to support pain attributions to
fish. (See, also, Chandroo *et al*. 2004 for a review.) While
the ACC is important to mammals, there remains the possibility that
other taxa may have functionally similar structures, such as the
*corticoidea dorsolateralis* in birds (Atoji & Wild 2005;
Dubbeldam 2009). Genetic knockout animals are also providing further
clues about the affective aspects of pain (see Shriver 2009 for a
review and application of these findings to animal welfare.)




Finally, it is worth noting that a major shift in veterinary practice
in regards to animal pain has occurred in the past decade. Whereas
surgery on animals was once routinely practiced without analgesics or
anesthetics, the vast majority of veterinary practitioners now accept
the basic premise that veterinarians can be trained to recognize
animal pain reliably, and that veterinary patients benefit from the
same kinds of pain alleviation treatments that are delivered to
humans. It has even been argued that animals possess the
neurobiological mechanisms responsible for phantom limb pain and
neuropathic pain (pain in the presence of no obvious tissue damage or
disease), and that these conditions may therefore be detectable and
treatable in nonhuman animals (Mathews 2008).



### 7.2 Animal emotions




The idea of animal emotions is, of course, prominent in Darwin's work
with his 1872 book *The Expression of the Emotions in Man and
Animals*. Willingness to see animals as emotional beings (and
humans, by contrast, as endowed with rationality that can override the
emotions) goes back at least to Ancient Greek philosophy. Konrad
Lorenz seems to have held a similar view, echoing Oskar Heinroth's
statement that "animals are highly emotional people of very
limited intelligence" (Lorenz 1971b, 334). These days it is more
fashionable to regard emotions as an important component of
intelligence. Regardless of the merits of that view, the scientific
study of animal emotions has gained its own momentum. Early in the
20th century, although they are not arguing for or about animal
consciousness, physiologists recognized that significance of emotion
in animal behavior. Dror (1999) explains how the emotional state of
animals was considered to be a source of noise in physiological
experiments at that time, and researchers took steps to ensure that
animals were calm before their experiments. According to Dror,
although physiologists were forced to deal with the problem of
emotional noise, attempts to treat emotion as a subject of study in
its own right never crystallized to the extent of generating a journal
or other institutional features (Dror 1999, 219).


 More recently, Jaak Panksepp (2004, 2005) has been conducting a
research program that he calls "affective neuroscience"
and that encompasses direct study of animal emotions (2004),
exemplified for example in the experimental investigation of rats
"laughing" and seeking further contact in response to
tickling by humans (Panksepp & Burgdorf 2003). Over several
decades, his work (reviewed in Panksepp 2005) has elucidated the
neuro- and molecular-physiological bases of several 'core
emotional systems' including 'seeking',
'fear', 'rage', 'lust',
'care', 'play', and
'panic'. Panksepp argues that these are shared by all
mammals, and may be more widely shared among vertebrates. 



Sufka *et al*. (2009) have proposed that animal models of
neuropsychiatric disorders may also support the experimental
investigation of animal emotions. Although depending on a more
anecdotal, non-experimental approach, Smuts (2001) and Bekoff (2007)
each defend the attribution of conscious emotions to animals from a
scientist's perspective. Bekoff has made much of play behavior as an
indicator of animal emotions, an idea that is also taken up by Cabanac
*et al*. (2009). 




Empathy in animals is also a topic of current investigation (e.g.,
Preston & de Waal 2002). Langford *et al*. (2002) argue for
empathy in mice based on experiments in mice who observe a cagemate
given a noxious stimulus, or in pain, are more sensitive to painful
stimuli than control mice who observe an unfamiliar mouse similarly
treated. Byrne *et al*. (2008) argue for empathy in elephants
as an inference to the best explanation of various capacities, such as
diagnosing animacy and goal directedness, and assessing the physical
abilities and emotional states of other elephants when these different
from their own.


