Human optokinetic afternystagmus. Effects of repeated stimulation

Normal human subjects were exposed to repeated optokinetic afternystagmus (OKAN) testing in either one direction or alternating directions of stripe movement. Sessions were conducted at intervals of either one week or several weeks. Repeated exposure to OKAN stimulation in one direction produced significant response decrements in cumulative displacement, short time constant, long time constant, and the coefficient of the long time constant component (C). The data suggest that the decrease in C and cumulative displacement occurred most noticeably between trials 3 and 4 of the first session. Retesting after 1 week, and up to 8 weeks later revealed no recovery. Repeated exposure to alternating leftward and rightward stimuli resulted in response decrement in both cumulative displacement and C. Responses to leftward stimuli were indistinguishable from responses to rightward stimuli.