Proprioceptive influences on auditory and visual spatial localization.
We evaluated the influence of proprioceptive information about arm position on the perceptual localization of auditory and visual targets attached to the hand. Our approach was to distort the perceived position of the restrained arm by means of mechanical vibration of the biceps brachii muscle; such vibration elicits compelling apparent extension of the stationary forearm (Goodwin, G. M., D. I. McCloskey, and P. B. C. Matthews (1972) Science 175: 1382-1384, Brain 95: 705-748), and subjects report changes in the apparent directions of the auditory and visual targets attached to their hand. These changes are in the same direction and plane as apparent arm motion and their onsets are coincident with or lag slightly behind the experienced displacement of the arm. While visual motion is being experienced, a subject's eyes remain steadily fixating the target light. The pattern of findings demonstrates that proprioceptive information about limb position can influence the central representation of gaze and auditory localization can be similarly influenced. The biasing of auditory localization indicates that identical patterns of arrival time and intensity cues at the two ears can give rise to the perception of sounds in widely disparate spatial positions in relation to the head and body, depending on the proprioceptive representation of the direction of the sound source.