 It is worth noting that almost all of the work, both theoretical
and empirical, on animal emotions has limited its scope to mammals, or
at least amniotes (For a notable recent exception, see Mendl et
al. 2011). This work has exploited certain deep homologies of,
e.g. brain structure and molecular neurophysiology (focusing
especially on hormones and neurotransmitters) in making arguments that
animals in these taxanomic groups share our emotions because they
share the mechanisms of our own emotions (as well as behaviors that
tend to indicate emotions in us, and bear the same relations to the
underlying physiological mechanisms). This approach is not available
to animals which are very distantly related to us,
i.e. invertebrates. The ancestors of vertebrates split off from the
rest of the animal phyla at a time when all animals were still
relatively simple, in terms of structure, tissue types, number of
neurons, bodily capacities for locomotion and other forms of
behavior. The elaboration of complex physiological systems occurred
independently in the various phyla. Therefore the physiological
systems underlying emotions in other phyla -- if these exist
-- may be very different, and hence difficult to identify, either
in terms of direct physiological observations or in terms of
observations of behavioral expressions of emotion. It is also possible
that the repertoire of emotions in other phyla might be different,
further problematizing the task of individuating non-vertebrate
emotions. (Further discussion and additional scientific references for
the topic of emotions and empathy in animals can be found in the
 section on emotions and empathy in the entry on 
 animal cognition.)


### 7.3 Perceptual phenomenology




The idea that careful psychophysical work with could help us
understand the nature of their subjective experiences of the world can
be traced at least to Donald Griffin's experimental tests of the
limits of bat echolocation. It is also behind the idea that knowing
that horses have near 360deg vision, or that raptors have two fovea
on each retina, may tell us something about the nature of their
experiences -- how the world appears to them -- if it is
granted that they have such experiences. Neural investigation adds a
further layer of analysis to scientific understanding of the nature of
perception. For instance, Leopold & Logothetis (1996) used neural
data to support inferences about the percepts of monkeys under
conditions of binocular rivalry (see also: Myserson *et
al*. 1981; Rees *et al*. 2002). And Leopold *et
al*. (2003) argue that neural recordings can be used to
corroborate the non-verbal "reports" of monkeys shown
ambiguous visual stimuli. (Think here of whether it is possible for
the monkey to report that it is subject to Gestalt switches like those
arising from ambiguous figures such as the duck-rabbit or figure-vase
illusions.)


 The phenomenon of blindsight, a form of unconscious visual
perception that arises with damage to specific areas of primary visual
cortex, has also been investigated in surgically lesioned monkeys
(Stoerig & Cowey 1997), with a close correspondence between the
monkeys' deficits and those of the human patients vis-a-vis
parts of the visual field that can be processed only unconsciously,
and those for which the patients retain consciousness. The non-verbal
approach to assessing visual awareness has been further validated by
Stoerig et al. (2002). Blindsight subjects, both human and monkey, do
not spontaneously respond to things presented to their scotomas (areas
where they are visually unaware), but must be trained to make
responses using a forced-response paradigm (Stoerig & Cowey
1997). 




The emphasis on visual perception in most of these examples, no doubt
reflects a primatocentric bias. We human primates are highly visual
creatures, and, as Nagel (1974) argued, we face considerable hurdles
in imagining (again, a visual metaphor) the subjective experiences of
creatures in modalities in which humans are weak or completely
unendowed. The examples of research also reflect an anthropocentric
bias in that much of the animal experimentation is explicitly targeted
at relieving human disorders. Although there is good work by
neuroethologists on the psychophysics of echolocation by bats and
dolphins, or on the sensory capacities of weakly electric fish,
questions of subjective awareness are generally not broached in that
literature.




As with the investigation of animal pain, fine-grained analysis of the
neural correlates of consciousness may reveal subtle differences
between different species. For instance, Rees *et al*. (2002)
report that while the behavior of rhesus monkeys is rather similar to
humans under conditions of binocular rivalry, "the firing of
most cells in and around V1 primarily reflects stimulus properties
rather than the conscious percept reported by the animal ... However,
several neuroimaging studies in humans have presented evidence that
argues for a stronger role of V1 in binocular rivalry and hence, by
implication, visual awareness." Nevertheless, it is noteworthy
that they take the behavioral evidence to be unproblematically
describable as report of a conscious percept by the monkey.


### 7.4 Mental Time Travel



A debate has unfolded in the literature over whether other animals,
like humans, are capable of thinking about past and future
events. Suddendorf and Corballis (1997, 2007) have argued that
so-called 'Mental Time Travel' is unique to humans, and
indeed plays a major role in explaining what is cognitively unique
about humans, including capacities for language and culture.

