Categorical perception occurs in newly learned faces, other-race faces, and inverted faces

Disruption of Anterior Temporal Lobe Reduces Distortions in Memory From Category Knowledge

Memory retrieval does not provide a perfect recapitulation of past events, but instead an imperfect reconstruction of event-specific details and general knowledge. However, it remains unclear whether this reconstruction relies on mixtures of signals from different memory systems, including one supporting general knowledge. Here, we investigate whether the anterior temporal lobe (ATL) distorts new memories because of prior category knowledge. In this preregistered experiment (n = 36), participants encoded and retrieved image-location associations. Most images' locations were clustered according to their category, but some were in random locations. With this protocol, we previously demonstrated that randomly located images were retrieved closer to their category cluster relative to their encoded locations, suggesting an influence of category knowledge. We combined this procedure with TMS delivered to the left ATL before retrieval. We separately examined event-specific details (error) and category knowledge (bias) to identify distinct signals attributable to different memory systems. We found that TMS to ATL attenuated bias in location memory, but this effect was limited to exploratory analyses of atypical category members of animal categories. The magnitude of error was not impacted, suggesting that a memory's fidelity can be decoupled from its distortion by category knowledge. This raises the intriguing possibility that retrieval is jointly supported by separable memory systems.

Differences Between East Asians and Westerners in the Mental Representations and Visual Information Extraction Involved in the Decoding of Pain Facial Expression Intensity

Effectively communicating pain is crucial for human beings. Facial expressions are one of the most specific forms of behavior associated with pain, but the way culture shapes expectations about the intensity with which pain is typically facially conveyed, and the visual strategies deployed to decode pain intensity in facial expressions, is poorly understood. The present study used a data-driven approach to compare two cultures, namely East Asians and Westerners, with respect to their mental representations of pain facial expressions (experiment 1, N=60; experiment 2, N=74) and their visual information utilization during the discrimination of facial expressions of pain of different intensities (experiment 3; N=60). Results reveal that compared to Westerners, East Asians expect more intense pain expressions (experiments 1 and 2), need more signal, and do not rely as much as Westerners on core facial features of pain expressions to discriminate between pain intensities (experiment 3). Together, those findings suggest that cultural norms regarding socially accepted pain behaviors shape the expectations about pain facial expressions and decoding visual strategies. Furthermore, they highlight the complexity of emotional facial expressions and the importance of studying pain communication in multicultural settings.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42761-023-00186-1.

Face templates for the Chicago Face Database

Researchers often need to manipulate faces, such as developing a continuum between two faces or averaging a set of faces. In order to do so, researchers use morphing software, but they first need to fit a template to the idiosyncratic landmarks in each face. In this paper, we present a set of landmark templates for the Chicago Face Database (CFD; Ma, D. S., Correll, J., & Wittenbrink, B. (2015). The Chicago Face Database: A free stimulus set of faces and norming data. Behavior Research Methods, 47(4), 1122-1135). The CFD is a free online face database containing images of faces of people from various races and genders. We provide templates for each of 597 neutral (non-expressive) faces in version two of the CFD. Our templates are unique because the facial landmarks were hand placed by researchers. Hand placing facial landmarks allows for more accurate placement of landmarks than a computer-generated template. Historically, hand-placed templates were created by individual labs and not shared. In this paper, we describe how our templates were created, and some possible uses for the templates. We hope that our templates ease the burden for other researchers to manipulate faces.

The myth of categorical perception

Categorical perception (CP) is likely the single finding from speech perception with the biggest impact on cognitive science. However, within speech perception, it is widely known to be an artifact of task demands. CP is empirically defined as a relationship between phoneme identification and discrimination. As discrimination tasks do not appear to require categorization, this was thought to support the claim that listeners perceive speech solely in terms of linguistic categories. However, 50 years of work using discrimination tasks, priming, the visual world paradigm, and event related potentials has rejected the strongest forms of CP and provided little strong evidence for any form of it. This paper reviews the origins and impact of this scientific meme and the work challenging it. It discusses work showing that the encoding of auditory input is largely continuous, not categorical, and describes the modern theoretical synthesis in which listeners preserve fine-grained detail to enable more flexible processing. This synthesis is fundamentally inconsistent with CP. This leads to a different understanding of how to use and interpret the most basic paradigms in speech perception-phoneme identification along a continuum-and has implications for understanding language and hearing disorders, development, and multilingualism.

