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Dichotic listening with the communicatively impaired: results from trials of a short British-English dichotic word test
Journal of Phonetics (1981) 9, 375-383
Dichotic listening with the communicatively impaired: results from trials of a short British- English dichotic word test Chris Code School of Speech Therapy, South Glamorgan Institute of Higher Education and University College, Cardiff, United Kingdom Received 20 July 1980
Abstract
The construction and testing of a new, short British-English dichotic word test, designed specifically for the communicatively impaired, is described. Sixteen normal, 6 aphasic and 6 stammering subjects were administered the test and a copy of the American-English original. Results show that the British-English version gives reliable ear preference scores, indicative of cere bralla teralization for language, and is suitable for use with subjects who have severe communication problems.
Introduction The ear preference shown on dichotic listening tasks is considered to be a well established indicator of lateral processing for language in the cerebral cortex. Kimura (196la, b) developed the dichotic listening paradigm from initial work by Broadbent (1954) and hundreds of empirical studies since have confirmed that when competing and different linguistic material is played simultaneously to separate ears, a right ear preference (REP) is observed with the great majority of dominantly right-handed normal subjects (Studdert-Kennedy & Shankweller, 1970). Berlin & McNiel (1976) have coded and analysed over 300 articles on dichotic listening. Kimura ( 196la) has proposed that the REP for verbal material (words, CV syllables, digits , nonsense words) reflects the superiority of the contralateral left hemisphere for speech processing, which is a function of the superior contralateral neural pathways between right ear and left temporal lobe . Dichotic listening studies have been carried out on subjects with diverse communication disorders, including aphasia (Schulhoff & Goodglass, 1969; Sparks et al,. 1970; Oscar-Berman, et al., 1975; Johnson et al., 1977; Brady, 1978; Warren & Crosson, 1978), stammering (Curry & Gregory, 1969; Quinn, 1972; Brady & Berson, 1975; Dorman & Porter, 1975 ; Sommers et al., 1975 ; Allen, 1980), language-disordered children (Helms, 1971 , Sommers & Taylor, 1972), articulation disorde red children (Sommers et al., 1972), dyslexic children (Sobotka, 1973) and Down's syndrome children (Sommers & Starkey , 1977). The relationships that are thought to exist between hemispheric asymmetries and language processing are central issues in neuropsychological research and experimental phonetics, and the studies referred to above reflect the growing importance of this area of research for speech pathology. Although the clinical application of dichotic listening is in an early stage of development, recent dichotic studies with aphasic subjects have indicated that a number 0095-4470/81/040375 + 09 $02.00/0
© 1981 Academic Press Inc. (London) Ltd.
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of prognostic factors may be related to apparent shifts in laterality in aphasic subjects, including severity of aphasia and time-since-onset of aphasia (Johnson et al., 1977). Dichotic studies with stammerers have produced conflicting results, with some studies producing evidence to support the hypothesis that stammerers may have incomplete or bilateral representation for speech (Curry & Gregory , 1969; Brady & Berson , 1975) and others failing to find differences in ear preference scores (Dolman & Porter, 1975). The co nflicting results may be due to research design differences , however, as the study by Brady & Berson (1975) suggests that there is a subset of stammerers who show left ear preference. Support for this view has been provided by Allen (1980) who has demonstrated that stammerers who are classified as severe produce higher left ear preference scores than stammerers who are classified as mild-moderate. The clinical application of the usual dichotic listening tests with patients who have severe communication problems has been difficult for a number of reasons. Dichotic listening tests are typically very long (up to 650 stimulus presentations in some cases), because as a general rule, the longer the test the more reliable the results . This kind of length is unacceptable for clinical use however, because it is time consuming and, more importantly, unsuitable for easily fatigued or distracted patients. So a test for clinical use should be as short as possible. Non-meaningful synthetic CV syllables or digits are often used in dichotic experiments and this clearly raises problems for subjects with impaired comprehension; therefore a dichotic test designed to measure the ear preferences of subjects with comprehension difficulties should consist of natural, high frequency, linguistically simple and meaningful words. Much has been made in the literature of the mode of presentation in dichotic tasks, with some tests requiring the subject to attend to 3 or more digits or words at each ear, and report as many as he can remember. Furthermore, there is evidence to suggest that an increased memory load increases right ear scores (Yeni-Komshian & Gordon, 1974). This method has serious drawbacks for testing the aphasic patient with poor auditory retention , for instance; consequently, a test suitable for use with such subjects should employ a single dichotic pair stimulus method . Finally, subjects in dichotic studies are usually asked to verbally report their choises, where this presents obvious difficulties for patients with expressive problems. Therefore , a dichotic test for use with patients who have severe expressive difficulties should provide a mode of response that is independent of verbal expression. A dichotic listening test for clinical use in speech pathology should be as short as possible, consisting of high frequency liguistically meaningul material, with an unambiguous mode of report that is independent of verbal expression and does not tax short-term auditory memory. Such a test, designed specifically for those with communication problems, has been developed and widely used in the United States (Starkey , 1974; Sommers eta!., 1975; Sommers & Starkey, 1977 ; Johnson eta!., 1975; Warren & Crosson , 1978 ; Brady, 1978 ; Petek , 1979), but due to differences in pronunciation between American- and British-English, is unsuitable for use with British subjects. The aim of the study reported here was to develop a BritishEnglish version of this successful and reliable dichotic test , and the purpose of this paper is to describe the test and report the results of trials carried out to examine its effectiveness and reliability in determining ear preferences.
Method Preparation of the dichotic listening tests A modified version of the method described by Rubino (1972) fo r making dichotic tapes was employed in preparing the British-English test.
