The subjects in this study maintained a vertical posture standing on a rigid support. Postural stability was assessed in terms of the standard deviations (sigma) from the mean amplitude of movements of the head relative to the null coordinate. Feedback at the vestibular input was created by transmastoid bipolar galvanic stimulation. Changes in the current in the feedback envelope were governed by a linear function based on the amplitude and rate of head movement. Variation in the coefficients of the feedback function could decrease the magnitude of sigma for lateral movements which were increased (compared with values in calm standing in the dark) by unilateral vibrational stimulation of the gluteus medialis muscle. These results provide evidence that "rate" and "position" information have different values for maintaining the vertical posture in different subjects. They also demonstrate the ability of the central nervous system (CNS) to reevaluate the weightings of the different types of information arriving via a single channel. These results support the hypothesis that galvanic vestibular input can provide the CNS with sufficient information relating to the current orientation of the body. This information can be used for postural stabilization.

Intact pigeons (Columba livia, n = 30) were rotated in a horizontal plane in the dark at different orientations relative to the axis of rotation. A total of 24 birds showed different directions of changes in the duration of contrarotatory nystamus (on transition from central rotation to eccentric), along with displacement of the otolith membranes in both the frontal and sagittal planes. These pigeons showed a direct relationship between changes in the duration of the primary phase of nystagmus and the peak rate of the slow component on the background of increasing centrifugal force, while no such relationship was seen in conditions of decreasing centrifugal force. Increases in the duration of the primary phase were accompanied by decreases in the duration of the secondary phase (i.e., the reversive phase) and vice versa. These data provide evidence that the otolith component is not decreased to zero by rotation at constant angular rates or immediately after this stopped; in conditions of negative angular acceleration, this component was biphasic. The results are in good agreement with a hypothesis [2] suggesting that the otolith component represents asymmetric (different in paired brain structures) neuronal activity modifying the canal component even when the level of asymmetry is itself insufficient to initiate eye movements.

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