Conceptual knowledge shapes visual working memory for complex visual information

Human visual working memory (VWM) is a memory store people use to maintain the visual features of objects and scenes. Although it is obvious that bottom-up information influences VWM, the extent to which top-down conceptual information influences VWM is largely unknown. We report an experiment in which groups of participants were trained in one of two different categories of geologic faults (left/right lateral, or normal/reverse faults), or received no category training. Following training, participants performed a visual change detection task in which category knowledge was irrelevant to the task. Participants were more likely to detect a change in geologic scenes when the changes crossed a trained categorical distinction (e.g., the left/right lateral fault boundary), compared to within-category changes. In addition, participants trained to distinguish left/right lateral faults were more likely to detect changes when the scenes were mirror images along the left/right dimension. Similarly, participants trained to distinguish normal/reverse faults were more likely to detect changes when scenes were mirror images along the normal/reverse dimension. Our results provide direct empirical evidence that conceptual knowledge influences VWM performance for complex visual information. An implication of our results is that cognitive scientists may need to reconceptualize VWM so that it is closer to "conceptual short-term memory".

Use of superordinate labels yields more robust and human-like visual representations in convolutional neural networks

Human visual recognition is outstandingly robust. People can recognize thousands of object classes in the blink of an eye (50–200 ms) even when the objects vary in position, scale, viewpoint, and illumination. What aspects of human category learning facilitate the extraction of invariant visual features for object recognition? Here, we explore the possibility that a contributing factor to learning such robust visual representations may be a taxonomic hierarchy communicated in part by common labels to which people are exposed as part of natural language. We did this by manipulating the taxonomic level of labels (e.g., superordinate-level [mammal, fruit, vehicle] and basic-level [dog, banana, van]), and the order in which these training labels were used during learning by a Convolutional Neural Network. We found that training the model with hierarchical labels yields visual representations that are more robust to image transformations (e.g., position/scale, illumination, noise, and blur), especially when images were first trained with superordinate labels and then fine-tuned with basic labels. We also found that Superordinate-label followed by Basic-label training best predicts functional magnetic resonance imaging responses in visual cortex and behavioral similarity judgments recorded while viewing naturalistic images. The benefits of training with superordinate labels in the earlier stages of category learning is discussed in the context of representational efficiency and generalization.

The upside-down self: One's own face recognition is affected by inversion

One's own face is recognized more efficiently than any other face, although the neural mechanisms underlying this phenomenon remain poorly understood. Considering the extensive visual experience that we have with our own face, some authors have proposed that self-face recognition involves a more analytical perceptual strategy (i.e., based on face features) than other familiar faces, which are commonly processed holistically (i.e., as a whole). However, this hypothesis has not yet been tested with brain activity data. In the present study, we employed an inversion paradigm combined with event-related potential (ERP) recordings to investigate whether the self-face is processed more analytically. Sixteen healthy participants were asked to identify their own face and a familiar face regardless of its orientation, which could either be upright or inverted. ERP analysis revealed an enhanced amplitude and a delayed latency for the N170 component when faces were presented in an inverted orientation. Critically, both the self and a familiar face were equally vulnerable to the inversion effect, suggesting that the self-face is not processed more analytically than a familiar face. In addition, we replicated the recent finding that the attention-related P200 component is a specific neural index of self-face recognition. Overall, our results suggest that the advantage for self-face processing might be better explained by the engagement of self-related attentional mechanisms than by the use of a more analytical visuoperceptual strategy.

Familiar faces as islands of expertise

Most people recognise and match pictures of familiar faces effortlessly, while struggling to match unfamiliar face images. This has led to the suggestion that true human expertise for faces applies only to familiar faces. This paper develops that idea to propose that we have isolated 'islands of expertise' surrounding each familiar face that allow us to perform better with faces that resemble those we already know. This idea is tested in three experiments. The first shows that familiarity with a person facilitates identification of their relatives. The second shows that people are better able to remember faces that resemble someone they already know. The third shows that while prompting participants to think about resemblance at study produces a large positive effect on subsequent recognition, there is still a significant effect if there is no such prompt. Face-space-R (Lewis, 2004) is used to illustrate a possible computational explanation of the processes involved.

The Influences of Category Learning on Perceptual Reconstructions

We explore different ways in which the human visual system can adapt for perceiving and categorizing the environment. There are various accounts of supervised (categorical) and unsupervised perceptual learning, and different perspectives on the functional relationship between perception and categorization. We suggest that common experimental designs are insufficient to differentiate between hypothesized perceptual learning mechanisms and reveal their possible interplay. We propose a relatively underutilized way of studying potential categorical effects on perception, and we test the predictions of different perceptual learning models using a two-dimensional, interleaved categorization-plus-reconstruction task. We find evidence that the human visual system adapts its encodings to the feature structure of the environment, uses categorical expectations for robust reconstruction, allocates encoding resources with respect to categorization utility, and adapts to prevent miscategorizations.

