Whole-body immobilization modulates visuotactile interaction.

Peripersonal space (PPS) is the space immediately around each body part. A previous study reported that hand-centered PPS shrank after hand immobilization; however, little is known about what happens in the PPS of other body parts. Here, we investigated the effect of whole-body immobilization on trunk-centered PPS by fixing the whole-body in a large box. Two experiments were conducted. Experiment 1 compared trunk-centered PPS with and without a large box. Experiment 2 manipulated the box size (large or small) to investigate the effects of box embodiment. Participants were tasked with responding as quickly as possible to a tactile stimulus on their chest while viewing a visual probe approaching from various distances. A visual facilitation effect in PPS was defined as the amount that the visual probe facilitated tactile detection in each distance condition. In addition, participants evaluated body immobilization under all conditions. The results showed that the visual facilitation effect on tactile detection was significantly greater in the with-box than in the without-box conditions in Experiment 1, and was significantly greater in the small box than in the large box conditions in Experiment 2. However, neither experiment clearly estimated PPS boundaries, although the visual probe located at farther distances had significantly less visual facilitation effect. Perceived body immobilization was stronger in the with-box than without-box conditions in Experiment 1 and was stronger in the small box than in the large box conditions in Experiment 2. These results suggest that body immobilization, rather than box embodiments, can induce stronger visuotactile interaction.