## 1. The Origins and Varieties of ST



The idea that we often arrive at representing other people's
mental states by mentally simulating those states in ourselves has a
distinguished history in philosophy and the human sciences. Robert
Gordon (1995) traces it back to David Hume (1739) and Adam
Smith's (1759) notion of sympathy; Jane Heal (2003) and Gordon
(2000) find simulationist themes in the *Verstehen* approach to
the philosophy of history (e.g., Dilthey 1894); Alvin Goldman (2006)
considers Theodor Lipps's (1903) account of empathy
(*Einfuhlung*) as a precursor of the notion of mental
simulation.



In its modern guise, ST was established in 1986, with the publication
of Robert Gordon's "Folk Psychology as Simulation"
and Jane Heal's "Replication and Functionalism".
These two articles criticized the Theory-Theory and introduced ST as a
better account of mindreading. In his article, Gordon discussed
psychological findings concerning the development of the capacity to
represent others' false beliefs. This attracted the interest of
developmental psychologists, especially Paul Harris (1989, 1992), who
presented empirical support for ST, and Alison Gopnik (Gopnik &
Wellman 1992) and Joseph Perner (Perner & Howes 1992), who argued
against it--Perner has since come to defend a hybrid version of
ST (Perner & Kuhberger 2005).



Alvin Goldman was an early and influential defender of ST (1989) and
has done much to give the theory its prominence. His work with the
neuroscientist Vittorio Gallese (Gallese & Goldman 1998) was the
first to posit an important connection between ST and the newly
discovered mirror neurons. Goldman's 2006 book *Simulating
Minds* is the clearest and most comprehensive account to date of
the relevant philosophical and empirical issues. Among other
philosophical proponents of ST, Gregory Currie and Susan Hurley have
been influential.



Since the late 1980s, ST has been one of the central players in the
philosophical, psychological, and neuroscientific discussions of
mindreading. It has however been argued that the fortunes of ST have
had a notable negative consequence: the expression "mental
simulation" has come to be used broadly and in a variety of
ways, making "Simulation Theory" a blanket term lumping
together many distinct approaches to mindreading. Stephen Stich and
Shaun Nichols (1997) already urged dropping it in favor of a
finer-grained terminology. There is some merit to this. ST is in fact
better conceived of as a *family of theories* rather than a
single theory. All the members of the family agree on the thesis that
mental simulation, rather than a body of knowledge about other minds,
plays a central role in mindreading. However, different members of the
family can differ from one another in significant respects.



One fundamental area of disagreement among Simulation Theorists is the
very nature of ST--what *kind* of theory ST is supposed to
be--and what philosophers can contribute to it. Some Simulation
Theorists take the question "How do people arrive at
representing others' mental states?" as a straightforward
empirical question about the cognitive processes and mechanisms
underlying mindreading (Goldman 2006; Hurley 2008). According to them,
ST is thus a theory in *cognitive science*, to which
philosophers can contribute exactly as theoretical physicists
contribute to physics: 



> 
> 
> theorists specialize in creating and tweaking theoretical structures
> that comport with experimental data, whereas experimentalists have the
> primary job of generating the data. (Goldman 2006: 22) 
> 
> 
> 



Other philosophical defenders of ST, however, do not conceive of
themselves as theoretical cognitive scientists at all. For example,
Heal (1998) writes that: 



> 
> 
> it is commonly taken that the inquiry into ... the extent of
> simulation in psychological understanding is empirical, and that
> scientific investigation is the way to tell whether ST ... is
> correct. But this perception is confused. It is an *a priori*
> truth ... that simulation must be given a substantial role in our
> personal-level account of psychological understanding. (Heal 1998:
> 477-478) 
> 
> 
> 



Adjudicating this meta-philosophical dispute goes well beyond the aim
of this entry. To be as inclusive as we can, we shall adopt a
"balanced diet" approach: we shall discuss the extent to
which ST is supported by empirical findings from psychology and
neuroscience, and, *at the same time*, we shall dwell on
"purely philosophical" problems concerning ST. We leave to
the reader the task of evaluating which aspects should be put at the
centre of the inquiry.



Importantly, even those who agree on the general nature of ST might
disagree on other crucial issues. We will focus on what are typically
taken to be the three most important bones of contention among
Simulation Theorists: what is meant by "mental
simulation"?
 (section 2).
 What types of simulation processes are there?
 (section 3).
 What is the role of mental simulation in mindreading?
 (section 4).
 After having considered what keeps Simulation Theorists apart, we
shall move to discuss what holds them together, i.e., the opposition
to the Theory-Theory of mindreading
 (section 5
 and
 section 6).
 This should give the reader a sense of the "unity amidst
diversity" that characterizes ST.


## 2. What is Meant by "Mental Simulation"?



In common parlance, we talk of putting ourselves in others'
shoes, or empathizing with other people. This talk is typically
understood as adopting someone else's point of view, or
perspective, in our imagination. For example, it is quite natural to
interpret the request "Try to show some empathy for John!"
as asking you to use your imaginative capacity to consider the world
from John's perspective. But what is it for someone to
imaginatively adopt someone else's perspective? To a first
approximation, according to Simulation Theorists, it consists of
*mentally* *simulating*, or re-creating, someone
else's mental states. Currie and Ravenscroft (2002) make this
point quite nicely: 



> 
> 
> Imagination enables us to project ourselves into another situation and
> to see, or think about, the world from another perspective. These
> situations and perspectives ... might be those of another actual
> person, [or] the perspective we would have on things if we believed
> something we actually don't believe, [or] that of a fictional
> character. ... *Imagination recreates the mental states of
> others*. (Currie & Ravenscroft 2002: 1, emphasis added). 
> 
> 
> 



Thus, according to ST, empathizing with John's sadness consists
of mentally simulating his *sadness*, and adopting Mary's
political point of view consists of mentally simulating her political
*beliefs*. This is the intuitive and general sense of mental
simulation that Simulation Theorists have in mind.



Needless to say, this intuitive characterization of "mental
simulation" is loose. What exactly does it mean to say that a
mental state is a mental simulation of another mental state? Clearly,
we need a precise answer to this question, if the notion of mental
simulation is to be the fundamental building block of a theory.
Simulation Theorists, however, differ over how to answer this
question. The central divide concerns whether "mental
simulation" should be defined in terms of *resemblance*
(Heal 1986, 2003; Goldman 2006, 2008a) or in terms of *reuse*
(Hurley 2004, 2008; Gallese & Sinigaglia 2011). We consider these
two proposals in turn.


### 2.1 Mental Simulation as Resemblance



The simplest interpretation of "mental simulation" in
terms of resemblance goes like this:




(RES-1) Token state *M*\* is a mental simulation of token state
*M* if and only if:


1. Both *M* and *M*\* are mental states
2. *M*\* resembles *M* in some significant respects




Two clarifications are in order. First, we will elaborate on the
"significant respects" in which a mental state has to
resemble another mental state in due course (see, in particular,
 section 3).
 For the moment, it will suffice to mention some relevant dimensions
of resemblance: similar functional role; similar content; similar
phenomenology; similar neural basis (an important discussion of this
topic is Fisher 2006). Second, RES-1 defines "mental
simulation" as a *dyadic* *relation* between
mental states (the relation *being a mental simulation of*).
However, the expression "mental simulation" is also often
used to pick out a *monadic property* of mental states
--the property *being a simulated mental state* (as will
become clear soon, "simulated mental state" does not refer
here to the state which is simulated, but to the state that does the
simulating). For example, it is common to find in the literature
sentences like "*M*\* is a mental simulation". To
avoid ambiguities, we shall adopt the following terminological
conventions:


* We shall use the expression "mental simulation of" to
express the relation *being a mental simulation of*.
* We shall use the expression "simulated mental state"
to express the property *being a simulated mental state*.
* We shall use the expression "mental simulation" in a
way that is deliberately ambiguous between "mental simulation
of" and "simulated mental state".



It follows from this that, strictly speaking,
 RES-1
 is a definition of "mental simulation of". Throughout
this entry, we shall characterize "simulated mental state"
in terms of "mental simulation of": we shall say that if
*M*\* is *a mental simulation* *of* *M*, then
*M*\* is a *simulated mental
 state*.[1]



With these clarifications in place, we will consider the strengths and
weaknesses of
 RES-1.
 Suppose that Lisa is seeing a yellow banana. At the present moment,
there is no yellow banana in my own surroundings; thus, I cannot have
that (type of) visual experience. Still, I can *visualize* what
Lisa is seeing. Intuitively, my visual imagery of a yellow banana is a
mental simulation of Lisa's visual experience.
 RES-1
 captures this, given that both my visual imagery and Lisa's
visual experience are mental states and the former resembles the
latter.



RES-1,
 however, faces an obvious problem (Goldman 2006). The resemblance
relation is symmetric: for any *x* and *y*, if *x*
resembles *y*, then *y* resembles *x*. Accordingly, it
follows from
 RES-1
 that Lisa's visual experience is a mental simulation of my
visual imagery. But this is clearly wrong. There is no sense in which
one person's perceptual experience can be a mental simulation of
another person's mental imagery (see Ramsey 2010 for other
difficulties with
 RES-1).



In order to solve this problem, Goldman (2006) proposes the following
resemblance-based definition of "mental simulation
of":




(RES-2) Token state *M*\* is a mental simulation of token state
*M* if and only if:


1. Both *M* and *M*\* are mental states
2. *M*\* resembles *M* in some significant respects
3. In resembling *M*, *M*\* fulfils at least one of its
functions




Under the plausible assumption that one of the functions of visual
imagery is to resemble visual experiences, RES-2 correctly predicts
that my visual imagery of a yellow banana counts as a mental
simulation of Lisa's visual experience. At the same time, since
visual experiences do not have the function of resembling visual
images, RES-2 does not run into the trouble of categorizing the former
as a mental simulation of the latter.


### 2.2 Mental Simulation as Reuse



Clearly,
 RES-2
 is a better definition of "mental simulation of" than
 RES-1.
 Hurley (2008), however, argued that it won't do either, since
it fails to distinguish ST from its main competitor, i.e., the
Theory-Theory (TT), according to which mindreading depends on a body
of information about mental states and processes
 (section 5).
 The crux of Hurley's argument is this. Suppose that a token
visual image *V*\* resembles a token visual experience *V*
and, in doing so, fulfils one of its functions. In this case,
 RES-2
 is satisfied. But now suppose further that visualization works like a
computer simulation: it generates its outputs on the basis of a body
of information about vision. On this assumption,
 RES-2
 still categorizes *V*\* as a mental simulation of *V*,
*even though *V*\* has been generated by exactly the kind of
process described by TT*: a theory-driven and information-rich
process.



According to Hurley (who follows here a suggestion by Currie &
Ravenscroft 2002), the solution to this difficulty lies in the
realization that "the fundamental ... concept of simulation
is *reuse*, not resemblance" (Hurley 2008: 758, emphasis
added). Hurley's reuse-based definition of "mental
simulation of" can be articulated as follows:




(REU) Token state *M*\* is a mental simulation of token state
*M* if and only if:


1. Both *M* and *M*\* are mental states
2. *M* is generated by token cognitive process *P*
3. *M*\* is generated by token cognitive process *P*\*
4. *P* is implemented by the *use* of a token cognitive
mechanism of type *C*
5. *P*\* is implemented by the *reuse* of a token
cognitive mechanism of type *C*




To have a full understanding of REU, we need to answer three
questions: (a) What is a cognitive *process*? (b) What is a
cognitive *mechanism*? (c) What is the difference between
*using* and *reusing* a certain cognitive mechanism?
Let's do it!



