Perceptual biases in processing facial identity and emotion

Normal observers demonstrate a bias to process the left sides of faces during perceptual judgments about identity or emotion. This effect suggests a right cerebral hemisphere processing bias. To test the role of the right hemisphere and the involvement of configural processing underlying this effect, young and older control observers and patients with right hemisphere damage completed two chimeric faces tasks (emotion judgment and face identity matching) with both upright and inverted faces. For control observers, the emotion judgment task elicited a strong left-sided perceptual bias that was reduced in young controls and eliminated in older controls by face inversion. Right hemisphere damage reversed the bias, suggesting the right hemisphere was dominant for this task, but that the left hemisphere could be flexibly recruited when right hemisphere mechanisms are not available or dominant. In contrast, face identity judgments were associated most clearly with a vertical bias favouring the uppermost stimuli that was eliminated by face inversion and right hemisphere lesions. The results suggest these tasks involve different neurocognitive mechanisms. The role of the right hemisphere and ventral cortical stream involvement with configural processes in face processing is discussed.     

Face processing is enhanced in the left and upper visual hemi-fields

We tested whether two known hemi-field asymmetries would affect visual search with face stimuli. Holistic processing of spatial configurations is better in the left hemi-field, reflecting a right hemisphere specialization, and object recognition is better in the upper visual field, reflecting stronger projections into the ventral stream. Faces tap into holistic processing and object recognition at the same time, which predicts better performance in the left and upper hemi-field, respectively. In the first experiment, participants had to detect a face with a gaze direction different from the remaining faces. Participants were faster to respond when targets were presented in the left and upper hemi-field. The same pattern of results was observed when only the eye region was presented. In the second experiment, we turned the faces upside-down, which eliminated the typical spatial configuration of faces. The left hemi-field advantage disappeared, showing that it is related to holistic processing of faces, whereas the upper hemi-field advantage related to object recognition persisted. Finally, we made the search task easier by asking observers to search for a face with open among closed eyes or vice versa. The easy search task eliminated the need for complex object recognition and, accordingly, the advantage of the upper visual field disappeared. Similarly, the left hemi-field advantage was attenuated. In sum, our findings show that both horizontal and vertical asymmetries affect the search for faces and can be selectively suppressed by changing characteristics of the stimuli.     

Neural perspectives on the other-race effect

Psychological studies have long shown that human memory is superior for faces of our own-race than for faces of other-races. In this paper, we review neural studies of own- versus other-race face processing. These studies divide naturally into those focused on socioaffective aspects of the other-race effect and those directed at high-level visual processing differences. The socioaffective studies consider how subconscious bias and emotional responses affect brain areas such as the amygdala, anterior cingulate cortex, and parahippocampal gyrus. The visual studies focus on face-selective areas in the ventral stream, such as the fusiform face area (FFA). In both cases, factors such as experience, familiarity, social/emotional responses, cultural learning, and bias modulate the patterns of neural activity elicited in response to own- and other-race faces.     

Probability matching in the right hemisphere

Previously it has been shown that the left hemisphere, but not the right, of split-brain patients tends to match the frequency of previous occurrences in probability-guessing paradigms (Wolford, Miller, & Gazzaniga, 2000). This phenomenon has been attributed to an "interpreter," a mechanism for making interpretations and forming hypotheses, thought to reside exclusively in the left hemisphere. In this study with a split-brain patient, we had him guess one of two types of faces, stimuli known to be preferentially processed in the right hemisphere of this patient. Unlike previous studies using other kinds of stimuli, the right hemisphere matched the frequency of the previous occurrences of a face-type, but the left hemisphere did not.     

中国学生的自我面孔识别

已有研究表明大脑右半球具有自我面孔再认的优势。为了进一步验证这个观点,该研究使用面孔识别任务,以13名右利手的中国大学生为被试,测量被试对morphing面孔的左右手反应差异。给被试呈现第一张面孔向第二张面孔的morphing过程,当被试看到morphing的面孔更像第二张面孔时报告停止。研究有两个morphing过程：一个为由自我面孔向名人面孔morphing,另一个为好朋友面孔（熟悉的）向名人面孔morphing。结果表明当用左手反应时,被试倾向于把morphing的面孔识别为自己,研究中自我面孔再认的左手优势与已有的发现一致。另外,研究还发现在一定trials条件下,熟悉面孔再认也具有左手优势,这一结果与西方被试的结果不一致,但东西方被试对熟悉面孔再认的差异与独立型自我和互倚型自我的观点一致。该文认为神经心理学有关自我的研究可能需要考虑文化和情境的复杂性。     

