DIFFERENT MOTION SENSITIVE UNITS ARE INVOLVED IN RECOVERING THE DIRECTION OF MOVING LINES

We studied direction discrimination for lines moving obliquely relativ e to their orientation. Manipulating contrast, length and duration of motion, we found systematic errors in direction discrimination at low contrast, long length and/or short durations. These errors can be acco unted for by a competition between ambiguous velocity signals originat ing from contour motion processing units and signals from fine termina tor processing units. The dynamic of this competition can be described by a simple model involving two different classes of processing units with different contrast thresholds, different integration time consta nts and different levels of response saturation.