Ear-eye reflexes while riding in a car.

Persons with diminished or absent vestibulo-ocular reflexes (VORs) are thought to have difficulty with ocular stabilization during sufficiently rapid head movements. This suggests the hypothesis that labyrinthine defective individuals might have impaired visual abilities when in a moving motor vehicle. Ten licensed drivers likely to have abnormal VORs were recruited to assess this possibility. Their labyrinthine function was indexed by measurements of ocular counterroll responses to static head tilt and the nystagmus induced with caloric stimulations. Each person was evaluated on a visual task, i.e., answers to questions about alphanumeric information read from a stationary sign while sitting still and while riding in a car. Comparisons of vision scores tend to be lower in the moving than in the still condition. Furthermore, these decrements appear more closely related to the magnitudes of ocular counterroll than to the caloric reflexes. These results have implications concerning otolithic vs. semicircular canal function, vehicle operations by vestibular-impaired individuals, and evaluations of clinical treatments which employ vestibulotoxic drugs.