Abstract
Vestibular inputs make a key contribution to the sense of one’s own spatial location. While the effects of vestibular stimulation on visuo-spatial processing in neurological patients have been extensively described, the normal contribution of vestibular inputs to spatial perception remains unclear. To address this issue, we used a line bisection task to investigate the effects of galvanic vestibular stimulation (GVS) on spatial perception, and on the transition between near and far space. Brief left-anodal and right-cathodal GVS or right-anodal and left-cathodal GVS were delivered. A sham stimulation condition was also included. Participants bisected lines of different lengths at six distances from the body using a laser pointer. Consistent with previous results, our data showed an overall shift in the bisection bias from left to right as viewing distance increased. This pattern suggests leftward bias in near space, and rightward bias in far space. GVS induced strong polarity dependent effects in spatial perception, broadly consistent with those previously reported in patients: left-anodal and right-cathodal GVS induced a leftward bisection bias, while right-anodal and left-cathodal GVS reversed this effect, and produced bisection bias toward the right side of the space. Interestingly, the effects of GVS were comparable in near and far space. We speculate that vestibular-induced biases in space perception may optimize gathering of information from different parts of the environment.
Highlights
The sense of one’s own position, orientation and motion in threedimensional space derives from the integration of a variety of signals, including muscles, joints, vision, touch, and vestibular inputs (Lackner and DiZio, 2005)
GALVANIC VESTIBULAR STIMULATION Bipolar galvanic vestibular stimulation (GVS) was used to deliver a boxcar pulse of 1 mA with 8 s of duration, via a commercial stimulator (Good Vibrations Engineering Ltd., Nobleton, Ontario, Canada)
Analysis of regression slopes showed a systematic shift in the bisection bias toward the right with increasing distance
Summary
The sense of one’s own position, orientation and motion in threedimensional space derives from the integration of a variety of signals, including muscles, joints, vision, touch, and vestibular inputs (Lackner and DiZio, 2005). The vestibular system contains two distinct structures: the semicircular canals, which detect changes in angular acceleration, and the otolith organs, which detect changes in linear acceleration and gravity. Both semicircular canals and otolith organs constantly provide information to the brain regarding our body’s position and movement. Patients with unilateral spatial neglect (USN) fail to detect objects or to perform movements in the space contralateral to the cerebral lesion. USN patients locate the bisection point shifted toward the ipsilesional side of the space, so that right hemisphere damaged patients produce a characteristic rightward error in bisection (Heilman and Valenstein, 1979; Schenkenberg et al, 1980; Milner et al, 1993; Doricchi and Angelelli, 1999; Daini et al, 2002)
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