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Liana E. Brown, Grzegorz Kroliczak, Brooke A. Halpert, Melvyn A. Goodale; A hand in sight: How blindsight is improved by hand location. Journal of Vision 2005;5(8):748. doi: https://doi.org/10.1167/5.8.748.
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© ARVO (1962-2015); The Authors (2016-present)
Bimodal visual-tactile neurons, located in the putamen, ventral premotor cortex, and posterior parietal cortex, respond both to visual and tactile stimuli presented near the hands, arms, and face. Single-cell recordings have shown that hand proximity to the visual stimulus determines the degree to which bimodal cells respond. We tested the hypothesis that hand proximity to a visually-presented target object may influence residual vision in the blind visual field of an individual with a lesion in the geniculostriate pathway. MB is a 26-year-old man with a dense upper-left quadrantanopia. He fixated one of 4 randomly-presented LEDs shown 40° to the upper-left, lower-left, upper-right, and lower-right of a central target location. One of 3 (small, medium, large) objects was presented for 150 ms, and MB responded in two ways with his right hand. For the action task, he reached for and grasped the target. For the perception task, he estimated target height by adjusting thumb-finger separation. Hand position was crossed with response type and both were randomly presented in blocks. In the hand-present condition, MB's left hand was placed just to the left of the target object. This placement ensured that this hand was always in the same visual field as the target. In the hand-absent condition, MB's left hand was placed out of view on his lap. Hand position had a significant effect on performance in MB's blind field. In the hand-absent condition, he showed little or no scaling of either peak grip aperture (PGA) or size-estimation aperture (SEA) to object size. In the hand-present condition, however, scaling of both PGA and SEA improved significantly. We saw no improvement in performance with hand-presence in his non-blind visual fields. The results imply that recruitment of bimodal cells can do more than simply improve visual detection in the blind field, they can also contribute to size perception. Potential mechanisms for this improvement will be presented.
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