Self-face perception in 12-month-old infants: A study using the morphing technique

The present study investigated self-face perception in 12-month-old infants using the morphing technique. Twenty-four 12-month-old infants participated in both the main and control experiments. In the main experiment, we used the participant's own face, an unfamiliar infant's face (age- and gender-matched), and a morphed face comprising 50 % each of the self and unfamiliar faces as stimuli. The control experiment followed the same procedure, except that the self-face was replaced with another unfamiliar face. In both experiments, two of these stimuli were presented side by side on a monitor in each trial, and infants' fixation duration was measured. Results showed that shorter fixation durations were found for the morphed face compared with the self-face and the unfamiliar face in the main experiment, but there were no significant preferences for any comparisons in the control experiment. The results suggest that 12-month-old infants could detect subtle differences in facial features between the self-face and the other faces, and infants might show less preference for the self-resembling morphed face due to increased processing costs, which can be interpreted using the uncanny valley hypothesis. Overall, representations of the self-face seem to a certain extent to be formed by the end of the first year of life through daily visual experience.

Categorical face perception in fish: How a fish brain warps reality to dissociate "same" from "different"

Categorical perception (CP) is the phenomenon by which a smoothly varying stimulus property undergoes a nonlinear transformation during processing in the brain. Consequently, the stimuli are perceived as belonging to distinct categories separated by a sharp boundary. Originally thought to be largely innate, the discovery of CP in tasks such as novel image discrimination has piqued the interest of cognitive scientists because it provides compelling evidence that learning can shape a category's perceptual boundaries. CP has been particularly closely studied in human face perception. In nonprimates, there is evidence for CP for sound and color discrimination, but not for image or face discrimination. Here, we investigate the potential for learned CP in a lower vertebrate, the damselfish Pomacentrus amboinensis. Specifically, we tested whether the ability of these fish to discriminate complex facial patterns tracked categorical rather than metric differences in the stimuli. We first trained the fish to discriminate sets of two facial patterns. Next, we morphed between these patterns and determined the just noticeable difference (JND) between a morph and original image. Finally, we tested for CP by analyzing the discrimination ability of the fish for pairs of JND stimuli along the spectrum of morphs between two original images. Discrimination performance was significant for the image pair straddling the boundary between categories, and chance for equivalent stimulus pairs on either side, thus producing the classic "category boundary" effect. Our results reveal how perception can be influenced in a top-down manner even in the absence of a visual cortex.

Exposure to linguistic labels during childhood modulates the neural architecture of race categorical perception

Perceptually categorizing a face to its racial belonging may have important consequences on interacting with people. However, race categorical perception (CP) has been scarcely investigated nor its developmental pathway. In this study, we tested the neurolinguistics rewiring hypothesis, stating that language acquisition modulates the brain processing of social perceptual categories. Accordingly, we investigated the electrophysiological correlates of race CP in a group of adults and children between 3 and 5 years of age. For both groups we found a greater modulation of the N400 connected with the processing of between category boundaries (i.e., faces belonging to different race groups) than within-category boundaries (i.e., different faces belonging to the same race group). This effect was the same in both adults and children, as shown by the comparable between-group amplitude of the differential wave (DW) elicited by the between-category faces. Remarkably, this effect was positively correlated with racial-labels acquisition, but not with age, in children. Finally, brain source analysis revealed the activation of a more modularized cortical network in adults than in children, with unique activation of the left superior temporal gyrus (STG) and the inferior frontal gyrus (IFG), which are areas connected to language processing. These are the first results accounting for an effect of language in rewiring brain connectedness when processing racial categories.

The effect of educational priming on face recognition from a silver alert

In a between-subjects' experimental design, we manipulated whether participants viewed an educational video on the importance of Silver Alerts before viewing an older Caucasian female in a Silver Alert. We also examined associations of target recognition with individual difference variables, including gender, ethnicity, Attitudes Towards Older People (ATOP), empathy, conscientiousness, as well as contact and experience with older adults. The results showed an advantage of the priming condition compared to the no-priming condition for correctly identifying the missing woman. Additionally, females correctly identified the missing woman more than males, and Caucasian participants correctly identified the missing woman more than African American participants. Lastly, participants who reported more experience with older adults were more likely to recognize the missing woman. The results suggest that preceding Silver Alerts with information about their importance may increase their effectiveness. Further research is needed to investigate how individual difference variables relate to recognition of missing senior citizens.