It is a commonplace that explanation in cognitive science is
structured into different levels. Given our aims, we can illustrate
this idea through the classical *tri-level hypothesis*
formulated by David Marr (1982). Suppose that one wants to explain a
certain *cognitive capacity*, say, vision (or mindreading, or
moral judgment). The first level of explanation, the most abstract
one, consists in describing what the cognitive capacity
does--what task it performs, what problem it solves, what
function it computes. For example, the task performed by vision is
roughly "to derive properties of the world from images of
it" (Marr 1982: 23). The second level of analysis specifies
*how* the task is accomplished: what algorithm our mind uses to
compute the function. Importantly, this level of analysis abstracts
from the particular physical structures that implement the algorithm
in our head. It is only at the third level of analysis that the
details of the *physical implementation* of the algorithm in
our brain are spelled out.



With these distinctions at hand, we can answer questions (a) and (b).
A *cognitive process* is a cognitive capacity considered as an
information-processing activity and taken in abstraction from its
physical implementation. Thus, cognitive processes are individuated in
terms of what function they perform and/or in terms of what algorithms
compute these functions (fair enough, the "and/or" is a
very big deal, but it is something we can leave aside here). This
means that the same (type of) cognitive process can be multiply
realized in different physical structures. For example, parsing
(roughly, the cognitive process that assigns a grammatical structure
to a string of signs) can be implemented both by a human brain and a
computer. On the contrary, *cognitive mechanisms* are
particular (types of) physical structures--e.g., a certain part
of the brain--implementing certain cognitive processes. More
precisely, cognitive mechanisms are organized structures carrying out
cognitive processes in virtue of how their constituent parts interact
(Bechtel 2008; Craver 2007; Machamer et al. 2000).



We now turn to question (c), which concerns the distinction between
use and reuse of a cognitive mechanism. At a first approximation, a
cognitive mechanism is *used* when it performs its primary
function, while it is *reused* when it is activated to perform
a different, non-primary function. For example, one is *using*
one's visual mechanism when one employs it to see, while one is
*reusing* it when one employs it to conjure up a visual image
(see Anderson 2008, 2015 for further discussion of the notion of
reuse). All this is a bit sketchy, but it will do.



Let's now go back to
 REU.
 The main idea behind it is that whether a mental state is a mental
simulation of another mental state depends on the *cognitive
processes* generating these two mental states, and on the
*cognitive mechanisms* implementing such cognitive processes.
More precisely, in order for mental state *M*\* to be a mental
simulation of mental state *M*, it has to be case that:
(*i*) cognitive processes *P*\* and *P*, which
respectively generate *M*\* and *M*, are both implemented by
the same (type of) cognitive mechanism *C*; (ii) *P* is
implemented by the *use* of *C*, while *P*\* is
implemented by the *reuse* of *C*. 



Now that we know what
 REU
 means, we can consider whether it fares better than
 RES-2
 in capturing the nature of the relation of mental simulation. It
would seem so. Consider this hypothetical scenario. Lisa is seeing a
yellow banana, and her visual experience has been generated by
cognitive process *V*1, which has been implemented by
the use of her visual mechanism. I am visualizing a yellow banana, and
my visual image has been generated by cognitive process
*V*2, which has been implemented by the reuse of my
visual mechanism. Rosanna-the-Super-Reasoner is also visualizing a
yellow banana, but her visual image has been generated by an
information-rich cognitive process: a process drawing upon
Rosanna's detailed knowledge of vision and implemented by her
incredibly powerful reasoning mechanism.
 REU
 correctly predicts that my visual image is a mental simulation of
Lisa's visual experience, but not vice versa. More importantly,
it also predicts that Rosanna's visual image does not count as a
mental simulation of Lisa's visual experience, given that
Rosanna's cognitive process was not implemented by the reuse of
the visual mechanism. In this way,
 REU
 solves the problem faced by
 RES-2
 in distinguishing ST from TT.



Should we then conclude that "mental simulation of" has to
be defined in terms of reuse, rather than in terms of resemblance?
Goldman (2008a) is still not convinced. Suppose that while Lisa is
seeing a yellow banana, I am using my visual mechanism to visualize
the Golden Gate Bridge. Now, even though Lisa's visual
experience and my visual image have been respectively generated by the
use and the reuse of the visual mechanism, it would be bizarre to say
that my mental state is a mental simulation of Lisa's. Why?
Because my mental state doesn't resemble Lisa's (she is
seeing a yellow banana; I am visualizing the Golden Gate Bridge!)
Thus--Goldman concludes--resemblance should be taken as
*the* central feature of mental simulation.


### 2.3 Relations, States, and Processes



In order to overcome the difficulties faced by trying to define
"mental simulation of" in terms of *either*
replication *or* reuse, philosophers have built on the insights
of both RES and
 REU
 and have proposed definitions that combine replication and reuse
elements (Currie & Ravenscroft 2002; in recent years, Goldman
himself seems to have favoured a mixed account; see Goldman 2012a).
Here is one plausible definition:




(RES+REU) Token state *M*\* is a mental simulation of token state
*M* if and only if:


1. Both *M* and *M*\* are mental states
2. *M*\* resembles *M* in some significant respects
3. *M* is generated by token cognitive process *P*
4. *M*\* is generated by token cognitive process *P*\*
5. *P* is implemented by the *use* of a token cognitive
mechanism of type *C*
6. *P*\* is implemented by the *reuse* of a token
cognitive mechanism of type *C*




RES+REU has at least three important virtues. The *first* is
that it solves all the aforementioned problems for RES and
 REU--we
 leave to the reader the exercise of showing that this is indeed the
case.



The *second* is that it fits nicely with an idea that loomed
large in the simulationist literature: the idea that *simulated
mental states* are "pretend" ("as if",
"quasi-") states--imperfect copies of, surrogates
for, the "genuine" states normally produced by a certain
cognitive mechanism, obtained by taking this cognitive mechanism
"off-line". Consider the following case. Frank is in front
of *Central Cafe* (and *believes* that he is
there). He *desires* to drink a beer and *believes* that
he can buy one at *Central Cafe*. When he feeds these
mental states into his decision-making mechanism, the mechanism
implements a decision-making process, which outputs the
*decision* to enter the cafe. In this case,
Frank's decision-making mechanism was
"on-line"--i.e., he *used* it; he employed it
for its primary function. My situation is different. I don't
believe I am in front of *Central Cafe*, nor do I desire
to drink a beer right now. Still, I can imagine believing and desiring
so. When I feed these imagined states into my decision-making
mechanism, I am not employing it for its primary function. Rather, I
am taking it off-line (I am *reusing* it). As a result, the
cognitive process implemented by my mechanism will output a *merely
imagined decision* to enter the cafe. Now, it seems fair to
say that my imagined decision resembles Frank's decision (more
on this in
 section 3).
 If you combine this with how these two mental states have been
generated, the result is that my imagined decision is a mental
simulation of Frank's decision, and thus it is a simulated
mental state. It is also clear why Frank's decision is
*genuine*, while my simulated mental state is just a
*pretend* decision: all else being equal, Frank's
decision to enter *Central Cafe* will cause him to enter
the cafe; on the contrary, no such behaviour will result from
my simulated decision. I have *not really* decided so. Mine was
just a *quasi*-decision--an imperfect copy of, a surrogate
for, Frank's genuine decision.



And here is
 RES+REU's
 *third* virtue. So far, we have said that "mental
simulation" can either pick out a dyadic relation between mental
states or a monadic property of mental states. In fact, its ambiguity
runs deeper than this, since philosophers and cognitive scientists
also use "mental simulation" to refer to a monadic
property of *cognitive processes*, namely, the property
*being a (mental) simulation process* (or: "process of
mental simulation", "simulational process",
"simulative process", etc.) As a first stab, a (mental)
simulation process is a cognitive process generating simulated mental
states.
 RES+REU
 has the resources to capture this usage of "mental
simulation" too. Indeed,
 RES+REU
*implicitly* contains the following definition of
"simulation process":




(PROC): Token process *P*\* is a (mental) simulation process if
and only if:


1. *P*\* generates token state *M*\*
2. *M*\* resembles another token state, *M*, in some
significant respects
3. Both *M* and *M*\* are mental states
4. *M* is generated by token process *P*
5. Both *P* and *P*\* are cognitive processes
6. *P* is implemented by the *use* of a token cognitive
mechanism of type *C*
7. *P*\* is implemented by the *reuse* of a token
cognitive mechanism of type *C*




Go back to the case in which Lisa was having a visual experience of a
yellow banana, while I was having a visual image of a yellow banana.
Our two mental states resembled one another, but different cognitive
processes generated them: *seeing* in Lisa's case, and
*visualizing* in my case. Moreover, Lisa's
*seeing* was implemented by the use of the visual mechanism,
while my *visualizing* was implemented by its reuse. According
to PROC, the latter cognitive process, but not the former, was thus a
simulation process.



To sum up,
 RES+REU
 captures many of the crucial features that Simulation Theorists
ascribe to mental simulation. For this reason, we shall adopt it as
our working definition of "mental simulation
of"--consequently, we shall adopt PROC as a definition of
"simulated mental
 state".[2]
 We can put this into a diagram.



![[a diagram consisting of a hexagon labelled 'C' with an arrow labeled 'use' pointing to a diamond labeled 'P' on the upper left, an arrow points from this diamond up to a rectangle labeled 'M'. From the hexagon is also an arrow labeled 're-use' pointing to a diamond labeled 'P*' on the upper right, an arrow points from this diamond up to a rectangle labeled 'M*'. The two rectangles are connected by a dashed double-headed arrow labeled 'resemblance']](figure1.svg)

Figure 1




The hexagon at the bottom depicts a cognitive mechanism *C* (it
could be, say, the visual mechanism). When *C* is used (arrow on
the left), it implements cognitive process *P* (say, seeing);
when it is re-used (arrow on the right), it implements cognitive
process *P*\* (say, visualizing). *P* generates mental state
*M* (say, a visual experience of a red tomato), while *P*\*
generates mental state *M*\* (say, a visual image of a red
tomato). These two mental states (*M* and *M*\*) resemble one
another. Given this: *M*\* is a *mental simulation of*
*M*; *M*\* is a *simulated mental state*; and
*P*\* is a *simulation
 process*.[3]


### 2.4 Final Worries



In this section, we shall finally consider three worries raised for
adopting
 RES+REU
 as a definition of "mental simulation of". If you have
already had enough of
 RES+REU,
 please feel free to move straight to
 section 3.



