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.     

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.     

Opposite effects of visual versus imagined presentation of faces on subsequent sex perception

Viewing faces of one sex changes the perception of subsequently seen ambiguous faces. Here we investigate if the mechanisms responsible for this sex aftereffect are also activated during mental imagery of faces. Participants categorized the sex of ambiguous faces after either viewing images of male or female actors' faces or imagining these same faces. As in previous studies, the ambiguous images were categorized as female more often after viewing male faces than after viewing female faces. The opposite effect was found for imagined faces, however; the ambiguous images were categorized as female more often after imagining female faces than after imagining male faces. Although our results are inconsistent with findings that imagined faces cause either no aftereffects or similar aftereffects to visually presented faces, our results are consistent with recent evidence that visual and imagined presentation of faces cause opposite adaptation effects on an early electrophysiological response associated with face processing.     

Face aftereffects indicate dissociable, but not distinct, coding of male and female faces

It has been claimed that exposure to distorted faces of one sex induces perceptual aftereffects for test faces that are of the same sex, but not for test faces of the other sex (A. C. Little, L. M. DeBruine, & B. C. Jones, 2005). This result suggests that male and female faces have separate neural coding. Given the high degree of visual similarity between faces of different sexes, this result is surprising. The authors reinvestigated male and female face coding using a different face distortion. In Experiment 1, participants adapted to distorted faces from one sex (e.g., male contracted faces) and were tested with faces of both sexes. Aftereffects were found for both male and female faces, suggesting the existence of common coding mechanisms. In Experiments 2 and 3, participants adapted to oppositely distorted faces from both sexes (male contracted and female expanded faces). Weak opposite aftereffects were found for male and female faces, suggesting the existence of sex-selective face coding mechanisms. Taken together, these results indicate that both common and sex-selective mechanisms code male and female faces.     

Representing young and older adult faces: Shared or age-specific prototypes?

ABSTRACT

Young adults recognize young adult faces more accurately than older adult faces and are more sensitive to how individual young faces deviate from a norm/prototype. Here we used an adaptation paradigm to examine whether young and older adult faces are represented by separable norms and the extent to which the coding dimensions for these two categories overlap. In Experiment 1, following adaptation to oppositely distorted young and older faces (e.g., expanded young and compressed older faces), adults’ normality judgments simultaneously shifted in opposite directions for the two face categories, providing evidence for separable norms. In Experiment 2, participants were adapted to distorted faces from a single age category (e.g., compressed young); aftereffects transferred across face age but were larger for the face age that matched adaptation. Collectively, these results provide evidence that young and older faces are processed with regard to separable norms that share some underlying coding dimensions.     

Perception and imagery of faces generate similar gender aftereffects

Visual adaptation is known to bias perception away from the properties of the adapting stimuli, toward opposite properties, resulting in perceptual aftereffects. For example, prolonged exposure to a face has been shown to produce an identity aftereffect, biasing perception of a subsequent face toward the opposite identity. Such repulsive aftereffects have been observed for both visually perceived and visually imagined faces, suggesting that both perception and imagery yield typical aftereffects. However, recent studies have reported opposite patterns of aftereffects for perception and imagery of face gender. In these studies, visually perceived faces produced typical effects in which perception of androgynous faces was biased away from the gender of the adaptor, whereas imagery of the same stimuli produced atypical aftereffects, biasing the perceived gender of androgynous faces toward the gender of the adaptor. These findings are highly unusual and warrant further research. The present study aimed to gather new evidence on the direction of gender aftereffects following perception and imagery of faces. Experiment 1 had participants view and imagine female and male faces of famous and non-famous individuals. To determine the effect of concomitant visual stimulation on imagery and adaptation, participants visualized faces both in the presence and in the absence of a visual input. In Experiment 2, participants were adapted to perceived and imagined faces of famous and non-famous actors matched on gender typicality. This manipulation allowed us to determine the effect of face familiarity on the magnitude of gender aftereffects. Contrary to evidence from previous studies, our results demonstrated that both perception and imagery produced typical aftereffects, biasing the perceived gender of androgynous faces in the opposite direction to the gender of the adaptor. Famous faces yielded largest adaptation effects across tasks. Experiment 2 confirmed that these effects depended on familiarity rather than on sexual dimorphism. In both experiments, this effect was greater for perception than imagery. Additionally, imagery of famous faces produced strongest aftereffects when it was performed in the absence of visual stimulation. The implications of these findings are discussed.     