Many mammals, birds and fish exhibit behavior such as food caching,
nest building, tool use, or migration that seems to suggest
foresight. For example, tayras -- a members of the weasel family
found in Central and South America -- hide bunches of bananas
inside of bromeliads, recovering them only when the bananas are ripe
(Soley et al. 2011). Skeptics are quick to point out that many of
these examples may be either a) 'instinctive' fixed-action
patterns shaped by natural selection or b) the result of classical or
operant conditioning, rather than behavior that is mediated by
'cognitive' processes such as episodic memory, insight, or
understanding. However, the novelty, flexibility and ability to make
situation-specific adjustments often calls such dismissals into
question. For example, tayras cache several species of bananas, and
accurately judge for bananas of each species when the banana is mature
enough to continue ripening once picked. This includes domestic
bananas, to which tayras have not been exposed over evolutionary
time-scales (Soley et al. 2011). 


 A variety of careful
experimental work with animals shows impressive abilities for
integrated what-where-when memory -- the ability to recall
details of an event together with its location and time. This work was
pioneered by Clayton and colleagues with scrub jays, focusing on their
caching behavior -- wherein the birds bury food and later recover
it (Clayton et al. 2003). For example, if scrub jays are prevented
from recovering their caches for long enough, they will recover only
nonperishable items (peanuts, in the study), ignoring their caches of
otherwise preferred but perishable food (mealworms, in the study)
(Clayton et al. 2003). Recent work has also documented what is
referred to as 'episodic-like memory' in rats (Crystal
2009), and the apparent ability to plan for the future (including in
novel ways that are not plausible ruled out as 'mere
instinct') in several animals, including nonhuman primates,
birds, rats and other mammals (Feeney et al. 2011 for an example of
recent experimental work; see Roberts 2012 for a review and
discussion). 


 This debate has been somewhat complicated by the fact that
proponents of the human-uniqueness of mental time travel tend to rely
on descriptions of the ability that are laden with researchers' and
subjects' phenomenological, introspective or intuitive descriptions of
the way their own minds work (e.g. Tulving 1985; Suddendorf and
Corbalis 2007), whereas animal behavior researchers must rely on
strict standards of behavioral evidence to support their
claims. Animal behavior researchers are typically circumspect in their
interpretations, limiting their claims to operationalizable terms such
as 'what-where-when' memory, or
'episodic-like' memory, rather than making claims about
the nature of the experience that may be involved in an animal's
performing a task. The situation may therefore represent a double
standard in the interpretation of evidence about human and nonhuman
animal subjects, with researchers uncritically making liberal
assumptions about human cognition that would not be allowed for animal
researchers -- an example of what Buckner (2013) has called
'anthropofabulation'. The question of to what extent, and
in what ways, humans' awareness of time differs from that of other
animals remains an open one, and an active line of research. 


### 7.5 Self-consciousness and metacognition




Systematic study of self-consciousness and theory of mind in nonhuman
animals has roots in an approach to the study of self-consciousness
pioneered by Gallup (1970). Gallup's rationale for linking
mirror-self recognition to self-awareness has already been discussed
above. The idea for the experiment came from observations well-known
to comparative psychologists that chimpanzees would, after a period of
adjustment, use mirrors to inspect their own images. Gallup used
these observations to develop a widely-replicated protocol that
appears to allow a scientific determination of whether it is merely
the mirror image *per se* that is the object of interest to the
animal inspecting it, or whether it is the image qua proxy for the
animal itself that is the object of interest. Taking chimpanzees who
had extensive prior familiarity with mirrors, Gallup anesthetized his
subjects and marked their foreheads with a distinctive dye, or, in a
control group, anesthetized them only. Upon waking, marked animals who
were allowed to see themselves in a mirror touched their own foreheads
in the region of the mark significantly more frequently than controls
who were either unmarked or not allowed to look into a mirror.


 Although it is typically reported that chimpanzees consistently
"pass" the mirror-mark test, a survey of the scientific
literature by Shumaker & Swartz (2002) indicates that of 163
chimpanzees tested, only 73 showed mark-touching behavior (although
there was considerable variation in the age and mirror experience
among these animals). Shumaker & Swartz also report mark-touching
behavior in 5 of 6 tested orang utans and 6 of 23 gorillas. They
suggest that the lower incidence of mark touching by gorillas may be
due to avoidance of socially-significant direct eye contact.



