Despite widespread popular belief that blind people have enhanced tactile acuity, there is little experimental evidence regarding this issue. The question of the tactile superiority of the blind is of significant theoretical interest, and also has practical implications for rehabilitation strategies involving sensory substitution devices. The objective of this research is to determine whether blindness results in compensatory functional improvement to the sense of touch, and if so, to identify the likely mechanism for this improvement. A series of computer automated psychophysical experiments will be performed on sighted and two groups of blind people, congenitally blind and late blind braille readers, to determine whether either group of blind people has tactile acuity superior to that of the sighted. Subjects will be tested on two tactile tasks, grating resolution and grating detection, each task run at two controlled stimulus force levels, and repeated to allow for improvement with practice. The results of the study will favor one of the following three hypotheses: Hypothesis 1: Extreme daily reliance on the sense of touch, regardless of the age at onset of blindness, leads to enhanced tactile acuity, perhaps by means of unimodal plasticity within the parietal cortex. Hypothesis 2: Visual deprivation beginning at birth leads to enhanced tactile acuity, perhaps by means of cross modal plasticity in which the occipital cortex is recruited by the sense of touch. Hypothesis 3: Human tactile acuity is at the limit established by peripheral receptor density, and is accordingly not modifiable by either visual deprivation or tactile experience.
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