Abstract social categories facilitate access to socially skewed words

Recent work has shown that listeners process words faster if said by a member of the group that typically uses the word. This paper further explores how the social distributions of words affect lexical access by exploring whether access is facilitated by invoking more abstract social categories. We conduct four experiments, all of which combine an Implicit Association Task with a Lexical Decision Task. Participants sorted real and nonsense words while at the same time sorting older and younger faces (exp. 1), male and female faces (exp. 2), stereotypically male and female objects (exp. 3), and framed and unframed objects, which were always stereotypically male or female (exp. 4). Across the experiments, lexical decision to socially skewed words is facilitated when the socially congruent category is sorted with the same hand. This suggests that the lexicon contains social detail from which individuals make social abstractions that can influence lexical access.

Opposite Aftereffects for Chinese and Caucasian Faces are Selective for Social Category Information and not Just Physical Face Differences

Opposite changes in perception (aftereffects) can be simultaneously induced for faces from different social categories—for example, Chinese and Caucasian faces. We investigated whether these aftereffects are generated in high-level face coding that is sensitive to the social category information in faces, or in earlier visual coding sensitive to simple physical differences between faces. We caricatured the race of face stimuli and created face continua ranging from caricatured Caucasian faces (SuperCaucasian) to caricatured Chinese faces (SuperChinese). Participants were adapted to oppositely distorted faces that were a fixed physical distance apart on the morph continua. Larger opposite aftereffects were found following adaptation to faces from different race categories (e.g., contracted Chinese and expanded Caucasian faces), than for faces that were the same physical distance apart on the morph continua, but were within a race category (e.g., contracted SuperChinese and expanded Chinese faces). These results suggest that opposite aftereffects for Chinese and Caucasian faces reflect the recalibration of face neurons tuned to high-level social category information.

Newly learned categories induce pre-attentive categorical perception of faces

Face perception is modulated by categorical information in faces, which is known as categorical perception (CP) of faces. However, it remains unknown whether CP of faces is humans’ inborn capability or the result of acquired categories. Here, we examined whether and when newly learned categories affect face perception. A short-term training method was employed in which participants learned new categories of face stimuli. Behaviorally, using an AB-X discrimination task, we found that the discrimination accuracy of face pairs from different learned categories was significantly higher than that of faces from the same category. Neurally, using a visual oddball task, we found that deviant stimuli whose category differed from standard stimuli evoked a larger N170. Importantly, the visual mismatch negativity (vMMN), starting from 140 ms after stimuli onset, was stronger with the between-category deviants than with the within-category deviants under the unattended condition. Altogether, our study provides empirical evidence indicating that CP of faces could be induced by newly learned categories, and this effect occurs automatically during an early stage of processing.

The Speed of Individual Face Categorization

How fast does the human visual system discriminate individual faces? To address this question, we used a continuous-stimulation paradigm in which event-related potentials (ERPs) to a face stimulus are recorded with respect to another face stimulus, rather than to a preceding blank-screen baseline epoch. Following the shift between two face stimuli, posterior sites showed an early negative ERP deflection that started at 130 ms and peaked at 160 ms, the latency of the N170, an ERP component associated with discriminating faces from objects. The ERP we recorded was larger in amplitude when the preceding stimulus was perceived as a different individual face rather than the same individual face, although face pairs were of equal physical distance in the two conditions. These findings provide direct evidence that individual face discrimination in humans can take place as early as 130 ms following stimulus onset, during the same time window as face detection.

Judged and Remembered Trustworthiness of Faces Is Enhanced by Experiencing Multisensory Synchrony and Asynchrony in the Right Order

This work builds on the enfacement effect. This effect occurs when experiencing a rhythmic stimulation on one’s cheek while seeing someone else’s face being touched in a synchronous way. This typically leads to cognitive and social-cognitive effects similar to self-other merging. In two studies, we demonstrate that this multisensory stimulation can change the evaluation of the other’s face. In the first study, participants judged the stranger’s face and similar faces as being more trustworthy after synchrony, but not after asynchrony. Synchrony interacted with the order of the stroking; hence trustworthiness only changed when the synchronous stimulation occurred before the asynchronous one. In the second study, a synchronous stimulation caused participants to remember the stranger’s face as more trustworthy, but again only when the synchronous stimulation came before the asynchronous one. The results of both studies show that order of stroking creates a context in which multisensory synchrony can affect the trustworthiness of faces.