Heal (1994) pointed out a problem with committing ST to a particular
account of the cognitive mechanisms that underlie it. Suppose that the
human mind contains two distinct decision-making mechanisms:
*Mec1*, which takes beliefs and desires as input, and generates
decisions as output; and *Mec2*, which works by following
exactly the same logical principles as *Mec1*, but takes
imagined beliefs and imagined desires as input and generates imagined
decisions as output. Consider again Frank's decision to enter
*Central Cafe* and my imagined decision to do so.
According to the two mechanisms hypothesis, Frank desired to drink a
beer and believed that he could buy one at *Central
Cafe*, fed these mental states into *Mec1*, which
generated the decision to enter the cafe. As for me, I fed the
imagined desire to drink a beer and the imagined belief that I could
buy one at *Central Cafe* into a distinct (type of)
mechanism, i.e., *Mec2*, which generated the imagined decision
to enter *Central Cafe*. Here is the question: does my
imagined decision to enter *Central Cafe* count as a
mental simulation of Frank's decision to do so? If your answer
is "Yes, it does", then
 RES+REU
 is in trouble, since my imagined decision was not generated by
reusing the same (type of) cognitive mechanism that Frank used to
generate his decision; his decision was generated by *Mec1*, my
imagined decision by *Mec2*. Thus, Heal concludes, a definition
"mental simulation of" should not contain any commitment
about cognitive mechanisms--it should not make any implementation
claim--but should be given at a more abstract level of
description.



In the face of this difficulty, a defender of
 RES+REU
 can say the following. First, she might reject the intuition that, in
the two mechanisms scenario, my imagined decision counts as a mental
simulation of Frank's decision. At a minimum, she might say that
this scenario does not elicit any robust intuition in one direction or
the other: it is not clear whether these two mental states stand in
the relation *being a mental simulation of*. Second, she might
downplay the role of intuitions in the construction of a definition
for "mental simulation of" and cognate notions. In
particular, if she conceives of ST as an empirical theory in cognitive
science, she will be happy to discount the evidential value of
intuitions *if countervailing theoretical considerations are
available*. This, e.g., is Currie and Ravenscroft's (2002)
position, who write that 



> 
> 
> there are two reasons ... why the Simulation Theorist should
> prefer [a one mechanism hypothesis]: ... first, the postulation
> of two mechanisms is less economical than the postulation of one;
> second, ... we have very good reasons to think that
> imagination-based decision making does not operate in isolation from
> the subject's real beliefs and desires. ... If imagination
> and belief operate under a system of inferential apartheid--as
> the two-mechanisms view has it--how could this happen? (Currie
> & Ravenscroft 2002: 67-68)
> 
> 
> 



A second worry has to do with the fact that
 RES+REU
 appears to be too liberal. Take this case. Yesterday, Angelina had
the visual experience of a red apple. On the night of June 15, 1815,
Napoleon conjured up the visual image of a red apple. Angelina used
her visual mechanism to see, while Napoleon reused his to imagine. If
we add to this that Napoleon's mental state resembled
Angelina's,
 RES+REU
 predicts that Napoleon's (token) visual image was a mental
simulation of Angelina's (token) visual experience. This might
strike one as utterly bizarre. In fact, not only did Napoleon not
*intend* to simulate Angelina's experience: he *could
not* even have intended to do it. After all, Angelina was born
roughly 150 years after Napoleon's death. By the same token, it
is also impossible that Napoleon's visual image has been
*caused* by Angelina's visual experience. As a matter of
fact, the visual image Napoleon had on the night of June 15, 1815 is
*entirely disconnected* from the visual experience that
Angelina had yesterday. Thus, how could the former be a mental
simulation of the latter? If you think about it, the problem is even
worse than this.
 RES+REU
 has it that Napoleon's visual image of a red apple is a mental
simulation of *all* the visual experiences of a red apple that
have obtained in the past, that are currently obtaining, and that will
obtain in the future. Isn't that absurd?



Again, a defender of
 RES+REU
 can give a two-fold answer. First, she can develop an argument that
this is not absurd at all. Intuitively, the following principle seems
to be true:




(TYPE): the mental state type *visual image of a red apple* is
a mental simulation of the mental state type *visual experience of
a red apple*.




If TYPE is correct, then the following principle has to be true as
well:




(TOKEN): Any token mental state of the type *visual image of a red
apple* is a mental simulation of every token mental state of the
type *visual experience of a red apple*.




But TOKEN entails that Napoleon's (token) visual image of a red
apple is a mental simulation of Angelina's (token) visual
experience of a red apple, which is exactly what
 RES+REU
 predicts. Thus,
 RES+REU's
 prediction, rather than being absurd, independently follows from
quite intuitive assumptions. Moreover, even though TOKEN and
 RES+REU
 make the same prediction about the Napoleon-Angelina case, TOKEN is
not entailed by
 RES+REU,
 since the latter contains a *restriction* on how visual images
have to be generated. Thus, if one finds TOKEN intuitively acceptable,
it is hard to see how one can find
 RES+REU
 to be *too liberal*.



The second component of the answer echoes one of the answers given to
Heal: for a Simulation Theorist who conceives of ST as a theory in
cognitive science, intuitions have a limited value in assessing a
definition of "mental simulation of". In fact, the main
aim of this definition is not that of capturing folk intuitions, but
rather that of offering a clear enough picture of the relation of
mental simulation on the basis of which an adequate theory of
mindreading can be built. So, if the proposed definition fails, say,
to help distinguishing ST from TT, or is of limited use in
theory-building, or is contradicted by certain important results from
cognitive science, then one has a good reason to abandon it. On the
contrary, it should not be a cause for concern if
 RES+REU
 does not match the folk concept MENTAL SIMULATION OF. The notion
"mental simulation of" is a term of art--like, say,
the notions of I-Language or of Curved Space. These notions
*do* poorly match the folk concepts of language and space, but
linguists and physicists do not take this to be a problem. The same
applies to the notion of mental simulation.



And here is the third and final worry.
 RES+REU
 is supposed to be a definition of "mental simulation of"
on the basis of which a theory of mindreading can be built. However,
neither
 RES+REU
 nor
 PROC
 make any reference to the idea of representing others' mental
states. Thus, how could these definitions help us to construct a
Simulation Theory *of mindreading*? The answer is simple: they
will help us exactly as a clear definition of
"computation", which has nothing to do with how the mind
works, helped to develop the Computational Theory of Mind (see entry
on
 computational theory of mind).



Here is another way to make the point. ST is made up of *two
distinct claims*: the first is that mental simulation is
psychologically real, i.e., that there are mental states and processes
satisfying
 RES+REU
 and
 PROC.
 The second claim is that mental simulation plays a central role in
mindreading. Clearly, the second claim cannot be true if the first is
false. However, the second claim can be false even if the first claim
is true: mental simulation could be psychologically real, but play no
role in mindreading at all. Hence, Simulation Theorists have to do
three things. First, they have to establish that mental simulation is
psychologically real. We consider this issue in
 section 3.
 Second, they have to articulate ST *as a theory of
mindreading*. That is, they have to spell out in some detail the
crucial role that mental simulation is supposed to play in
representing others' mental states, and contrast the resulting
theory with other accounts of mindreading. We dwell on this in
sections
 4
 and
 5.
 Finally, Simulation Theorists have to provide evidence in support of
their theory of mindreading--that is, they have to give us good
reasons to believe that mental simulation does play a crucial role in
representing others' mental states. We discuss this issue in
 section 6.


## 3. Two Types of Simulation Processes



Now that we have definitions of "mental simulation of" and
cognate notions, it is time to consider which mental states and
processes satisfy them, if any. Are there really *simulated mental
states*? That is, are there mental states generated by the
*reuse* of cognitive mechanisms? And do these mental states
*resemble* the mental states generated by the use of such
mechanisms? For example, is it truly the case that visual images are
*mental simulations of* visual experiences? What about
decisions, emotions, beliefs, desires, and bodily sensations? Can our
minds generate simulated counterparts of all these types of mental
states? In this section, we consider how Simulation Theorists have
tackled these problems. We will do so by focusing on the following
question: are there really *simulation processes* (as defined
by
 PROC)?
 If the answer to this question is positive, it follows that there are
mental states standing in the relation of mental simulation (as
defined by
 RES+REU),
 and thus simulated mental states.



Following Goldman (2006), it has become customary among Simulation
Theorists to argue for the existence of two types of simulation
processes: *high-level simulation* *processes* and
*low-level simulation processes* (see, however, de Vignemont
2009). By exploring this distinction, we begin to articulate the
cognitive architecture underlying mental simulation proposed by
ST.


### 3.1 High-Level Simulation Processes



High-level simulation processes are cognitive processes with the
following features: (a) they are typically conscious, under voluntary
control, and stimulus-independent; (b) they satisfy
 PROC,
 that is, they are implemented by the *reuse* of a certain
cognitive mechanism, *C*, and their output states
*resemble* the output states generated by the use of
 *C*.[4]
 Here are some cognitive processes that, according to Simulation
Theorists, qualify as high-level simulation processes. Visualizing:
the cognitive process generating visual images (Currie 1995; Currie
& Ravenscroft 2002; Goldman 2006); motor imagination: the
cognitive process generating imagined bodily movements and actions
(Currie & Ravenscroft 1997, 2002; Goldman 2006); imagining
deciding: the cognitive process generating decision-like imaginings
(Currie & Ravenscroft 2002); imagining believing: the cognitive
process generating belief-like imaginings (Currie & Ravenscroft
2002); imagining desiring: the cognitive process generating
desire-like imaginings (Currie 2002). In what follows, we shall
consider a couple of them in some detail.



Visualizing first. It is not particularly hard to see why visualizing
satisfies condition (a). Typically: one can decide to visualize (or
stop visualizing) something; the process is not driven by perceptual
stimuli; and at least some parts of the visualization process are
conscious. There might be cases in which visualizing is not under
voluntary control, is stimulus-driven and, maybe, even entirely
unconscious. This, however, is not a problem, since we know that there
are clear cases satisfying (a).



Unsurprisingly, the difficult task for Simulation Theorists is to
establish that visualizing has feature (b), that is: it is implemented
by the *reuse* of the visual mechanism; and its outputs (that
is, visual images) *resemble* genuine visual experiences.
Simulation Theorists maintain that they have strong empirical evidence
supporting the claim that visualizing satisfies
 PROC.
 Here is a sample (this and further evidence is extensively discussed
in Currie 1995, Currie & Ravenscroft 2002, and in Goldman
2006):


1. visualizing recruits some of the brain areas involved in vision
(Kosslyn et al. 1999);
2. left-neglect patients have the same deficit in both seeing and
visualizing--i.e., they do not have perceptual experience of the
left half of the visual space and they also fail to imagine the left
half of the imagined space (Bisiach & Luzzatti 1978);
3. ocular movements occurring during visualizing approximate those
happening during seeing (Spivey et al. 2000);
4. some patients systematically mistake visual images for perceptual
states (Goldenberg et al. 1995);
5. visual perception and visualizing exhibit similar patterns of
information-processing (facilitations, constraints, illusions) (Decety
& Michel 1989; Kosslyn et al. 1999)



On this basis, Simulation Theorists conclude that visualizing is
indeed implemented by the *reuse* of the visual mechanism
(evidence i and ii) and that its outputs, i.e., visual images, do
*resemble* visual experiences (evidence iii, iv, and v). Thus,
visualizing is a process that qualifies as high-level simulation, and
visual images are simulated mental states.