Infant preference for female faces occurs for same‐ but not other‐race faces

There has been a recent surge of interest in the question of how infants respond to the social attributes of race and gender information in faces. This work has demonstrated that by 3 months of age, infants will respond preferentially to same‐race faces and faces depicting the gender of the primary caregiver. In the current study, we investigated emergence of the female face preference for same‐ versus other‐race faces to examine whether the determinants of preference for face gender and race are independent or interactive in young infants. In Expt 1, 3‐month‐old Caucasian infants displayed a preference for female over male faces when the faces were Caucasian, but not when the faces were Asian. In Expt 2, new‐born Caucasian infants did not demonstrate a preference for female over male faces for Caucasian faces. The results are discussed in terms of a face prototype that becomes progressively tuned as it is structured by the interaction of the gender and race of faces that are experienced during early development.     

Segregated processing of facial identity and emotion in the human brain: A pet study

Abstract

The brain is organized into segregated areas of relative functional autonomy and specialization. This basic principle of cerebral organization is well documented for cognitive functions that differ drastically from one another, but less so for functions that belong to the same domain, such as face processing. Yet several sources of evidence point to a functional and structural dissociation of various aspects of face processing, as suggested by (1) an analysis of the perceptual and cognitive demands made by the processing of diverse properties conveyed by facial configurations, (2) selective impairment of aspects of face processing in brain-damaged patients, and (3) different localizations of face cells responsive to properties conveyed by faces such as identity and emotion in the monkey's brain. This study used positron emission tomography (PET) and magnetic resonance imaging (MRI) to delineate better the neurofunctional organization of face processing in the human brain, by measuring cerebral blood flow while subjects performed tasks involving the recognition of faces or the recognition of emotions expressed by faces. The results showed segregated processing of facial identity and facial emotion, with the former being performed predominantly in the ventro-mesial region of the right hemisphere including the limbic system, whereas the latter was carried out predominantly in the latter part of the right hemisphere and the dorsal region of the limbic system. This structural organization allows the parallel processing of different information contained in physiognomies and underlies the high efficiency with which humans process faces.     

Hemispheric asymmetry in discriminating faces differing for featural or configural (second-order relations) aspects

The human capacity to discriminate among different faces relies on distinct parallel subprocesses, based either on the analysis of configural aspects or on the sequential analysis of the single elements of a face. A particular type of configural processing consists of considering whether two faces differ in terms of internal spacing among their features, referred to as second-order relations processing. Findings from electrophysiological, neuroimaging, and lesion studies suggest that, overall, configural processes rely more on the right hemisphere, whereas analysis of single features would involve more the left. However, results are not always consistent, and behavioral evidence for a right-hemisphere specialization in second-order relations processing is lacking. Here, we used divided visual field presentation to investigate the possible different contributions of the two hemispheres to face discrimination based on relational versus featural processing. Our data indicate a right-hemispheric specialization in relational processing of upright (but not inverted) faces. Furthermore, we provide evidence regarding the involvement of both the right and left hemispheres in the processing of faces differing for inner features, suggesting that both analytical and configural modes of processing are at play.     

Order of feature recognition in familiar and unfamiliar faces

Three experiments measured order of processing for single faces presented to the left or right visual field (VF) using a same-different matching task. In contrast to earlier studies, the stimuli in the present experiments were carefully matched for overall similarity prior to the actual experiments. Experiments 1 and 2 showed that a significant top-to-bottom order of processing occurred for line drawings of unfamiliar faces but not for line drawings of familiar faces. Experiment 3 found evidence supporting top-to-bottom processing for unfamiliar photographic face stimuli. The photographic stimuli in Experiment 3 were matched more quickly when presented in the left VF (right hemisphere); however, this VF asymmetry was not related to previously reported differences in order of processing. It is suggested that under some conditions faces presented to the right hemisphere may be processed more like familiar faces than faces presented to the left hemisphere; however, this difference is not critical for the left VF (right hemisphere) superiority often found in face recognition tasks.     