Artificial faces are harder to remember

Observers interact with artificial faces in a range of different settings and in many cases must remember and identify computer-generated faces. In general, however, most adults have heavily biased experience favoring real faces over synthetic faces. It is well known that face recognition abilities are affected by experience such that faces belonging to "out-groups" defined by race or age are more poorly remembered and harder to discriminate from one another than faces belonging to the "in-group." Here, we examine the extent to which artificial faces form an "out-group" in this sense when other perceptual categories are matched. We rendered synthetic faces using photographs of real human faces and compared performance in a memory task and a discrimination task across real and artificial versions of the same faces. We found that real faces were easier to remember, but only slightly more discriminable than artificial faces. Artificial faces were also equally susceptible to the well-known face inversion effect, suggesting that while these patterns are still processed by the human visual system in a face-like manner, artificial appearance does compromise the efficiency of face processing.

Multisensory integration and cross-modal learning in synaesthesia: A unifying model

Recent research into synaesthesia has highlighted the role of learning, yet synaesthesia is clearly a genetic condition. Here we ask how can the idea that synaesthesia reflects innate, genetic differences be reconciled with models that suggest it is driven by learning. A number of lines of evidence suggest that synaesthesia relies on, or at least interacts with, processes of multisensory integration that are common across all people. These include multisensory activations that arise in early regions of the brain as well as feedback from longer-term cross-modal associations generated in memory. These cognitive processes may interact independently to influence the phenomenology of the synaesthetic experience, as well as the individual differences within particular types of synaesthesia. The theoretical framework presented here is consistent with both an innate difference as the fundamental driver of the condition of synaesthesia, and with experiential and semantic influences on the eventual phenotype that emerges. In particular, it proposes that the internally generated synaesthetic percepts are treated similarly to other sensory information as the brain is learning the multisensory attributes of objects and developing cross-modal associations that merge in the concept of the object.

Perceptual discrimination difficulty and familiarity in the Uncanny Valley: more like a "Happy Valley"

The Uncanny Valley Hypothesis (UVH) predicts that greater difficulty perceptually discriminating between categorically ambiguous human and humanlike characters (e.g., highly realistic robot) evokes negatively valenced (i.e., uncanny) affect. An ABX perceptual discrimination task and signal detection analysis was used to examine the profile of perceptual discrimination (PD) difficulty along the UVH' dimension of human likeness (DHL). This was represented using avatar-to-human morph continua. Rejecting the implicitly assumed profile of PD difficulty underlying the UVH' prediction, Experiment 1 showed that PD difficulty was reduced for categorically ambiguous faces but, notably, enhanced for human faces. Rejecting the UVH' predicted relationship between PD difficulty and negative affect (assessed in terms of the UVH' familiarity dimension), Experiment 2 demonstrated that greater PD difficulty correlates with more positively valenced affect. Critically, this effect was strongest for the ambiguous faces, suggesting a correlative relationship between PD difficulty and feelings of familiarity more consistent with the metaphor happy valley. This relationship is also consistent with a fluency amplification instead of the hitherto proposed hedonic fluency account of affect along the DHL. Experiment 3 found no evidence that the asymmetry in the profile of PD along the DHL is attributable to a differential processing bias (cf. other-race effect), i.e., processing avatars at a category level but human faces at an individual level. In conclusion, the present data for static faces show clear effects that, however, strongly challenge the UVH' implicitly assumed profile of PD difficulty along the DHL and the predicted relationship between this and feelings of familiarity.

Knowledge is power: how conceptual knowledge transforms visual cognition

In this review, we synthesize the existing literature demonstrating the dynamic interplay between conceptual knowledge and visual perceptual processing. We consider two theoretical frameworks that demonstrate interactions between processes and brain areas traditionally considered perceptual or conceptual. Specifically, we discuss categorical perception, in which visual objects are represented according to category membership, and highlight studies showing that category knowledge can penetrate early stages of visual analysis. We next discuss the embodied account of conceptual knowledge, which holds that concepts are instantiated in the same neural regions required for specific types of perception and action, and discuss the limitations of this framework. We additionally consider studies showing that gaining abstract semantic knowledge about objects and faces leads to behavioral and electrophysiological changes that are indicative of more efficient stimulus processing. Finally, we consider the role that perceiver goals and motivation may play in shaping the interaction between conceptual and perceptual processing. We hope to demonstrate how pervasive such interactions between motivation, conceptual knowledge, and perceptual processing are in our understanding of the visual environment, and to demonstrate the need for future research aimed at understanding how such interactions arise in the brain.

