BRAIN
AND
LANGUAGE
Cerebral
7, 191-200 (1979)
Dominance
in Aphasia
Recovery
JOHN M. PETTIT Conley
Speech
and Hearing
Center,
University
of Maine
AND
J. DOUGLASNOLL Purdue
University
This investigation studied the patterns of ear preference of a group of 25 aphasic adults through the administration of two verbal dichotic tests and retests over a 2-month interval of time. These dichotic tests were a Dichotic Digits Test (DDT) and a Dichotic Animal Names Test (DANT). Schuell’s short test of aphasia was given twice over this interval to assess language recovery. Results indicated that as aphasics improve in language, cerebral dominance becomes more firmly established in the right cerebral hemisphere. The data in this study tend to support a dominance shift hypothesis in the recovery of language after aphasia.
INTRODUCTION
An unresolved issue for students of aphasia concerns the roles of the two hemispheres in recovery from cerebral damage. Two opposing hypotheses may be framed as questions: (1) Does the damaged (dominant) hemisphere reorganize language processes in undamaged centers, or (2) are language functions assumed by the undamaged (nondominant) hemisphere? Quadfasel has said “ . . . the crucial empirical test of this notion of contralateral substitution of hemispheres in the process of recovery from aphasia has not yet been made” (Osgood & Miron, 1963, p. 35). Fifteen years earlier, after an extensive examination of the theory that the right hemisphere assumes the language function after cerebral damage, Kurt Goldstein said: “I think it will be better to say ‘we do not know’ . . . Our uncertainty in this respect is regrettable” (1948, p. 53). Finally, more recently, Penfield said (1971, p. 25): Requests for reprints should be sent to Dr. John Pettit, Conley Speech and Hearing Center, North Stevens Hall, University of Maine, Orono, ME 04473. 191 0093-934X/79/020191-10$02.00/0 Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
192
PETTIT
AND NOLL
When the major speech center is severely injured in adult life, the adult cannot do what he might have done as a child. He may improve but he is apt to be using the remaining uninjured cortex on the side of the injury. He can never establish a completely new center on the non-dominant side, as far as our experience goes.
Studies have shown that cerebral dominance for speech appears to be related to ear preference as assessed through the use of verbal dichotic listening tests (Kimura, 1961a, 1961b; Milner, 1972). By presenting simultaneous but different verbal material to each ear, it is possible to determine which of the two hemispheres is likely to be dominant in language functions. One does this by counting the number of items a subject correctly (or incorrectly) identifies for each ear. The “better ear” (as reflected by better scores) is assumed to represent the dominant hemisphere on the contralateral side. Thus, it seemed appropriate to investigate the patterns of ear preference of a group of aphasic adults by administering verbal dichotic auditory tests and retests during a period of time when language recovery or improvement could be shown to be taking, or have taken, place. MATERIALS
AND METHODS
Subjects The subjects were 25 randomly selected aphasic adults (experimental group) and 25 normal subjects with no history of brain pathology (control group) who were all righthanded. The age of the 25 aphasic adults ranged from 22 to 76 years with a mean age of 50 years. The 25 subjects in the control group ranged in age from 22 to 77 years with a mean age of 42 years. All of the aphasic subjects received some speech or language therapy throughout the duration of this investigation. Twenty-two of the subjects in this group had had a cerebrovascular accident and three had experienced some type of traumatic head injury. Information regarding specific site of lesion damage for each patient was not available. Confirmation that damage had occurred to the left hemisphere was made from neurological examinations, electroencephalograms, and angiography. Any subject suspected of bilateral involvement from any of these examination procedures was excluded from the study. All subjects were required to pass an audiometric screening test for both ears at 25 dB IS0 through the speech frequencies of 500, 1000, and 2000 Hz.
Dichotic
Tests
Two verbal dichotic listening tests were constructed and administered to both the control (normal) and the experimental (aphasia) groups. The stimuli consisted of a Dichotic Digits Test (DDT) and a Dichotic Animal Names Test (DANT). Both tests were constructed by pairing all possible combinations from nine digits and nine animal names. The numbers included from 1 to 10, excluding 7. The animal names were dog, bull, sheep, duck, cat, bird, goat, pig, and goose. All of these nine words are CVC syllables and are listed as words understood by children in the fourth grade or below (Thorndike & Lorge, 1944). When all possible pairs are arranged, one can construct 36 pairs of names and 36 pairs of digits. For each test, these pairs were arranged in sets of three so that there were 12 sets. The interstimulus time (time between pairs) was .5 set and the time between the end and beginning of a set was 10 sec. Each completedichotic test consisted of 36 pairs of stimuli played twice (72 pairs). Thus a perfect score could be expressed as 72 stimuli correctly identified for each ear or zero errors for the left ear and zero errors for the right ear.
