How do humans recognize humans?

December 13, 2017

A requirement for a system that has evolved to live in a social environment is to be able to recognize rapidly entities with which it can engage in interactions, above all, conspecifics. The human brain has developed high sensitivity to visual signals that cue the presence of a biological entity (an animal) in the environment, such as facial and body configurations, animacy, and a specific type of motion called “biological motion”.

A recent fMRI work on adult participants adds to this list a perceptual sensitivity, or preference, to bipedal motion. Brain areas involved in the perception of biological entities in the superior temporal sulcus of the right hemisphere, respond more strongly to the view of a walking man and a walking chicken, two bipeds, than to quadrupeds such as a walking cat and a crawling 7-months-old baby, even if the latter is a human. The study identifies another brain network in the left hemisphere that, beyond their physical/perceptual differences, categorizes man and baby together and as separated from chicken and cat.

In sum, the human perceptual network recognizes the bipedalism as a distinctive characteristic of the human species, even at the cost of “false positive” responses to nonhuman bipeds (the chicken) and “false negative” responses to non-bipedal humans (the baby). Higher-order brain areas in the left-hemisphere correct these imperfect perceptual decisions.

The study was carried out in collaboration with Moritz Wurm and Nikolaas Oosterhof (University of Trento) and Alfonso Caramazza (Harvard University) and papered on Scientific Report the last October 25.