Visual images are mental simulations of perceptual states. Are there
high-level simulation processes whose outputs instead are mental
simulations of propositional attitudes? (If you think that visual
experiences are propositional attitudes, you can rephrase the question
as follows: are there high-level simulation processes whose outputs
are mental simulations of non-sensory states?) Three candidate
processes have received a fair amount of attention in the
simulationist literature: imagining desiring, imagining deciding, and
imagining believing. The claims made by Simulation Theorists about
these cognitive processes and their output states have generated an
intense debate (Doggett & Egan 2007; Funkhouser & Spaulding
2009; Kieran & Lopes 2003; Nichols 2006a, 2006b; Nichols &
Stich 2003; Velleman 2000). We do not have space to review it here
(two good entry points are the introduction to Nichols 2006a and the
entry on
 imagination).
 Rather, we shall confine ourselves to briefly illustrating the
simulationist case in favour of the thesis that imagining believing is
a high-level simulation process.



I don't believe that Rome is in France, but I can imagine
believing it. Imagining believing typically is a conscious,
stimulus-independent process, under voluntary control. Thus, imagining
believing satisfies condition (a). In order for it to count as an
instance of high-level *simulation* process, it also needs to
have feature (b), that is: (b.i) its outputs (i.e., belief-like
imaginings) have to *resemble* genuine beliefs in some
significant respects; (b.ii) it has to be implemented by the
*reuse* of the cognitive mechanism (whose use implements the
cognitive process) that generates genuine beliefs--let us call it
"the belief-forming mechanism". Does imagining believing
satisfy (b)? Currie and Ravenscroft (2002) argue in favour of (b.i).
Beliefs are individuated in terms of their content and functional
role. Belief-like imaginings--Currie and Ravenscroft
say--have the same content and a similar functional role to their
genuine counterparts. For example, the belief that Rome is in France
and the belief-like imagining that Rome is in France have exactly the
same propositional content: *that Rome is in France*. Moreover,
belief-like imaginings mirror the inferential role of genuine beliefs.
If one believes both that Rome is in France and that French is the
language spoken in France, one can infer the belief that French is the
language spoken in Rome. Analogously, from the belief-like imagining
that Rome is in France and the genuine belief that French is the
language spoken in France, one can infer the belief-like imagining
that French is the language spoken in Rome. So far, so good (but see
Nichols 2006b).



What about (b.ii)? Direct evidence bearing on it is scarce. However,
Simulation Theorists can give an argument along the following lines.
First, one owes an explanation of why belief-like imaginings are,
well, belief-like--as we have said above, it seems that they have
the same type of content as, and a functional role similar to, genuine
beliefs. A possible explanation for this is that both types of mental
states are generated by (cognitive processes implemented by) the same
cognitive mechanism. Second, it goes without saying that our mind
contains a mechanism for generating beliefs (the belief-forming
mechanism), and that there must be some mechanism or another in charge
of generating belief-like imaginings. It is also well known that
cognitive mechanisms are evolutionary costly to build and maintain.
Thus, evolution might have adopted the parsimonious strategy of
redeploying a pre-existing mechanism (the belief-forming mechanism)
for a non-primary function, i.e., generating belief-like
imaginings--in general, this hypothesis is also supported by the
idea that neural reuse is one of the fundamental organizational
principle of the brain (Anderson 2008). If one puts these two strands
of reasoning together, one gets a *prima facie* case for the
claim that imagining believing is implemented by the reuse of the
belief-forming mechanism--that is, a *prima facie* case
for the conclusion that imagining believing satisfies (b.ii). Since
imagining believing appears also to satisfy (b.i) and (a), lacking
evidence to the contrary, Simulation Theorists are justified in
considering it to be a high-level simulation process.



Let's take stock. We have examined a few suggested instances of
high-level simulation processes. If Simulation Theorists are correct,
they exhibit the following commonalities: they satisfy
 PROC
 (this is why they are *simulation* processes); they are
typically conscious, under voluntary control, and stimulus-independent
(this is why they are *high-level*). Do they have some other
important features in common? Yes, they do--Simulation Theorists
say. They all are *under the control* of a single cognitive
mechanism: imagination (more precisely, Currie & Ravenscroft
(2002) talk of Re-Creative Imagination, while Goldman (2006, 2009)
uses the expression "Enactment Imagination"). The
following passage will give you the basic gist of the proposal:



> 
> 
> What is distinctive to high-level simulation is the psychological
> mechanism ... that produces it, the mechanism of imagination.
> This psychological system is capable of producing a wide variety of
> simulational events: simulated seeings (i.e., visual imagery),
> ... simulated motor actions (motor imagery), simulated beliefs,
> ... and so forth. ... In producing simulational outputs,
> imagination does not operate all by itself. ... For example, it
> recruits parts of the visual system to produce visual imagery
> .... Nonetheless, imagination "'takes the
> lead"' in directing or controlling the other systems it
> enlists for its project. (Goldman 2009: 484-85)
> 
> 
> 



Here is another way to make the point. We already know that, according
to ST, visualizing is implemented by the reuse of the visual
mechanism. In the above passage, Goldman adds that the reuse of the
visual mechanism is initiated, guided and controlled by imagination.
The same applies, *mutatis mutandis*, to all cases of
high-level simulation processes. For example, in imagining hearing,
imagination "gets in control" of the auditory mechanism,
takes it off-line, and (re)uses it to generate simulated auditory
experiences. Goldman (2012b, Goldman & Jordan 2013) supports this
claim by making reference to neuroscientific data indicating that the
same core brain network, the so-called "default network",
subserves all the following self-projections: prospection (projecting
oneself into one's future); episodic memory (projecting oneself
into one's past); perspective taking (projecting oneself into
other minds); and navigation (projecting oneself into other places)
(see Buckner & Carroll 2007 for a review). These different
self-projections presumably involve different high-level simulation
processes. However, they all have something in common: they all
involve imagination-based perspectival shifts. Therefore, the fact
that there is one brain network common to all these self-projections
lends some support to the claim that there is one common cognitive
mechanism, i.e., imagination, which initiates, guides, and controls
all high-level simulation processes. 



If Goldman is right, and all high-level simulation processes are
guided by imagination, we can then explain why, in our common
parlance, we tend to describe high-level simulation processes and
outputs in terms of imaginings, images, imagery, etc. More
importantly, we can also explain why high-level simulation processes
are conscious, under voluntary control, and stimulus-independent.
These are, after all, typical properties of imaginative processes.
However, there are simulation processes that typically are neither
conscious, nor under voluntary control, nor stimulus independent. This
indicates that they are not imagination-based. It is to this other
type of simulation processes that we now turn.


### 3.2 Low-Level Simulation Processes



Low-level simulation processes are cognitive processes with these
features: (a\*) they are typically unconscious, automatic, and
stimulus-driven; (b) they satisfy
 PROC,
 that is, they are implemented by the *reuse* of a certain
cognitive mechanism, *C*, and their output states
*resemble* the output states generated by the use of *C*.
What cognitive processes are, according to ST, instances of low-level
simulation? The answer can be given in two words: mirroring processes.
Clarifying what these two words mean, however, will take some
time.



The story begins at the end of the 1980s in Parma, Italy, where the
neuroscientist Giacomo Rizzolatti and his team were investigating the
properties of the neurons in the macaque monkey ventral premotor
cortex. Through single-cell recording experiments, they discovered
that the activity of neurons in the area F5 is correlated with
goal-directed motor actions and not with particular movements
(Rizzolatti et al. 1988). For example, some F5 neurons fire when the
monkey grasps an object, regardless of whether the monkey uses the
left or the right hand. A plausible interpretation of these results is
that neurons in monkey area F5 encode *motor intentions* (i.e.,
those intentions causing and guiding actions like reaching, grasping,
holding, etc.) and not mere *kinematic instructions* (i.e.,
those representations specifying the fine-grained motor details of an
action). (In-depth philosophical analyses of the notion of motor
intention can be found in: Brozzo forthcoming; Butterfill &
Sinigaglia 2014; Pacherie 2000). This was an already interesting
result, but it was not what the Parma group became famous for. Rather,
their striking discovery happened a few years later, helped by
serendipity. Researchers were recording the activity of F5 neurons in
a macaque monkey performing an object-retrieval task. In between
trials, the monkey stood still and watched an experimenter setting up
the new trial, with microelectrodes still measuring the monkey's
brain activity. Surprisingly, some of the F5 neurons turned out to
fire when the monkey *saw* the experimenter grasping and
placing objects. This almost immediately led to new experiments, which
revealed that a portion of F5 neurons not only fire when the monkey
performs a certain goal-directed motor action (say, bringing a piece
of food to the mouth), but also when it sees another agent performing
the same (type of) action (di Pellegrino et al. 1992; Gallese et al.
1996; Rizzolatti et al. 1996). For this reason, these neurons were
aptly called "*mirror neurons*", and it was
proposed that they encode motor intentions both during action
execution and action observation (Rizzolatti & Sinigaglia 2007,
forthcoming). Later studies found mirror neurons also in the macaque
monkey inferior parietal lobule (Gallese et al. 2002), which together
with the ventral premotor cortex constitutes the monkey *cortical
mirror neuron circuit* (Rizzolatti & Craighero 2004).



Subsequent evidence suggested that an *action mirror
mechanism*--that is, a cognitive mechanism that gets
activated both when an individual performs a certain goal-directed
motor action and when she sees another agent performing the same
action--also exists in the human brain (for reviews, see
Rizzolatti & Craighero 2004, and Rizzolatti & Sinigaglia
forthcoming). In fact, it appears that there are *mirror
mechanisms* in the human brain outside the action domain as well:
a mirror mechanism for disgust (Wicker et al. 2003), one for pain
(Singer at al. 2004; Avenanti et al. 2005), and one for touch
(Blakemore et al. 2005). Given the variety of mirror mechanisms, it is
not easy to give a definition that fits them all. Goldman (2008b) has
quite a good one though, and we will draw from it: a cognitive
mechanism is a mirror mechanism if and only if it gets activated both
when an individual undergoes a certain mental event
*endogenously* and when she *perceives a sign* that
another individual is undergoing the same (type of) mental event. For
example, the pain mirror mechanism gets activated both when
individuals experience "a painful stimulus and ... when
they observe a signal indicating that [someone else] is receiving a
similar pain stimulus" (Singer et al. 2004: 1157).



Having introduced the notions of mirror neuron and mirror mechanism,
we can define the crucial notion of this section: *mirroring
process*. We have seen that mirror mechanisms can get activated in
two distinct modes: (i) endogenously; (ii) in the perception mode. For
example, my action mirror mechanism gets endogenously activated when I
grasp a mug, while it gets activated in the perception mode when I see
you grasping a mug. Following again Goldman (2008b), let us say that a
cognitive process is a mirroring process if and only if it is
constituted by the activation of a mirror mechanism *in the
perception mode*. For example, what goes on in my brain when I see
you grasping a mug counts as a mirroring process.



Now that we know what mirroring processes are, we can return to our
initial problem--i.e., whether they are low-level simulation
processes (remember that a cognitive process is a low-level simulation
process if and only if: (a\*) it is typically unconscious, automatic,
and stimulus-driven; (b) it satisfies
 PROC).
 For reasons of space, we will focus on disgust mirroring only.



Wicker et al. (2003) carried out an fMRI study in which participants
first observed videos of disgusted facial expressions and subsequently
underwent a disgust experience via inhaling foul odorants. It turned
out that the same neural area--the left anterior
insula--that was preferentially activated during the experience
of disgust was also preferentially activated during the observation of
the disgusted facial expressions. These results indicate the existence
of a disgust mirror *mechanism*. Is disgust *mirroring*
(the activation of the disgust mirror mechanism in the perception
mode) a low-level simulation process? Simulation Theorists answer in
the affirmative.