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In order to make the necessary comparisons between the British and original American tests , both had to be as similar as possible. The version of the American test to be compared utilized 6 pairs of words , and when the non-rhyming pair (in British pronunciation) "balldoll ", and the diphthongal pair (in British pronunciation) "coat-goat" were removed , this left 4 word pairs. The remaining pairs were "top-pop , pig- dig, cat-bat, bun-gun" . The word pairs chosen for the British version were "dart- tart , cap- tap , gun-bun , cat-bat" , and the high frequency of these words was confirmed by the Thorndike- Lorge word count (Thorndike & Lorge , 1944). The unwanted word pairs were edited out of the American tape . The 8 words chosen for the British test were recorded in an acoustically treated room by a trained phonetician (RP) at 7! ips on a Ferrograph Series Seven tape recorder on fresh Memorex tape. The pairs to be presented dichotically were recorded 2 s apart, and a 10 s gap was left between each pair. The recording level was checked on the VU meter of the tape recorder, and each word was recorded between 80 and 100 dB. This tape was then spliced into 4loops, each bearing a pair of words 2 s apart. Two Tandberg mono tape recorders were arranged side by side in such a way that a chosen tape loop passed through both playback heads of the tape recorders . Both Tandbergs were then connected to the 2 separate channels of a Gould Advance OS4000 Digital Storage Oscilloscope to check for simultaneity and amplitude . The Tandbergs were both switched to playback , and gradually moved closer to each other or further apart until the playback onsets of the two words were seen to be within ± 2 ms simultaneity on the screen of the oscilloscope. The outputs of the Tandbergs were then connected to the 2 separate channels of a Revox A77 2-track stereo tape recorder loaded with fresh Memorex tape, and the amplitudes of the two words were again checked for equivalence by reference to the separate VU meters of the Revox. The 2 words were then recorded onto the separate channels of the Revox, and afterwards rechecked for simultaneity with the oscilloscope . It was decided , following findings by Johnson et al. (1977), to obtain a large amplitude of 90 ± 4dB at the ear, as larger dB levels tend to produce stronger right ear scores. The recording and playback heads of all the recording equipment used in the construction of the tape had previously been cleaned. All 4 pairs of words were recorded in the way decribed above at 10 s intervals , ensuring that each pair occurred 6 times with one word of the pair occurring 3 times on each channel. The word pairs were also arranged on the tape in such a way that half way through the test (after 12 presentations) the headphones could be reversed to eliminate any between channel asymmetries in the playback equipment during testing. A dichotic practice tape was then prepared to preceed the dichotic test , where each of the words used in the test would be presented to the subject via the headphones one at a time. On this tape, each of the 8 words was arranged in random order at 5 s intervals, to occur twice, making 16 practice trials in all. Although the original American tape did not include a dichotic practice trial, one was prepared in the same way from the dichotic pairs to standardize presentation of both tests . Line drawings had been prepared of objects representing all the words used in both dichotic tests and practice trials. Foil pictures depicting common objects were also prepared. Plates were prepared by arranging 2 pictures representing the dichotic choice in random sequence with 2 foil pictures, and photocopying the arrangement . This produced 40 response plates for each test (1 6 trial plates plus 24 dichotic plates), each depicting 2 dichotic choice words and 2 foils . Each picture was approximately 15 by 11 em and each photocopied plate appro ximately 21 by 30 em in size. An example of one of the response plates used is shown in Fig. 1.
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Figure 1
One of the picture pointing response plates used in the trials for the dichotic pair "cap-tap". Each plate included pictures of the dichotically presented pair and 2 fo il pictures as illustrated.
Subjects Three groups of subjects were selected to be tested on both dichotic tasks: 16 normal subjects (8 male, 8 female), 6 randomly selected stammerers (3 male , 3 female) and 6 randomly selected aphasic subjects (5 male , I female) . The age range of the 8 normal subjects was 19-60 years with a mean of 33 .25 years , and for the 8 female normal subjects the range was 18-65 years with a mean of 31.65 years. The age range of the male stammerers was 16-60 years with a mean of 33 years, and for the female stammerers the range was 15-45 years with a mean of 23.6 years. The age of the aphasic subjects was 38-68 years with a mean of 57.83 years . All subjects were administered the Edinburgh handedness questionnaire (Oldfield, 1971), and in the case of the normal and aphasic subjects all were classified as right-handed . Three of the stammerers were classified as left-handed. All subjects had normal hearing by self-report which was verified in the case of the aphasic subjects by audiometric assessment. Testing procedure All subjects listened to both the American- and British-English tests one after the other in a quiet acoustically treated room over noise excluding headphones. Half the subjects across all groups were played the American test first, and half the subjects were played the BritishEnglish test first . Before the practice tape all subjects were read the following instructions. You are going to hear some words through these headphones. After you hear each word, I will show you some pictures. There will be four pictures on each page. After you hear the word, I want you to decide which one it is by pointing to the picture of that word on the page. Remember, point to only one picture. Are you ready? Upon successful completion of the practice tape, the subject was then read the following instructions before administration of the dichotic test.
