Expansion of space for visuotactile interaction during visually induced self-motion.

Peripersonal space (PPS), which refers to space immediately around an individual's body, plays an important role in interacting with external objects and avoiding unsafe situations. Studies suggest that, during self-motion perception, PPS expands in the direction in which a person perceives himself/herself to be traveling. In the present study, we built on this by investigating, using visually induced self-motion (vection), how visual self-motion information modulates PPS representation. In our experiment, large-field visual motion was presented through a head-mounted display that caused observers to perceive themselves as moving forward in a tunnel (LF condition). To clarify the effects of self-motion information, we compared the findings for this condition with those of another condition, in which small-field visual motion was presented; here, only the central visual field represented motion, which caused the observers to perceive relatively little self-motion (SF condition). Two speeds were tested for both conditions: 1.5 m/s and 6.0 m/s. For measurement, we used a visuotactile-interaction task in which participants, while observing a visual probe object approaching from various distances, were instructed to press a response key as soon as they detected tactile stimuli delivered to their chest. We measured the distance at which the visual approaching probe object facilitated tactile detection (visual-facilitation effect); this was determined through comparisons with trials when no probe was presented. The results showed that the visual facilitation effects were observed for larger distance in the LF than SF conditions, irrespective of tested speeds. These results suggest that visual self-motion information can modulate PPS representation. This finding fits well with the view that PPS representation contributes to protecting the body from potential threats in the environment.