Percept7ial and M o t o ~Skills, 1979, 48, 290.
@ Perceptual and Motor Skills 1979
MANUAL ASYMMETRY FOR TACTILE DISCRIMINATION JAMES HARRIMAN .AND LINDSAY CASTELL1 University of Bristol Many studies of both normal and clinical subjects have shown that the right cerebral hemisphere is functionally superior for the processing of spatial information ( 2 ) . However, despite the strong connection between each hand and the contralateral cerebral hemisphere, few of these studies have investigated lateral asymmetries for tactile perception in normal adults. The present experiment tested the ability of adult subjects to make a tactile discrimination between two spatial patterns. The stimuli were small Braille symbols formed on shellaced card; only those composed of 3, 4 , or 5 dots were used. The adjacent dots were 2.5 cm. apart, and they protruded by 0.25 mm. On each of the 96 experimental trials a pair of symbols, both with the same number of dots, was presented. On 48 of the trials the cwo symbols were identical; in the other 48 trials the symbols were different and did not include mirror-image patterns. The test pairs were mounted flat on a base card, in line one above the other. They were separated by a space of 1 un. with no .salient discontinuities and were surrounded by a raised guide. Subjects were shown a diagram of the trial configuration and were instructed to scan the stimuli rapidly from top to bottom with a single unidirectional movement of the index finger. After 8 practice trials, two balanced blocks of 48 trials were presented beneath a horizontal screen on a table at which the subject was seared. A signal-detecrion procedure was used, in which subjects made their responses verbally according to the rating categories; Certain Same, Uncertain Same, Uncertain Different, Certain Different ( 3 ) . Knowledge of results was given only after the practice rrials. The subjects were 32 female students, all of whom reported being strongly right-handed. By random allocation, 16 subjects used only the right index fingers, and 16 used only the left index fingers. This design was used to avoid asymmetrical bilateral transfer between the hands, which had been found in a related study ( 4 ) . Prior to an analysis of variance, the rating responses were converted to 2 arcsin P ( A ) values which gave a mean score of 1.898 for subjects using the right hand and 2.068 for subjects using the left hand. The analysis showed that discrimination was significantly more ac. 0 1 ) . An index of task curate for subjects using the left hand (K,sa = 8.37, p difficulty is given by the average error scores, which were 34.5 and 27.9 respectively for subjects using the right and left hands. These results agree with previous findings of a n advantage for the left hand in reading of Braille by sighted and by blind children ( 1 , 4 ) . In both cases this was attributed to a superiority of the right hemisphere for the processing of spatial information. REFERENCES 1. HERMELIN, B., & O'CONNOR, N. Functional asymmetry in the reading of Braille. Neuropsychologia, 1971, 9 , 4 3 1-435. 2. LEVY, J. Cerebral lareralization and spatial ability. Behavior Gemtics, 1976, 6 , 171188. 3. MCNICOL,D. A primer of signnl detection theory. London: Allen & Unwin, 1972. 4. RUDEL,R . G., DENCKLA, h4. B., & SPALTEN,E. The functional asymmetry of braille letter learning in normal, sighted children. Neurology, 1974, 24, 733-738. Accepted February 7 , 1979. =We are grateful to the Royal National Institute for the Blind for the provision of the Braille alphabet cards. Request reprints from J. C. Harriman, Department of Psychology, University of Bristol, 8-10, Berkeley Square, Bristol, BS8 1HH. England. Additional data are on file in Document NAPS-03363 with Microfiche Publications, 440 Park Avenue South, New York, N. Y. 10016. Remit $3.00 for microfiche or $6.50 for photocopy.
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@ Perceptual and Motor Skills 1979
MANUAL ASYMMETRY FOR TACTILE DISCRIMINATION JAMES HARRIMAN .AND LINDSAY CASTELL1 University of Bristol Many studies of both normal and clinical subjects have shown that the right cerebral hemisphere is functionally superior for the processing of spatial information ( 2 ) . However, despite the strong connection between each hand and the contralateral cerebral hemisphere, few of these studies have investigated lateral asymmetries for tactile perception in normal adults. The present experiment tested the ability of adult subjects to make a tactile discrimination between two spatial patterns. The stimuli were small Braille symbols formed on shellaced card; only those composed of 3, 4 , or 5 dots were used. The adjacent dots were 2.5 cm. apart, and they protruded by 0.25 mm. On each of the 96 experimental trials a pair of symbols, both with the same number of dots, was presented. On 48 of the trials the cwo symbols were identical; in the other 48 trials the symbols were different and did not include mirror-image patterns. The test pairs were mounted flat on a base card, in line one above the other. They were separated by a space of 1 un. with no .salient discontinuities and were surrounded by a raised guide. Subjects were shown a diagram of the trial configuration and were instructed to scan the stimuli rapidly from top to bottom with a single unidirectional movement of the index finger. After 8 practice trials, two balanced blocks of 48 trials were presented beneath a horizontal screen on a table at which the subject was seared. A signal-detecrion procedure was used, in which subjects made their responses verbally according to the rating categories; Certain Same, Uncertain Same, Uncertain Different, Certain Different ( 3 ) . Knowledge of results was given only after the practice rrials. The subjects were 32 female students, all of whom reported being strongly right-handed. By random allocation, 16 subjects used only the right index fingers, and 16 used only the left index fingers. This design was used to avoid asymmetrical bilateral transfer between the hands, which had been found in a related study ( 4 ) . Prior to an analysis of variance, the rating responses were converted to 2 arcsin P ( A ) values which gave a mean score of 1.898 for subjects using the right hand and 2.068 for subjects using the left hand. The analysis showed that discrimination was significantly more ac. 0 1 ) . An index of task curate for subjects using the left hand (K,sa = 8.37, p difficulty is given by the average error scores, which were 34.5 and 27.9 respectively for subjects using the right and left hands. These results agree with previous findings of a n advantage for the left hand in reading of Braille by sighted and by blind children ( 1 , 4 ) . In both cases this was attributed to a superiority of the right hemisphere for the processing of spatial information. REFERENCES 1. HERMELIN, B., & O'CONNOR, N. Functional asymmetry in the reading of Braille. Neuropsychologia, 1971, 9 , 4 3 1-435. 2. LEVY, J. Cerebral lareralization and spatial ability. Behavior Gemtics, 1976, 6 , 171188. 3. MCNICOL,D. A primer of signnl detection theory. London: Allen & Unwin, 1972. 4. RUDEL,R . G., DENCKLA, h4. B., & SPALTEN,E. The functional asymmetry of braille letter learning in normal, sighted children. Neurology, 1974, 24, 733-738. Accepted February 7 , 1979. =We are grateful to the Royal National Institute for the Blind for the provision of the Braille alphabet cards. Request reprints from J. C. Harriman, Department of Psychology, University of Bristol, 8-10, Berkeley Square, Bristol, BS8 1HH. England. Additional data are on file in Document NAPS-03363 with Microfiche Publications, 440 Park Avenue South, New York, N. Y. 10016. Remit $3.00 for microfiche or $6.50 for photocopy.
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