Expert Face Processing Research Articles

Neural sensitivity to trustworthiness cues from realistic face images is associated with temperament: An electrophysiological study with 6-month-old infants

ABSTRACT Discriminating facial cues to trustworthiness is a fundamental social skill whose developmental origins are still debated. Prior investigations used computer-generated faces, which might fail to reflect infants’ face processing expertise. Here, Event-Related Potentials (ERPs) were recorded in Caucasian adults (N = 20, 7 males, M age = 25.25 years) and 6-month-old infants (N = 21, 10 males) in response to variations in trustworthiness intensity expressed by morphed images of realistic female faces associated with explicit trustworthiness judgments (Study 1). Preferential looking behavior in response to the same faces was also investigated in infants (N = 27, 11 males) (Study 2). ERP results showed that both age groups distinguished subtle stimulus differences, and that interindividual variability in neural sensitivity to these differences were associated with infants’ temperament. No signs of stimulus differentiation emerged from infants’ looking behavior. These findings contribute to the understanding of the developmental origins of human sensitivity to social cues from faces by extending prior evidence to more ecological stimuli and by unraveling the mediating role of temperament.

Sensitivity to face animacy and inversion in childhood: Evidence from EEG data

Adults exhibit relative behavioral difficulties in processing inanimate, artificial faces compared to real human faces, with implications for using artificial faces in research and designing artificial social agents. However, the developmental trajectory of inanimate face perception is unknown. To address this gap, we used electroencephalography to investigate inanimate faces processing in cross-sectional groups of 5–10-year-old children and adults. A face inversion manipulation was used to test whether face animacy processing relies on expert face processing strategies. Groups of 5-7-year-olds (N = 18), 8-10-year-olds (N = 18), and adults (N = 16) watched pictures of real or doll faces presented in an upright or inverted orientation. Analyses of event-related potentials revealed larger N170 amplitudes in response to doll faces, irrespective of age group or face orientation. Thus, the N170 is sensitive to face animacy by 5–7 years of age, but such sensitivity may not reflect high-level, expert face processing. Multivariate pattern analyses of the EEG signal additionally assessed whether animacy information could be reliably extracted during face processing. Face orientation, but not face animacy, could be reliably decoded from occipitotemporal channels in children and adults. Face animacy could be decoded from whole scalp channels in adults, but not children. Together, these results suggest that 5-10-year-old children exhibit some sensitivity to face animacy over occipitotemporal regions that is comparable to adults.

The left-side bias is not unique to own-race face processing.

Humans show a clear left-side bias in face processing. A chimeric face constructed with the left side (from the viewer's perspective) of a face and its mirror image is usually rated as more resemblant to the original face than a chimeric face constructed with the right side of the same face. Previous studies have characterized the left-side bias mainly with own-race faces, but it remains unclear whether this effect is race specific or if it reflects an universal visual expertise. One hundred and five Chinese students completed two versions of a chimeric face-identification task. The results revealed a significant left-side bias for both own-race (Chinese) and other-race (Caucasian) faces, suggesting that the left-side bias reflects an universal visual expertise in face processing.

Developmental changes in the processing of faces as revealed by EEG decoding

Rapidly and accurately processing information from faces is a critical human function that is known to improve with developmental age. Understanding the underlying drivers of this improvement remains a contentious question, with debate continuing as to the presence of early vs. late maturation of face-processing mechanisms. Recent behavioural evidence suggests an important ‘hallmark’ of expert face processing – the face inversion effect – is present in very young children, yet neural support for this remains unclear. To address this, we conducted a detailed investigation of the neural dynamics of face processing in children spanning a range of ages (6–11 years) and adults. Uniquely, we applied multivariate pattern analysis (MVPA) to the electroencephalogram signal (EEG) to test for the presence of a distinct neural profile associated with canonical upright faces when compared both to other objects (houses) and to inverted faces. Results revealed robust discrimination profiles, at the individual level, of differentiated neural activity associated with broad face categorization and further with its expert processing, as indexed by the face inversion effect, from the youngest ages tested. This result is consistent with an early functional maturation of broad face processing mechanisms. Yet, clear quantitative differences between the response profile of children and adults is suggestive of age-related refinement of this system with developing face and general expertise. Standard ERP analysis also provides some support for qualitative differences in the neural response to inverted faces in children in contrast to adults. This neural profile is in line with recent behavioural studies that have reported impressively expert early face abilities during childhood, while also providing novel evidence of the ongoing neural specialisation between child and adulthood.

Correlations between holistic processing, Autism quotient, extraversion, and experience and the own-gender bias in face recognition.

