Tactile capture of auditory localization is modulated by hand posture

It is well known that spatial discrepancies between synchronized auditory and visual events can lead to mislocalizations of the auditory stimulus toward the visual stimulus, the so-called ventriloquism effect. Recently, a similar effect of touch on audition has been reported. This study investigated whether this audio-tactile ventriloquism effect depends on hand posture. Participants reported the perceived location of brief auditory stimuli that were presented from left, right, and center locations, either alone or with concurrent tactile stimuli to the fingertips situated at the left and right sides of the speaker array. Compared to unimodal presentations, auditory localization was biased toward the side of the concurrent tactile stimulus in the bimodal trials. This effect was reduced but still significant when participants adopted a crossed-hands posture. In this condition a partial (incomplete) localization bias was observed only for large audio-tactile spatial discrepancies. However, localization was still shifted toward the external location of the tactile stimulus, and not toward the side of the anatomical hand that was stimulated. These results substantiate recent evidence for the existence of an audio-tactile ventriloquism effect and extend these findings by demonstrating that this illusion operates predominantly in an external coordinate system.