HUMAN EYE-MOVEMENT RESPONSE TO Z-AXIS LINEAR ACCELERATION - THE EFFECT OF VARYING THE PHASE-RELATIONSHIPS BETWEEN VISUAL AND VESTIBULAR INPUTS

We investigated the effect of systematically varying the phase relatio nship between 0.5-Hz sinusoidal z-axis optokinetic (OKN) and linear ac celeration stimuli upon the resulting vertical eye movement responses of five humans. Subjects lay supine on a linear sled which accelerated them sinusoidally along their z-axis at 0.4 g peak acceleration (peak velocity 1.25 m/s). A high-contrast, striped z-axis OKN stimulus movi ng sinusoidally at 0.5 Hz, 70 degrees/s peak velocity was presented ei ther concurrently or with the acceleration stimulus or alone. Subjects ' vertical eye movements were recorded using scleral search coils. Whe n stimuli were paired in the naturally occurring relationship (e.g., v isual stripes moving upward paired with downward physical acceleration ), the response was enhanced over the response to the visual stimulus presented alone. When the stimuli were opposed (e.g., visual stripes m oving upward during upward physical acceleration, a combination that d oes not occur naturally), the response was not significantly different from the response to the visual stimulus presented alone. Enhancement was maximized when the velocities of the visual and motion stimuli we re in their normal phase relationship, while the response took interme diate values for other phase relationships. The phase of the response depended upon the phase difference between the two inputs. We suggest that linear self-motion processing looks at agreement between the two stimuli - a sensory conflict model.