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Auditory perception of speech and speech sounds in recent and recovered cases of aphasia
BRAIN
AND
LANGUAGE
Auditory
4, 572-579 (1977)
Perception of Speech and Speech Sounds Recent and Recovered Cases of Aphasia TAPANIJAUHIAINEN Helsinki
E.N.T.
Hospital
in
ANDARTO NUUTILA and Suitia Rehabilitation
Center
Auditory perception of speech and speech sounds was examined in three groups of patients with cerebral damage in the dominant hemisphere. Two groups consisted of brain-injured war veterans, one group of patients with high-frequency hearing loss and the other, a group of patients with a flat hearing loss. The third group consisted of patients with recent cerebral infarcts due to vascular occlusion of the middle cerebral and internal carotid artery. Word and phoneme discrimination as well as phoneme confusions in incorrect responses were analyzed from conventional speech audiometry tests with bisyllabic Finnish words fed close to the speech reception threshold of the patient. The results were compared with those of a control group with no cerebral disorders and normal hearing. The speech discrimination scores of veterans with high-frequency hearing loss and patients with recent cerebral infarcts were some 15-20% lower than those of controls or veterans with flat hearing loss. Speech sound feature discrimination, analyzed in terms of place of articulation and distinctive features, was distorted especially in cases of recent cerebral infarcts, whereas general information transmission of phonemes was more impaired in patients with high-frequency hearing loss.
In central disorders of speech communication, auditory perceptual processing of speech and speech sounds can be impaired, due either to disturbance in the analysis of the incoming signals or to distortion of the internal perceptual or motor patterns used for comparisons, for coding or decoding purposes (Labrun, 1970; Carpenter & Rutherford, 1973; Rees, 1973). Of course, auditory speech sound perception is also impaired in cases of different degrees and types of peripheral hearing loss (Schultz, 1964), and, furthermore, aging affects speech perception. This investigation was designed to collect some data on the problem of whether auditory perception of speech and speech sounds is distorted in three groups of patients with old and recent lesions of the dominant cerebral hemisphere. METHODS Two of the groups consisted of brain-injured war veterans, the first group having flat hearing loss, the second having high-frequency hearing loss due to age and exposure to noise. Requests for reprints should be sent to Dr. Tapani Jauhiainen, Department of Audiology, Helsinki University E.N.T. Hospital, 00290 Helsinki 29, Finland. 572 Copyright All rights
0 1977 by Academic Ress. Inc. of reoroduction in anv form reserved.
,
573
SPEECH PERCEPTION IN APHASIA
These groups were examined at Suitia Rehabilitation Center. In the acute phase, 29-34 years earlier, all patients had had aphasic symptoms of at least of 1 month’s duration. The third group consisted of patients with recent occlusions of the internal carotid artery or middle cerebral artery of the dominant hemisphere. They were examined at the Department of Audiology, Helsinki University E.N.T. Hospital. All of them had clear aphasic symptoms during the period of auditory tests. Mean ages and times elapsed from injury as well as mean hearing levels and acoustic levels at which the speech discrimination test was conducted are given in Table 1. The table also includes data on the control group of 20 subjects with normal hearing and no case history of cerebral disease. The test-word material consisted of 180 bisyllabic Finnish words used in clinical speech audiometry and presented monaurally to the patients at the ear contralateral to the injured hemisphere, at a signal level somewhat above the speech reception threshold (Table 1). A low signal level was used in order to obtain incorrect response words which could be subjected to further analysis. The patients were asked to repeat the test words as they heard them. The responses, which were either correct, incorrect, or omitted, were analyzed for correct test-word discrimination, correct phoneme discrimination, use of phonemes in incorrect response words, as well as phoneme confusions (Jauhiainen, 1974).