The variability in the own-gender bias (OGB) in face-recognition is thought to be based on experience and the engagement of expert face processing mechanisms for own-gender faces. Experience is also associated with personality characteristics such as extraversion and Autism, yet the effects of these variables on the own-gender bias has not been explored. We ran a face recognition study exploring the relationships between own-gender experience, holistic processing (measured using the face-inversion effect, composite face effect, and the parts-and-wholes test), personality characteristics (extraversion and Autism Quotient) and the OGB. Findings did not support a mediational account where experience increases holistic processing and this increases the OGB. Rather, there was a direct relationship between extraversion and Autism Quotient and the OGB. We interpret this as personality characteristics having an effect on the motivation to process own-gender faces more deeply than opposite-gender faces.

The development of face expertise: Evidence for a qualitative change in processing

There is conflicting evidence regarding the development of expert face recognition, as indexed by the face-inversion effect (FIE; de Heering, Rossion, & Maurer, 2011; Young and Bion, 1981) potentially due to the nature of the stimuli used in previous research. The developmental trajectory of the FIE was assessed in participants aged between 5- and 18-years using age-matched and adult stimuli. Four experiments demonstrated that upright face recognition abilities improved linearly with age (presumably due to improved memory storage capacities) and this was larger than for inverted faces. The FIE followed a stepped function, with no FIE for participants younger than 9-years of age. These results indicate maturation of expert face processing mechanisms that occur at the age of 10-years, similar to expertise in other domains.

The development of the own-race advantage in school-age children: A morphing face paradigm.

Previous studies examining the other-race effect in school-age children mostly focused on recognition memory performance. Here we investigated perceptual discriminability for Asian-like versus Caucasian-like morph faces in school-age Taiwanese children and adults. One-hundred-and-two 5- to 12-year-old children and twenty-three adults performed a sequential same/different face matching task, where they viewed an Asian- or a Caucasian-parent face followed by either the same parent face or a different morphed face (containing 15%, 30%, 45%, or 60% contribution from the other parent face) and judged if the two faces looked the same. We computed the d’ as the sensitivity index for each age groups. We also analyzed the group mean rejection rates as a function of the morph level and fitted with a cumulative normal distribution function. Results showed that the adults and the oldest 11-12-year-old children exhibited a greater sensitivity (d’) and a smaller discrimination threshold (μ) in the Asian-parent condition than those in the Caucasian-parent condition, indicating the presence of an own-race advantage. On the contrary, 5- to 10-year-old children showed an equal sensitivity and similar discrimination thresholds for both conditions, indicating an absence of the own-race advantage. Moreover, a gradual development in enhancing the discriminability for the Asian-parent condition was observed from age 5 to 12; however, the progression in the Caucasian-parent condition was less apparent. In sum, our findings suggest that expertise in face processing may take the entire childhood to develop, and supports the perceptual learning view of the other-race effect—the own-race advantage seen in adulthood likely reflects a result of prolonged learning specific to faces most commonly seen in one’s visual environment such as own-race faces.

The Impact of Face Inversion on Animacy Categorization

Face animacy perception is categorical: Gradual changes in the real/artificial appearance of a face lead to nonlinear behavioral responses. Neural markers of face processing are also sensitive to face animacy, further suggesting that these are meaningful perceptual categories. Artificial faces also appear to be an “out-group” relative to real faces such that behavioral markers of expert-level processing are less evident with artificial faces than real ones. In the current study, we examined how categorical processing of real versus doll faces was impacted by the face inversion effect, which is one of the most robust markers of expert face processing. We examined how explicit categorization of faces drawn from a real/doll morph continuum was affected by face inversion (Experiment 1) and also how the response properties of the N170 were impacted by face animacy and inversion. We found that inversion does not change the position or steepness of the category boundary measured behaviorally. Further, neural markers of face processing are equally impacted by inversion regardless of whether they are elicited by real faces or doll faces. On balance, our results indicate that inversion has a limited impact on the categorical perception of face animacy.

Personal familiarity enhances sensitivity to horizontal structure during processing of face identity.

What makes identification of familiar faces seemingly effortless? Recent studies using unfamiliar face stimuli suggest that selective processing of information conveyed by horizontally oriented spatial frequency components supports accurate performance in a variety of tasks involving matching of facial identity. Here, we studied upright and inverted face discrimination using stimuli with which observers were either unfamiliar or personally familiar (i.e., friends and colleagues). Our results reveal increased sensitivity to horizontal spatial frequency structure in personally familiar faces, further implicating the selective processing of this information in the face processing expertise exhibited by human observers throughout their daily lives.

Perceptual learning and face processing in infancy.

Configural information (spacing between features) contributes to face-processing expertise in adulthood. We examined whether infants can be "trained" to process this information. In Experiment 1, 3.5-month-olds failed to discriminate changes in the spacing between facial features. However, in Experiments 2 and 3, infants processed the same information after being primed with faces in which the spacing was repeatedly altered. Experiment 4 found that priming was not effective with inverted faces or with faces depicting changes in features but not relations among features, indicating that the priming exhibited in Experiments 2 and 3 was specific to upright faces depicting spacing changes. Thus, even young infants who do not readily process facial configural information can be induced to do so through priming. These findings suggest that learning to encode critical structural information contributes to the development of face processing expertise.

