Presenting directions with a vibrotactile torso display

Vibrotactile displays covering the torso present spatial information in an intuitive way since the stimuli are directly mapped to the body coordinates; left is left, front is front, etc. The present study investigated the direction in the horizontal plane to which a specific torso location is mapped using a 15 tactor linear display. Participants indicated the observed external direction of a localized vibration by positioning a remotely controlled cursor. The results show that the observed direction is toward the midsagittal plane (i.e. the navel or the spine) compared to the tactor direction. This bias is consistent over the observers tested, and up to 10 degrees for the oblique directions. Inspection of the response patterns revealed that observers did not use the body midaxis as the origin for the observed direction, but used two spatially separated internal reference points, one for each body half. Therefore, the use of a torso-related transfer function in applications that require a high level of precision is suggested. The variability of the responses also depends on the tactor direction. It is higher for the left - right direction and lower for the fore - aft direction, which may be caused by the spine and navel acting as anchor points. The present results are relevant for tactile navigation displays for visually handicapped individuals or for jet pilots.