Extending visual dominance over touch for input off the body.

Vision tends to dominate over touch in the majority of experimental situations, particularly when visual information is presented on, or near to, the body. We combined two visual dominance paradigms in order to investigate crossmodal interactions between vision and touch for stimuli on versus off the body: 1) The Colavita visual dominance effect, which has recently been extended to vision and touch, and 2) The rubber hand illusion, which has often been used to probe visuotactile interactions. Specifically, we investigated whether moving a visual stimulus off the participant's body would affect visual dominance, and how this dominance would be mediated by the presence/absence of a rubber hand (given the rubber hand illusion provides a way of extending the representation of one's own body in space). Participants made speeded detection/discrimination responses to a random sequence of visual-only, tactile-only, and visuotactile targets. While participants responded near-perfectly on the unimodal target trials, their performance on the visuotactile target trials was deleteriously affected by the simultaneous presentation of a visual stimulus on (as opposed to away from) their body. In particular, when the visual stimulus was presented to their fingertip, participants failed to respond to far more of the tactile than visual stimuli on bimodal trials. The magnitude of this visual dominance effect decreased significantly when the visual stimulus was moved off the body. When a rubber hand was placed at the off-body location, a similar (albeit reduced) visual dominance effect was observed in both positions. These results therefore suggest that visuotactile interactions are strongest when visual stimuli are presented on a body (no matter whom that body, or body-part, belongs to).