Abstract
We examined differences in the characteristics of visual and cutaneous vection (sensation of illusory self-motion in the absence of physical movement). In experiments, we measured the latency of vection from the beginning of visual and non-visual stimulation. In Experiment 1, we compared the effects of vestibular sensory stimuli upon the visual vection with those upon the cutaneous vection. Velocity of wind as a cutaneous stimulus ranged from 0.6 to 5.5 m/sec by the use of air multiplier while the visual stimulus was expansion of 4,000 random dots on a flat display ranged from 37.5 to 114.3 arc deg/sec. Vestibular stimulus was vibration of the horse-riding simulator which corresponded to a horse walk with a velocity of 1.78 m/sec. The latencies of both visual vection and cutaneous vection were well fitted to positive quadratic functions of velocity of wind or optical flow, respectively. We found obvious difference of the shortest latency between the visual vection (8.0 sec) and cutaneous vection (31.0 sec). In Experiment 2, we examined the effect of vestibular stimulus on visual vection and cutaneous vection. Vestibular sensory stimuli were movement of a ride with velocity of 0.95 cm/sec. Velocity of wind as a cutaneous stimulus was fixed at 3.0 m/sec while the visual stimulus was expansion of 2,000 random dots on a flat display with 132.3 arc deg/sec. We found that the latency of the visual vection (8.2 sec) was significantly shorter than that of cutaneous vection (22.1 sec) without vestibular stimulation while there was not significant difference in latency between the visual vection (7.5 sec) and cutaneous vection (5.6 sec) with vestibular stimulation. These results suggest that some common mechanisms underlie the visual vection and also non-visual vection while contribution of each modality on vection varies with velocity of multisensory stimulus.