Figural aftereffects in the perception of faces

We examined figural aftereffects in images of human faces, for which changes in configuration are highly discriminable. Observers either matched or rated faces before or after viewing distorted images of faces. Prior adaptation strongly biases face perception by causing the original face to appear distorted in a direction opposite to the adapting distortion. Aftereffects transferred across different faces and were similar for upright or inverted faces, but were weaker when the adapting and test faces had different orientations (e.g., adapt inverted and test upright). Thus the aftereffects depend on which images are distorted, and not simply on the type of distortion introduced. We further show that the aftereffects are asymmetric, for adapting to the original face has little effect on the perception of a distorted face. This asymmetry suggests that adaptation may play an important normalizing role in face perception. Our results suggest that in normal viewing, figural aftereffects may strongly influence form perception and could provide a novel method for probing properties of human face perception.     

Adaptation and the perception of facial age

We examined how the perceived age of adult faces is affected by adaptation to younger or older adult faces. Observers viewed images of a synthetic male face simulating ageing over a modelled range from 15 to 65 years. Age was varied by changing shape cues or textural cues. Age level was varied in a staircase to find the observer's subjective category boundary between “old” and “young”. These boundaries were strongly biased by adaptation to the young or old face, with significant aftereffects induced by either shape or textural cues. A further experiment demonstrated comparable aftereffects for photorealistic images of average older or younger adult faces, and found that aftereffects showed some selectivity for a change in gender but also strongly transferred across gender. This transfer shows that adaptation can adjust to the attribute of age somewhat independently of other facial attributes. These findings suggest that perceived age, like many other natural facial dimensions, is highly susceptible to adaptation, and that this adaptation can be carried by both the structural and textural changes that normally accompany facial ageing.     

Face aftereffects suggest interdependent processing of expression and sex and of expression and race

Bruce and Young (1986) proposed that functionally different aspects of faces (e.g., sex, identity, and expression) are processed independently. Although interdependent processing of identity and expression and of identity and sex have been demonstrated previously, evidence for interdependent processing of sex and expression is equivocal. Using a visual adaptation paradigm, we show that expression aftereffects can be simultaneously induced in different directions along anger–fear continua for male and female faces (Experiment 1) and for East Asian and Black African faces (Experiment 2). These findings for sex- and race-contingent expression aftereffects suggest that processing of expression is interdependent with processing of sex and race and are therefore problematic for models of face perception that have emphasized independent processing of functionally different aspects of faces. By contrast, our findings are consistent with models of face processing that propose that invariant physical aspects of faces and changeable social cues can be processed interdependently.     

Face encoding is not categorical: Consistent evidence across multiple types of contingent aftereffects

ABSTRACT

Race-contingent aftereffects indicate that faces of different races are encoded via dissociable visual channels. Race-contingent aftereffects reflect perceptions of typicality, indicating a gradual transition of activity across channels as faces change from looking more typical of one race to the other We examine whether faces forming more discrete categories (sex: male/female; species: human/monkey) are encoded in a similar fashion, or whether they are instead encoded via more dichotomous categorical judgements. Curves representing the rate of change of aftereffect magnitude as stimuli changed from male to female produced shallow slopes, closely resembling ratings of typicality, but differing significantly from slopes for categorical judgements. For species, aftereffect slopes were significantly shallower than both ratings of typicality and categorical judgements. Overall, these results suggest that the encoding of facial properties such as these is not categorical, but instead involves a graded response as stimulus typicality varies. Aftereffect slopes were similar across the two experiments, raising the possibility of a common system that is recruited during contingent adaptation, regardless of the specific dimension involved or the categories used by the experimenter.     

Face adaptation to gender: Does adaptation transfer across age categories?

We examined gender adaptation effects for the faces of children and adults and measured the transfer of these effects across age categories. Face gender adaptation is defined by a bias to classify the gender of a gender-neutral face to be opposite to that of an adapting face. An androgynous face, for example, appears male following adaptation to a female face. Participants adapted to male or female faces from the two age categories and classified the gender of morphed adult and child faces from a male–female morph trajectory. Gender adaptation effects were found for children's and adults’ faces and for the transfer between the age categories. The size of these effects was comparable when participants adapted to adult faces and identified the gender of either adult or child faces, and when participants adapted to child faces and identified the gender of child faces. A smaller adaptation effect was found when participants adapted to a child's face but identified the gender of an adult's face. The results indicate an interconnected and partially shared representation of the gender information for child and adult faces. The lack of symmetry in adaptation transfer between child and adult faces suggests that adaptation to adult faces is more effective than adaptation to child faces in activating a gender representation that generalizes across age categories.     

