Time constants in the perception of a change in the direction of motion in humans.

Motion signals are subject to spatio-temporal filtering at early stages of processing. In general, motion can be characterized by two parameters: speed and direction. This study sought to determine the time constants for the filtering of the directional component of the motion signal. In a forced-choice discrimination task, subjects were asked to choose the more abrupt change in direction of a target that moved through two 90 degrees corners. At each corner, direction of motion was low-pass filtered. Subjects were able to reliably perform this task if the filter time constants differed by >20 ms.