Optokinetic reactions in man elicited by localized retinal motion stimuli

Abstract

The role of different parts of the human retina in eliciting optokinetic pursuit was investigated with continuously moving random dot or grid patterns (dia up to 30°). The retinal location and velocity of the stimulus could be fixed by servo control of the stimulus position by the eye position, and artificial scotomata could be inserted into the stimulus. Under these conditions (opened optokinetic feedback loop) pursuit velocity became much larger than the stimulus velocity. With a central stimulus, pursuit velocity (gain) in the 8 principal directions showed individual, but no systematic differences. In the periphery, a centrifugal stimulus movement was much more effective than a centripetal movement. This directional preference may assist foveation. Pursuit open-loop gain was only moderately diminished by a decrease of the stimulus diameter, but much more severely by deleting small parts in the centre. This indicates that the fovea is more powerful than the periphery in eliciting optokinetic pursuit. The distribution of fast and slow nystagmic phases with respect to the primary position was unaffected by the use of open-loop conditions or central scotomata. For all peripheral stimuli, the responses were strongly enhanced by the subject's specific attention.