Human optokinetic nystagmus: competition between stationary and moving displays.

We reported earlier that occlusion of the central retina and stationary edges have highly interactive effects on the gain of optokinetic nystagmus (OKN; Murasugi, Howard, & Ohmi, 1986). In this study, we explored this effect in more detail. A central occluding band of variable height, flanked by vertical bars, was superimposed onto an array of dots moving at 30 degrees per second. The height of the occluding band required to abolish OKN increased with the separation of the vertical bars. For bars 3.5 degrees apart, OKN was abolished in most subjects when a band only 6' high ran between them. For bars 75 degrees apart, a band at least 20 degrees in height was required to abolish the response. The effects of the stationary figure depended to some extent on the subject's attention, but only at intermediate values of bar separation. Both low- and high-level mechanisms are proposed to account for the results.