Category-specific face prototypes are emerging, but not yet mature, in 5-year-old children

Adults’ expertise in face recognition has been attributed to norm-based coding. Moreover, adults possess separable norms for a variety of face categories (e.g., race, sex, age) that appear to enhance recognition by reducing redundancy in the information shared by faces and ensuring that only relevant dimensions are used to encode faces from a given category. Although 5-year-old children process own-race faces using norm-based coding, little is known about the organization and refinement of their face space. The current study investigated whether 5-year-olds rely on category-specific norms and whether experience facilitates the development of dissociable face prototypes. In Experiment 1, we examined whether Chinese 5-year-olds show race-contingent opposing aftereffects and the extent to which aftereffects transfer across face race among Caucasian and Chinese 5-year-olds. Both participant races showed partial transfer of aftereffects across face race; however, there was no evidence for race-contingent opposing aftereffects. To examine whether experience facilitates the development of category-specific prototypes, we investigated whether race-contingent aftereffects are present among Caucasian 5-year-olds with abundant exposure to Chinese faces (Experiment 2) and then tested separate groups of 5-year-olds with two other categories with which they have considerable experience: sex (male/female faces) and age (adult/child faces) (Experiment 3). Across all three categories, 5-year-olds showed no category-contingent opposing aftereffects. These results demonstrate that 5years of age is a stage characterized by minimal separation in the norms and associated coding dimensions used for faces from different categories and suggest that refinement of the mechanisms that underlie expert face processing occurs throughout childhood.

An adaptation study of internal and external features in facial representations

Prior work suggests that internal features contribute more than external features to face processing. Whether this asymmetry is also true of the mental representations of faces is not known. We used face adaptation to determine whether the internal and external features of faces contribute differently to the representation of facial identity, whether this was affected by familiarity, and whether the results differed if the features were presented in isolation or as part of a whole face. In a first experiment, subjects performed a study of identity adaptation for famous and novel faces, in which the adapting stimuli were whole faces, the internal features alone, or the external features alone. In a second experiment, the same faces were used, but the adapting internal and external features were superimposed on whole faces that were ambiguous to identity. The first experiment showed larger aftereffects for unfamiliar faces, and greater aftereffects from internal than from external features, and the latter was true for both familiar and unfamiliar faces. When internal and external features were presented in a whole-face context in the second experiment, aftereffects from either internal or external features was less than that from the whole face, and did not differ from each other. While we reproduce the greater importance of internal features when presented in isolation, we find this is equally true for familiar and unfamiliar faces. The dominant influence of internal features is reduced when integrated into a whole-face context, suggesting another facet of expert face processing.

Early visual deprivation from congenital cataracts disrupts activity and functional connectivity in the face network

The development of the face-processing network has been examined with functional neuroimaging, but the effect of visual deprivation early in life on this network is not known. We examined this question in a group of young adults who had been born with dense, central cataracts in both eyes that blocked all visual input to the retina until the cataracts were removed during infancy. We used functional magnetic resonance imaging to examine regions in the “core” and “extended” face networks as participants viewed faces and other objects, and performed a face discrimination task. This task required matching faces on the basis of facial features or on the spacing between the facial features. The Cataract group (a) had reduced discrimination performance on the Spacing task relative to Controls; (b) used the same brain regions as Controls when passively viewing faces or making judgments about faces, but showed reduced activation during passive viewing of faces, especially in extended face-network regions; and (c) unlike Controls, showed activation in face-network regions for objects. In addition, the functional connections of the fusiform gyri with the rest of the face network were altered, and these brain changes were related to Cataract participants’ performance on the face discrimination task. These results provide evidence that early visual input is necessary to set up or preserve activity and functional connectivity in the face-processing network that will later mediate expert face processing.

Averted eye-gaze disrupts configural face encoding

Faces are processed in a configural manner (i.e., without decomposition into individual face features), an effect attributed to humans having a high degree of face processing expertise. However, even when perceiver expertise is accounted for, configural processing is subject to a number of influences, including the social relevance of a face. In the current research, we present two experiments that document the influence of eye-gaze direction (direct or averted) on configural encoding of faces. Experiment 1 uses a version of the composite face paradigm to investigate how eye-gaze influences configural encoding. The results indicate that averted gaze disrupts configural encoding compared to direct eye-gaze. Experiment 2 manipulates whether perceivers can engage in configural encoding using face-inversion, and finds the inversion effects are greater for faces with direct than averted-gaze. We interpret these results as evidence that averted eye-gaze signals that a face is subjectively unimportant, thereby disrupting configural encoding.