Haptic categorical perception of shape

Categorization and categorical perception have been extensively studied, mainly in vision and audition. In the haptic domain, our ability to categorize objects has also been demonstrated in earlier studies. Here we show for the first time that categorical perception also occurs in haptic shape perception. We generated a continuum of complex shapes by morphing between two volumetric objects. Using similarity ratings and multidimensional scaling we ensured that participants could haptically discriminate all objects equally. Next, we performed classification and discrimination tasks. After a short training with the two shape categories, both tasks revealed categorical perception effects. Training leads to between-category expansion resulting in higher discriminability of physical differences between pairs of stimuli straddling the category boundary. Thus, even brief training can alter haptic representations of shape. This suggests that the weights attached to various haptic shape features can be changed dynamically in response to top-down information about class membership.

Male and female faces are only perceived categorically when linked to familiar identities--and when in doubt, he is a male

Categorical perception (CP) is a fundamental cognitive process that enables us to sort similar objects in the world into meaningful categories with clear boundaries between them. CP has been found for high-level stimuli like human faces, more precisely, for the perception of face identity, expression and ethnicity. For sex however, which represents another important and biologically relevant dimension of human faces, results have been equivocal so far. Here, we reinvestigate CP for sex using newly created face stimuli to control two factors that to our opinion might have influenced the results in earlier studies. Our new stimuli are (a) derived from single face identities, so that changes of sex are not confounded with changes of identity information, and (b) "normalized" in their degree of maleness and femaleness, to counteract natural variations of perceived masculinity and femininity of faces that might obstruct evidence of categorical perception. Despite careful normalization, we did not find evidence of CP for sex using classical test procedures, unless participants were specifically familiarized with the face identities before testing. These results support the single-route hypothesis, stating that sex and identity information in faces are not processed in parallel, in contrast to what was suggested in the classical Bruce and Young model of face perception. Besides, interestingly, our participants show a consistent bias, before and after perceptual normalization of the male-female range of the test morph continua, to judge faces as male rather than female.

Categorical perception effects for facial identity in robustly represented familiar and self-faces: the role of configural and featural information

Categorical perception of robustly represented faces (self, friend) and unfamiliar faces is investigated, and the relative roles of configural and featural information are examined. Participants performed identification and discrimination tasks on morph series containing the self-face and a friend's face (self-Friend 1), two friends' faces (Friend 2-Friend 3), and two unfamiliar faces (Unfamiliar 1-Unfamiliar 2), presented in upright and inverted orientations. For upright faces, categorical perception effects were observed for both familiar morph series but not for the unfamiliar morph series, suggesting that robust representation is a requirement for categorical perception in facial identity. For inverted faces, categorical perception was observed for the self-Friend 1 morph series only. This suggests that categorical perception is tied to configural processing for familiar non-self-faces, but can be observed for self-faces during featural processing-consistent with evidence that self-face representations contain strong configural and featural components. Finally, categorical perception is not enhanced by the presence of the self-face relative to other familiar faces when upright, but shows a trend of being enhanced for self-faces when inverted, adding to the debate on the ways in which robustly represented faces can elicit categorical perception.

Perception and Motivation in Face Recognition

Although humans possess well-developed face processing expertise, face processing is nevertheless subject to a variety of biases. Perhaps the best known of these biases is the Cross-Race Effect—the tendency to have more accurate recognition for same-race than cross-race faces. The current work reviews the evidence for and provides a critical review of theories of the Cross-Race Effect, including perceptual expertise and social cognitive accounts of the bias. The authors conclude that recent hybrid models of the Cross-Race Effect, which combine elements of both perceptual expertise and social cognitive frameworks, provide an opportunity for theoretical synthesis and advancement not afforded by independent expertise or social cognitive models. Finally, the authors suggest future research directions intended to further develop a comprehensive and integrative understanding of biases in face recognition.

