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From the Department of Neurology (Dr. Van Boven), Northwestern University Medical School, Chicago, IL; and the Laboratory for Magnetic Brain Stimulation (Drs. Keenan and Pascual–Leone, R.H. Hamilton and T. Kauffman), Behavioral Neurology Unit, Department of Neurology, Beth Israel-Deaconess Medical Center and Harvard Medical School, Boston, MA.
Address correspondence and reprint requests to Dr. Robert W. Van Boven, Laboratory of Brain and Cognition, NIMH, Building 10, Room 4C104, 10 Center Drive, MSC 1366, Bethesda, MD 20892-1366; e-mail: robert_vanboven{at}nih.gov or Dr. Alvaro Pascual–Leone, Department of Neurology, Beth Israel-Deaconess Medical Center, 330 Brookline Avenue, KS452, Boston, MA 02215; e-mail: apleone@caregroup.harvard.edu
OBJECTIVE: To determine if blind people have heightened tactile spatial acuity.
BACKGROUND: Recently, studies using magnetic source imaging and somatosensory evoked potentials have shown that the cortical representation of the reading fingers of blind Braille readers is expanded compared to that of fingers of sighted subjects. Furthermore, the visual cortex is activated during certain tactile tasks in blind subjects but not sighted subjects. The authors hypothesized that the expanded cortical representation of fingers used in Braille reading may reflect an enhanced fidelity in the neural transmission of spatial details of a stimulus. If so, the quantitative limit of spatial acuity would be superior in blind people.
METHODS: The authors employed a grating orientation discrimination task in which threshold performance is accounted for by the spatial resolution limits of the neural image evoked by a stimulus. The authors quantified the psychophysical limits of spatial acuity at the middle and index fingers of 15 blind Braille readers and 15 sighted control subjects.
RESULTS: The mean grating orientation threshold was significantly (p = 0.03) lower in the blind group (1.04 mm) compared to the sighted group (1.46 mm). The self-reported dominant reading finger in blind subjects had a mean grating orientation threshold of 0.80 mm, which was significantly better than other fingers tested. Thresholds at non-Braille reading fingers in blind subjects averaged 1.12 mm, which were also superior to sighted subjects’ performances.
CONCLUSION: Superior tactile spatial acuity in blind Braille readers may represent an adaptive, behavioral correlate of cortical plasticity.
Key words: Touch—Blindness—Discrimination learning—Form perception.
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