Category contingent aftereffects for faces of different races, ages and species

Exposure to faces biases perceptions of subsequently viewed faces such that normality judgments of similar faces are increased. Simultaneously inducing such an aftereffect in opposite directions for two groups of faces might indicate discrete responding of the neural populations coding for those groups. Here we show such "category contingent" aftereffects following exposure to faces differing in eye-spacing (wide versus narrow) for European versus African faces, adult versus infant faces, and human versus monkey faces. As aftereffects reflect changes in responses of neural populations that code faces, our results may then suggest that functionally distinct neural populations code faces of different ages, races and species and that the human brain potentially contains discrete representations of these categories.     

View-specific coding of face shape

Monkey and human cortex contain view-specific face neurons, but it remains unclear whether they code face shape. We tested the view specificity of face-shape coding by inducing figural face aftereffects at one viewpoint (3/4 left) and testing generalization to different viewpoints (front view and 3/4 right). The aftereffects were induced by adaptation to consistent figural distortions (contracted or expanded), which shifts the distortion perceived as most normal toward the adapting distortion. The strong aftereffect that was observed at the adapting view was significantly and substantially reduced for both front-view test faces and mirror-image (3/4 right) test faces, indicating view specificity. The limited transfer across mirror views is strong evidence of view specificity, given their figural similarity. The aftereffects survived a size change between adaptation and test faces (Experiment 2), a result that rules out low-level adaptation as an explanation. These results provide strong evidence that face-shape coding is view-specific.     

Fitting the child's mind to the world: adaptive norm-based coding of facial identity in 8-year-olds

In adults, facial identity is coded by opponent processes relative to an average face or norm, as evidenced by the face identity aftereffect: adapting to a face biases perception towards the opposite identity, so that a previously neutral face (e.g. the average) resembles the identity of the computationally opposite face. We investigated whether children as young as 8 use adaptive norm-based coding to represent faces, a question of interest because 8-year-olds are less accurate than adults at recognizing faces and do not show the adult neural markers of face expertise. We found comparable face identity aftereffects in 8-year-olds and adults: perception of identity in both groups shifted in the direction predicted by norm-based coding. This finding suggests that, by 8 years of age, the adaptive computational mechanisms used to code facial identity are like those of adults and hence that children's immaturities in face processing arise from another source.     

Category-contingent face adaptation for novel colour categories: Contingent effects are seen only after social or meaningful labelling

A face appears normal when it approximates the average of a population. Consequently, exposure to faces biases perceptions of subsequently viewed faces such that faces similar to those recently seen are perceived as more normal. Simultaneously inducing such aftereffects in opposite directions for two groups of faces indicates somewhat discrete representations for those groups. Here we examine how labelling influences the perception of category in faces differing in colour. We show category-contingent aftereffects following exposure to faces differing in eye spacing (wide versus narrow) for blue versus red faces when such groups are consistently labelled with socially meaningful labels (Extravert versus Introvert; Soldier versus Builder). Category-contingent aftereffects were not seen using identical methodology when labels were not meaningful or were absent. These data suggest that human representations of faces can be rapidly tuned to code for meaningful social categories and that such tuning requires both a label and an associated visual difference. Results highlight the flexibility of the cognitive visual system to discriminate categories even in adulthood.     