Here is why disgust mirroring satisfies (a\*): the process is
*stimulus-driven*: it is sensitive to certain perceptual
stimuli (disgusted facial expressions); it is *automatic*; and
it is typically *unconscious* (even though its output, i.e.,
"mirrored disgust", is sometimes conscious). What about
condition (b)? Presumably, the primary (evolutionary) function of the
disgust mechanism is to produce a disgust response to spoiled food,
germs, parasites etc. (Rozin et al. 2008). In the course of evolution,
this mechanism could have been subsequently co-opted to also get
activated by the perception (of a sign) that someone else is
experiencing disgust, in order to facilitate social learning of food
preferences (Gariepy et al. 2014). If this is correct, then
disgust mirroring is implemented by the *reuse* of the disgust
mechanism (by employing this mechanism for a function different than
its primary one). Moreover, the output of disgust mirroring
*resembles* the genuine experience of disgust in at least two
significant respects: first, both mental states have the same neural
basis; second, when conscious, they share a similar phenomenology.
Accordingly, (b) is satisfied. By putting all this together,
Simulation Theorists conclude that disgust mirroring is a low-level
simulation process, and mirrored disgust is a simulated mental state
(Goldman 2008b; Barlassina 2013)


## 4. The Role of Mental Simulation in Mindreading



In the previous section, we examined the case for the psychological
reality of mental simulation. We now turn to ST *as a theory of
mindreading*. We will tackle two main issues: the extent to which
mindreading is simulation-based, and how simulation-based mindreading
works.


### 4.1 The Centrality of Mental Simulation in Mindreading



ST proposes that mental simulation plays a *central role* in
mindreading, i.e., it plays a central role in the capacity to
represent and reason about others' mental state. What does
"central" mean here? Does it mean *the* central
role, with other contributors to mindreading being merely peripheral?
This is an important question, since in recent years there have been
proposed hybrid models according to which both mental simulation and
theorizing play important roles in mindreading (see
 section 5.2).
 



A possible interpretation of the claim that mental simulation plays a
central role in representing others' mental states is that
mindreading events are *always* simulation-based, even if they
sometimes also involve theory. Some Simulation Theorists, however,
reject this interpretation, since they maintain that there are
mindreading events in which mental simulation plays no role at all
(Currie & Ravenscroft 2002). For example, if I know that Little
Jimmy is happy every time he finds a dollar, and I also know that he
has just found a dollar, I do not need to undergo any simulation
process to conclude that Little Jimmy is happy right now. I just need
to carry out a simple logical inference.



However, generalizations like, "Little Jimmy is happy every time
he finds a dollar," are *ceteris paribus* rules. People
readily recognize exceptions: for example, we recognize situations in
which Jimmy would probably not be happy even if he found a dollar,
including some in which finding a dollar might actually make him
unhappy. Rather than applying some additional or more complex rules
that cover such situations, it is arguable that putting ourselves in
Jimmy's situation and using "good common sense" alerts us
to to these exceptions and overrides the rule. If that is correct,
then simulation is acting as an overseer or governor even when people
appear to be simply applying rules. 



Goldman (2006) suggests that we cash out the central role of mental
simulation in representing others' mental states as follows:
mindreading is *often* simulation-based. Goldman's
suggestion, however, turns out to be empty, since he explicitly
refuses to specify what "often" means in this context.




> 
> 
> How often is often? Every Tuesday, Thursday, and Saturday? Precisely
> what claim does ST mean to make? It is unreasonable to demand a
> precise answer at this time. (Goldman 2006: 42; see also Goldman 2002;
> Jeannerod & Pacherie 2004)
> 
> 
> 



Perhaps a better way to go is to characterize the centrality of mental
simulation for mindreading not in terms of *frequency of use*,
but in terms of *importance*. Currie and Ravenscroft make the
very plausible suggestion that "one way to see how important a
faculty is for performing a certain task is to examine what happens
when the faculty is lacking or damaged" (Currie &
Ravenscroft 2002: 51). On this basis, one could say that mental
simulation plays a *central* role in mindreading if and only
if: if one's simulational capacity (i.e., the capacity to
undergo simulation processes/simulated mental states) were impaired,
then one's mindreading capacity would be *significantly*
impaired. 



An elaboration of this line of thought comes from Gordon (2005)--
see also Gordon (1986, 1996) and Peacocke (2005)--who argues that
someone lacking the capacity for mental simulation would not be able
to represent mental states as such, since she is incapable of
representing anyone as having a mind in the first place.
Gordon's argument is essentially as follows:




We represent something as having a mind, as having mental states and
processes, only if we represent it as a subject ("subject of
experience," in formulations of "the hard problem of
consciousness"), where "a subject" is understood as
a generic "I". This distinguishes it from a "mere
object" (and also is a necessary condition for a more benevolent
sort of empathy).



To represent something as another "I" is to represent it
as a possible target of self-projection: as something one might (with
varying degrees of success) imaginatively put oneself in the place of.
(Of course, one can fancifully put oneself in the place of just about
anything--a suspension bridge, even; but that is not a
*reductio ad absurdum*, because one can also fancifully
represent just about anything as having a mind.) 




It is not clear, however, what consequences Gordon's conceptual
argument would have for mindreading, if any. Even if a capacity to
self-project were needed for representing mental states as such, would
lack of this capacity necessarily impair mindreading? That is,
couldn't one predict explain, predict, and coordinate behavior using a
theory of internal states, without conceptualizing these as states of
an I or subject? As a more general point, Simulation Theorists have
never provided a principled account of what would constitute a
"significant impairment" of mindreading capacity.



To cut a long story short, ST claims that mental simulation plays a
central role in mindreading, but at the present stage its proponents
do not agree on what this centrality exactly amounts to. We will come
back to this issue in
 section 5,
 when we shall discuss the respective contributions of mental
simulation and theorizing in mindreading.



We now turn to a different problem: how does mental simulation
contribute to mindreading when it does? That is, how does
simulation-based mindreading work? Here again, Simulation Theorists
disagree about what the right answer is. In what follows, we explore
some dimensions of disagreement.


### 4.2 Constitution or Causation?



Some Simulation Theorists defend a *strong view* of
simulation-based mindreading (Gordon 1986, 1995, 1996; Gallese et al.
2004; Gallese & Sinigaglia 2011). They maintain that many
simulation-based mindreading events are (entirely)
*constituted* by mental simulation events (where mental
simulation events are simulated mental states or simulation
processes). In other words, some Simulation Theorists claim that,
*on many occasions*, the fact that a subject *S* is
representing someone else's mental states is nothing over and
above the fact that *S* is undergoing a mental simulation event:
the former fact reduces to the latter. For example, Lisa's
undergoing a mirrored disgust experience as a result of observing
John's disgusted face would count as a mindreading event:
Lisa's simulated mental state would represent John's
disgust (Gallese et al. 2004). Let us call this "the
*Constitution View*".



We shall elaborate on the details of the Constitution View in
 section 4.3.
 Before doing that, we consider an argument that has been directed
against it over and over again, and which is supposed to show that the
Constitution View is a non-starter (Fuller 1995; Heal 1995; Goldman
2008b; Jacob 2008, 2012). Lacking a better name, we will call it
"the *Anti-Constitution argument*". Here it is. By
definition, a mindreading event is a mental event in which a subject,
*S*, represents another subject, *Q*, as having a certain
mental state *M*. Now--the argument continues--*the
only way* in which *S* can represent *Q* as having
*M* is this: *S* has to employ the *concept* of that
mental state and form the *judgment*, or the *belief*,
that *Q* is in *M*. Therefore, a mindreading event is
identical to an event of judging that someone else has a certain
mental state (where this entails the application of mentalistic
concepts). It follows from this that mental simulation events cannot
be constitutive of mindreading events, since the former events are not
events of judging that someone else has a certain mental state. An
example should clarify the matter. Consider Lisa again, who is
undergoing a mirrored *disgust experience* as a result of
observing John's disgusted face. Clearly, undergoing such a
simulated disgust experience is a different mental event from
*judging* that John is experiencing disgust. Therefore,
Lisa's mental simulation does not constitute a mindreading
event.



In
 section 4.3,
 we will discuss how the defenders of the Constitution View have
responded to this argument. Suppose for the moment that the
Anti-Constitution argument is sound. What alternative pictures of
simulation-based mindreading are available? Those Simulation Theorists
who reject the Constitution View tend to endorse the *Causation
View*, according to which mental simulation events never
constitute mindreading events, but only *causally contribute*
to them. The best developed version of this view is Goldman's
(2006) *Three-Stage Model* (again, this is our label, not his),
whose basic structure is as follows:




STAGE 1. *Mental simulation*: Subject *S* undergoes a
simulation process, which outputs a token simulated mental state
*m\**.



STAGE 2. *Introspection*: *S* introspects *m\** and
categorizes/conceptualizes it *as* (a state of type)
*M*.



STAGE 3. *Judgment*: *S* attributes (a state of type)
*M* to another subject, *Q*, through the judgment
**Q* is in *M**.



(The causal relations among these stages are such that: STAGE 1 causes
STAGE 2, and STAGE 2 in turn causes STAGE 3. See Spaulding 2012 for a
discussion of the notion of causation in this context.)




Here is our trite example. On the basis of observing John's
disgusted facial expression, Lisa comes to *judge* that John is
having a disgust experience. How did she arrive at the formation of
this judgment? Goldman's answer is as follows. The observation
of John's disgusted facial expression triggered a disgust
mirroring process in Lisa, resulting in Lisa's undergoing a
mirrored disgust experience (STAGE 1). This caused Lisa to introspect
her simulated disgust experience and to categorize it as a disgust
experience (STAGE 2) (the technical notion of introspection used by
Goldman will be discussed in
 section 4.4).
 This, in turn, brought about the formation of the judgment *John
is having a disgust experience* (STAGE 3). Given that, according
to Goldman, mindreading events are identical to events of judging that
someone else has a certain mental state, it is only this last stage of
Lisa's cognitive process that constitutes a mindreading event.
On the other hand, the previous two stages were merely causal
contributors to it. But mental simulation entirely took place at STAGE
1. This is why the Three-Stage Model is a version of the Causation
View: according to the model, mental simulation events *causally
contribute* to, but do not constitute, mindreading events.


### 4.3 Mindreading without Judgement



The main strategy adopted by the advocates of the Constitution View in
responding to the Anti-Constitution argument consists in impugning the
identification of mindreading events with events of *judging*
that someone else has a certain mental state. A prominent version of
this position is Gordon's (1995, 1996) *Radical
Simulationism*, according to which representing someone
else's mental states does not require the formation of
*judgments* involving the application of *mentalistic
concepts*. Rather, Gordon proposes that the main bulk of
mindreading events are *non-conceptual representations* of
others' mental states, where these non-conceptual
representations are constituted by mental simulation events. If this
is true, many mindreading events are *constituted* by mental
simulation events, and thus the Constitution View is correct.



