Further observations on the effects of head position on vertical OKN and OKAN in normal subjects.

Vertical optokinetic nystagmus (VOKN) and vertical optokinetic after-nystagmus (VOKAN) were studied in three head positions (upright, lateral, and head-hanging) in normal subjects by use of full-field OKN stimulation. Mean vertical OKN gain asymmetry (downbeating greater than upbeating) was noted for the upright position at stripe velocities of 40, 50, and 60 deg/sec. In three subjects, mean VOKN gain asymmetry was eliminated in the head-hanging position, but only slightly reduced in the lateral position.