We can determine a person's sex just by observing the way they walk. This can be done very accurately, even when people are represented by 15 dots of light attached to the major joints of the body.
Gene Stoner and his colleagues at the Salk Institute's Visual Center Laboratory used the biomotion light walker, a computer simulation of human gait, to show that observers were more sensitive to female attributes after watching the walking motions of a male. This suggests that there are visual cortical neurons specialized for the task of determining sex from gait.
In their experiments, described in the advance online edition of Nature Neuroscience, Stoner and his team morphed the gait of the biomotion light walker to display varying degress of 'maleness' and 'femaleness'. Participants reported seeing a woman when the 'maleness' of the figure being observed was 49% or less, and reported seeing a man when the value was higher than 49%. But when a very masculine or feminine figure was observed, the participants were far more sensitive to the atributes of the opposite sex.
It has long been known that there are cells in the visual cortex which respond to certain low-level characteristics of objects, such as shape and colour. The pioneering work of neurophysiologists David Hubel and Torsten Weisel showed that other cells in the visual cortex respond to the orientation of moving edges and to movement in a specific direction.
Higher-level processing of information about such characteristics allows us to identify objects. The cells whose existence is theorized by Stoner's team use global motion to provide information about the structure of objects. Visual cortical cells exhibit the property of adaptation, which serves to exaggerate the differences between objects. For example, if one looks at a red object and then another of a neutral colour, one usually sees green.
"Our judgment of gender can adapt within seconds," says Stoner. The adaptation of the postulated 'gait' cells allows us to determine the sex of a person from their gait despite cultural and geographical differences in how people walk.
"We think…that there are neurons in the brain that fire if, and only if, they 'see' a male gait and others that fire if, and only if, they 'see' a female gait, says lead author Heather Jordan, a former member of the Visual Center lab who is now an assistant professor at York University, Toronto.
Mo Costandi 