Abstract
We measured observers' perceived direction of self-motion resulting from the simultaneous presentation of visual and vestibular information, each simulating a different direction of motion. Sakurai et al. (2003, ECVP) reported that when observers experience real leftward/rightward motion while viewing a visual expanding/contracting optic flow pattern consistent with forward/backward self-motion, their perceived motion direction was intermediate to those specified by visual and vestibular information. This experiment extends that study and generalizes those findings, exploring other visual/vestibular combinations. Specifically, we explored more visual patterns including translational optic flow – consistent with upward/downward or leftward/rightward motion as well as our previous patterns of expanding/contracting optic flow, consistent with forward/backward motion. Observers were seated on an oscillating motor-driven swing providing real motion, while they viewed optic flow patterns, phase-locked to the swing motion, consisting of sine wave gratings in each of four conditions: 1) forward/backward real motion paired with upward/downward translational oscillatory optic flow (horizontal gratings), 2) forward/backward real motion paired with leftward/rightward translational oscillatory optic flow (vertical gratings), 3) leftward/rightward real motion paired with upward/downward optic flow, 4) leftward/rightward real motion paired with expanding/contracting optic flow. Observers were cued to indicate their perceived direction of self-motion during one half of the swing period, by setting a virtual pointer presented at the center of the head mounted display. In every combination of orthogonally directed visual and vestibular stimulation, observers reported distorted directions intermediate to those specified by visual and vestibular information. For example, reported self-motion directions were forward and downward, backward and upward in condition 1, forward and rightward, backward and leftward in condition 2, leftward and downward, rightward and upward in condition 3, leftward and forward, rightward and backward in condition 4. Observers reported the opposite distortions of perceived self-motions for the complementary stimulus pairs in each condition.
Supported by Grant-in-Aid of MEXT for Specially Promoted Research (no. 19001004).