Optokinetic nystagmus: the effects of stationary edges, alone and in combination with central occlusion.

In Experiment 1 we investigated the independent and combined effects of horizontal OKN of stationary edges and occlusion of the central retina. For a display 60 degrees wide moving at 30 degrees/sec a symmetrically placed pair of vertical nonoccluding bars suppressed OKN when near the center of the display but had no effect when 30 degrees apart. A 7 degrees-high 60 degrees-wide central occluder reduced OKN gain by 37%. However, a central occluder with edges only 30 degrees wide abolished OKN. In Experiment 2 this interaction between central occlusion and stationary edges was confirmed with a wider display over a range of stimulus velocities and configurations. A functional explanation of this interaction is presented.