CEREBRAL
DOMINANCE
IN APHASIA
193
Aphasia Test Schuell’s A Short Examination for Aphasia (Schuell, 1957) was administered as a means of assessing language improvement over the 2-month interval of time studied. The test consists of four parts or sections: A, = Auditory Disturbances; A2 = Reading Disturbances; A3 = Speech and Language Disturbances; and A, = Visual and Writing Disturbances. This test was used for the following reasons: (I) it is a relatively simple test to administer, (2) the amount of time needed to complete the test is approximately 30 min, (3) it is possible to analyze scores numerically, and (4) it is a generally accepted tool. Furthermore, Toubbeh (1965) reported that the Schuell Short Examination for Aphasia correlates highly with various other tests of aphasia, and he concluded that it can be used as a test-retest instrument in situations where a general overview of the patient’s progress is to be measured.
Procedures Control group. Each subject was given both verbal dichotic tests. The tests were administered by means of an Ampex 351 dual-channel tape recorder through matched TDH-39 earphones. The channels were balanced by passing each channel through a Bruel and Kjaer Model 2304 power level recorder. A reference tone of 1000 Hz which preceded each test could then be adjusted independently for each channel to balance the stimuli within ? 2dB SPL. Each subject took each test twice. The earphones were switched for the second presentation. Even-numbered subjects began the task with channel one presented to the left ear and channel two to the right ear. After 36 pairs the earphones (channels) were switched to complete the test. Odd-numbered subjects began the test with channel one to the right ear and channel two to the left ear. These methods were employed to eliminate the possibility of any bias that might be introduced by difference in the channels, stimuli, etc. After each subject was familiarized with the procedure he was instructed to listen to both ears until the three-pair set was completed and then to write down as many of the items (digits or words) as he could remember in any order.
Experimental group. Each of the 25 subjects in the experimental group was given the verbal dichotic tests (DDT and DANT) and A Short Examination for Aphasia (Schuell, 1957) twice. An interval of 2 months was maintained between the test and retest conditions. The aphasia test was administered in order to assess improvement in language recovery over this interval. The dichotic tests were administered in order to assess the changes in ear preference (cerebral dominance) that took place over this 2-month interval. The interval between test and retest for the experimental group ranged from 55 to 109 days with a mean of 66 days. The same procedure used to administer the dichotic tests to the control group was followed in presenting these tests to the aphasic subjects. Before each dichotic test, a subject was given instructions about the test and in addition was given an opportunity to practice listening to the stimuli. The experimenter randomly presented numbers or animal names in series of one, two, three, four, five, and six stimuli and then had each subject respond in three different ways. The response modes included verbal repetition, writing or pointing to 3-in. felt numbers or colored pictures of the nine animals on 3.5 x 3.5 in. cards. Thus it was possible to
194
PETTIT
AND
NOLL
choose the most appropriate means for having a subject respond. The written response mode was used by only 5 of the 25 subjects while 16 pointed to the numbers or pictures. The other 4 responded verbally by repeating the items. The tape was stopped after every three pair set until each subject indicated that he had completed his response and needed no more time. RESULTS
Control Group
The left and right ear error scores on the DDT and DANT were submitted to a two-tailed t test for related measures (Winer, 1962). The results can be found in Table 1. It can be seen that the control group showed a significant right ear preference (i.e., left cerebral hemisphere dominance) for both the DDT and DANT. Experimental Group Aphasia test. The data from the two presentations (test-retest) of Schuell’s Short Test (Schuell, 1957) were analyzed by submitting them to a two-factor analysis of variance (subtests and test-retest) with fully repeated measures. (Winer, 1962) An inspection of the data displayed in Fig. 1 indicates that when the group of aphasic subjects were tested initially, they made no more than 36% errors on any of the four subtests. In fact error scores on the reading disturbances subtest (AZ) initially averaged only 18%. Analysis of the data over time indicated a significant reduction in the number of errors. Subsequent analysis of the main effects indicated that over the 2-month interval of time, aphasic subjects made significantly fewer errors for the three subtests of auditory disturbances, speech, and language disturbances and visual and writing disturbances (P < .05). There was no significant difference in the reduction of errors over time for the subtest concerned with reading disturbances. An analysis of the data for individuals (not presented here) revealed
COMPARISON SUBJECTS (DANT).