RESULTS
AND DISCUSSION
Correct Test- Word Discrimination The results are shown in Table 1. Although a number of different factors are involved in speech perception measurements at low sensation levels, the results indicate that statistically significant differences could be found between controls and veterans with high-frequency hearing loss and between controls and patients with recent cerebral infarcts. No significant difference was observed between controls and veterans with flat hearing loss. TABLE 1 SPEECH DISCRIMINATION
VetCillS wth flat hearmg loss Vet.CrZinS with high frequency hearing loss Recent cerebral Infarcts Controlx
GROUPS OF PATIENTS
age lyeFIrs)
Mean tm~e elapsed from l”J”ry (years)
MGVl hearmg level (db ISO)
12
s4
30
37
12
57
30
I9 20
46 29
1 -
Mea,! GKWp
IN THREE
N
n Standard error of the mean. D The number m parentheses gives the extrapolated
Mean level of speech test (db SL)
WITH
CEREBRAL
Correct discrlmmatmn
LESIONS
Discrimination loss compared with controls
(RI Meall
SEM’
8
x3
2.1
3
37
I4
72
2.x
22
II 3
4 4 x I4
55 70 X6
2.5 3.0 1.6
I5
cw
-
-
value.
WI
574
JAUHIAINEN
AND NUUTILA
The discrimination loss of about 15-20% found in the present study is comparable with the results reported by Aten, Johns, and Darley (1971), who showed that patients with apraxia of speech had only about a 10% discrimination loss at a comfortable listening level. In other studies concerning cases of temporal lobe damage involving the contralateral auditory cortex, conventional speech audiometric tests revealed a discrimination loss of about IO%, unless time- or frequency-distorted speech tests were used (Korsan-Bengtsen, 1973). Since the peripheral hearing loss was the only essential difference between the two groups of veterans, it is likely that the high-frequency hearing loss was responsible for the discrimination loss in the second group. High-frequency loss is known to be combined with impairment of word discrimination (Carhart &Porter, 1971; Niemeyer, 1972; Aniansson, 1973). It can further be concluded that the veterans had almost recovered from their aphasic disorders. In comparison with the control series, there is, in addition, a marked difference in age. However, speech hearing loss which exceeds that predicted by pure tone hearing loss should not be evident until the sixth and seventh decades (Farrimond, 1962; Kirikae,
t
mean
mean
•l
front/labial
q half front /dental n back/palatal + velar FIG. 1. Mean discrimination, expressed as a percentage, for phonemes grouped according to the place of articulation, as a difference from the mean of all vowels (V) and consonants (C), respectively. Arabic numerals give the different groups of subjects: normal controls (I), veterans with flat hearing loss (2), veterans with high-frequency hearing loss (3), and recent cerebral infarcts (4).
SPEECH PERCEPTION IN APHASIA
575
0
Cl Compact/diffuse n grave/acute FIG. 2. Mean discrimination, expressed as a percentage, for phonemes grouped according to distinctive features, as a difference from the mean of all vowels (V) and consonants (C), respectively. Arabic numerals give the different groups of subjects: normal controls (l), veterans with flat hearing loss (2) veterans with high-frequency hearing loss (3) and recent cerebral infarcts (4).