Neural Trade-Offs between Recognizing and Categorizing Own- and Other-Race Faces

Behavioral research has suggested a trade-off relationship between individual recognition and race categorization of own- and other-race faces, which is an important behavioral marker of face processing expertise. However, little is known about the neural mechanisms underlying this trade-off. Using functional magnetic resonance imaging (fMRI) methodology, we concurrently asked participants to recognize and categorize own- and other-race faces to examine the neural correlates of this trade-off relationship. We found that for other-race faces, the fusiform face area (FFA) and occipital face area (OFA) responded more to recognition than categorization, whereas for own-race faces, the responses were equal for the 2 tasks. The right superior temporal sulcus (STS) responses were the opposite to those of the FFA and OFA. Further, recognition enhanced the functional connectivity from the right FFA to the right STS, whereas categorization enhanced the functional connectivity from the right OFA to the right STS. The modulatory effects of these 2 couplings were negatively correlated. Our findings suggested that within the core face processing network, although recognizing and categorizing own- and other-race faces activated the same neural substrates, there existed neural trade-offs whereby their activations and functional connectivities were modulated by face race type and task demand due to one's differential processing expertise with own- and other-race faces.

Perceptual specialization and configural face processing in infancy

Adults’ face processing expertise includes sensitivity to second-order configural information (spatial relations among features such as distance between eyes). Prior research indicates that infants process this information in female faces. In the current experiments, 9-month-olds discriminated spacing changes in upright human male and monkey faces but not in inverted faces. However, they failed to process matching changes in upright house stimuli. A similar pattern of performance was exhibited by 5-month-olds. Thus, 5- and 9-month-olds exhibited specialization by processing configural information in upright primate faces but not in houses or inverted faces. This finding suggests that, even early in life, infants treat faces in a special manner by responding to changes in configural information more readily in faces than in non-face stimuli. However, previously reported differences in infants’ processing of human versus monkey faces at 9 months of age (but not at younger ages), which have been associated with perceptual narrowing, were not evident in the current study. Thus, perceptual narrowing is not absolute in the sense of loss of the ability to process information from other species’ faces at older ages.

The functional architecture for face-processing expertise: FMRI evidence of the developmental trajectory of the core and the extended face systems

Expertise in processing faces is a cornerstone of human social interaction. However, the developmental course of many key brain regions supporting face preferential processing in the human brain remains undefined. Here, we present findings from an FMRI study using a simple viewing paradigm of faces and objects in a continuous age sample covering the age range from 6 years through adulthood. These findings are the first to use such a sample paired with whole-brain FMRI analyses to investigate development within the core and extended face networks across the developmental spectrum from middle childhood to adulthood. We found evidence, albeit modest, for a developmental trend in the volume of the right fusiform face area (rFFA) but no developmental change in the intensity of activation. From a spatial perspective, the middle portion of the right fusiform gyrus most commonly found in adult studies of face processing was increasingly likely to be included in the FFA as age increased to adulthood. Outside of the FFA, the most striking finding was that children hyperactivated nearly every aspect of the extended face system relative to adults, including the amygdala, anterior temporal pole, insula, inferior frontal gyrus, anterior cingulate gyrus, and parietal cortex. Overall, the findings suggest that development is best characterized by increasing modulation of face-sensitive regions throughout the brain to engage only those systems necessary for task requirements.

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.

The Allure of Status: High-Status Targets Are Privileged in Face Processing and Memory

The current research tests the hypothesis that face processing is attuned to high-status faces. Across three experiments, faces of high-status targets were better recognized than faces of low-status targets. In Experiment 2, this memory advantage for high-status targets also extended to an attentional bias toward high-status targets and to stronger sociospatial memory (identity-location link) for high-status targets. Finally, Experiment 3 finds that high-status faces received more expert-style holistic processing than did low-status faces. This suggests that high-status faces also benefit more from the strategic deployment of expert face processing resources than low-status faces. Taken together, these data indicate that perceivers strategically allocate face processing resources to targets perceived to be high in status.

The Effects of Face Expertise Training on the Behavioral Performance and Brain Activity of Adults with High Functioning Autism Spectrum Disorders

The effect of expertise training with faces was studied in adults with ASD who showed initial impairment in face recognition. Participants were randomly assigned to a computerized training program involving either faces or houses. Pre- and post-testing included standardized and experimental measures of behavior and event-related brain potentials (ERPs), as well as interviews after training. After training, all participants met behavioral criteria for expertise with the specific stimuli on which they received training. Scores on standardized measures improved after training for both groups, but only the face training group showed an increased face inversion effect behaviorally and electrophysiological changes to faces in the P100 component. These findings suggest that individuals with ASD can gain expertise in face processing through training.