Improvement of a figure copying deficit during sub-sensory galvanic vestibular stimulation.

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We describe the effects of galvanic vestibular stimulation (GVS) on an individual who, following right hemisphere stroke, is unable to copy figures accurately. His copies contain most of the constituent elements, but are poorly integrated and drawn in a seemingly haphazard manner. To test whether GVS could help overcome these difficulties, we administered the Rey-Osterrieth complex figure copy task while manipulating both the presence and laterality of the galvanic signal. The signal was applied at a level that was too low to elicit sensation which ensured that the individual was unaware of either when or on what side he was being stimulated. Relative to a sham condition, two consecutive blocks of GVS increased both the accuracy with which the main configural elements of the figure were reconstructed, and there was some, albeit less consistent evidence, that these were drawn in a more wholistic as opposed to piecemeal manner. Improvement was not reliant on the polarity of the stimulating electrodes. These results suggest that GVS can help overcome difficulties in the perception and/or reconstruction of hierarchical visual form, and thereby uncover a new link between vestibular information processing and visual task performance.