Time course of the change in subjective straight-ahead after vestibular stimulation

We measured the change in subjective straight-ahead (SSA) as a function of time after vestibular stimulation. Blindfolded subjects were exposed to sudden stops after constant velocity (72 degrees/s) z-axis rotation. They were then asked to open their eyes and continuously adjust the position of a laser spot to the position perceived as straight ahead (visual localization of SSA) immediately, or after a 10 s or 20 s delay following the sudden stop. The deviation of SSA increased to 20 s in the opposite direction of acceleration and then decreased gradually when the visual localization task was started immediately after sudden stops. The time courses changed systematically when the task was started after a delay of 10 s or 20 s following sudden stops: the initial increase component and maximum magnitude of the SSA deviation fell off with delay length, but the increase-decrease pattern was preserved. These delay effects on the time course of the SSA deviation might reflect that the velocity-to-orientation/position integrator for perception of body orientation in vestibular system might be inactivated temporarily during the delay period after vestibular stimulation without visual input.