Changes in oculomotor function in relation to the vestibular-visual conflict sickness (pitch) in squirrel monkeys.

Based on the susceptibility of vestibular-visual conflict sickness in pitch, the oculomotor response was compared between 4 conflict sickness susceptible squirrel monkeys and 4 non-susceptibles. The time lag of nystagmic direction change in the nose-down position was longer in susceptibles than that in non-susceptibles. The irregularity of vertical eye nystagmus in susceptibles built up gradually during the exposure to conflict. After the emetic incidence, a sharp decline in the aforementioned time lag (in nose-down position) and improved regularity were found. These changes in oculomotor function could be a parallel symptom of the sensory conflict-evoked sickness and emesis.