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You are now going to hear the same words through these headphones, but this time the words will be in pairs. This time there will be one word in your left ear and one word in your right ear. After you hear each pair of words I will again show you some pictures. There will be four pictures on each page. After you hear the pair of words, I want you to decide which word you are most sure of and point to the picture of that word on the page. Remember, point to only one picture - the one you are most sure of. Are you ready? Both tests were administered to all subjects in this way, and in no case did any subject in any group pick a foil picture. Responses to the tests were recorded on an appropriate record form . Results Details of the ear preference scores for the normal group on both dichotic tests are shown in Table 1, and similar details for the other 2 groups are shown in Table 2 . Laterality quotients (LQs) were determined in the usual way by the equation (R- L)/(R + L) x 100, where the right ear score ( R ES) minus the left ear score (LES) is divided by the RES plus the LES , multiplied by 100. In order to examine whether the British-English test would produce similar ear preference scores to the American original , the RES of all subjects in all 3 groups were subjected to Pearson product-moment correlation analysis. This produced an r of 0.9648 (p < 0.005 ; df= 26 ; one-tailed test). The RES of the 3 groups were taken separately and also subjected to Pearson product-moment correlation analysis . The normal group produced an r of 0 .8341 (p < 0.005; df = 14; one-tailed test), the aphasic group produced an r of 0.9447 (p < 0.01 ; df = 4 ; one-tailed test) , and the group of stammerers produ ced an r of 0 .8892 (p < 0.01; df = 4; one-tailed test) . These results would indicate that there is a high degree of correlation
Table 1 Details of the ear preference scores (EPS) for 16 normal subjects on the British-English (BE) and American-English (AE) dichotic word tests BE Subject I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
AE
Left ear
Right ear
LQ
Left ear
Right ear
LQ
Handedness
9 8 8 7 8 9 9 9 8 10 9 7 9 10 16 8
15 16 16 17 16 15 15 15 16 14 15 17 15 14 8 16
25 .0 33.3 33.3 41.6 33.3 25.0 25 .0 25.0 33 .3 16.6 25 .0 41.6 25.0 16 .6 -33.3* 33 .3
10 8 9 10 9 10 9 9 10 9 8 9 10 10 15 9
14 16 15 14 15 14 15 15 14 15 16 15 14 14 9 15
16.6 33.3 25 .0 16.6 25.0 16.6 25.0 25 .0 16 .6 25 .0 33 .3 25.0 16.6 16 .6 - 25.0* 25 .0
R R R R R R R R R R R R R R R R
*Indicates a left ear preference score(- ).
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380
Table 2 Details of the ear preference scores (EPS) for the 6 aphasic subjects and the 6 stammerers on the British-English (BE) and American-English (AE) dichotic word tests
BE Subject
Left ear
Right ear
Aphasics 1 2 3 4 5 6
16 23 17 10 6 13
8 1 7 14 18 11
Stammerers 1 10 2 14 3 14 4 9 5 6 6 8
14 10 10 15 18 16
AE LQ
Left ear
Right ear
LQ
- 33 .3* -91.6 -41.6 16.6 50.0 -8.3
19 24 16 10 10 13
5 0 8 14 14 11
-58.3 -100.0 -33.3 16.6 16 .6 -8 .3
R R
16.6 -16.6 -16.6 25.0 50.0 33 .3
10 13 16 8 8 10
14 11 8 16 16 14
16.6 -8.3 -33.3 33.3 33.3 16.6
R L L L L
Handedness
R R R R
R
*Indicates a left ear preference score(- ).
between the scores on both the British and American versions of the test, demonstrating that both tests produce very similar ear preference scores.
Test-retest reliability The reliability of the American test has been well established in the studies referred to above . In order to estimate the reliability of British-English version , 8 normal subjects (4 male, 4 female) were randomly selected and retested one week later. The RES on test and retest were analysed using the Pearson product-moment correlation, and an r of 0.8284 was obtained (p < 0.01; df = 6; one-tailed test) suggesting that the British-English tests is reliable on retest.
Phonetic effects The right ear preference observed in dichotic listening studies appears to be significantly dependent upon the different phonetic characteristics of the competing stimuli (StuddertKennedy & Shankweiler, 1970; Berlin & Cullen, 1977; Hayden et al., 1979), such that subjects tend to show a preference in their report for voiceless over voiced stops, for velars over alveolars and for velars and alveolars over bilabials. Berlin & McNeil (1976) have made the point that these phonetic effects are so strong that if a dichotic tape is not properly balanced with regard to phonetic preferences a consistent left ear preference could be obtained from a normal population. Sommers & Starkey (1977) have reported on the influences of the phonetic characteristics of the American test, and Fig. 2 presents a breakdown of the ear preference scores of the normal group on the British-English test. Strong phonetic effects can be observed in the word pairs "cat-bat" and "bun-gun". Particularly in the pair "catbat", where "cat" occurs at the left ear and "bat" at the right ear, it can be seen that the usual ear preference is not strong enough in the majority of subjects tested to overcome the phonetic effect of voiceless velar vs . voiced bilabial.
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Right
Left
(%) I
I
I
I
I
I
I
I
I
100 75 50 25 0 25 50 75 100
Figure 2
Ear preference scores of 16 normal subjects for the 8 pairs of dichotic stop vowel- stop words on the British-English test, expressed in percentages.
Discussion No discussion of the ear preference scores of the 2 pathological groups included in the trials will be presented here , as both groups are too small to make any serious contribution to the literature in this area. Both groups were included to examine the reliability of the test, and its suitability for use with subjects with communication disorders. However, a glance at Table 2 shows that 4 aphasic subjects demonstrated a left ear preference, considered by many to reflect a shift in lateralization for language processing, and 2 stammerers showed a left ear preference (both left-handed) . .Further discussion of these interesting areas of research can be found in the studies already cited. The results of the trial reported here would appear to demonstrate that a British-English version of a well established American-English dichotic word test produces reliable ear preference scores, despite the fact that it is shorter than the usual dichotic test-although the version of the American test used by Johnson et al. (1977) in their study of the ear preferences of aphasic subjects was just 30 items long. The picture-pointing response method- as the American work has already shown-makes the test particularly useful for obtaining reliable ear preference scores from patients with severe expressive problems, and the pre-test trial enables subjects with comprehension problems to be tested to determine whether they can manage the dichotic trial. An added advantage of the practice trial is that subjects are made aware of the choices that are open to them when they come to listen to the dichotic test , which helps to ensure that subjects do not perseverate on one word of a pair, and report that word each time the pair is dichotically presented. Pilot studies carried out without a trial tape revealed that the occasional subject
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(normal as well as aphasic subjects) would 'lock on' in this report that word each time the pair was pre sented. In conclusion, the results of the trials carried out and short, linguistically simple and meaningful dichotic word suitable for clinical use with subjects who have severe difficulties.
