Galit Yovel

The fusiform face area: a cortical region specialized for the perception of faces.

Faces are among the most important visual stimuli we perceive, informing us not only about a persons identity, but also about their mood, sex, age and direction of gaze. The ability to extract this information within a fraction of a second of viewing a face is important for normal social interactions and has probably played a critical role in the survival of our primate ancestors. Considerable evidence from behavioural, neuropsychological and neurophysiological investigations supports the hypothesis that humans have specialized cognitive and neural mechanisms dedicated to the perception of faces (the face-specificity hypothesis). Here, we review the literature on a region of the human brain that appears to play a key role in face perception, known as the fusiform face area (FFA). Section 1 outlines the theoretical background for much of this work. The face-specificity hypothesis falls squarely on one side of a longstanding debate in the fields of cognitive science and cognitive neuroscience concerning the extent to which the mind/brain is composed of: (i) special-purpose (‘domain-specific’) mechanisms, each dedicated to processing a specific kind of information (e.g. faces, according to the face-specificity hypothesis), versus (ii) general-purpose (‘domain-general’) mechanisms, each capable of operating on any kind of information. Face perception has long served both as one of the prime candidates of a domain-specific process and as a key target for attack by proponents of domain-general theories of brain and mind. Section 2 briefly reviews the prior literature on face perception from behaviour and neurophysiology. This work supports the face-specificity hypothesis and argues against its domain-general alternatives (the individuation hypothesis, the expertise hypothesis and others). Section 3 outlines the more recent evidence on this debate from brain imaging, focusing particularly on the FFA. We review the evidence that the FFA is selectively engaged in face perception, by addressing (and rebutting) five of the most widely discussed alternatives to this hypothesis. In §4, we consider recent findings that are beginning to provide clues into the computations conducted in the FFA and the nature of the representations the FFA extracts from faces. We argue that the FFA is engaged both in detecting faces and in extracting the necessary perceptual information to recognize them, and that the properties of the FFA mirror previously identified behavioural signatures of face-specific processing (e.g. the face-inversion effect). Section 5 asks how the computations and representations in the FFA differ from those occurring in other nearby regions of cortex that respond strongly to faces and objects. The evidence indicates clear functional dissociations between these regions, demonstrating that the FFA shows not only functional specificity but also area specificity. We end by speculating in §6 on some of the broader questions raised by current research on the FFA, including the developmental origins of this region and the question of whether faces are unique versus whether similarly specialized mechanisms also exist for other domains of high-level perception and cognition.

Face Perception: Domain Specific, Not Process Specific

Evidence that face perception is mediated by special cognitive and neural mechanisms comes from fMRI studies of the fusiform face area (FFA) and behavioral studies of the face inversion effect. Here, we used these two methods to ask whether face perception mechanisms are stimulus specific, process specific, or both. Subjects discriminated pairs of upright or inverted faces or house stimuli that differed in either the spatial distance among parts (configuration) or the shape of the parts. The FFA showed a much higher response to faces than to houses, but no preference for the configuration task over the part task. Similarly, the behavioral inversion effect was as large in the part task as the configuration task for faces, but absent in both part and configuration tasks for houses. These findings indicate that face perception mechanisms are not process specific for parts or configuration but are domain specific for face stimuli per se.

TMS Evidence for the Involvement of the Right Occipital Face Area in Early Face Processing

Extensive research has demonstrated that several specialized cortical regions respond preferentially to faces. One such region, located in the inferior occipital gyrus, has been dubbed the occipital face area (OFA). The OFA is the first stage in two influential face-processing models, both of which suggest that it constructs an initial representation of a face, but how and when it does so remains unclear. The present study revealed that repetitive transcranial magnetic stimulation (rTMS) targeted at the right OFA (rOFA) disrupted accurate discrimination of face parts but had no effect on the discrimination of spacing between these parts. rTMS to left OFA had no effect. A matched part and spacing discrimination task that used house stimuli showed no impairment. In a second experiment, rTMS to rOFA replicated the face-part impairment but did not produce the same effect in an adjacent area, the lateral occipital cortex. A third experiment delivered double pulses of TMS separated by 40 ms at six periods after stimulus presentation during face-part discrimination. Accuracy dropped when pulses were delivered at 60 and 100 ms only. These findings indicate that the rOFA processes face-part information at an early stage in the face-processing stream.

Diagnosing prosopagnosia: Effects of ageing, sex, and participant-stimulus ethnic match on the cambridge face memory test and cambridge face perception test

The Cambridge Face Memory Test (CFMT) and Cambridge Face Perception Test (CFPT) have provided the first theoretically strong clinical tests for prosopagnosia based on novel rather than famous faces. Here, we assess the extent to which norms for these tasks must take into account ageing, sex, and testing country. Data were from Australians aged 18 to 88 years (N = 240 for CFMT; 128 for CFPT) and young adult Israelis (N = 49 for CFMT). Participants were unselected for face recognition ability; most were university educated. The diagnosis cut-off for prosopagnosia (2 SDs poorer than mean) was affected by age, participant–stimulus ethnic match (within Caucasians), and sex for middle-aged and older adults on the CFPT. We also report internal reliability, correlation between face memory and face perception, correlations with intelligence-related measures, correlation with self-report, distribution shape for the CFMT, and prevalence of developmental prosopagnosia.

