Cross-coupling in a body-translating reaction: interaural optokinetic stimulation reflects a gravitational cue.

ABSTRACT

CONCLUSION: The velocity storage integrator does not play a dominant role in the postural response to vertical visual cues; more likely, retinal slip provides the main driving force. By contrast, sideways eye movement can drive the velocity storage integrator and preserve a gravitational cue, which would be observed as a cross-coupling effect on the postural response. OBJECTIVES: To investigate the mechanism by which optokinetic stimulation causes the body to translate and to determine whether the optokinetic information is accompanied by a gravitational cue, which would appear as a cross-coupling effect. MATERIALS AND METHODS: Directionally diverse optokinetic stimuli were presented to seven healthy subjects, with and without a fixation target, and the body-translation of the subjects was recorded. RESULTS: Horizontal optokinetic stimulation with a fixation target caused the body to translate in the same direction as the optic flow. Upward or downward vertical optokinetic stimulation caused the body to translate backward or forward, respectively, only when a fixation target was present. When the subject's interaural axis was parallel to the optokinetic flow, diagonal optokinetic stimulation in the absence of a fixation target elicited responses in the pitch plane similar to those elicited by vertical stimulation in the presence of a fixation target.