For non-human primates outside the great apes, the evidence for mirror
self-recognition has been sparse. Gallup himself regards it as a
phenomenon restricted to the great apes only, and he was among the
first to challenge Hauser's report that cotton top tamarins engaged in
mirror-guided self-directed behaviors after their distinctive white
tufts had been dyed neon colors, a stimulus that Hauser and coauthors
argued was presumably more salient than the red dot used by Gallup
(Hauser *et al*. 1995). Faced with Gallup's challenge, Hauser
himself was unable to replicate his initial results (Hauser *et
al*. 2001). However, the idea that Gallup's protocol uses a
stimulus that is not particularly salient to monkeys continues to have
some currency. For example, Rajala *et al*. (2010) have
presented quantitative and videographic evidence that rhesus monkeys
with surgical implants in their heads use mirrors to inspect the
implants, as well as other parts of their bodies that they cannot
usually see.




Modified versions of Gallup's experiment have also been conducted with
non-primate species. Notoriously, Epstein *et al*. (1981)
trained pigeons to peck at a mark on their own bodies that was visible
only in a mirror, and they used this to call into question the
attribution of "self-awareness" on the basis of the
mirror-mark test, preferring an associative learning
explanation. Gallup *et al*. (2002) reject the claimed
equivalence, pointing out that chimpanzees were not trained to touch
marks before the test was administered. Reiss & Marino (2001) have
offered evidence of mirror self-recognition in bottlenose
dolphins. Using a modified version of Gallup's procedure that involved
no anesthesia, they inferred self-recognition from bodily contortions
in front of the mirror (self-touching being anatomically impossible
for dolphins). This evidence has been disputed (e.g. Wynne 2004). The
mirror-mark test continues to be an area of active investigation in
various species including elephants (Plotnik *et al*. 2006) and
magpies (Prior *et al*. 2008). Various commentators have
pointed out that the mirror test may not be entirely fair for species
which depend more heavily on senses other than vision (Mitchell 2002;
Bekoff and Burghardt 2002). 


An intriguing line of research into animals' knowledge of their own
mental states considers the performance of animals in situations of
cognitive uncertainty. When primates and dolphins are given a
"bailout" response allowing them to avoid making difficult
discriminations, they have been shown to choose the bailout option in
ways that are very similar to humans (Smith *et al*. 2003). The
fact that animals who have no bailout option and are thus forced to
respond to the difficult comparisons do worse than those who have the
bailout option but choose to respond to the test has been used to
argue for some kind of higher-order self understanding. The original
experiments have attracted both philosophical criticism of the
second-order interpretation (e.g. Carruthers 2008) and methodological
criticism by psychologists (reviewed by Crystal & Foote 2009),
although alternative approaches to establishing metacognition in
non-linguistic animals may be capable of avoiding these criticisms
(Terrace & Son 2009).


In the literature on human cognition, awareness of what one knows
is called "metacognition" and it is associated with a
"feeling of knowing". Smith and colleagues claim that
investigating metacognition in animals could provide information about
the relation of self-awareness to other-awareness (theory of mind),
and that their results already show that "animals have
functional features of or parallels to human conscious
cognition" (Smith *et al*. 2003; Smith 2009). They also
raise the question of what this might tell us about the phenomenal
features of that cognition. Browne (2004) argues that the dolphin
research cannot support the connection to theory of mind, but that it
nevertheless is relevant to consciousness in dolphins, particularly
within the theoretical framework provided by Lycan, described
above. The notion of metacognition also seems relevant to questions
about access consciousness. (For additional discussion of self
awareness and metacognition, readers are referred to the section on
 theory of mind and
metacognition in the entry on 
 animal cognition.)


## 8. Summary


An article such as this perhaps raises more questions than it
answers, but the topic would be of little philosophical interest if it
were otherwise. 



It is clear that for many philosophers, the topic of animal
consciousness is no longer only of peripheral interest. There is
increasing interest in animal cognition from a range of philosophical
perspectives, including ethics, philosophy of mind, and the philosophy
of science. Philosophers working in all of these areas are
increasingly attentive to the particular details of scientific theory,
methods, and results. Many scientists and philosophers believe that
the groundwork has been laid for addressing at least some of the
questions about animal consciousness in a philosophically
sophisticated yet empirically tractable way. Yet there remain critics
from both sides: on the one hand are those who still think that
subjective phenomena are beyond the pale of scientific research, and
on the other are those who think that science and philosophy have not
moved far enough or fast enough to recognize animal consciousness.
The arguments on both sides are by no means exhausted.