Why does picture-plane inversion sometimes dissociate perception of features and spacing in faces, and sometimes not? Toward a new theory of holistic processing

Classically, it has been presumed that picture-plane inversion primarily reduces sensitivity to spacing/configural information in faces (distance between location of the major features) and has little effect on sensitivity to local feature information (e.g., eye shape or color). Here, we review 22 published studies relevant to this claim. Data show that the feature inversion effect varied substantially across studies as a function of the following factors: whether the feature change was shape only or included color/brightness, the number of faces in the stimulus set, and whether the feature was in facial context. For shape-only changes in facial context, feature inversion effects were as large as typical spacing inversion effects. Small feature inversion effects occurred only when a task could be efficiently solved by visual-processing areas outside whole-face coding. The results argue that holistic/configural processing for upright faces integrates exact feature shape and spacing between blobs. We describe two plausible approaches to this process.

Prosopagnosia as an impairment to face-specific mechanisms: Elimination of the alternative hypotheses in a developmental case

For more than 35 years, researchers have debated whether face recognition is carried out by face-specific mechanisms or whether it involves more general mechanisms that are also used for objects. Prosopagnosic patients have furnished powerful evidence for face-specific mechanisms. Yet for each case that has been tested there have always been several untested alternative explanations that could account for the case. As such, each of these individuals has not been sufficiently tested to provide conclusive evidence for face-specific processes. Here we make a stronger argument with a single case of severe developmental prosopagnosia by exhaustively addressing all extant alternatives. We reject each in turn and thus eliminate all alternative accounts. Because this case is developmental in etiology the results also indicate that face recognition involves developmental mechanisms different from those producing other visual recognition mechanisms.

The asymmetry of the fusiform face area is a stable individual characteristic that underlies the left-visual-field superiority for faces

Recognition of faces is better when faces are presented in the left than right-visual-field. Furthermore, this perceptual asymmetry is a stable individual characteristic. Although it has been commonly assumed that the right hemispheric dominance for face processing underlies this left-visual-field superiority in face recognition, this neural-behavioral association has never been directly demonstrated. Here we applied functional MRI (fMRI) to measure the magnitude of the asymmetric response to faces for each subject. To determine whether the asymmetric neural response to faces is stable across sessions, subjects returned for a second fMRI session. In addition, subjects performed a behavioral experiment outside the scanner where they had to recognize centrally presented chimeric faces, which presented different identities in the right- and left-visual-field. This task yielded a measure of the magnitude of the left-visual-field bias for each subject. Our findings show that the magnitude of the asymmetry of the face-selective area in the fusiform gyrus (FFA) is highly consistent for each individual across scans. We then show that the behavioral left-visual-field asymmetry, measured outside the scanner, was strongly and specifically correlated with the asymmetry of the FFA across subjects, but not with other face-specific or nearby object-general regions. Our findings provide the first empirical evidence for the prevalent idea that perceptual asymmetries in face recognition are associated with the well-known hemispheric asymmetry for faces. We conclude that the FFA asymmetry is a highly stable individual characteristic that underlies the well-established left-visual-field superiority for face recognition.

Event-Related Potential and Functional MRI Measures of Face-Selectivity are Highly Correlated: A Simultaneous ERP-fMRI Investigation

A face‐selective neural signal is reliably found in humans with functional MRI and event‐related potential (ERP) measures, which provide complementary information about the spatial and temporal properties of the neural response. However, because most neuroimaging studies so far have studied ERP and fMRI face‐selective markers separately, the relationship between them is still unknown. Here we simultaneously recorded fMRI and ERP responses to faces and chairs to examine the correlations across subjects between the magnitudes of fMRI and ERP face‐selectivity measures. Findings show that the face‐selective responses in the temporal lobe (i.e., fusiform gyrus—FFA) and superior temporal sulcus (fSTS), but not the face‐selective response in the occipital cortex (OFA), were highly correlated with the face‐selective N170 component. In contrast, the OFA was correlated with earlier ERPs at about 110 ms after stimulus‐onset. Importantly, these correlations reveal a temporal dissociation between the face‐selective area in the occipital lobe and face‐selective areas in the temporal lobe. Despite the very different time‐scale of the fMRI and EEG signals, our data show that a correlation analysis across subjects may be informative with respect to the latency in which different brain regions process information. Hum Brain Mapp, 2010.

No global processing deficit in the Navon task in 14 developmental prosopagnosics

Faces are represented in a more configural or holistic manner than other objects. Substantial evidence indicates that this representation results from face-specific mechanisms, but some have argued that it is produced by configural mechanisms that can be applied to many objects including words. The face-specific hypothesis predicts that non-face configural processes will often be normal in prosopagnosic subjects, whereas the domain-general configural hypothesis predicts they will be deficient on all configural tasks. Although the weight of the evidence favors the face-specific hypothesis, a recent study reopened this issue when it was found that three out of five developmental prosopagnosics showed a larger local processing bias than controls in a global-local task (i.e. a Navon task). To examine this issue more thoroughly we tested a significantly larger sample of prosopagnosics (14 participants) who had severe face memory and face perception deficits. In contrast to the previous report, the developmental prosopagnosics performed normally in the global-local task. Like controls, they showed a typical global advantage and typical global-to-local consistency effects. The results demonstrate that the configural processing required by the Navon task is dissociable from face configural processing.

Hemispheric asymmetries for global and local visual perception: effects of stimulus and task factors.

Although neurotogical and physiological studies indicate a right hemisphere superiority in global processing and a left hemisphere superiority in local processing of Navon-type hierarchical letters (D. Navon, 1977), most investigations of lateralized perception in healthy participants report neither asymmetry. In 6 experiments the authors examined the influence of attentional demands, stimulus properties, and mode of response on perceptual asymmetries for global and local perception. Consistent with their theoretical predictions, asymmetries were more robust on divided- than focused-attention tasks and in response to stimuli in which local and global levels were equally salient compared with those with greater global than local saliency. Contrary to their prediction, perceptual asymmetries were not influenced by the complexity of the motor response.