Fourty years after Ungerleider and Mishkin proposed our current model of the primate cortex as using two major visual pathway along its ventral and dorsal surfaces that respectively specialize in computing the 'what' and 'where' content of visual stimuili,
Pitcher and Ungerleider now summarize evidence that this picture has to be expanded to include a third pathway specialized for moving social visual perceptions, especially of faces. Here are their core points, following by a descriptive graphic from their article.
The two-visual pathway model of primate visual cortex needs to be updated. We propose the existence of a third visual pathway on the lateral brain surface that is anatomically segregated from the dorsal and ventral pathways.
The third pathway exists in human and non-human primates. In humans, the third pathway projects from early visual cortex into the superior temporal sulcus (STS). In macaques the third pathway projects from early visual cortex into the dorsal bank and fundus of the STS.
The third pathway has distinct functional properties. It selectively responds to moving faces and bodies. Visual field-mapping studies show that the third pathway responds to faces across the visual field to a greater extent than the ventral pathway.
The third pathway computes a range of higher sociocognitive functions based on dynamic social cues. These include facial expression recognition, eye gaze discrimination, the audiovisual integration of speech, and interpreting the actions and behaviors of other biological organisms.
