Colour Selectivity in Motion After-effect

Abstract

STATIONARY lines appear to move upwards after prolonged visual exposure to downward moving lines. The experiment reported here shows that the movement after-effect is appreciably diminished when the moving lines observed during inspection are seen in red light and the stationary test lines are viewed in green light. We expected to obtain colour selectivity in the movement after-effect following the demonstration of motion-specific colour after-effects by Hepler¹. She found that alternate exposure to downward moving green lines and upward moving red lines caused downward moving lines later seen in white light to appear red and upward moving lines green. Hepler proposed that motion detectors in the human visual system are also selective to wavelength so that during exposure to one stimulus only the neural analysers tuned to both the specific direction of motion and the wavelength are excited. Because these analysers adapt during inspection and are suppressed for a period of time afterwards, the downward moving lines presented in white light as the test stimulus are signalled via downward-selective motion detectors tuned to the opposite colour. McCollough² has offered a similar explanation of colour after-effects which are specific to contour orientation.