PMC7294583_01
PMC7294583_02
Boxological representation of bottom-up vs top-down models of perception.
nihms-1582270-f0001.jpg
PMC7294583_02_nihms-1582270-f0001.jpg
F1
I broadly divide the hierarchy of processing into three parts: lower-level perception, higher-level perception, and cognitive. Information can be considered to be top-down if it jumps between these parts (Fig. 1).
Feedback pathways carrying top-down information to the early visual system in the adult brain. Blue arrows represent the feedforward, bottom-up connections across the hierarchy of visual regions. Red arrows represent feedback, top-down connections. Information from diverse cortical regions and systems is conveyed in top-down fashion to the visual system: Motor/efference copy, attention, expectation, and executive functions. Reproduced from
). Top-down influences on visual processing. Nature Reviews Neuroscience, 14, 350-363 with permission.
nihms-1582270-f0002.jpg
PMC7294583_10_nihms-1582270-f0002.jpg
F2
The clear presence of top-down neuroanatomical connections throughout in the mature, adult brain (e.g., within perceptual systems and between cognitive and perceptual systems) is a strong piece of evidence in favor of top-down mechanisms later in life (see Fig. 2).
Classic evidence of frontal lobe involvement in visual perception. Left panel, found increased frontal lobe activity when visual images were masked (i.e., are difficult to perceive) but not when stimuli were unmasked (i.e., easy to perceive). Right panel, found that when the probability of seeing a certain type of stimulus (e.g., a face in a block when there were a high proportion of faces presented), there are increases in the top-down connections from the frontal lobe to the visual system. Figures reproduced with permission.
nihms-1582270-f0003.jpg
PMC7294583_02_nihms-1582270-f0003.jpg
F3
Specifically, they found that the presentation of a given stimulus (e.g., a face) modulates bottom-up connections within the visual system and that expectation for a specific stimulus (e.g., being in a block with many face stimuli that results in a face expectation) strengthens top-down connections from the frontal cortex to the visual system (see Fig. 3). Similarly, found that adults activate their frontal cortex when experiencing unclear or difficult to process perceptual information (see for a specific theory as to how these prefrontal cortex signals may be biasing visual perception and Fig. 3).
PMC7294583_03
and provide direct evidence of top-down effects of expectation and feedback on perceptual processing in young infants. Top panel, functional near-infrared spectroscopy (fNIRS) recordings of the temporal and occipital cortex of 6-month-old infants revealed expected sensory cortex responses to both audiovisual stimuli (A+V+) and occipital lobe activity during the presentation of an auditory cue, but the unexpected omission of the visual stimulus (A+V-omission). This occipital cortex response is not a response to auditory only stimuli when infants are not expecting the visual stimulus (A+V-control,). Bottom: Twelve-month-old infants were presented with visual stimuli that were either validly predicted by an auditory cue or invalidly predicted. The validity of the cue modulated two components of the event-related potentials (ERPs,). Figures reproduced with permission.
nihms-1582270-f0004.jpg
PMC7294583_03_nihms-1582270-f0004.jpg
F4
Thus, the visual system responded when no visual stimulus was presented, indicating that top-down signals are modulating the visual system as early as 6 months of age and after only a couple of minutes of experience (see Fig. 4).a
PMC7294583_04
PMC7294583_05
PMC7294583_06
PMC7294583_07
PMC7294583_08
Infants can use their object knowledge to disambiguate perceptual input. Top panel, gave 3- to 4-month-old infants' experience with a pac-man shape (left). After this experience, infants used this pac-man knowledge to override their Gestalt perceptual-grouping principles when receiving ambiguous experience (middle) as evidenced by infants exhibiting a novelty preference for the circle at test. This novelty preference is a marked departure from looking preferences without that prior pac-man experience. Bottom panel, 8.5-month-old infants were able to employ their object knowledge of a key ring to generalize to an ambiguous display as evidenced by longer looking to the "move-apart" event compared to the "move-together" event. Consistent with the view that infants are using their object knowledge to disambiguate this scene, when a similar object is presented that does not fit the category of a key ring, infants looked longer at the "move-together" event. Figures reproduced with permission.
nihms-1582270-f0005.jpg
PMC7294583_09_nihms-1582270-f0005.jpg
F5
Across numerous studies using the same task shown in Fig. 5, this group has demonstrated that 4.5-month-old infants are able to use prior experience and object knowledge to segment an ambiguous visual scene. Fig. 5. Finally, showed that older infants (8.5 months) use the features of a familiar category (keys) to disambiguate novel exemplars of this category. Specifically, the more similar the novel visual scene was to keys, the longer infants looked when the ring was moved independently from the keys, demonstrating that they are segmenting the scene consistent with the familiar category (see Fig. 5).