way to one word in a pair, and reported here suggest that the test described is reliable, and expressive and comprehension
The author would like to express his gratitude to Prof. Ronald K. Sommers for his help and for making available a copy of the American tape; to Drs John Johnson, William Brady and Dave Muller for help and encouragement ; D. T. Davies and Allen Jones for technical assistance, and to Prof. Stuart Dimond for advice and support. References Allen, J. (1980). Hemispherical specialization in stuttering. Paper presented at the Institute of Acoustics: Speech Group Meeting. Speech Production and Perception in the Disabled, London, February, 1980. Berlin, C. I. & Cullen, J. K. (1977). Acoustic problems in dichotic listening tasks. In Language Development and Neurological Theory S. J. Segalowitz and F. A. Gruber (Eds), New York: Academic Press. Berlin, C. I. & McNeil, M. R. (1976) Dichotic listening. In Contemporary Issues in Experimental Phonetics (N.J. Lass, Ed.) . New York: Academic Press. Brady, W. A. (1978). Auditory and visual response patterns of right and left temporo-parietal lobe damaged patients for linguistic and non-linguistic dichotic stimuli. Ph.D . Dissertation. Kent State University. Brady, J.P. & Berson, J. (1975). Stuttering, dichotic listening, and cerebral dominance. Archives of General Psychiatry, 32, 1449-1452. Broadbent, D. E. (1954). The role of auditory localization in attention and memory span. Journal of Experimental Psychology, 46, 365-372. Curry, F. K. W. and Gregory, H. H. (1969). The performance of stutters on dichotic listening tasks thought to reflect cerebral dominance, Journal of Speech and Hearing Research, 12, 73-82. Dorman, M. F . & Porter, R . J. (197 5). Hemispheric lateralization for speech perception in stutterers. Cortex, 11,181-185. Hayden, M. E., Kirstein, E. & Singh, S. (1979). Role of distinctive features in dichotic presentation of 21 English consonants.J.A.S.A. 65, 1039-1046. Helms, S. B. (1971)_ Verbal processing in language disordered children as measured by dichotic listening task. Unpublished Master's Thesis, University of Maine. Johnson, J.P., Sommers, R. K. & Weidner, W. E. (1977). Dichotic ear preference in aphasia. Journal of Speech and Hearing Research, 20, 116-129. Kimura, D. (1961a). Some effects of temporal-lobe damage on auditory perception. Canadian Journal of Psychology, 15, 156-165. Kimura, D. (1961b). Cerebral dominance and the perception of verbal stimuli. Canadian Journal of Psychology, 15, 166-171. Oldfield, R. C. (1971). The assessment of handedness: The Edinburgh inventory . Neuropsychologia, 9, 97 - 111. Oscar-Berman, M., Zurif, E. B. & Blumstein, S. (1975). Effects of unilateral brain damage on the processing of speech sounds. Brain and Language, 2, 345-355. Petek, A. A. (1979)_ Dichotic listening: the influence of word or syllable stimuli and response mode on ear effects. Unpublished Master's Thesis. Kent State University. Quinn, P. (1972). Stuttering, cerebral dominance, and the dichotic word test. Medical Journal of Australia, 2, 639-643. Rubino, C. A. (1972). A simple procedure for constructing dichotic listening tapes. Cortex, 8, 335 - 338. Schulhoff, C. & Goodglass, H. (1969) Dichotic listening, side of brain injury, and cerebral dominance. Neuropsychologia, 7, 149- 160. Sobotka, K. (1973). Neuropsychological and neurophysiological correlates of reading disability. Unpublished Master's Thesis. Louisiana State University. Sommers, R. K., Brady, W. A. & Moore, W. H. (1975). Dichotic ear preferences of stuttering children and adults. Perception and Motor Skills, 41, 931-938 . Sommers, R. K., Moore, W. H. Brady, W. A. & Jackson, P. (1972) . Cerebral speech dominance, laterality, and fine motor skills of articulatory defective children. Journal of Special Education, 10,5-14. Sommers, R. K. & Taylor, M. (1972). Cerebral speech dominance in language-disordered and normal children. Cortex, 8, 224-232. Sommers, R. K. & Starkey, K. L. (1977). Dichotic verbal processing in Down's syndrome children having
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qualitatively different speech and language skills. American Journal of Mental Deficiency, 82, 44-5 3. Sparks, R., Goodglass, H. & Nickel, B. (1970). Ipsilateral versus contralateral extinction in dichotic listening resulting from hemisphere lesions. Cortex, 8, 249 - 260. Starkey, K. (1974). The dichotic testing of young children: a new test for the speach and hearing impaired. Unpublished Master's Thesis. Kent State University. Studdert-Kennedy, M. & Shankweiler, D. (1970) . Hemispheric specialization for speech perception. J.A. S.A., 48, 579-594 . Thorndike, E. L. & Lorge, I. (1944). The Teacher 's Word Book of 30,000 Words. New York : Bureau of Publications, Teacher's College, Columbia University. Warren, R. L. & Crosson, B. (1978). Dichotic listening in Broca's and Wernickes's aphasia. Paper presented at Annual Meeting of th e American Speech and Hearing Association, San Francisco, California. Yeni-Komshian, G. H. & Gordon, J. F. (1974). The effect of memory load on the right ear advantage in dichotic listening. Brain and Language, 1, 375-381.
