Studies on Habituation of Vestibular Reflexes: VII. Habituation in Light of Calorically Induced Nystagmus, laterotorsion, and vertigo in man

Fifteen normal subjects received 12 consecutive caloric irrigations with water of 30°C in the right ear. The calorizations were performed in full light except the 1st and the 12th ones, used as tests to make possible comparisons with a previously reported series with all irrigations made in darkness. Four qualities were compared: (1) eye-velocity, (2) duration of nystagmus, (3) laterotorsion, and (4) vertigo.The tests revealed the same extent of response decline from calorizations in light as in darkness and also the same order of habituation rate.When the light was turned on there was a sudden decrease and when it was turned off a sudden increase of nystagmus and laterotorsion but not of vertigo, which declined in the same manner independently of light and darkness. At the end of the habituation trials in light, laterotorsion was often the only observable effect of the calorizations.With increasing habituation the dysrhythmia of nystagmus increased more in light than in darkness.