Aperture Problem

The motion of a homogeneous contour is locally ambiguous. This is so because a motion sensor has a finite receptive field: it "looks" at the world through something like an aperture (Hildreth, 1984,1987). Within that aperture, different physical motions are indistinguishable. Here, for instance, a set of lines moving right to left produce the same spatiotemporal structure as a set of lines moving top to bottom. The aperture problem implies that motion sensitive neurons in the visual primary cortex will always respond to a contour that crosses their receptive field, independently of its true length and orientation, as long as its direction is consistent with the preferred direction of the neuron. P. Stumpf is credited with first describing the aperture problem in motion (Stumpf, 1911/1996).

created by Fauzia Moscaand Nicola Bruno