Dichotic listening with the communicatively impaired: results from trials of a short British- English dichotic word test Chris Code School of Speech Therapy, South Glamorgan Institute of Higher Education and University College, Cardiff, United Kingdom Received 20 July 1980
Abstract
The construction and testing of a new, short British-English dichotic word test, designed specifically for the communicatively impaired, is described. Sixteen normal, 6 aphasic and 6 stammering subjects were administered the test and a copy of the American-English original. Results show that the British-English version gives reliable ear preference scores, indicative of cere bralla teralization for language, and is suitable for use with subjects who have severe communication problems.
Introduction The ear preference shown on dichotic listening tasks is considered to be a well established indicator of lateral processing for language in the cerebral cortex. Kimura (196la, b) developed the dichotic listening paradigm from initial work by Broadbent (1954) and hundreds of empirical studies since have confirmed that when competing and different linguistic material is played simultaneously to separate ears, a right ear preference (REP) is observed with the great majority of dominantly right-handed normal subjects (Studdert-Kennedy & Shankweller, 1970). Berlin & McNiel (1976) have coded and analysed over 300 articles on dichotic listening. Kimura ( 196la) has proposed that the REP for verbal material (words, CV syllables, digits , nonsense words) reflects the superiority of the contralateral left hemisphere for speech processing, which is a function of the superior contralateral neural pathways between right ear and left temporal lobe . Dichotic listening studies have been carried out on subjects with diverse communication disorders, including aphasia (Schulhoff & Goodglass, 1969; Sparks et al,. 1970; Oscar-Berman, et al., 1975; Johnson et al., 1977; Brady, 1978; Warren & Crosson, 1978), stammering (Curry & Gregory, 1969; Quinn, 1972; Brady & Berson, 1975; Dorman & Porter, 1975 ; Sommers et al., 1975 ; Allen, 1980), language-disordered children (Helms, 1971 , Sommers & Taylor, 1972), articulation disorde red children (Sommers et al., 1972), dyslexic children (Sobotka, 1973) and Down's syndrome children (Sommers & Starkey , 1977). The relationships that are thought to exist between hemispheric asymmetries and language processing are central issues in neuropsychological research and experimental phonetics, and the studies referred to above reflect the growing importance of this area of research for speech pathology. Although the clinical application of dichotic listening is in an early stage of development, recent dichotic studies with aphasic subjects have indicated that a number 0095-4470/81/040375 + 09 $02.00/0
© 1981 Academic Press Inc. (London) Ltd.
376
C. Code
of prognostic factors may be related to apparent shifts in laterality in aphasic subjects, including severity of aphasia and time-since-onset of aphasia (Johnson et al., 1977). Dichotic studies with stammerers have produced conflicting results, with some studies producing evidence to support the hypothesis that stammerers may have incomplete or bilateral representation for speech (Curry & Gregory , 1969; Brady & Berson , 1975) and others failing to find differences in ear preference scores (Dolman & Porter, 1975). The co nflicting results may be due to research design differences , however, as the study by Brady & Berson (1975) suggests that there is a subset of stammerers who show left ear preference. Support for this view has been provided by Allen (1980) who has demonstrated that stammerers who are classified as severe produce higher left ear preference scores than stammerers who are classified as mild-moderate. The clinical application of the usual dichotic listening tests with patients who have severe communication problems has been difficult for a number of reasons. Dichotic listening tests are typically very long (up to 650 stimulus presentations in some cases), because as a general rule, the longer the test the more reliable the results . This kind of length is unacceptable for clinical use however, because it is time consuming and, more importantly, unsuitable for easily fatigued or distracted patients. So a test for clinical use should be as short as possible. Non-meaningful synthetic CV syllables or digits are often used in dichotic experiments and this clearly raises problems for subjects with impaired comprehension; therefore a dichotic test designed to measure the ear preferences of subjects with comprehension difficulties should consist of natural, high frequency, linguistically simple and meaningful words. Much has been made in the literature of the mode of presentation in dichotic tasks, with some tests requiring the subject to attend to 3 or more digits or words at each ear, and report as many as he can remember. Furthermore, there is evidence to suggest that an increased memory load increases right ear scores (Yeni-Komshian & Gordon, 1974). This method has serious drawbacks for testing the aphasic patient with poor auditory retention , for instance; consequently, a test suitable for use with such subjects should employ a single dichotic pair stimulus method . Finally, subjects in dichotic studies are usually asked to verbally report their choises, where this presents obvious difficulties for patients with expressive problems. Therefore , a dichotic test for use with patients who have severe expressive difficulties should provide a mode of response that is independent of verbal expression. A dichotic listening test for clinical use in speech pathology should be as short as possible, consisting of high frequency liguistically meaningul material, with an unambiguous mode of report that is independent of verbal expression and does not tax short-term auditory memory. Such a test, designed specifically for those with communication problems, has been developed and widely used in the United States (Starkey , 1974; Sommers eta!., 1975; Sommers & Starkey, 1977 ; Johnson eta!., 1975; Warren & Crosson , 1978 ; Brady, 1978 ; Petek , 1979), but due to differences in pronunciation between American- and British-English, is unsuitable for use with British subjects. The aim of the study reported here was to develop a BritishEnglish version of this successful and reliable dichotic test , and the purpose of this paper is to describe the test and report the results of trials carried out to examine its effectiveness and reliability in determining ear preferences.
Method Preparation of the dichotic listening tests A modified version of the method described by Rubino (1972) fo r making dichotic tapes was employed in preparing the British-English test.
