Directional conflict between vestibular and visual inputs in the squirrel monkey.

The directional conflict between vestibular and visual stimuli was studied in the squirrel monkey. Sinusoidal rotation was given to the subject and the direction of his visual target movement was reversed by installing a mirror in a 45 degree plane in front of the eyes. A large interindividual variance was noticed in controlling vestibular-visual conflict. The degree of vestibular-visual conflict and stimulus magnitude had no linear relationship. Also no relationship existed between vestibular-visual conflict and the provocation of vestibular nystagmus. Under the situation of vestibular-visual conflict, visual target pursuit failed to improve when two daily trials were given twice a week, for five weeks. The reduction of vestibular input created by surgery resulted in the reduction of vestibular evoked nystagmus and vestibular-visual conflict. However, their degrees were not necessarily parallel. Inter-individual difference in response of vestibular-visual conflict was related to vestibular-visual coordination.