WHAT DIRECTION OF MOTION DO WE SEE IF LUMINANCE BUT NOT COLOR CONTRAST IS REVERSED DURING DISPLACEMENT - PSYCHOPHYSICAL EVIDENCE FOR A SIGNED-COLOR INPUT TO MOTION DETECTION

To investigate the effects of colour upon motion detection, directiona l discrimination by human observers was determined using two-frame kin ematograms in which the two classes of element composing the pattern c ould differ either in luminance alone (achromatic condition), or in bo th colour and luminance (chromatic condition). The elements in the sec ond frame could either have the same colour/luminance as corresponding elements in the first frame, or they could be changed (swapped) in co lour and/or luminance. The angular size of the elements was varied by changing the viewing distance. Changing colour between frames disrupte d motion detection when the angular size of elements was large (0.9 de g) but not when they were small (0.225 deg), replicating a previous re sult. Detection of motion with chromatic patterns was generally superi or to that with achromatic patterns, particularly with large element s ize. Luminance swap combined with colour swap produced the ''reverse p hi'' phenomenon: however, when luminance was swapped with colour stayi ng the same between frames, forward motion was seen, suggesting that f orward motion based on colour dominated over reversed motion based on luminance. We conclude that signed chromatic information has an input to motion detection at low but less so at high spatial frequencies. In formation across colour and luminance is combined in a final common pa thway for motion detection, resulting either in enhancement if they ar e in agreement, or in disruption if they conflict.