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In order to make the necessary comparisons between the British and original American tests , both had to be as similar as possible. The version of the American test to be compared utilized 6 pairs of words , and when the non-rhyming pair (in British pronunciation) "balldoll ", and the diphthongal pair (in British pronunciation) "coat-goat" were removed , this left 4 word pairs. The remaining pairs were "top-pop , pig- dig, cat-bat, bun-gun" . The word pairs chosen for the British version were "dart- tart , cap- tap , gun-bun , cat-bat" , and the high frequency of these words was confirmed by the Thorndike- Lorge word count (Thorndike & Lorge , 1944). The unwanted word pairs were edited out of the American tape . The 8 words chosen for the British test were recorded in an acoustically treated room by a trained phonetician (RP) at 7! ips on a Ferrograph Series Seven tape recorder on fresh Memorex tape. The pairs to be presented dichotically were recorded 2 s apart, and a 10 s gap was left between each pair. The recording level was checked on the VU meter of the tape recorder, and each word was recorded between 80 and 100 dB. This tape was then spliced into 4loops, each bearing a pair of words 2 s apart. Two Tandberg mono tape recorders were arranged side by side in such a way that a chosen tape loop passed through both playback heads of the tape recorders . Both Tandbergs were then connected to the 2 separate channels of a Gould Advance OS4000 Digital Storage Oscilloscope to check for simultaneity and amplitude . The Tandbergs were both switched to playback , and gradually moved closer to each other or further apart until the playback onsets of the two words were seen to be within ± 2 ms simultaneity on the screen of the oscilloscope. The outputs of the Tandbergs were then connected to the 2 separate channels of a Revox A77 2-track stereo tape recorder loaded with fresh Memorex tape, and the amplitudes of the two words were again checked for equivalence by reference to the separate VU meters of the Revox. The 2 words were then recorded onto the separate channels of the Revox, and afterwards rechecked for simultaneity with the oscilloscope . It was decided , following findings by Johnson et al. (1977), to obtain a large amplitude of 90 ± 4dB at the ear, as larger dB levels tend to produce stronger right ear scores. The recording and playback heads of all the recording equipment used in the construction of the tape had previously been cleaned. All 4 pairs of words were recorded in the way decribed above at 10 s intervals , ensuring that each pair occurred 6 times with one word of the pair occurring 3 times on each channel. The word pairs were also arranged on the tape in such a way that half way through the test (after 12 presentations) the headphones could be reversed to eliminate any between channel asymmetries in the playback equipment during testing. A dichotic practice tape was then prepared to preceed the dichotic test , where each of the words used in the test would be presented to the subject via the headphones one at a time. On this tape, each of the 8 words was arranged in random order at 5 s intervals, to occur twice, making 16 practice trials in all. Although the original American tape did not include a dichotic practice trial, one was prepared in the same way from the dichotic pairs to standardize presentation of both tests . Line drawings had been prepared of objects representing all the words used in both dichotic tests and practice trials. Foil pictures depicting common objects were also prepared. Plates were prepared by arranging 2 pictures representing the dichotic choice in random sequence with 2 foil pictures, and photocopying the arrangement . This produced 40 response plates for each test (1 6 trial plates plus 24 dichotic plates), each depicting 2 dichotic choice words and 2 foils . Each picture was approximately 15 by 11 em and each photocopied plate appro ximately 21 by 30 em in size. An example of one of the response plates used is shown in Fig. 1.
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Figure 1
One of the picture pointing response plates used in the trials for the dichotic pair "cap-tap". Each plate included pictures of the dichotically presented pair and 2 fo il pictures as illustrated.
Subjects Three groups of subjects were selected to be tested on both dichotic tasks: 16 normal subjects (8 male, 8 female), 6 randomly selected stammerers (3 male , 3 female) and 6 randomly selected aphasic subjects (5 male , I female) . The age range of the 8 normal subjects was 19-60 years with a mean of 33 .25 years , and for the 8 female normal subjects the range was 18-65 years with a mean of 31.65 years. The age range of the male stammerers was 16-60 years with a mean of 33 years, and for the female stammerers the range was 15-45 years with a mean of 23.6 years. The age of the aphasic subjects was 38-68 years with a mean of 57.83 years . All subjects were administered the Edinburgh handedness questionnaire (Oldfield, 1971), and in the case of the normal and aphasic subjects all were classified as right-handed . Three of the stammerers were classified as left-handed. All subjects had normal hearing by self-report which was verified in the case of the aphasic subjects by audiometric assessment. Testing procedure All subjects listened to both the American- and British-English tests one after the other in a quiet acoustically treated room over noise excluding headphones. Half the subjects across all groups were played the American test first, and half the subjects were played the BritishEnglish test first . Before the practice tape all subjects were read the following instructions. You are going to hear some words through these headphones. After you hear each word, I will show you some pictures. There will be four pictures on each page. After you hear the word, I want you to decide which one it is by pointing to the picture of that word on the page. Remember, point to only one picture. Are you ready? Upon successful completion of the practice tape, the subject was then read the following instructions before administration of the dichotic test.
