On the loss of apparent motion between isolated chromatic stimuli near isoluminance

Long range apparent motion (AM) between two isolated stimuli breaks down following prolonged inspection. Time-till-breakdown (TTB) for AM between random-dot squares (red or green) on a red random-dot background was measured as a function of luminance contrast of the stimuli against the background. For the same-color (red squares on the red background) and the different-color (green squares on the red background) conditions, TTB showed clear dependence on the luminance contrast, diminishing with decreasing the contrast. Near isoluminance (luminance contrast of approx. -14 to +14%), AM for the same-color condition disappeared, but AM for the different-color condition was clearly seen and persisted for 7-14 sec. These results show that AM can be produced by color alone. Previous controversial question on the loss of long range AM near isoluminance may be explained by taking into account the contrast dependence of the breakdown effect and the experimental procedures employed.