Human optokinetic afternystagmus. Charging characteristics and stimulus exposure time dependence in the two-component model.

The dependence of human optokinetic afternystagmus (OKAN) velocity storage (charging) and optokinetic nystagmus (OKN) characteristics on optokinetic (OK) stimulus exposure time was investigated, using the two-component double exponential model for OKAN decay. Results are compatible with our previously proposed concept of two velocity storage integrators, one responsible for the short time constant decay (pursuit-mediated) and the other for the long time constant decay (OK system-mediated). The dependence of the long time constant integrator of OKAN on stimulus exposure time was clearly demonstrated. The short time constant integrator appeared to be independent of stimulus exposure time within the range studied. We conclude that the charging time-course of each component is distinct from that of the other. The time constants of each component decay were found to be invariant. A left-right asymmetry observed in both OKN and OKAN responses suggests that the integrators are direction sensitive.