Abstract
An important unresolved question in sensory neuroscience is whether, and if so with what time course, tactile perception is enhanced by visual deprivation. In three experiments involving 158 normally sighted human participants, we assessed whether tactile spatial acuity improves with short-term visual deprivation over periods ranging from under 10 to over 110 minutes. We used an automated, precisely controlled two-interval forced-choice grating orientation task to assess each participant's ability to discern the orientation of square-wave gratings pressed against the stationary index finger pad of the dominant hand. A two-down one-up staircase (Experiment 1) or a Bayesian adaptive procedure (Experiments 2 and 3) was used to determine the groove width of the grating whose orientation each participant could reliably discriminate. The experiments consistently showed that tactile grating orientation discrimination does not improve with short-term visual deprivation. In fact, we found that tactile performance degraded slightly but significantly upon a brief period of visual deprivation (Experiment 1) and did not improve over periods of up to 110 minutes of deprivation (Experiments 2 and 3). The results additionally showed that grating orientation discrimination tends to improve upon repeated testing, and confirmed that women significantly outperform men on the grating orientation task. We conclude that, contrary to two recent reports but consistent with an earlier literature, passive tactile spatial acuity is not enhanced by short-term visual deprivation. Our findings have important theoretical and practical implications. On the theoretical side, the findings set limits on the time course over which neural mechanisms such as crossmodal plasticity may operate to drive sensory changes; on the practical side, the findings suggest that researchers who compare tactile acuity of blind and sighted participants should not blindfold the sighted participants.
Highlights
Does visual deprivation cause tactile acuity enhancement? This question, important to neuroscientific understanding of tactile perception and of the interaction between the senses, has been investigated for decades.Early studies reported that tactile perception improved upon prolonged simultaneous deprivation of multiple sensory modalities
Zubek et al [5,6] demonstrated that seven days of visual deprivation produced tactile acuity enhancement, as assessed by two-point and tactile fusion tasks; the investigators observed facilitatory effects of visual deprivation when participants were completely light deprived, and when participants were deprived of patterned vision
In three experiments involving 158 participants, we assessed whether tactile spatial acuity improves with short-term visual deprivation
Summary
Does visual deprivation cause tactile acuity enhancement? This question, important to neuroscientific understanding of tactile perception and of the interaction between the senses, has been investigated for decades. Participants were presented with successive air jets at progressively increasing frequencies until the stimuli become perceptually fused; fusion at higher frequencies was indicative of better performance These findings were soon followed by reports that prolonged visual deprivation alone sufficed to improve tactile perception. Because tactile responsiveness of occipital cortex occurred within 90 minutes of blindfolding according to one study [26] (but required 5 days of blindfolding according to another [27]), an important unresolved question is whether short-term visual deprivation results in tactile acuity improvement The literature on this topic has been controversial. In agreement with the earlier literature [29,30,31,32,33], that passive tactile spatial acuity is resistant to short-term visual deprivation
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