Abstract
Purpose: A study is reported of the relations between vection by optical flow and virtual acceleration by galvanic vestibular stimulation. Vection is the illusory impression of self motion that can be obtained when an observer views a large screen display containing a translating pattern. However, when the simulated motion under virtual reality applications exploit only visually induced self-motion, the lack of confirming vestibular information will undermine the fidelity of the intended sensations. Galvanic vestibular stimulation (GVS) can produce directly the sensation of virtual acceleration as the vestibular information. Methods: Experiments were conducted using a large screen front-projection 2.25×1.8[m] display. Subjects stood and observed at the viewing distance of 1[m]. The visual stimulation was an optical flow of randomly scattered dots under constant downward velocity 30[deg/s] with multi-frequency sinusoidal lateral shift from 0.05 through 0.47 Hz. GVS was delivered by the maximum 2.0[mA] synchronizing in-phase or anti-phase with the lateral shift through the electrodes behind both ears. The movements of subject's body were measured by OPTOTRAK. Results: All of subjects reported that the vection under the anti-phase GVS is stronger than the vection under the in-phase GVS. The sway of their body under the anti-phase GVS is smaller than the sway under the in-phase GVS. The sway of their body under the in-phase GVS is larger than the sway by only visual vection. Conclusions: In the case of in-phase GVS, the objective strength of the bodily movement is largest among the cases while the subjective sensation of vection is smallest. From the viewpoint of visual-vestibular interaction, the sense of vection by the optic flow conflicts to the vestibular information not only when the GVS is anti-phase but also when the stimulus is delivered by only vision. This result suggests that a sensation of conflict might be reported as a part of vection in previous studies.