The following case should help to get Radical Simulationism across.
Suppose that I want to represent the mental state that an
individual--call him "Mr Tees"--is in right now.
According to Gordon, there is a false assumption behind the idea that,
in order to do so, I need to form a judgment with the content *Mr
Tees is in *M** (where "*M*" is a
placeholder for a mentalistic concept). The false assumption is that
the only thing that I can do is to simulate *myself* in Mr
Tees's situation. As Gordon points out, it is also possible for
me to simulate *Mr Tees* in his situation. And if I do so, my
very simulation of Mr Tees *constitutes* a representation of
his mental state, without the need of forming any judgment. This is
how Gordon makes his point:



> 
> 
> To simulate Mr Tees in his situation requires an egocentric shift, a
> recentering of my egocentric map on Mr Tees. He becomes in my
> imagination the referent of the first person pronoun "I".
> ... Such recentering is the prelude to transforming myself in
> imagination into Mr Tees as much as actors become the characters they
> play. ... But once a personal *transformation* has been
> accomplished, ... I am already representing *him* as being
> in a certain state of mind. (Gordon 1995: 55-56)
> 
> 
> 



It is important to stress the dramatic difference between
Gordon's Radical Simulationism and Goldman's Three-Stage
Model. According to the latter, mental simulation events *causally
contribute* to representing other people's mental states,
but the mindreading event proper is *always* constituted by a
judgment (or a belief). Moreover, Goldman maintains that the ability
to form such judgments requires both the capacity to
*introspect* one's own mental states (more in this in
 section 4.4)
 and possession of *mentalistic concepts*. None of this is true
of Radical Simulationism. Rather, Gordon proposes that, in the large
majority of cases, it is the very mental simulation event itself that
*constitutes* a representation of someone else's mental
states. Furthermore, since such mental simulation events neither
require the capacity for introspection nor possession of mentalistic
concepts, Radical Simulationism entails the surprising conclusion that
these two features play at best a very minor role in mindreading. A
testable corollary is that social interaction often relies on an
understanding of others that does not require the explicit application
of mental state concepts.


### 4.4 Mindreading and Introspection



From what we have said so far, one could expect that Gordon should
agree with Goldman on at least one point. Clearly, Gordon has to admit
that there are *some cases* of mindreading in which a subject
attributes a mental state to someone else through a judgment involving
the application of mentalistic concepts. Surely, Gordon cannot deny
that there are occasions in which we think things like *Mary
believes that John is late* or *Pat desires to visit
Lisbon*. Being a Simulation Theorist, Gordon will also presumably
be eager to maintain that many such mindreading events are based on
mental simulation events. But if Gordon admits that much, should he
not also concede that Goldman's Three-Stage Model is the right
account of *at least* those simulation-based mindreading
events? Surprising as it may be, Gordon still disagrees.



Gordon (1995) accepts that there are occasions in which a subject
arrives at a *judgment* about someone else's mental state
on the basis of some mental simulation event. He might also concede to
Goldman that such a judgment involves mentalistic concepts (but see
Gordon's 1995 distinction between *comprehending* and
*uncomprehending* ascriptions). *Contra* Goldman,
however, Gordon argues that *introspection* plays no role at
all in the generation of these judgments. Focusing on a specific
example will help us to clarify this further disagreement between
Goldman and Gordon.



Suppose that I know that Tom believes that (1) and (2):


1. *Fido is a dog*
2. *All dogs enjoy watching TV*



On this basis, I attribute to Tom the further belief that (3):


3. *Fido enjoys watching TV*



Goldman's Three-Stage Model explains this mindreading act in the
following way. FIRST STAGE: I imagine believing what Tom believes
(i.e., I imagine believing that (1) and (2)); I then feed those
belief-like imaginings into my reasoning mechanism (in the off-line
mode); as a result, my reasoning mechanism outputs the imagined belief
that (3). The SECOND STAGE of the process consists in introspecting
this simulated belief and categorizing it *as* a belief.
Crucially, in Goldman's model, "introspection" does
not merely refer to the capacity to self-ascribe mental states.
Rather, it picks out a *distinctive cognitive method* for
self-ascription, a method which is typically described as
*non-inferential* and *quasi-perceptual* (see the
section Inner sense accounts in the entry on
 self-knowledge).
 In particular, Goldman (2006) characterizes introspection as a
transduction process that takes the neural properties of a mental
state token as input and outputs a categorization of the type of
state. In the case that we are considering, my introspective mechanism
takes the neural properties of my token simulated belief as input and
categorizes it *as* a belief as output. After all this, the
THIRD STAGE occurs: I project the categorized belief onto Tom, through
the judgment *Tom believes* *that Fido enjoys watching
TV*. (You might wonder where the *content* of Tom's
belief comes from. Goldman (2006) has a story about that too, but we
will leave this aside).



What about Gordon? How does he explain, in a simulationist fashion but
without resorting to introspection, the passage from knowing that Tom
believes that (1) and (2) to judging that Tom believes that (3)?
According to Gordon, the first step in the process is, of course,
imagining *to be Tom*--thus believing, *in the context
of the simulation*, that (1) and (2). This results (again in the
context of the simulation) in the formation of the belief that (3).
But how do I now go about discovering that \*I\*, Tom, believe that (3)?
How can one perform such a self-ascription if not via introspection? A
suggestion given by Gareth Evans will show us how--Gordon
thinks.



Evans (1982) famously argued that we answer the question "Do I
believe that *p*?" by answering another question, namely
"Is it the case that *p*?" In other words, according
to Evans, we ascribe beliefs to ourselves not by introspecting, or by
"looking inside", but by looking "outside" and
trying to ascertain how the world is. If, e.g., I want to know whether
I believe that Manchester is bigger than Sheffield, I just ask myself
"Is Manchester bigger than Sheffield?" If I answer in the
affirmative, then I believe that Manchester is bigger than Sheffield.
If I answer in the negative, then I believe that Manchester is
*not* bigger than Sheffield. If I do not know what to answer,
then I do *not* have any belief with regard to this subject
matter.



Gordon (1986, 1995) maintains that this self-ascription
strategy--which he labels "the *ascent
routine*" (Gordon 2007)--is also the strategy that we
employ, in the context of a simulation, to determine the mental states
of the simulated agent:



> 
> 
> In a simulation of *O*, I settle the question of whether *O*
> believes that *p* by simply asking ... whether it is the
> case that *p*. That is, I simply concern myself with the
> world--*O*'s world, the world from *O*'s
> perspective. ... Reporting *O*'s beliefs *is*
> just reporting what is there. (Gordon 1995: 60)
> 
> 
> 



So, this is how, in Gordon's story, I come to judge that Tom has
the belief that Fido enjoys watching TV. In the context of the
simulation, \*I\* asked \*myself\* (where both "\*I\*" and
"\*myself\*" in fact refer to Tom) whether \*I\* believe that
Fido enjoys watching TV. And \*I\* answered this question by answering
another question, namely, whether it is the case that Fido enjoys
watching TV. Given that, from \*my\* perspective, Fido enjoys watching
TV (after all, from \*my\* perspective, Fido is a dog and all dogs enjoy
watching TV), \*I\* *expressed* my belief by saying: "Yes,
\*I\*, Tom, believe that Fido enjoys watching TV". As you can see,
in such a story, introspection does not do anything. (We will come
back to the role of introspection in mindreading in
 section 6.2).


### 4.5 Summary



In sections 2, 3, and 4 we dwelt upon the "internal"
disagreements among Simulation Theorists. It goes without saying that
such disagreements are both wide and deep. In fact, different
Simulation Theorists give different answers to such fundamental
questions as: "What is mental simulation?", "How
does mental simulation contribute to mindreading?, 'What is the
role of introspection in mindreading?" In light of such
differences of opinion in the simulationist camp, one might conclude
that, after all, Stich and Nichols (1997) were right when saying that
there is no such thing as the Simulation *Theory*. However, if
one considers what is shared among Simulation Theorists, one will
realize that there is unity amidst this diversity. A good way to
reveal the commonalities among different versions of ST is by
contrasting ST with its arch-enemy, i.e., the Theory-Theory of
mindreading. This is what we do in the next section.


## 5. Simulation Theory and Theory-Theory



ST is only one of several accounts of mindreading on the market. A
rough-and-ready list of the alternatives should at least include: the
Intentional Stance Theory (Dennett 1987; Gergely & Csibra 2003;
Gergely et al. 1995); Interactionism (Gallagher 2001; Gallagher &
Hutto 2008; De Jaegher at al. 2010); and the Theory-Theory (Gopnik
& Wellman 1992; Gopnik & Meltzoff 1997; Leslie 1994; Scholl
& Leslie 1999). In this entry, we will discuss the Theory-Theory
(TT) only, given that the TT-ST controversy has constituted the focal
point of the debate on mindreading during the last 30 years or so.


### 5.1 The Theory-Theory



As suggested by its name, the Theory-Theory proposes that mindreading
is grounded by the possession of a Theory of Mind ("a folk
psychology")--i.e., it is based on the tacit knowledge of
the following body of information: a number of "folk" laws
or principles connecting mental states with sensory stimuli,
behavioural responses, and other mental states. Here are a couple of
putative examples:




*Law of sight*: If *S* is in front of object *O*,
*S* directs her eye-gaze to *O*, *S*'s visual
system is properly functioning, and the environmental conditions are
optimal, then *ceteris paribus* *S* will see *O*.



*Law of the practical syllogism*: If *S* desires a certain
outcome *G* and *S* believes that by performing a certain
action *A* she will obtain *G*, then *ceteris
paribus* *S* will decide to perform *A*.




The main divide among Theory-Theorists concerns how the Theory of Mind
is acquired--i.e., it concerns where this body of knowledge comes
from. According to the Child-Scientist Theory-Theory (Gopnik &
Wellman 1992; Gopnik & Meltzoff 1997), a child constructs a Theory
of Mind exactly as a scientist constructs a scientific theory: she
collects evidence, formulates explanatory hypotheses, and revises
these hypotheses in the light of further evidence. In other words,
"folk" laws and principles are obtained through hypothesis
testing and revision--a process that, according to proponents of
this view, is guided by a general-purpose, Bayesian learning mechanism
(Gopnik & Wellman 2012). On the contrary, the Nativist
Theory-Theory (Carruthers 2013; Scholl & Leslie 1999) argues that
a significant part of the Theory of Mind is innate, rather than
learned. More precisely, Nativists typically consider the core of the
Theory of Mind as resulting from the maturation of a cognitive module
specifically dedicated to representing mental states



These disagreements notwithstanding, the main tenet of TT is clear
enough: attributions of mental states to other people are guided by
the possession of a Theory of Mind. For example, if I know that you
desire to buy a copy of *The New York Times* and I know that
you believe that if you go to *News & Booze* you can buy a
copy, then I can use the *Law of the Practical Syllogism* to
infer that you will decide to go to *News & Booze*.



TT has been so popular among philosophers and cognitive scientists
that the explanation it proposes has ended up being the name of the
very phenomenon to be explained: on many occasions, scholars use the
expression "Theory of Mind" as a synonym of
"mindreading". Simulation Theorists, however, have never
been particularly impressed by this. According to them, there is
*no need* to invoke the tacit knowledge of a Theory of Mind to
account for mindreading, since a more *parsimonious*
explanation is available: we *reuse* our own cognitive
mechanisms to mentally simulate others' mental states. For
example, why do I need to know the *Law of the Practical
Syllogism*, if I can employ my own decision-making mechanism
(which I have anyway) to simulate your decision? It is
*uneconomical*--Simulation Theorists say--to resort
to an information-rich strategy, if an information-poor strategy will
do equally as well.



