Abstract
Vection (visually-induced self-motion perception) has been investigated for static observers generally. We aimed to investigate effects of walking (body action) on vection perception. Viewpoint motion along a line-of-sight was simulated in a three-dimensional cloud of dots (2 km/h, 1626 dots visible in average), and its optic flow was presented on a 120-inch rear-screen (91 x 75 deg). The direction of simulated motion was forward (expansion) or backward (contraction). Naive participants observed the stimulus during walking forward or backward on a treadmill (2 km/h) at 1.2 m viewing distance for 60 s. All four combinations of 2 optic-flow directions and 2 walking directions were repeated 4 times for each participant, and their vection latency and duration were measured. Vection latency was shorter in the backward vection condition than the forward vection condition. For the forward vection condition, its latency was longer when observers walked forward than backward. For the backward vection condition, its latency was longer when observers walked backward than forward. Thus, the vection perception was inhibited when observers' walking was in the direction of simulated viewpoint motion (direction of optic flow). These results seem to be paradoxical. Since the self-motion perception is a multi-modal perception fusing visual, vestibular, and propriceptive senses with different weights (weak fusion model), we speculated that the weight of visual self-motion (vection) is increased without walking or with incongruent walking (proprioception). On the contrary, the weight of vection is relatively decreased with veridical walking because both visual and proprioceptive information are available and congruent.
Supported by Grant-in-Aid for JSPS Fellows MEXT Japan to SO, Nissan Science Foundation to MK, and The Global COE program ‘Frontiers of Intelligent Sensing’.