One of the more stunning examples of the resourcefulness of human vision is the
ability to see 'biological motion', which was first shown with an adaptation of
earlier cinematic work: illumination of only the joints of a walking person is
enough to convey a vivid, compelling impression of human animation, although the
percept collapses to a jumble of meaningless lights when the walker stands still.
The information is sufficient to discriminate the sex and other details of the
walker, and can be interpreted by young infants. Here we measure the ability of
the visual system to integrate this type of motion information over space and
time, and compare this capacity with that for viewing simple translational motion.
Sensitivity to biological motion increases rapidly with the number of illuminated
joints, far more rapidly than for simple motion. Furthermore, this information
is summed over extended temporal intervals of up to 3 seconds (eight times longer
than for simple motion). The steepness of the summation curves indicates that
the mechanisms that analyse biological motion do not integrate linearly over space
and time with constant efficiency, as may occur for other forms of complex motion,
but instead adapt to the nature of the stimulus.
Maintained by Francis F. Steen, Communication Studies, University of California Los Angeles