Own-species bias in the representations of monkey and human face categories in the primate temporal lobe

Face categorization is fundamental for social interactions of primates and is crucial for determining conspecific groups and mate choice. Current evidence suggests that faces are processed by a set of well-defined brain areas. What is the fine structure of this representation, and how is it affected by visual experience? Here, we investigated the neural representations of human and monkey face categories using realistic three-dimensional morphed faces that spanned the continuum between the two species. We found an "own-species" bias in the categorical representation of human and monkey faces in the monkey inferior temporal cortex at the level of single neurons as well as in the population response analyzed using a pattern classifier. For monkey and human subjects, we also found consistent psychophysical evidence indicative of an own-species bias in face perception. For both behavioural and neural data, the species boundary was shifted away from the center of the morph continuum, for each species toward their own face category. This shift may reflect visual expertise for members of one's own species and be a signature of greater brain resources assigned to the processing of privileged categories. Such boundary shifts may thus serve as sensitive and robust indicators of encoding strength for categories of interest.

Perceptual awareness and categorical representation of faces: evidence from masked priming

How internal categories influence how we perceive the world is a fundamental question in cognitive sciences. Yet, the relation between perceptual awareness and perceptual categorization has remained largely uncovered so far. Here, we addressed this question by focusing on face perception during subliminal and conscious perception. We used morphed continua between two face identities and we assessed, through a masked priming paradigm, the perceptual processing of these morphed faces under subliminal and supraliminal conditions. We found that priming from subliminal faces followed linearly the information present in the primes, while priming from visible faces revealed a non-linear profile, indicating a categorical processing of face identities. Our results thus point to a special relation between perceptual awareness and categorical processing of faces, and support the dissociation between two modes of information processing: a subliminal mode involving analog treatment of stimuli information, and a supraliminal mode relying on discrete representation.

N170 – An Index of Categorical Face Perception?

The N170 ERP component is larger for human faces than objects and sensitive to their orientation and race. To learn how it reflects the processing of faces of different species, we recorded event-related potentials in response to upright or inverted unfamiliar faces of human beings, monkeys, and dogs of different races as well as objects. Upright and inverted faces were presented in a between-subject design and elicited a reliable N170. It decreased from human to monkey to dog faces, and inversion enhanced and delayed it for all categories. We suggest that the results favor categorical over prototypical processing.

The Tipping Point of Animacy

Faces capture humans’ attention; yet, beyond aesthetic appreciation, it is presumably not the face itself that interests people but the mind behind it. Minds think, feel, and act in ways that have direct consequences for well-being, but despite their importance, how minds are perceived in faces is not well understood. We investigated this mechanism by presenting participants with morphed images created from animate (human) and inanimate (mannequin) faces. Life and mind were perceived to “appear” at a consistent location on the morph continuum, close to the human endpoint. This location constituted a categorical boundary, as evidenced by increased sensitivity to differences in image pairs that straddled this tipping point. Additionally, the impression of life was gleaned from the eyes more than from other facial features. These results suggest that human beings are highly attuned to specific facial cues, carried largely in the eyes, that gate the categorical perception of life.

Reading chimpanzee faces: evidence for the role of verbal labels in categorical perception of emotion

Categorical perception (CP) occurs when continuously varying stimuli are perceived as belonging to discrete categories. Thereby, perceivers are more accurate at discriminating between stimuli of different categories than between stimuli within the same category (Harnad, 1987; Goldstone, 1994). The current experiments investigated whether the structural information in the face is sufficient for CP to occur. Alternatively, a perceiver's conceptual knowledge, by virtue of expertise or verbal labeling, might contribute. In two experiments, people who differed in their conceptual knowledge (in the form of expertise, Experiment 1; or verbal label learning, Experiment 2) categorized chimpanzee facial expressions. Expertise alone did not facilitate CP. Only when perceivers first explicitly learned facial expression categories with a label were they more likely to show CP. Overall, the results suggest that the structural information in the face alone is often insufficient for CP; CP is facilitated by verbal labeling.

Categorical perception for unfamiliar faces. The effect of covert and overt face learning

Robust findings show that categorical perception (CP) occurs in identification of familiar faces. CP has also been observed for unfamiliar morphed faces after sufficient learning of the original, unmorphed faces has taken place. We previously suggested that CP arises when the activation of inconsistent visual and verbal representations creates a conflict between perceptual and category information. In the present study, we conducted two experiments in which the endpoint faces of an unfamiliar morphed continuum were presented in either a covert training regime (famous vs. nonfamous judgments) or an overt training regime (previously seen vs. unseen judgments). In both experiments, participants' reaction times to repeated targets decreased relative to reaction times to control items during training. After overt training, CP was observed for the previously unfamiliar faces. No CP was observed for covertly trained faces. We conclude that individual faces must be explicitly categorized before CP can be established for the morphed continuum between them.

