Fusiform face area

The fusiform face area (FFA) is a part of the human visual system which might be specialized for facial recognition, although there is some evidence that it also processes categorical information about other objects, particularly familiar ones. It is located in the fusiform gyrus (Brodmann area 37).

Localization
The FFA is located in the ventral stream on the ventral surface of the temporal lobe on the lateral side of the fusiform gyrus. It is lateral to the parahippocampal place area. It displays some lateralization, usually being larger in the right hemisphere.

The FFA was discovered and continues to be investigated in humans using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies. Usually, a participant views images of faces, objects, places, bodies, scrambled faces, scrambled objects, scrambled places and scrambled bodies. This is called a functional localizer. Comparing the neural response between faces and scrambled faces will reveal areas that are face-responsive, while comparing cortical activation between faces and objects will reveal areas that are face-selective.

Functional role
The human FFA was first described by Justine Sergent in 1992 and by Nancy Kanwisher in 1997 who proposed that the existence of the FFA is evidence for domain specificity in the visual system. More recently, it has been suggested that the FFA processes more than just faces. Some groups, including Isabel Gauthier and others, maintain that the FFA is an area for recognizing fine distinctions between well-known objects. Gauthier et al. tested both car and bird experts, and found some activation in the FFA when car experts were identifying cars and when bird experts were identifying birds. A paper by Kalanit Grill-Spector et al. also suggests that processing in the FFA is not exclusive to faces, although an erratum was later published which brought to light some errors. The debate about the functional role of the FFA is ongoing.

A 2009 magnetoencephalography study found that objects incidentally perceived as faces, an example of pareidolia, evoke an early (165 ms) activation in the FFA, at a time and location similar to that evoked by faces, whereas other common objects do not evoke such activation. This activation is similar to a slightly earlier peak at 130 ms seen for images of real faces. The authors suggest that face perception evoked by face-like objects is a relatively early process, and not a late cognitive reinterpretation phenomenon.

One case study on prosopagnosia provided evidence that faces are processed in a special way. A patient known as C. K., who suffered brain damage as a result of a car accident, later developed object agnosia. He experienced great difficulty with basic level object recognition, also extending to body parts, but performed very well at recognizing faces. A later study showed that C. K. was unable to recognize faces that were inverted or otherwise distorted, even in cases where they could easily be identified by normal subjects. This is taken as evidence that the fusiform face area is specialized for processing faces in a normal orientation.

Based on these advances IBM in 2010 applied for a patent on how to extract mental images of human faces from the human brain. The proposed design builds on a feedback loop based on brain measurements of the fusiform gyrus area in the brain assuming that activation is proportional with facial familiarity.