Flash induced afterimage versus single spot visual object influence on visual-vestibular interaction in detection threshold for self-motion perception.

In seven healthy subjects we studied the effect of flash induced afterimage on perceptual threshold for self-motion during sinusoidal vertical axis rotation compared to rotation in darkness, and rotation with subject's gaze fixed on a 'real' visual object rotated with him. For a real object we used light-emitting diode (LED) aligned with subject's head. A MOOG motion platform was used to generate motion. Single cycles of sinusoidal acceleration at four frequencies: 0.1, 0.2, 0.5, and 1Hz were used as motion stimuli. The results show that the threshold when subjects stare at an afterimage during rotation is consistently lower compared to rotation in darkness. However, compared to the threshold during rotation with a 'real' object visual fixation it is higher, significantly at frequencies 0.5 and 0.2Hz (p<0.05). The threshold is frequency dependent - it decreases with increase of the frequency (p<0.01). The probable mechanism of afterimage influence on perceptual threshold for self-motion is discussed.