How do we recognise faces? The vast majority of research into face perception has attempted to answer this question by restricting their investigations to a small section of the fusiform gyrus, which Kanwisher and colleagues named the Fusiform Face Area (FFA) in 1997. It is commonly proposed that the FFA handles not only the detection but also the recognition of individual faces. A recent paper by Kriegeskorte et al (2007) suggests that instead, a region in the right anterior inferotemporal cortex (aIT – ahead of and above the FFA) encodes information about different faces, while the FFA does not. In order to understand the finer points of this finding, it is necessary to explain the basic assumptions of univariate neuroimaging analysis, and how it is used to identify the FFA. Skip ahead a paragraph if this is familiar territory.
The classic fMRI or PET analysis consists of taking an experimental condition and a control condition, and asking “which areas respond significantly more to the experimental condition than the control?” The resulting activations can be said to constitute areas that are specifically implicated in the experimental condition. For example, the FFA is usually defined as the part of the fusiform gyrus that responds more to faces than to houses. Note that there is an element of inference or assumption involved in then concluding that this bit of brain is the bit that does faces, since other areas might also respond to faces without being detected in a relatively insensitive univariate whole-brain analysis. The common acceptance of this type of contrast analysis stems in part from its practical utility. For example, the FFA corresponds closely to the critical lesion site that causes prosopagnosia (an inability to recognise faces), and activation in this area can be correlated with behavioural performance at various face recognition tasks.
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