The difference between TT and ST can be further illustrated through a
nice example given by Stich and Nichols (1992). Suppose that you want
to predict the behavior of an airplane in certain atmospheric
conditions. You can collect the specifications of the airplane and
infer, on the basis of aerodynamic *theory*, how the airplane
will behave. Alternatively, you can build a model of the airplane and
run a *simulation*. The former scenario approximates the way in
which TT describes our capacity to represent others' mental
states, while the latter approximates ST. Two points need to be
stressed, though. First, while knowledge of aerodynamic theory is
explicit, TT says that our knowledge of the Theory of Mind is
typically *implicit* (or tacit). That is, someone who knows
aerodynamic theory is *aware* of the theory's laws and
principles and is able to report them correctly, while the laws and
principles constituting one's Theory of Mind typically lie
outside awareness and reportability. Second, when we run a simulation
of someone else's mental states, we do not need to build a
model: we *are* the model--that is, we use *our own
mind* as a model of others' minds.



Simulation Theorists maintain that the *default state* for the
"model" is one in which the simulator simply makes no
adjustments when simulating another individual. That is, ST has it
that we are automatically disposed to attribute to a target mental
states no different from our own current states. This would often
serve adequately in social interaction between people who are
cooperating or competing in what is for practical purposes the same
situation. We tend to depart from this default when we perceive
relevant differences between others' situations and our own. In
such cases, we might find ourselves adjusting for situational
differences by putting ourselves imaginatively in what we consider the
other's situation to be.



We might also make adjustments for individual differences. An
acquaintance will soon be choosing between candidate *a* and
candidate *b* in an upcoming election. To us, projecting
ourselves imaginatively into that voting situation, the choice is
glaringly obvious: candidate *a*, by any reasonable criteria.
But then we may wonder whether this imaginative projection into the
voting situation adequately represents *our acquaintance* in
that situation. We might recall things the person has said, or
peculiarities of dress style, diet, or entertainment, that might seem
relevant. Internalizing such behavior ourselves, trying to "get
behind" it as an actor might get behind a scripted role, we
might then put, as it were, a different person into the voting
situation, one who might choose candidate *b*.



Such a transformation would require quarantining some of our own
mental states, preferences, and dispositions, inhibiting them so that
they do not contaminate our off-line decision-making in the role of
the other. Such inhibition of one's own mental states would be
cognitively demanding. For that reason, ST predicts that mindreading
will be subject to *egocentric errors*--that is, it
predicts that we will often attribute to a target the mental state
that we would have if we were in the target's situation, rather
than the state the target is actually in (Goldman 2006). In
 section 6.2,
 we shall discuss whether this prediction is borne out by the
data.


### 5.2 Collapse or Cooperation?



On the face of it, ST and TT could not be more different from one
another. Some philosophers, however, have argued that, on closer
inspection, ST collapses into TT, thus revealing itself as a form of
TT in disguise. The collapse argument was originally formulated by
Daniel Dennett (1987):



> 
> 
> If I make believe I am a suspension bridge and wonder what I will do
> when the wind blows, what "comes to my mind" in my
> make-believe state depends on... my *knowledge* of
> physics... Why should my making believe I have your beliefs be
> any different? In both cases, knowledge of the imitated object is
> needed to drive the... "simulation", and the
> knowledge must be... something like a *theory*. (Dennett
> 1987: 100-101, emphasis added)
> 
> 
> 



Dennett's point is clear. If I imagine being, say, a bridge,
what I imagine will depend on my theory of bridges. Suppose that I
have a folk theory of bridges that contains the following principle:
"A bridge cannot sustain a weight superior to its own
weight". In this case, if I imagine an elephant weighing three
tons walking over a bridge weighing two tons, I will imagine the
bridge collapsing. Since my "bridge-simulation" is
entirely *theory-driven*, "simulation" is a
misnomer. The same carries over to "simulating other
people"s mental states', Dennett says. If I try to imagine
your mental states, what I imagine will depend entirely on my Theory
of Mind. Therefore, the label "mental simulation" is
misleading.



Heal (1986) and Goldman (1989) promptly replied to Dennett. Fair
enough, if a system *S* tries to simulate the state of a
radically different system *Q* (e.g., if a human being tries to
simulate the state of a bridge), then *S*'s simulation must
be guided by a theory. However, if a system *S* tries to simulate
the state of a *relevantly similar* system *S*\*, then
*S*'s simulation can be entirely *process-driven*:
to simulate the state which *S*\* is in, *S* simply has to
run in itself a process similar to the one *S*\* underwent. Given
that, for all intents and purposes, human beings are relevantly
similar to each other, a human being can mentally simulate what
follows from having another human being's mental states without
resorting to a body of theoretical knowledge about the mind's
inner workings. She will just need to reuse her own cognitive
mechanisms to implement a simulation process.



This reply invited the following response (Jackson 1999). If the
possibility of process-driven simulation is grounded in the similarity
between the simulator and the simulated, then I have to assume that
you are relevantly similar to me, when I mentally simulate your mental
states. This particular assumption, in turn, will be derived from a
*general principle*--something like "Human beings
are psychologically similar". Therefore, mental simulation is
grounded in the possession of a theory. The threat of collapse is
back! One reply to Jackson's arguments is as follows (for other
replies see Goldman 2006): the fact that process-driven simulation is
*grounded* in the similarity among human beings does not entail
that, in order to run a simulation, a simulator must know (or believe,
or assume) that such similarity obtains; no more, indeed, than the
fact that the solubility of salt is *grounded* in the molecular
structure of salt entails that a pinch of salt needs to know chemistry
to dissolve in water.



Granting that ST and TT are distinct theories, we can now ask a
different question: are the theories better off individually or should
they join forces somehow? Let us be more explicit. Can ST on its own
offer an adequate account of mindreading (or at least of the great
majority of its episodes)? And what about TT? A good number of
theorists now believe that neither ST nor TT alone will do. Rather,
many would agree that these two theories need to cooperate, if they
want to reach a satisfactory explanation of mindreading. Some authors
have put forward TT-ST hybrid models, i.e., models in which the tacit
knowledge of a Theory of Mind is the central aspect of mindreading,
but it is in many cases supplemented by simulation processes
(Botterill & Carruthers 1999; Nichols & Stich 2003). Other
authors have instead defended ST-TT hybrid models, namely, accounts of
mindreading where the pride of place is given to mental simulation,
but where the possession of a Theory of Mind plays some non-negligible
role nonetheless (Currie & Ravenscroft 2002; Goldman 2006; Heal
2003). Since this entry is dedicated to ST, we will briefly touch upon
one instance of the latter variety of hybrid account.



Heal (2003) suggested that the domain of ST is restricted to those
mental processes involving *rational transitions* among
*contentful* mental states. To wit, Heal maintains that mental
simulation is the cognitive routine that we employ to represent other
people's *rational processes*, i.e., those cognitive
processes which are sensitive to the semantic content of the mental
states involved. On the other hand, 



> 
> 
> when starting point and/or outcome are [states] without content,
> and/or the connection is not [rationally] intelligible, there is no
> reason ... to suppose that the process ... can be simulated.
> (Heal 2003: 77)
> 
> 
> 



An example will clarify the matter. Suppose that I know that you
desire to eat sushi, and that you believe that you can order sushi by
calling *Yama Sushi*. To reach the conclusion that you will
decide to call *Yama Sushi*, I only need to imagine desiring
and believing what you desire and believe, and to run a simulated
decision-making process in myself. No further knowledge is required to
predict your decision: simulation alone will do the job. Consider, on
the other hand, the situation in which I know that you took a certain
drug and I want to figure out what your mental states will be. In this
case--Heal says--my prediction cannot be based on mental
simulation. Rather, I need to resort to a body of information about
the likely psychological effects of that drug, i.e., I have to resort
to a Theory of Mind (fair enough, I can also take the drug myself, but
this will not count as mental simulation). This, according to Heal,
generalizes to all cases in which a mental state is the input or the
output of a *mere causal* process. In those cases, mental
simulation is ineffective and should be replaced by theorizing. Still,
those cases do not constitute the central part of mindreading. In
fact, many philosophers and cognitive scientists would agree that the
crucial component of human mindreading is the ability to reason about
others' *propositional attitudes*. And this is exactly
the ability that, according to Heal, should be explained in term of
mental simulation. This is why Heal's proposal counts as an
ST-TT hybrid, rather than the other way around.


## 6. Simulation Theory: Pros and Cons



ST has sparked a lively debate, which has been going on since the end
of the 1980s. This debate has dealt with a great number of theoretical
and empirical issues. On the theoretical side, we have seen
philosophical discussions of the relation between ST and functionalism
(Gordon 1986; Goldman 1989; Heal 2003; Stich & Ravenscroft 1992),
and of the role of tacit knowledge in cognitive explanations (Davies
1987; Heal 1994; Davies & Stone 2001), just to name a few.
Examples of empirical debates are: how to account for mindreading
deficits in Autism Spectrum Disorders (Baron-Cohen 2000; Currie &
Ravenscroft 2002), or how to explain the evolution of mindreading
(Carruthers 2009; Lurz 2011). It goes without saying that discussing
all these bones of contention would require an entire book (most
probably, a *series* of books). In the last section of this
entry, we confine ourselves to briefly introducing the reader to a
small sample of the main open issues concerning ST.


### 6.1 The Mirror Neurons Controversy



We wrote that ST proposes that mirroring processes (i.e., activations
of mirror mechanisms *in the perception mode*): (A) are
(low-level) simulation processes, and (B) contribute (either
constitutively or causally) to mindreading (Gallese et al. 2004;
Gallese & Goldman 1998; Goldman 2006, 2008b; Hurley 2005). Both
(A) and (B) have been vehemently contested by ST's
opponents.



Beginning with (A), it has been argued that mirroring processes do not
qualify as simulation processes, because they fail to satisfy the
definition of "simulation process" (Gallagher 2007;
Herschbach 2012; Jacob 2008; Spaulding 2012) and/or because they are
better characterized in different terms, e.g., as enactive perceptual
processes (Gallagher 2007) or as elements in an information-rich
process (Spaulding 2012). As for (B), the main worry runs as follows.
Granting that mirroring processes are simulation processes, what
evidence do we have for the claim that they contribute to mindreading?
This, in particular, has been asked with respect to the role of
mirroring processes in "action understanding" (i.e., the
interpretation of an agent's behavior in terms of the
agent's intentions, goals, etc.). After all, the neuroscientific
evidence just indicates that action mirroring *correlates* with
episodes of action understanding, but correlation is not causation,
let alone constitution. In fact, there are no studies examining
whether disruption of the monkey mirror neuron circuit results in
action understanding deficits, and the evidence on human action
understanding following damage to the action mirror mechanism is
inconclusive at best (Hickok 2009). In this regard, some authors have
suggested that the most plausible hypothesis is instead that action
mirroring follows (rather than causes or constitutes) the
understanding of others' mental states (Csibra 2007; Jacob
2008). For example, Jacob (2008) proposes that the job of mirroring
processes in the action domain is just that of computing a
representation of the observed agent's next *movement*,
on the basis of a *previous representation* of the
agent's intention. Similar deflationary accounts of the action
mirror mechanism have been given by Brass et al. (2007), Hickok
(2014), and Vannuscorps and Caramazza (2015)--these accounts
typically take the STS (superior temporal sulcus, a brain region
lacking mirror neurons) to be the critical neural area for action
understanding.