PMC7294583_09
Infants can use their object knowledge to disambiguate perceptual input. Top panel, gave 3- to 4-month-old infants' experience with a pac-man shape (left). After this experience, infants used this pac-man knowledge to override their Gestalt perceptual-grouping principles when receiving ambiguous experience (middle) as evidenced by infants exhibiting a novelty preference for the circle at test. This novelty preference is a marked departure from looking preferences without that prior pac-man experience. Bottom panel, 8.5-month-old infants were able to employ their object knowledge of a key ring to generalize to an ambiguous display as evidenced by longer looking to the "move-apart" event compared to the "move-together" event. Consistent with the view that infants are using their object knowledge to disambiguate this scene, when a similar object is presented that does not fit the category of a key ring, infants looked longer at the "move-together" event. Figures reproduced with permission.
nihms-1582270-f0005.jpg
PMC7294583_09_nihms-1582270-f0005.jpg
F5
Across numerous studies using the same task shown in Fig. 5, this group has demonstrated that 4.5-month-old infants are able to use prior experience and object knowledge to segment an ambiguous visual scene. Fig. 5. Finally, showed that older infants (8.5 months) use the features of a familiar category (keys) to disambiguate novel exemplars of this category. Specifically, the more similar the novel visual scene was to keys, the longer infants looked when the ring was moved independently from the keys, demonstrating that they are segmenting the scene consistent with the familiar category (see Fig. 5).
PMC7294583_10
Feedback pathways carrying top-down information to the early visual system in the adult brain. Blue arrows represent the feedforward, bottom-up connections across the hierarchy of visual regions. Red arrows represent feedback, top-down connections. Information from diverse cortical regions and systems is conveyed in top-down fashion to the visual system: Motor/efference copy, attention, expectation, and executive functions. Reproduced from
). Top-down influences on visual processing. Nature Reviews Neuroscience, 14, 350-363 with permission.
nihms-1582270-f0002.jpg
PMC7294583_10_nihms-1582270-f0002.jpg
F2
The clear presence of top-down neuroanatomical connections throughout in the mature, adult brain (e.g., within perceptual systems and between cognitive and perceptual systems) is a strong piece of evidence in favor of top-down mechanisms later in life (see Fig. 2).
Young infants generalize based on variable visual experience. For example, found that when 3- to 4-month-old infants experienced one of three contours constructed from different elements (i.e., requiring infants to use the Gestalt perceptual-grouping principle of similarity), they could not generalize this experience to an unambiguous contour at test. This indicates that they could not perceive the contour using these elements. However, if infants were exposed to all three of these contours, they could generalize at test. Thus, variable experience supported better perception than more experience with a single type of stimulus. Figures reproduced with permission.
nihms-1582270-f0006.jpg
PMC7294583_10_nihms-1582270-f0006.jpg
F6
Across three experiments, these researchers investigated three different types of scenes, each composed of different elements that infants could distinguish and yet, infants consistently failed at this perceptual task (Fig. 6, left panel). However, the authors found that exposing infants to a combination of all three scene types resulted in successful perceptual performance (Fig. 6, right panel).
Increases in both global connectivity and long-range connections in early development. Left panel from presents (top row) structure MR images of neonates, 6-month olds, and adults, (middle row) images of long-range fiber tracks identified using diffusion tensor imaging (DTI) with notable differences in connection density between age groups, and (bottom row) brain networks represented as weighted graphs. Each size of each node represents the proportional node degree, or how many connections this area of the brain has. A large node will be a network hub. Again, there are notable differences in the relative size of the nodes and the distribution of connections between the nodes. Right panel from presents a graphical representation of the neonate and 2-year-old brain with nodes shaded by lobes. Neonate connections are largely local and nodes within each lobe are clustered together; however, by age 2 there are networks that span lobes as seen by less clear clustering by lobes. Moreover, there is a clear increase in the distance between connections as visualized in the graph. Distance is normalized to the size of the brain at each age. Figures reproduced with permission.
nihms-1582270-f0007.jpg
PMC7294583_10_nihms-1582270-f0007.jpg
F7
There are convergent findings in the measures of both functional connectivity and structural connectivity of this direction of development (Fig. 7).