Influence of self-motion speed on the spatial extent of human peripersonal space

Abstract

Peripersonal space (PPS) is the space immediately surrounding the human body parts. PPS is important because humans directly interact with their surrounding environment within this space. Previous studies have shown that PPS expands during self-motion perception and that an increase in the speed of an approaching object increases the range of PPS. However, it is not clear how self-motion speed influences the range of PPS. The present study investigates this issue by using visually induced forward self-motion perception (vection). The PPS range was measured using visuotactile interaction. The experimental conditions included the slow (1.5 m/s) and fast (6.0 m/s) self-motion speed conditions and the control condition (without-vection). Participants wore head-mounted displays (HMDs) and were asked to quickly respond to tactile stimuli delivered to their chest while seeing vection-inducing stimuli and a visual stimulus approaching their chest from various distances (1.3 m, 1.95 m, 2.6 m, 3.25 m, and 3.9 m). While reaction time reduction (compared to the tactile-only condition) was observed only close to the body (1.3 m) for the control condition, it was observed for all the distance conditions during vection irrespective of its speed. This suggests that PPS boundaries expand more for self-motion than for control condition, and that differences in self-motion speed may be observed when objects approach from farther distances or when larger speed differences are used.