OF MEAN
ON THE DICHOTIC
DIGITS
Mean Test DDT DANT *Significant
AND
LANGUAGE
Cerebral
7, 191-200 (1979)
Dominance
in Aphasia
Recovery
JOHN M. PETTIT Conley
Speech
and Hearing
Center,
University
of Maine
AND
J. DOUGLASNOLL Purdue
University
This investigation studied the patterns of ear preference of a group of 25 aphasic adults through the administration of two verbal dichotic tests and retests over a 2-month interval of time. These dichotic tests were a Dichotic Digits Test (DDT) and a Dichotic Animal Names Test (DANT). Schuell’s short test of aphasia was given twice over this interval to assess language recovery. Results indicated that as aphasics improve in language, cerebral dominance becomes more firmly established in the right cerebral hemisphere. The data in this study tend to support a dominance shift hypothesis in the recovery of language after aphasia.
INTRODUCTION
An unresolved issue for students of aphasia concerns the roles of the two hemispheres in recovery from cerebral damage. Two opposing hypotheses may be framed as questions: (1) Does the damaged (dominant) hemisphere reorganize language processes in undamaged centers, or (2) are language functions assumed by the undamaged (nondominant) hemisphere? Quadfasel has said “ . . . the crucial empirical test of this notion of contralateral substitution of hemispheres in the process of recovery from aphasia has not yet been made” (Osgood & Miron, 1963, p. 35). Fifteen years earlier, after an extensive examination of the theory that the right hemisphere assumes the language function after cerebral damage, Kurt Goldstein said: “I think it will be better to say ‘we do not know’ . . . Our uncertainty in this respect is regrettable” (1948, p. 53). Finally, more recently, Penfield said (1971, p. 25): Requests for reprints should be sent to Dr. John Pettit, Conley Speech and Hearing Center, North Stevens Hall, University of Maine, Orono, ME 04473. 191 0093-934X/79/020191-10$02.00/0 Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
192
PETTIT
AND NOLL
When the major speech center is severely injured in adult life, the adult cannot do what he might have done as a child. He may improve but he is apt to be using the remaining uninjured cortex on the side of the injury. He can never establish a completely new center on the non-dominant side, as far as our experience goes.
Studies have shown that cerebral dominance for speech appears to be related to ear preference as assessed through the use of verbal dichotic listening tests (Kimura, 1961a, 1961b; Milner, 1972). By presenting simultaneous but different verbal material to each ear, it is possible to determine which of the two hemispheres is likely to be dominant in language functions. One does this by counting the number of items a subject correctly (or incorrectly) identifies for each ear. The “better ear” (as reflected by better scores) is assumed to represent the dominant hemisphere on the contralateral side. Thus, it seemed appropriate to investigate the patterns of ear preference of a group of aphasic adults by administering verbal dichotic auditory tests and retests during a period of time when language recovery or improvement could be shown to be taking, or have taken, place. MATERIALS
AND METHODS
Subjects The subjects were 25 randomly selected aphasic adults (experimental group) and 25 normal subjects with no history of brain pathology (control group) who were all righthanded. The age of the 25 aphasic adults ranged from 22 to 76 years with a mean age of 50 years. The 25 subjects in the control group ranged in age from 22 to 77 years with a mean age of 42 years. All of the aphasic subjects received some speech or language therapy throughout the duration of this investigation. Twenty-two of the subjects in this group had had a cerebrovascular accident and three had experienced some type of traumatic head injury. Information regarding specific site of lesion damage for each patient was not available. Confirmation that damage had occurred to the left hemisphere was made from neurological examinations, electroencephalograms, and angiography. Any subject suspected of bilateral involvement from any of these examination procedures was excluded from the study. All subjects were required to pass an audiometric screening test for both ears at 25 dB IS0 through the speech frequencies of 500, 1000, and 2000 Hz.
Dichotic
Tests
Two verbal dichotic listening tests were constructed and administered to both the control (normal) and the experimental (aphasia) groups. The stimuli consisted of a Dichotic Digits Test (DDT) and a Dichotic Animal Names Test (DANT). Both tests were constructed by pairing all possible combinations from nine digits and nine animal names. The numbers included from 1 to 10, excluding 7. The animal names were dog, bull, sheep, duck, cat, bird, goat, pig, and goose. All of these nine words are CVC syllables and are listed as words understood by children in the fourth grade or below (Thorndike & Lorge, 1944). When all possible pairs are arranged, one can construct 36 pairs of names and 36 pairs of digits. For each test, these pairs were arranged in sets of three so that there were 12 sets. The interstimulus time (time between pairs) was .5 set and the time between the end and beginning of a set was 10 sec. Each completedichotic test consisted of 36 pairs of stimuli played twice (72 pairs). Thus a perfect score could be expressed as 72 stimuli correctly identified for each ear or zero errors for the left ear and zero errors for the right ear.
