VOR gain and phase in active head rotation tests of normal subjects and patients with peripheral labyrinthine lesions.

The gain and phase of the vestibulo-ocular reflex (VOR) were studied by active head rotation tests in normal subjects and in patients with unilateral or bilateral lesions of vestibular function. The examination was performed under two conditions: alert-in-dark and with spatially-fixed target. The results were evaluated using a simplified model of vestibular response. Under alert-in-dark condition, the VOR grain and phase deficits were observed on rotation to the affected side in patients with unilateral lesions and bilaterally in patients with bilateral lesions. Under spatially-fixed-target condition, these patients showed a decrease in gain at higher frequencies but no phase lag was observed. The principally new advantage was that not only VOR gain but also VOR phase could be quantified using this active head rotation test. Therefore, for diagnosing VOR dysfunction, this active head rotation test is more useful than the active head rotation tests previously reported.