Visual interference on vestibular response. A case study.

Eliminating opportunity for visual fixation as well as providing for the maintenance of an optimal degree of a patient's mental alertness are necessary for a valid assessment of nystagmic response to caloric stimulation. Controlling only for alertness can result in suppressed, absent, or dysrhythmic nystagmus. Data from four normal patients dramatically illustrate the suppressing effects of fixation opportunity despite an alert state. A new clinical instrument for obtaining optimal control over visual influences is described.