Effects of colour substitutions upon motion detection in spatially random patterns

To investigate the effects of colour upon motion detection, the short-range motion displacement limit (Dmax) was determined using two-frame kinematograms in which the two classes of square comprising the pattern differed both in luminance and in colour. In the second motion frame, the squares retained either the same luminance and colour as in the first frame, or they changed their colour while retaining their luminance. The experiment was repeated at three different viewing distances to investigate the effects of element angular size. Two of the four observers had normal trichromatic colour vision; the other two were dichromats (protanopes). For the trichromatic observers, the change of colour between frames made motion displacements harder to detect when the squares were large, but not when they were small. The result accords with an input of colour into motion detection at low but not at high spatial frequencies. For the dichromats, the colour change had little effect at any of the viewing distances, thus ruling out the possibility that the deleterious effects of colour substitution upon motion detection in trichromats was due to chromatic aberration or other artefacts.