Contours from motion: the effect of speed and density reveals an integrative mechanism

BARRAZA J.F.; CHEN V.J.

Budapest, Hungría

Congreso; 27th European Conference on Visual Perception; 2004

ECVP

We studied the effects of speed and dot density on the perception of illusory contours produced by moving the modulation of luminance on a random dot pattern. The stimulus consisted of a circular patch surrounded by an annulus, both containing the same kind of modulated dot pattern. The background of the stimulus was homogeneous and no dots ever moved relative to the background. We used a vernier acuity test between the central patch and the surround annulus to evaluate how sharp the contour was perceived in each condition. To do this, we manipulated the phase of the modulation in both the central patch and the surround annulus. Results show that the vernier threshold decreases with increasing speed up to a saturation value that depends on density: the lower is the density the higher is the speed of saturation. This result suggests that there is a finite temporal window in which the rate of sampling must exceed a threshold for the contour to be perceived. Importantly, when the dot density is too low the saturation speed cannot be reached, perhaps because the distances between dots exceed a certain amount – range limit of lateral interaction of neural mechanisms.