CEREBRAL
DOMINANCE
IN APHASIA
193
Aphasia Test Schuell’s A Short Examination for Aphasia (Schuell, 1957) was administered as a means of assessing language improvement over the 2-month interval of time studied. The test consists of four parts or sections: A, = Auditory Disturbances; A2 = Reading Disturbances; A3 = Speech and Language Disturbances; and A, = Visual and Writing Disturbances. This test was used for the following reasons: (I) it is a relatively simple test to administer, (2) the amount of time needed to complete the test is approximately 30 min, (3) it is possible to analyze scores numerically, and (4) it is a generally accepted tool. Furthermore, Toubbeh (1965) reported that the Schuell Short Examination for Aphasia correlates highly with various other tests of aphasia, and he concluded that it can be used as a test-retest instrument in situations where a general overview of the patient’s progress is to be measured.
Procedures Control group. Each subject was given both verbal dichotic tests. The tests were administered by means of an Ampex 351 dual-channel tape recorder through matched TDH-39 earphones. The channels were balanced by passing each channel through a Bruel and Kjaer Model 2304 power level recorder. A reference tone of 1000 Hz which preceded each test could then be adjusted independently for each channel to balance the stimuli within ? 2dB SPL. Each subject took each test twice. The earphones were switched for the second presentation. Even-numbered subjects began the task with channel one presented to the left ear and channel two to the right ear. After 36 pairs the earphones (channels) were switched to complete the test. Odd-numbered subjects began the test with channel one to the right ear and channel two to the left ear. These methods were employed to eliminate the possibility of any bias that might be introduced by difference in the channels, stimuli, etc. After each subject was familiarized with the procedure he was instructed to listen to both ears until the three-pair set was completed and then to write down as many of the items (digits or words) as he could remember in any order.
Experimental group. Each of the 25 subjects in the experimental group was given the verbal dichotic tests (DDT and DANT) and A Short Examination for Aphasia (Schuell, 1957) twice. An interval of 2 months was maintained between the test and retest conditions. The aphasia test was administered in order to assess improvement in language recovery over this interval. The dichotic tests were administered in order to assess the changes in ear preference (cerebral dominance) that took place over this 2-month interval. The interval between test and retest for the experimental group ranged from 55 to 109 days with a mean of 66 days. The same procedure used to administer the dichotic tests to the control group was followed in presenting these tests to the aphasic subjects. Before each dichotic test, a subject was given instructions about the test and in addition was given an opportunity to practice listening to the stimuli. The experimenter randomly presented numbers or animal names in series of one, two, three, four, five, and six stimuli and then had each subject respond in three different ways. The response modes included verbal repetition, writing or pointing to 3-in. felt numbers or colored pictures of the nine animals on 3.5 x 3.5 in. cards. Thus it was possible to
194
PETTIT
AND
NOLL
choose the most appropriate means for having a subject respond. The written response mode was used by only 5 of the 25 subjects while 16 pointed to the numbers or pictures. The other 4 responded verbally by repeating the items. The tape was stopped after every three pair set until each subject indicated that he had completed his response and needed no more time. RESULTS
Control Group
The left and right ear error scores on the DDT and DANT were submitted to a two-tailed t test for related measures (Winer, 1962). The results can be found in Table 1. It can be seen that the control group showed a significant right ear preference (i.e., left cerebral hemisphere dominance) for both the DDT and DANT. Experimental Group Aphasia test. The data from the two presentations (test-retest) of Schuell’s Short Test (Schuell, 1957) were analyzed by submitting them to a two-factor analysis of variance (subtests and test-retest) with fully repeated measures. (Winer, 1962) An inspection of the data displayed in Fig. 1 indicates that when the group of aphasic subjects were tested initially, they made no more than 36% errors on any of the four subtests. In fact error scores on the reading disturbances subtest (AZ) initially averaged only 18%. Analysis of the data over time indicated a significant reduction in the number of errors. Subsequent analysis of the main effects indicated that over the 2-month interval of time, aphasic subjects made significantly fewer errors for the three subtests of auditory disturbances, speech, and language disturbances and visual and writing disturbances (P < .05). There was no significant difference in the reduction of errors over time for the subtest concerned with reading disturbances. An analysis of the data for individuals (not presented here) revealed
COMPARISON SUBJECTS (DANT).
OF MEAN
ON THE DICHOTIC
DIGITS
Mean Test DDT DANT *Significant