Generalization of affective learning about faces to perceptually similar faces

Different individuals have different (and different-looking) significant others, friends, and foes. The objective of this study was to investigate whether these social face environments can shape individual face preferences. First, participants learned to associate faces with positive, neutral, or negative behaviors. Then, they evaluated morphs combining novel faces with the learned faces. The morphs (65% and 80% novel faces) were within the categorical boundary of the novel faces: They were perceived as those faces in a preliminary study. Moreover, a second preliminary study showed that following the learning, the morphs' categorization as similar to the learned faces was indistinguishable from the categorization of actual novel faces. Nevertheless, in the main experiment, participants evaluated morphs of "positive" faces more positively than morphs of "negative" faces. This learning generalization effect increased as a function of the similarity of the novel faces to the learned faces. The findings suggest that general learning mechanisms based on similarity can account for idiosyncratic face preferences.

The influence of categories on perception: explaining the perceptual magnet effect as optimal statistical inference

A variety of studies have demonstrated that organizing stimuli into categories can affect the way the stimuli are perceived. We explore the influence of categories on perception through one such phenomenon, the perceptual magnet effect, in which discriminability between vowels is reduced near prototypical vowel sounds. We present a Bayesian model to explain why this reduced discriminability might occur: It arises as a consequence of optimally solving the statistical problem of perception in noise. In the optimal solution to this problem, listeners' perception is biased toward phonetic category means because they use knowledge of these categories to guide their inferences about speakers' target productions. Simulations show that model predictions closely correspond to previously published human data, and novel experimental results provide evidence for the predicted link between perceptual warping and noise. The model unifies several previous accounts of the perceptual magnet effect and provides a framework for exploring categorical effects in other domains.

Categorization of Ambiguous Human/Ape Faces: Protection of Ingroup but Not Outgroup Humanity

In two studies, we tested the hypothesis that categorization of ambiguous human/ape faces depends on group membership: people are inclined to protect ingroup humanity, but not that of the outgroup. We used as stimuli: human, ape, ambiguous human/ape faces. Ambiguous human/ape faces were generated using a computerized morphing procedure. Participants categorized stimuli as human or ape. Two conditions were introduced: in the ingroup condition, participants were informed that human exemplars were ingroup members, in the outgroup condition that they were outgroup members. We expected participants, in an effort to protect ingroup humanity, to categorize ambiguous stimuli as ape more often in the ingroup than outgroup condition. Predictions were confirmed. Results are discussed in the context of infrahumanization theory.

Psychophysical evidence for a non-linear representation of facial identity

It has been proposed that faces are represented in the visual brain as points within a multi-dimensional “face space”, with the average at its origin. We adapted a psychophysical procedure that measures non-linearities in contrast transduction (by measuring discrimination around different reference/pedestal levels of contrast) to examine the encoding of facial-identity within such a notional space. Specifically we had subjects perform identity discrimination at various pedestal levels of identity (varying from average/0% to caricature/125% identity) to derive “identity dipper functions”. Results indicate that subjects are generally best at spotting identity change in neither average nor full-identity faces, but rather in faces containing an intermediate level of identity (which varies from face-to-face). The overall pattern of results is consistent with the neural encoding of faces involving a single modest non-linear transformation of identity that is consistent across faces and subjects, but that it scaled according to the distinctiveness of the face.

Atypical categorical perception in autism: autonomy of discrimination?

A diminished top-down influence has been proposed in autism, to account for enhanced performance in low-level perceptual tasks. Applied to perceptual categorization, this hypothesis predicts a diminished influence of category on discrimination. In order to test this hypothesis, we compared categorical perception in 16 individuals with and 16 individuals without high-functioning autism. While participants with and without autism displayed a typical classification curve, there was no facilitation of discrimination near the category boundary in the autism group. The absence of influence of categorical knowledge on discrimination suggests an increased autonomy of low-level perceptual processes in autism, in the form of a reduced top-down influence from categories toward discrimination.

Face familiarity, distinctiveness, and categorical perception

Four experiments with faces support the original interpretation of categorical perception (CP) as only present for familiar categories. Unlike in the results of Levin and Beale (2000), no evidence is found for face identity CP with unfamiliar faces. Novel face identities were shown to be capable of encoding for immediate sorting purposes but the representations utilized do not have the format of perceptual categories. One possibility explored was that a choice of a distinctive face as an end-point in a morphed continuum can spuriously produce effects that resemble CP. Such morphed continua provided unequal psychological responses to equal physical steps though much more so in a better likeness paradigm than for forced-choice recognition. Thus, researchers doing almost the same experiments may produce very different results and come to radically different conclusions.