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

Abstract

Faces are among the most important visual stimuli we perceive, informing us not only about a person's 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 section 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 section 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.

Figure 1

Tsao et al. recorded the response of single cells within an fMRI identified face-selective patch of cortex. The figure shows the average response across all 320 visually responsive neurons in the face-selective patches of two monkeys, to 96 different stimulus images, indicating very high selectivity for faces by the cells in this patch.

Figure 2

Face-selective activation (faces > objects, p<0.0001) on an inflated brain of one subject, shown from lateral and ventral views of the right and left hemispheres. Three face-selective regions are typically found: the FFA in the fusiform gyrus along the ventral part of the brain, the OFA in the lateral occipital area and the fSTS in the posterior region of the superior temporal sulcus.

Figure 3

Face and house stimuli designed to test the face-specificity hypothesis, from a study by Yovel & Kanwisher (Kanwisher et al. 1997; Yovel & Kanwisher 2004). House stimuli were constructed in exactly the same way as the face stimuli: the faces or houses differed in either their parts (eyes and mouth for faces, and windows and door for houses) or the spacing among these parts. Subjects performed a discrimination task on pairs of faces or houses that differed in either spacing or parts. Performance was matched across the stimuli and the spacing and part conditions. Thus, discrimination of the faces and of the houses are very similar in overall difficulty and in the nature of the perceptual discriminations required. Thus, the threefold higher FFA response for the face tasks than the house tasks (Kanwisher et al. 1997; Yovel & Kanwisher 2004) provides strong support to the face-specificity hypothesis and is inconsistent with the individuation hypothesis and with the hypothesis that the FFA conducts domain-general processing of configuration/spacing information.

Figure 4

The response of the FFA and LOC to the face and house stimuli (see figure 3) when subjects discriminate the stimuli based on their parts (eyes and mouth for faces, and windows and doors for houses) or the spacing among the parts. Findings show a clear dissociation between the FFA, which responds more strongly to faces than houses but similarly on the spacing and part tasks versus the LOC, which shows a similar response to faces and houses and a higher response when subjects discriminate stimuli based on parts than based on the spacing among the parts.