The basis of area and dot number effects in random dot motion perception.

Random dot kinematograms present a patch of random dots, uniformly displaced from one frame to the next. We have re-examined the question of whether the limiting displacement for this short-range apparent motion is determined by the retinal angle or by the number of pixels across which the patch is displaced; our data support the former hypothesis. The number of dots in the patch is not a confounding variable, and in fact has very little effect. Increasing the area of the patch does increase the displacement limit, apparently due to the invasion of greater retinal eccentricities.