Object recognition in Williams syndrome: uneven ventral stream activation

Williams syndrome (WS) is a genetic disorder associated with severe visuospatial deficits, relatively strong language skills, heightened social interest, and increased attention to faces. On the basis of the visuospatial deficits, this disorder has been characterized primarily as a deficit of the dorsal stream, the occipitoparietal brain regions that subserve visuospatial processing. However, some evidence indicates that this disorder may also affect the development of the ventral stream, the occipitotemporal cortical regions that subserve face and object recognition. The present studies examined ventral stream function in WS, with the hypothesis that faces would produce a relatively more mature pattern of ventral occipitotemporal activation, relative to other objects that are also represented across these visual areas. Using functional magnetic imaging, we compared activation patterns during viewing of human faces, cat faces, houses and shoes in individuals with WS (age 14-27), typically developing 6-9-year-olds (matched approximately on mental age), and typically developing 14-26-year-olds (matched on chronological age). Typically developing individuals exhibited changes in the pattern of activation over age, consistent with previous reports. The ventral stream topography of individuals with WS differed from both control groups, however, reflecting the same level of activation to face stimuli as chronological age matches, but less activation to house stimuli than either mental age or chronological age matches. We discuss the possible causes of this unusual topography and implications for understanding the behavioral profile of people with WS.     

Ratings of emotion in faces are influenced by the visual field to which stimuli are presented

This experiment was designed to assess the differential impact of initially presenting affective information to the left versus right hemisphere on both the perception of and response to the input. Nineteen right-handed subjects were presented with faces expressing happiness and sadness. Each face was presented twice to each visual field for an 8-sec duration. The electro-oculogram (EOG) was monitored and fed back to subjects to train them to keep their eyes focused on the central fixation point as well as to eliminate trials confounded by eye movement artifact. Following each slide presentation, subjects rated the intensity of the emotional expression depicted in the face and their emotional reaction to the face on a series of 7-point rating scales. Subjects reported perceiving more happiness in response to stimuli initially presented to the left hemisphere (right visual field) compared to presentations of the identical faces to the right hemisphere (left visual field). This effect was predominantly a function of ratings on sad faces. A similar, albeit less robust, effect was found on self-ratings of happiness (the degree to which the face elicited the emotion in the viewer). These data challenge the view that the right hemisphere is uniquely involved in all emotional behavior. The implications of these findings for theories concerning the lateralization of emotional behavior are discussed.     

Lateralised processing of the internal and the external facial features of personally familiar and unfamiliar faces: a visual half-field study

In this visual half field (VHF) experiment, we investigated possible differences between the left and the right hemisphere in the processing of the internal and external features of familiar and unfamiliar faces. Previous studies using famous and unknown faces had indicated that both hemispheres use the same qualitative mode of processing with the internal features being more important for the perception of familiar faces. In this experiment, personally familiar faces rather than famous faces are used. There are several, mainly methodological, reasons why personally familiar faces are more appropriate stimuli to investigate face processing. The results of the present study showed that no overall visual field effect occurred, but more importantly, that face processing in the left hemisphere differed qualitatively from that in the right hemisphere. The theoretical repercussions of these findings are discussed.     

Holistic processing impairment can be restricted to faces in acquired prosopagnosia: Evidence from the global/local Navon effect

Previous studies have shown that acquired prosopagnosia is characterized by impairment at holistic/configural processing. However, this view is essentially supported by studies performed with patients whose face recognition difficulties are part of a more general visual (integrative) agnosia. Here, we tested the patient PS, a case of acquired prosopagnosia whose face‐specific recognition difficulties have been related to the inability to process individual faces holistically (absence of inversion, composite, and whole–part effects with faces). Here, we show that in contrast to this impairment, the patient presents with an entirely normal response profile in a Navon hierarchical letter task: she was as fast as normal controls, faster to identify global than local letters, and her sensitivity to global interference during identification of local letters was at least as large as normal observers. These observations indicate that holistic processing as measured with global/local interference in the Navon paradigm is functionally distinct from the ability to perceive an individual face holistically.     