Atypical updating of face representations with experience in children with autism

Face identity aftereffects are significantly diminished in children with autism relative to typical children, which may reflect reduced perceptual updating with experience. Here, we investigated whether this atypicality also extends to non‐face stimulus categories, which might signal a pervasive visual processing difference in individuals with autism. We used a figural aftereffect task to measure directly perceptual updating following exposure to distorted upright faces, inverted faces and cars, in typical children and children with autism. A size‐change between study and test stimuli limited the likelihood that any processing atypicalities reflected group differences in adaptation to low‐level features of the stimuli. Results indicated that, relative to typical children, figural aftereffects for upright faces, but not inverted faces or cars, were significantly attenuated in children with autism. Moreover, the group difference was amplified when we isolated the ‘face‐selective’ component of the aftereffect, by partialling out the mid‐level shape adaptation common to upright and inverted face stimuli. Notably, the aftereffects of typical children were disproportionately larger for upright faces than for inverted faces and cars, but the magnitude of aftereffects of autistic children was not similarly modulated according to stimulus category. These findings are inconsistent with a pervasive adaptive coding atypicality relative to typical children, and suggest that reduced perceptual updating may constitute a high‐level, and possibly face‐selective, visual processing difference in children with autism.     

特征关联的类别间面孔适应

研究通过系列实验探讨了面孔适应不仅仅发生在形状选择性上, 也能发生在任务相关的特征上有内在关联的两个不同类别的物体间。实验1以带有明显性别倾向的物品图片作为适应刺激, 让被试对男女之间morphing程度不同的图片面孔进行性别辨别, 考察了不同适应刺激呈现时间的类别间面孔适应。结果表明适应刺激呈现时间大于50 ms时均存在类别间面孔适应效应。实验2评估了“性别”这一特征以及适应刺激形式在类别间面孔适应中所起的作用, 结果发现带有性别倾向的物品图片、相应的物品名称和性别文字(“男性”、“女性”) 3种适应刺激类型均能产生类别间适应。实验3通过操纵适应刺激上的注意负荷(高负荷、低负荷和无负荷), 探究了注意对类别间面孔适应的影响。结果表明随着注意负荷的增加, 类别间面孔适应效应减小。3个实验报告了一个新异的类别间适应后效, 证明了适应也能发生于在任务相关特征上有内在关联的两个不同类别的物体间。     

Visual perception and visual mental imagery of emotional faces generate similar expression aftereffects

What is the relationship between visual perception and visual mental imagery of emotional faces? We investigated this question using a within-emotion perceptual adaptation paradigm in which adaptation to a strong version of an expression was paired with a test face displaying a weak version of the same emotion category. We predicted that within-emotion adaptation to perception and imagery of expressions would generate similar aftereffects, biasing perception of weak emotional test faces toward a more neutral value. Our findings confirmed this prediction. Adaptation to mental images yielded aftereffects that inhibited emotion recognition of test expressions, as participants were less accurate at recognising these stimuli compared to baseline. While the same inhibitory effect was observed when expressions were visually perceived, the size of the aftereffects was greater for perception than imagery. These findings suggest the existence of expression-selective neural mechanisms that subserve both visual perception and visual mental imagery of emotional faces.     

Not just the norm: Exemplar-based models also predict face aftereffects

The face recognition literature has considered two competing accounts of how faces are represented within the visual system: Exemplar-based models assume that faces are represented via their similarity to exemplars of previously experienced faces, while norm-based models assume that faces are represented with respect to their deviation from an average face, or norm. Face identity aftereffects have been taken as compelling evidence in favor of a norm-based account over an exemplar-based account. After a relatively brief period of adaptation to an adaptor face, the perceived identity of a test face is shifted toward a face with attributes opposite to those of the adaptor, suggesting an explicit psychological representation of the norm. Surprisingly, despite near universal recognition that face identity aftereffects imply norm-based coding, there have been no published attempts to simulate the predictions of norm- and exemplar-based models in face adaptation paradigms. Here, we implemented and tested variations of norm and exemplar models. Contrary to common claims, our simulations revealed that both an exemplar-based model and a version of a two-pool norm-based model, but not a traditional norm-based model, predict face identity aftereffects following face adaptation.     

Lecturers' faces fatigue their students: Face identity aftereffects for dynamic and static faces

Face adaptation has been used as a tool to probe our representations for facial identity. It has also been claimed to play a functional role in face processing, perhaps calibrating the visual system towards encountered faces. However, for this to be so, face aftereffects must be observable following adaptation to ecologically valid moving stimuli, not just after prolonged viewing of static images. We adapted our participants to videos, static image sequences or single images of the faces of lecturers who were personally familiar to them. All three stimulus types produced significant, and equivalent, face identity aftereffects, demonstrating that aftereffects are not confined to static images but can occur after exposure to more naturalistic stimuli. It is also further evidence against explanations of face adaptation effects solely in terms of low-level visual processing.