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You are now going to hear the same words through these headphones, but this time the words will be in pairs. This time there will be one word in your left ear and one word in your right ear. After you hear each pair of words I will again show you some pictures. There will be four pictures on each page. After you hear the pair of words, I want you to decide which word you are most sure of and point to the picture of that word on the page. Remember, point to only one picture - the one you are most sure of. Are you ready? Both tests were administered to all subjects in this way, and in no case did any subject in any group pick a foil picture. Responses to the tests were recorded on an appropriate record form . Results Details of the ear preference scores for the normal group on both dichotic tests are shown in Table 1, and similar details for the other 2 groups are shown in Table 2 . Laterality quotients (LQs) were determined in the usual way by the equation (R- L)/(R + L) x 100, where the right ear score ( R ES) minus the left ear score (LES) is divided by the RES plus the LES , multiplied by 100. In order to examine whether the British-English test would produce similar ear preference scores to the American original , the RES of all subjects in all 3 groups were subjected to Pearson product-moment correlation analysis. This produced an r of 0.9648 (p < 0.005 ; df= 26 ; one-tailed test). The RES of the 3 groups were taken separately and also subjected to Pearson product-moment correlation analysis . The normal group produced an r of 0 .8341 (p < 0.005; df = 14; one-tailed test), the aphasic group produced an r of 0.9447 (p < 0.01 ; df = 4 ; one-tailed test) , and the group of stammerers produ ced an r of 0 .8892 (p < 0.01; df = 4; one-tailed test) . These results would indicate that there is a high degree of correlation
Table 1 Details of the ear preference scores (EPS) for 16 normal subjects on the British-English (BE) and American-English (AE) dichotic word tests BE Subject I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
AE
Left ear
Right ear
LQ
Left ear
Right ear
LQ
Handedness
9 8 8 7 8 9 9 9 8 10 9 7 9 10 16 8
15 16 16 17 16 15 15 15 16 14 15 17 15 14 8 16
25 .0 33.3 33.3 41.6 33.3 25.0 25 .0 25.0 33 .3 16.6 25 .0 41.6 25.0 16 .6 -33.3* 33 .3
10 8 9 10 9 10 9 9 10 9 8 9 10 10 15 9
14 16 15 14 15 14 15 15 14 15 16 15 14 14 9 15
16.6 33.3 25 .0 16.6 25.0 16.6 25.0 25 .0 16 .6 25 .0 33 .3 25.0 16.6 16 .6 - 25.0* 25 .0
R R R R R R R R R R R R R R R R
*Indicates a left ear preference score(- ).
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Table 2 Details of the ear preference scores (EPS) for the 6 aphasic subjects and the 6 stammerers on the British-English (BE) and American-English (AE) dichotic word tests
BE Subject
Left ear
Right ear
Aphasics 1 2 3 4 5 6
16 23 17 10 6 13
8 1 7 14 18 11
Stammerers 1 10 2 14 3 14 4 9 5 6 6 8
14 10 10 15 18 16
AE LQ
Left ear
Right ear
LQ
- 33 .3* -91.6 -41.6 16.6 50.0 -8.3
19 24 16 10 10 13
5 0 8 14 14 11
-58.3 -100.0 -33.3 16.6 16 .6 -8 .3
R R
16.6 -16.6 -16.6 25.0 50.0 33 .3
10 13 16 8 8 10
14 11 8 16 16 14
16.6 -8.3 -33.3 33.3 33.3 16.6
R L L L L
Handedness
R R R R
R
*Indicates a left ear preference score(- ).
between the scores on both the British and American versions of the test, demonstrating that both tests produce very similar ear preference scores.
Test-retest reliability The reliability of the American test has been well established in the studies referred to above . In order to estimate the reliability of British-English version , 8 normal subjects (4 male, 4 female) were randomly selected and retested one week later. The RES on test and retest were analysed using the Pearson product-moment correlation, and an r of 0.8284 was obtained (p < 0.01; df = 6; one-tailed test) suggesting that the British-English tests is reliable on retest.
Phonetic effects The right ear preference observed in dichotic listening studies appears to be significantly dependent upon the different phonetic characteristics of the competing stimuli (StuddertKennedy & Shankweiler, 1970; Berlin & Cullen, 1977; Hayden et al., 1979), such that subjects tend to show a preference in their report for voiceless over voiced stops, for velars over alveolars and for velars and alveolars over bilabials. Berlin & McNeil (1976) have made the point that these phonetic effects are so strong that if a dichotic tape is not properly balanced with regard to phonetic preferences a consistent left ear preference could be obtained from a normal population. Sommers & Starkey (1977) have reported on the influences of the phonetic characteristics of the American test, and Fig. 2 presents a breakdown of the ear preference scores of the normal group on the British-English test. Strong phonetic effects can be observed in the word pairs "cat-bat" and "bun-gun". Particularly in the pair "catbat", where "cat" occurs at the left ear and "bat" at the right ear, it can be seen that the usual ear preference is not strong enough in the majority of subjects tested to overcome the phonetic effect of voiceless velar vs . voiced bilabial.
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Right
Left
(%) I
I
I
I
I
I
I
I
I
100 75 50 25 0 25 50 75 100
Figure 2
Ear preference scores of 16 normal subjects for the 8 pairs of dichotic stop vowel- stop words on the British-English test, expressed in percentages.
Discussion No discussion of the ear preference scores of the 2 pathological groups included in the trials will be presented here , as both groups are too small to make any serious contribution to the literature in this area. Both groups were included to examine the reliability of the test, and its suitability for use with subjects with communication disorders. However, a glance at Table 2 shows that 4 aphasic subjects demonstrated a left ear preference, considered by many to reflect a shift in lateralization for language processing, and 2 stammerers showed a left ear preference (both left-handed) . .Further discussion of these interesting areas of research can be found in the studies already cited. The results of the trial reported here would appear to demonstrate that a British-English version of a well established American-English dichotic word test produces reliable ear preference scores, despite the fact that it is shorter than the usual dichotic test-although the version of the American test used by Johnson et al. (1977) in their study of the ear preferences of aphasic subjects was just 30 items long. The picture-pointing response method- as the American work has already shown-makes the test particularly useful for obtaining reliable ear preference scores from patients with severe expressive problems, and the pre-test trial enables subjects with comprehension problems to be tested to determine whether they can manage the dichotic trial. An added advantage of the practice trial is that subjects are made aware of the choices that are open to them when they come to listen to the dichotic test , which helps to ensure that subjects do not perseverate on one word of a pair, and report that word each time the pair is dichotically presented. Pilot studies carried out without a trial tape revealed that the occasional subject
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(normal as well as aphasic subjects) would 'lock on' in this report that word each time the pair was pre sented. In conclusion, the results of the trials carried out and short, linguistically simple and meaningful dichotic word suitable for clinical use with subjects who have severe difficulties.