Early development of letter specialization in left fusiform is associated with better word reading and smaller fusiform face area

A functional region of left fusiform gyrus termed “the visual word form area” (VWFA) develops during reading acquisition to respond more strongly to printed words than to other visual stimuli. Here, we examined responses to letters among 5‐ and 6‐year‐old early kindergarten children (N = 48) with little or no school‐based reading instruction who varied in their reading ability. We used functional magnetic resonance imaging (fMRI) to measure responses to individual letters, false fonts, and faces in left and right fusiform gyri. We then evaluated whether signal change and size (spatial extent) of letter‐sensitive cortex (greater activation for letters versus faces) and letter‐specific cortex (greater activation for letters versus false fonts) in these regions related to (a) standardized measures of word‐reading ability and (b) signal change and size of face‐sensitive cortex (fusiform face area or FFA; greater activation for faces versus letters). Greater letter specificity, but not letter sensitivity, in left fusiform gyrus correlated positively with word reading scores. Across children, in the left fusiform gyrus, greater size of letter‐sensitive cortex correlated with lesser size of FFA. These findings are the first to suggest that in beginning readers, development of letter responsivity in left fusiform cortex is associated with both better reading ability and also a reduction of the size of left FFA that may result in right‐hemisphere dominance for face perception.     

Infants rapidly detect human faces in complex naturalistic visual scenes

Infants respond preferentially to faces and face‐like stimuli from birth, but past research has typically presented faces in isolation or amongst an artificial array of competing objects. In the current study infants aged 3‐ to 12‐months viewed a series of complex visual scenes; half of the scenes contained a person, the other half did not. Infants rapidly detected and oriented to faces in scenes even when they were not visually salient. Although a clear developmental improvement was observed in face detection and interest, all infants displayed sensitivity to the presence of a person in a scene, by displaying eye movements that differed quantifiably across a range of measures when viewing scenes that either did or did not contain a person. We argue that infant's face detection capabilities are ostensibly “better” with naturalistic stimuli and artificial array presentations used in previous studies have underestimated performance.     

Expertise training with novel objects leads to left-lateralized facelike electrophysiological responses

Scalp event-related potentials (ERPs) in humans indicate that face and object processing differ approximately 170 ms following stimulus presentation, at the point of the N170 occipitotemporal component. The N170 is delayed and enhanced to inverted faces but not to inverted objects. We tested whether this inversion effect reflects early mechanisms exclusive to faces or whether it generalizes to other stimuli as a function of visual expertise. ERPs to upright and inverted faces and novel objects (Greebles) were recorded in 10 participants before and after 2 weeks of expertise training with Greebles. The N170 component was observed for both faces and Greebles. The results are consistent with previous reports in that the N170 was delayed and enhanced for inverted faces at recording sites in both hemispheres. For Greebles, the same effect of inversion was observed only for experts, primarily in the left hemisphere. These results suggest that the mechanisms underlying the electrophysiological face-inversion effect extend to visually homogeneous nonface object categories, at least in the left hemisphere, but only when such mechanisms are recruited by expertise.     

Cuing effects of faces are dependent on handedness and visual field

Faces are unlike other visual objects we encounter, in that they alert us to potentially relevant social information. Both face processing and spatial attention are dominant in the right hemisphere of the human brain, with a stronger lateralization in right- than in left-handers. Here, we demonstrate behavioral evidence for an effect of handedness on performance in tasks using faces to direct attention. Nonpredictive, peripheral cues (faces or dots) directed exogenous attention to contrast-varying stimuli (Gabor patches)—a tilted target, a vertical distractor, or both; observers made orientation discriminations on the target stimuli. Whereas cuing with dots increased contrast sensitivity in both groups, cuing with faces increased contrast sensitivity in right- but not in left-handers, for whom opposite hemifield effects resulted in no net increase. Our results reveal that attention modulation by face cues critically depends on handedness and visual hemifield. These previously unreported interactions suggest that such lateralized systems may be functionally connected.     

Selective orienting of attention to masked threat faces in social anxiety

The aims of the study were two-fold: to examine whether previous evidence of a pre-attentive bias for masked threat faces in anxious individuals could be replicated, and to assess the relationship between the predicted bias and measures of trait and social anxiety. Pairs of face stimuli were briefly displayed and masked in a modified version of the visual probe task. Results indicated that high anxious individuals were faster to respond to probes occurring in the spatial location of masked threat rather than neutral faces; consistent with their attention being automatically captured by sub-threshold threat cues. Furthermore, this vigilance effect for masked threat faces appeared to be primarily a function of social anxiety and social avoidance, rather than trait anxiety. It was also more apparent when threat faces were presented in the left visual field, suggestive of right hemisphere involvement.