CONTRIBUTION OF COLOR TO THE MOTION AFTEREFFECT AND MOTION PERCEPTION

The aim in this work was to assess the contribution which colour infor mation makes to the perception of motion. Two dependent variables were measured: the reaction time to a sudden cessation of motion (motion-e nd RT) and the duration of the motion aftereffect (MAE). In each case, a baseline measure of performance was made with the aid of a monochro me stimulus with a given contrast and added luminance noise. This was compared with performance when red/green colour modulation was added t o the luminance display. Any difference between these measures would r eveal the extent of chromatic input. For motion-end RT the addition of colour had little effect under conditions where the stimulus had a st rong luminance component and little added luminance noise. Increasing departures from these conditions revealed the contribution of a colour -sensitive mechanism. In general, the chromatic contribution to MAE du ration was much smaller than was the equivalent contribution to motion -end RT, thus possibly indicating a neurological dissociation between the mechanisms subserving these effects. The results of an experiment in which the effect of different temporal frequencies of the added lum inance noise was assessed supported this dissociation between MAE and motion-end RT. The findings are therefore consistent with there being two motion (sub)systems, which differe in the extent of chromatic inpu t. The subsystem revealed by MAE measures is less affected by colour i nformation.