Global and fine information coded by single neurons in the temporal visual cortex

Abstract

When we see a person's face, we can easily recognize their species, individual identity and emotional state. How does the brain represent such complex information? A substantial number of neurons in the macaque temporal cortex respond to faces. However, the neuronal mechanisms underlying the processing of complex information are not yet clear. Here we recorded the activity of single neurons in the temporal cortex of macaque monkeys while presenting visual stimuli consisting of geometric shapes, and monkey and human faces with various expressions. Information theory was used to investigate how well the neuronal responses could categorize the stimuli. We found that single neurons conveyed two different scales of facial information in their firing patterns, starting at different latencies. Global information, categorizing stimuli as monkey faces, human faces or shapes, was conveyed in the earliest part of the responses. Fine information about identity or expression was conveyed later, beginning on average 51 ms after global information. We speculate that global information could be used as a 'header' to prepare destination areas for receiving more detailed information.

Autism and the development of face processing

“…The N700 is significantly larger for faces than for other stimuli [116], suggesting local generation by face-selective modules in the occipito-temporal cortex. These findings are consistent with identity-sensitive, late, unit responses from face-selective cells in the primate temporal cortex [126].…”

Spatial grouping determines temporal integration.

“…Hence, complex grouping interactions may well be implemented by simple neural circuits, in accordance with physiological findings (Yasuko Sugase, Yamane, & Ueno, 1999), and contrary to assumptions that grouping happens after basic visual processing is accomplished (e.g. Palmer et al, 2003 …”

Learning and inference in the brain

“…This is because the representations at higher levels must emerge before backward afferents can reshape the response profile of neurons in lower areas. This temporal delay, in the emergence of selectivity, is precisely what one sees empirically: Sugase, Yamane, Ueno, and Kawano (1999) recorded neurons in macaque temporal cortex during the presentation of faces and objects. The faces were either human or monkey faces and were categorised in terms of identity (whose face it was) and expression (happy, angry, etc.).…”