way to one word in a pair, and reported here suggest that the test described is reliable, and expressive and comprehension
The author would like to express his gratitude to Prof. Ronald K. Sommers for his help and for making available a copy of the American tape; to Drs John Johnson, William Brady and Dave Muller for help and encouragement ; D. T. Davies and Allen Jones for technical assistance, and to Prof. Stuart Dimond for advice and support. References Allen, J. (1980). Hemispherical specialization in stuttering. Paper presented at the Institute of Acoustics: Speech Group Meeting. Speech Production and Perception in the Disabled, London, February, 1980. Berlin, C. I. & Cullen, J. K. (1977). Acoustic problems in dichotic listening tasks. In Language Development and Neurological Theory S. J. Segalowitz and F. A. Gruber (Eds), New York: Academic Press. Berlin, C. I. & McNeil, M. R. (1976) Dichotic listening. In Contemporary Issues in Experimental Phonetics (N.J. Lass, Ed.) . New York: Academic Press. Brady, W. A. (1978). Auditory and visual response patterns of right and left temporo-parietal lobe damaged patients for linguistic and non-linguistic dichotic stimuli. Ph.D . Dissertation. Kent State University. Brady, J.P. & Berson, J. (1975). Stuttering, dichotic listening, and cerebral dominance. Archives of General Psychiatry, 32, 1449-1452. Broadbent, D. E. (1954). The role of auditory localization in attention and memory span. Journal of Experimental Psychology, 46, 365-372. Curry, F. K. W. and Gregory, H. H. (1969). The performance of stutters on dichotic listening tasks thought to reflect cerebral dominance, Journal of Speech and Hearing Research, 12, 73-82. Dorman, M. F . & Porter, R . J. (197 5). Hemispheric lateralization for speech perception in stutterers. Cortex, 11,181-185. Hayden, M. E., Kirstein, E. & Singh, S. (1979). Role of distinctive features in dichotic presentation of 21 English consonants.J.A.S.A. 65, 1039-1046. Helms, S. B. (1971)_ Verbal processing in language disordered children as measured by dichotic listening task. Unpublished Master's Thesis, University of Maine. Johnson, J.P., Sommers, R. K. & Weidner, W. E. (1977). Dichotic ear preference in aphasia. Journal of Speech and Hearing Research, 20, 116-129. Kimura, D. (1961a). Some effects of temporal-lobe damage on auditory perception. Canadian Journal of Psychology, 15, 156-165. Kimura, D. (1961b). Cerebral dominance and the perception of verbal stimuli. Canadian Journal of Psychology, 15, 166-171. Oldfield, R. C. (1971). The assessment of handedness: The Edinburgh inventory . Neuropsychologia, 9, 97 - 111. Oscar-Berman, M., Zurif, E. B. & Blumstein, S. (1975). Effects of unilateral brain damage on the processing of speech sounds. Brain and Language, 2, 345-355. Petek, A. A. (1979)_ Dichotic listening: the influence of word or syllable stimuli and response mode on ear effects. Unpublished Master's Thesis. Kent State University. Quinn, P. (1972). Stuttering, cerebral dominance, and the dichotic word test. Medical Journal of Australia, 2, 639-643. Rubino, C. A. (1972). A simple procedure for constructing dichotic listening tapes. Cortex, 8, 335 - 338. Schulhoff, C. & Goodglass, H. (1969) Dichotic listening, side of brain injury, and cerebral dominance. Neuropsychologia, 7, 149- 160. Sobotka, K. (1973). Neuropsychological and neurophysiological correlates of reading disability. Unpublished Master's Thesis. Louisiana State University. Sommers, R. K., Brady, W. A. & Moore, W. H. (1975). Dichotic ear preferences of stuttering children and adults. Perception and Motor Skills, 41, 931-938 . Sommers, R. K., Moore, W. H. Brady, W. A. & Jackson, P. (1972) . Cerebral speech dominance, laterality, and fine motor skills of articulatory defective children. Journal of Special Education, 10,5-14. Sommers, R. K. & Taylor, M. (1972). Cerebral speech dominance in language-disordered and normal children. Cortex, 8, 224-232. Sommers, R. K. & Starkey, K. L. (1977). Dichotic verbal processing in Down's syndrome children having
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qualitatively different speech and language skills. American Journal of Mental Deficiency, 82, 44-5 3. Sparks, R., Goodglass, H. & Nickel, B. (1970). Ipsilateral versus contralateral extinction in dichotic listening resulting from hemisphere lesions. Cortex, 8, 249 - 260. Starkey, K. (1974). The dichotic testing of young children: a new test for the speach and hearing impaired. Unpublished Master's Thesis. Kent State University. Studdert-Kennedy, M. & Shankweiler, D. (1970) . Hemispheric specialization for speech perception. J.A. S.A., 48, 579-594 . Thorndike, E. L. & Lorge, I. (1944). The Teacher 's Word Book of 30,000 Words. New York : Bureau of Publications, Teacher's College, Columbia University. Warren, R. L. & Crosson, B. (1978). Dichotic listening in Broca's and Wernickes's aphasia. Paper presented at Annual Meeting of th e American Speech and Hearing Association, San Francisco, California. Yeni-Komshian, G. H. & Gordon, J. F. (1974). The effect of memory load on the right ear advantage in dichotic listening. Brain and Language, 1, 375-381.