Human eye movements in response to dynamic otolith stimulation evoked during earth horizontal axis (EHA) rotations will be investigated in both normals and carefully selected patients. The pilot data from previously investigated EHA rotation eye movement responses in the dark will be extended to include confidence intervals for normal limits and also to characterize a new component, """"""""periodic gaze,"""""""" found in my preliminary experiments. New protocols for EHA visual-vestibular interactions will allow the characterization of these previously uninvestigated responses. The primary rotational stimulus will be velocity trapezoids of 60, 90 and 120 degrees/second which last for approximately 60 seconds. A limited number of small angular displacement 1.0 Hz sinusoidal stimulus runs will also be made to investigate the effect of mean head position (nose up, right ear down, etc.) upon eye movement responses. Prolonged exposure to EHA is nauseogenic, so a relatively large number of subjects will each be given only a few EHA tests. Subjects will also be tested using analogous earth vertical axis (EVA) rotation protocols to investigate hypotheses concerning inter-axes rotations. These inter-axis tests will: 1) permit the isolation of the dynamic otolithic response components under several sensory input conditions, and 2) allow investigation of the notion that the supposedly separate EHA linear acceleration and EVA angular rate induced eye movement response components may in fact be interrelated as suggested by my preliminary data. Thus, the fairly high degree of intersubject variability will be exploited because it will permit correlations between hypothetically interrelated pairs of responses from the same individual. In collaboration with two experienced faculty otologists, selected patients having clearly defined vestibular anomalies will be classified into four categories. The categories are: unilateral labyrinthectomies; begin paroxysmal positional vertigo (BPPV); acoustic neuromas without brainstem compression; and acoustic neuromas with marked brainstem compression. The responses from these categories will be compared with each other and with data from normals to determine the specificity and sensitivity of these protocols for potential use as a clinical test of dynamic otolith function.