There are various ways to respond to these criticisms. A strong
response argues that they are based on a misunderstanding of the
relevant empirical findings, as well as on a mischaracterization of
the role that ST attributes to the action mirror mechanism in action
understanding (Rizzolatti & Sinigaglia 2010, 2014). A weaker
response holds that the focus on action understanding is a bit of a
red herring, given that the most robust evidence in support of the
central role played by mirroring processes in mindreading comes from
the emotion domain (Goldman 2008b). We will consider the weaker
response here.



Goldman and Sripada (2005) discuss a series of paired deficits in
emotion production and face-based emotion mindreading. These
deficits--they maintain--are best explained by the
hypothesis that one attributes emotions to someone else through
simulating these emotions in oneself: when the ability to undergo the
emotion breaks down, the mindreading capacity breaks down as well.
Barlassina (2013) elaborates on this idea by considering
Huntington's Disease (HD), a neurodegenerative disorder
resulting in, among other things, damage to the disgust mirror
mechanism. As predicted by ST, the difficulties individuals with HD
have in experiencing disgust co-occur with an impairment in
attributing disgust to someone else on the basis of observing her
facial expression--despite perceptual abilities and knowledge
about disgust being preserved in this clinical population. Individuals
suffering from HD, however, exhibit an intact capacity for disgust
mindreading on the basis of non-facial visual stimuli. For this
reason, Barlassina concludes by putting forward an ST-TT hybrid model
of disgust mindreading on the basis of visual stimuli.


### 6.2 Self and Others



ST's central claim is that we reuse *our own* cognitive
mechanisms to arrive at a representation of *other*
people's mental states. This claim raises a number of issues
concerning how ST conceptualizes the self-other relation. We will
discuss a couple of them.



Gallagher (2007: 355) writes that 



> 
> 
> given the large diversity of motives, beliefs, desires, and behaviours
> in the world, it is not clear how a simulation process ... can
> give me a reliable sense of what is going on in the other
> person's mind. 
> 
> 
> 



There are two ways of interpreting Gallagher's worry. First, it
can be read as saying that if mindreading is based on mental
simulation, then it is hard to see how mental state attributions could
be *epistemically justified*. This criticism, however, misses
the mark entirely, since ST is not concerned with whether mental state
attributions count as knowledge, but only with how, *as a matter of
fact*, we go about forming such attributions. A second way to
understand Gallagher's remarks is this: *as a matter of
fact*, we are pretty successful in understanding other minds;
however, given the difference among individual minds, this pattern of
successes cannot be explained in terms of mental simulation.



ST has a two-tier answer to the second reading of Gallagher's
challenge. First, human beings are very similar with regard to
cognitive processes such as perception, theoretical reasoning,
practical reasoning, etc. For example, there is a very high
probability that if both you and I look at the same scene, we will
have the same visual experience. This explains why, in the large
majority of cases, I can reuse my visual mechanism to successfully
simulate your visual experiences. Second, even though we are quite
good at recognizing others' mental states, we are nonetheless
prone to *egocentric errors*, i.e., we tend to attribute to a
target the mental state that *we* would undergo if we were in
the target's situation, rather than the actual mental state the
target is in (Goldman 2006). A standard example is the *curse of
knowledge* bias, where we take for granted that other people know
what we know (Birch & Bloom 2007). ST has a straightforward
explanation of such egocentric errors (Gordon 1995; Goldman 2006): if
we arrive at attributing mental states via mental simulation, the
attribution accuracy will depend on our capacity to
"quarantine" our genuine mental states, when they do not
match the target's, and to replace them with more appropriate
simulated mental states. This "adjustment" process,
however, is a demanding one, because our genuine mental states exert a
powerful tendency. Thus, Gallagher is right when he says that, on some
occasions, "if I project the results of my own simulation onto
the other, I understand only myself in that other's situation,
but I don't understand the other" (Gallagher 2007: 355).
However, given how widespread egocentric errors are, this counts as a
point in favour of ST, rather than as an argument against it (but see
de Vignemont & Mercier 2016, and Saxe 2005).



Carruthers (1996, 2009, 2011) raises a different problem for ST: no
version of ST can adequately account for self-attributions of mental
states. Recall that, according to Goldman (2006), simulation-based
mindreading is a three-stage process in which we first mentally
simulate a target's mental state, we then *introspect*
and categorize the simulated mental state, and we finally attribute
the categorized state to the target. Since Goldman's model has
it that attributions of mental states to others asymmetrically depend
on the ability to introspect one's own mental states, it
predicts that: (A) introspection is (ontogenetically and
phylogenetically) prior to the ability to represent others'
mental states; (B) there are cases in which introspection works just
fine, but where the ability to represent others' mental states
is impaired (presumably, because the mechanism responsible for
projecting one's mental states to the target is damaged).
Carruthers (2009) argues that neither (A) nor (B) are borne out by the
data. The former because there are no creatures that have
introspective capacities but at the same time lack the ability to
represent others' mental states; the latter because there are no
dissociation cases in which an intact capacity for introspection is
paired with an impairment in the ability to represent others'
mental states.



How might a Simulation Theorist respond to this objection? As we said
in
 section 4,
 Gordon's (1986, 1995, 1996) *Radical Simulationism* does
not assign any role to introspection in mindreading. Rather, Gordon
proposes that self-ascriptions are guided by ascent routines through
which we answer the question "Do I believe that *p*?"
by answering the lower-order question "Is it the case that
*p*?" Carruthers (1996, 2011) thinks that this won't
do either. Here is one of the many problems that Carruthers raises for
this suggestion--we can call it "*The Scope
Problem"*: 



> 
> 
> this suggestion appears to have only a limited range of application.
> For even if it works for the case of belief, it is very hard to see
> how one might extend it to account for our knowledge of our own goals,
> decisions, or intentions--let alone our knowledge of our own
> attitudes of wondering, supposing, fearing, and so on. (Carruthers
> 2011: 81)
> 
> 
> 



Carruthers' objections are important and deserve to be taken
seriously. To discuss them, however, we would need to introduce a lot
of further empirical evidence and many complex philosophical ideas
about self-knowledge. This is not a task that we can take up here (the
interested reader is encouraged to read, in addition to Gordon (2007)
and Goldman (2009), the SEP entries on
 self-knowledge
 and on
 introspection).
 The take-home message should be clear enough nonetheless: anybody who
puts forward an account of mindreading should remember that such an
account has to cohere with a plausible story about the cognitive
mechanisms underlying self-attribution.


### 6.3 Developmental Findings



The development of mindreading capacities in children has been one of
the central areas of empirical investigation. In particular,
developmental psychologists have put a lot of effort into detailing
how the ability to attribute false beliefs to others develops. Until
2005, the central experimental paradigm to test this ability was the
*verbal false belief task* (Wimmer & Perner 1983). Here is
a classic version of it. A subject is introduced to two dolls, Sally
and Anne, and three objects: Sally's ball, a basket, and a box.
Sally puts her ball in the basket and leaves the scene. While Sally is
away, Anne takes the ball out of the basket and puts it into the box.
Sally then returns. The subject is asked where she thinks Sally will
look for the ball. The correct answer, of course, is that Sally will
look inside the basket. To give this answer, the subject has to
attribute to Sally the *false belief* that the ball is in the
basket. A number of experiments have found that while four-year old
children pass this task, three-year old children fail it (for a
review, see Wellman et al. 2001). For a long time, the mainstream
interpretation of these findings has been that children acquire the
ability to attribute false beliefs only around their fourth birthday
(but see Clements & Perner 1994 and Bloom & German 2000).



In 2005, this developmental timeline was called into question.
Kristine Onishi and Renee Baillargeon (2005) published the
result of a *non-verbal* version of the false belief task,
which they administered to 15-month old infants. The experiment
involves three steps. First, the infants see a toy between two boxes,
one yellow and one green, and then an actor hiding the toy inside the
green box. Next, the infants see the toy sliding out of the green box
and hiding inside the yellow box. In the true belief condition (TB),
the actor notices that the toy changes location, while in the false
belief condition (FB) she does not. Finally, half of the infants see
the actor reaching into the green box, while the other half sees the
actor reaching into the yellow box. According to the
*violation-of-expectation paradigm*, infants reliably look for
a longer time at unexpected events. Therefore, if the infants expected
the actor to search for the toy *on the basis of* the
actor's belief about its location, then when the actor had a
*true belief* that the toy was hidden in one box, the infants
should look longer when the actor reached into the other box instead.
Conversely, the infants should look longer at one box when the actor
*falsely believed* that the toy was hidden in the other box.
Strikingly, these predictions were confirmed in both the (TB) and (FB)
conditions. On this basis, Onishi and Baillargeon (2005) concluded
that children of 15 months possess the capacity to represent
others' false beliefs.



This and subsequent versions of non-verbal false belief tasks
attracted a huge amount of interest (at the current stage of research,
there is evidence that sensitivity to others' false beliefs is
present in infants as young as 7 months--for a review, see
Baillargeon at al. 2016). Above all, the following two questions have
been widely discussed: why do children pass the non-verbal false
belief task at such an early age, but do not pass the verbal version
before the age of 4? Does passing the non-verbal false belief task
really indicate the capacity to represent others' false beliefs?
(Perner & Ruffman 2005; Apperly & Butterfill 2009; Baillargeon
et al. 2010; Carruthers 2013; Helming et al. 2014).



Goldman and Jordan (2013) maintain that ST has a good answer to both
questions. To begin with, they argue that it is implausible to
attribute to infants such sophisticated meta-representational
abilities as the ability to represent others' false beliefs.
Thus, Goldman and Jordan favour a deflationary view, according to
which infants are *sensitive* to others' false beliefs,
but do not represent them *as such*. In particular, they
propose that rather than believing that another subject **S*
(falsely) believes that *p**, infants simply imagine how the
world is from *S*'s perspective--that is, they simply
imagine that *p* is the case. This--Goldman and Jordan
say--is a more primitive psychological competence than
mindreading, since it does not involve forming a judgment about
others' mental states. This brings us to Goldman and
Jordan's answer to the question "why do children pass the
verbal false belief task only at four?" Passing this task
requires fully-fledged mindreading abilities and executive functions
such as inhibitory control. It takes quite a lot of time--around
3 to 4 years--before these functions and abilities come
online.


## 7. Conclusion



Since the late 1980s, ST has received a great amount of attention from
philosophers, psychologists, and neuroscientists. This is not
surprising. Mindreading is a central human cognitive capacity, and ST
challeges some basic assumptions about the cognitive processes and
neural mechanisms underlying human social behavior. Moreover, ST
touches upon a number of major philosophical problems, such as the
relation between self-knowledge and knowledge of other minds, and the
nature of mental concepts, including the concept of mind itself. In
this entry, we have considered some of the fundamental empirical and
philosophical issues surrounding ST. Many of them remain open. In
particular, while the consensus view is now that both mental
simulation and theorizing play important role in mindreading, the
currently available evidence falls short of establishing what their
respective roles are. In other words, it is likely that we shall end
up adopting a hybrid model of mindreading that combines ST and TT,
but, at the present stage, it is very difficult to predict what this
hybrid model will look like. Hopefully, the joint work of philosophers
and cognitive scientists will help to settle the matter.