Visual-vestibular interaction studied with stroboscopically illuminated visual patterns

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Abstract
Horizontal DC-electrooculograms were recorded in subjects rotating on a horizontal turntable sinusoidally at 0.1 Hz and 35 to 40° amplitude. The subjects either fixated a stroboscopically illuminated vertically striped pattern (1.15 to 3.45° period) rotating with the turntable or initiated Sigma-OKN before the rotation began and tried to maintain Sigma-OKN during rotation. In a third paradigm, interaction of vestibulo-ocular reflex (VOR) and Phi OKN was studied. (1) VOR-suppression by fixation was complete within the limits of EOG-recording precision (±1° · s-1) for flash frequencies fs>10 flashes · s-1. VOR-suppression decreased monotonically with fs between 10 and 1 flashes · s-1. (2) A similar dependency on fs was found for VOR-suppression during Sigmaor Phi-OKN. Above 10 flashes · s-1 VOR-suppression remained incomplete; below 5 flashes · s-1 VOR-suppression was stronger with the Sigma-OKN paradigm than during fixation and depended on spatial frequency of the pattern. (3) During sinewave rotation of the subject the perceived speed Vp of Sigma-movement correlated to the movement of gaze in space and not to the movement of the eye in head. (4) In a control experiment with normal optokinetic stimulation, OKN-suppression by fixating a small flashing target was found to depend on fs in a similar way as VOR-suppression in the experiments described above.