Dmax: Motion seen better in the periphery than in the fovea

Abstract

We present a rare example of peripheral vision being better than foveal vision, based upon Dmax (Braddick, Vision Res. 1974). A field of dense random dots jumps clockwise around a circular orbit while remaining upright (without rotating). Viewed foveally, the field appears to “twinkle” randomly (like dynamic visual noise). In peripheral vision, the circling motion is clearly seen. Our results show that Dmax is smallest for small dots and progressively larger for large dots and clumps of dots. In the fovea, individual dots jump through distances exceeding their own Dmax, and therefore look random, masking out the circling motion of low-frequency random clumps of dots. In the periphery, low spatial acuity filters out this masking twinkle, revealing the circling clumps. By varying the jump size and dot size, we showed that jumps through a distance of x dot diameters gave visible circling only at eccentricities proportional to x^0.68 or greater. Thus Dmax is determined not by dot size per se, but by the ratio of jump size to dot size.

Meeting abstract presented at VSS 2015