Sato, and Shitara, 1963; Korsan-Bengtsen, 1968; Kirikae, 1969; Konig, 1969; Palva & Jokinen, 1970). The speech discrimination loss in the group of patients with recent occlusions of the cerebral arteries mentioned above can be attributed to the cerebral lesion itself rather than to age. In this group, too, the mean pure tone hearing loss was within normal limits. Further, in this group, correct word discrimination showed no correlation with the results of the Token test according to Spearman’s rank-order correlation, with the location of the vascular insult to the middle cerebral or internal carotid artery, with the severity of the EEG disturbance recorded, or with the quality of speech production of the patients. The last finding agrees with the results obtained by Shankweiler and Harris (1966) and Aten et al. (1971). An analysis of phoneme discrimination in the different groups of patients shows that, in all groups including the controls, vowels and consonants with back place of articulation are discriminated more easily than other phonemes (Fig. 1). This tendency, however, is especially prominent for consonants among patients with recent cerebral infarcts and in the group of veterans with high-frequency hearing loss. No clear tendencies could be seen when phoneme discrimination was analyzed in terms of
576
JAUHIAINEN
AND NUUTILA
manner of articulation. Vowels with the distinctive feature grave, /a/, /o/, and /u/, were also easily discriminated by patients with recent cerebral infarcts, since they are the back vowels (Fig. 2) and the same applies for consonants with compact features such as /k/. Actually, the controls discriminated diffuse consonants, /m/, In/, /p/, and It/, more easily than compact ones. These results only present tendencies obtained in phoneme discrimination, and no statistical analyses are given, because the results are calculated from meaningful bisyllabic words instead of logathomes. Use of Phonemes in Incorrect Response Words (Fig. 3) This showed that the veterans with flat hearing loss tended to use back vowels as substitutes more often than would be expected from their frequency of occurrence. Veterans with high-frequency hearing loss used vowels with half-front place of articulation instead, and front vowels dominated in incorrect responses in patients with recent cerebral infarcts. In the case of consonants (Fig. 3), veterans with flat hearing loss showed a pattern similar to that of controls, i.e., front and back place of articulation dominated in incorrect response words. Labial consonants, however,
[_I
front/labial
n
half back
I
front/dental / palatal
+velar
FIG. 3. Phoneme responses, expressed as a percentage, grouped according to the place of articulation as a difference from the predicted values, calculated from the frequency of occurrence of phonemes in Finnish. Arabic numerals give the different groups of subjects: normal controls (I), veterans with flat hearing loss (2), veterans with high-frequency hearing loss (3), and recent cerebral infarcts (4).
SPEECH PERCEPTION
IN APHASIA
577
were not used as frequently as in the other two groups of patients: those with recent cerebral infarcts and veterans with high-frequency hearing loss. Analysis of the use of consonants in incorrect response words in terms of manner of articulation showed a similar pattern in all three groups of patients as well as in controls, i.e., a tendency for the frequent use of plosives. Analysis of the use of phonemes in incorrect response words in terms of distinctive features revealed, in addition, that acute vowels, /e/, /iI, lyl, /a~/,/ii/, were dominant in contrast to the grave ones, /a/, /o/,/u/, especially in recent cerebral infarcts. Replacement of acute phonemes for grave ones also seems to be a characteristic feature of young children (Jakobson, 1941; Pollack & Rees, 1972). Thus, speech sound confusions in cerebral lesions may be a symptom of regression. Analysis ofphoneme confusions revealed no distinct differences as compared with normals in any of the three groups of patients, except for the veterans with high-frequency hearing loss who showed the following tendencies: In the case of consonants, a voiceless stop ltl replaced a voiced stop /d/, the converse being the case in controls. Tremulant lrl is replaced by stops lkl and It/ as well as by labiodental fricative Iv/, instead of by Ill or lhl as in controls. These differences may be due to the hearing loss component of this group. Among vowels, the veterans with high-frequency loss also showed substitutions due to difficulties in discriminating the second formant frequency differences, as for example between lul and lel. In the group of veterans with flat hearing loss, however, a certain tendency appears: demonstration of some difficulty in discrimination of the first formant frequency in confusions between /el and Ii/, for example. Otherwise, phoneme confusions parallel those observed in controls. Information
Transmitted
The information transmitted by vowels and consonants was calculated from phoneme confusion matrices according to Garner and Hake (1951) (Table 2). The greatest differences were found in the group of veterans with high-frequency hearing loss, whereas veterans with flat hearing loss were equal to the controls, and those with recent cerebral infarcts were close to the controls. Thus, the results indicate that the greatest loss in information transmission of phonemes is due to the loss of hearing at high frequencies rather than to cerebral damage causing aphasia. The recent cerebral infarcts had, however, a 15% discrimination loss compared to controls, when correct word discrimination is considered, whereas, according to phoneme information transmission analysis, the difference in bits was not as great. This discrepancy may be due to the disability of the
578
JAUHIAINEN
AND NUUTILA
TABLE 2 INFORMATION
TRANSMISSION BY PHONEMES THREE GROUPS OF PATIENTS
IN SPEECH SOUND PERCEPTION WITH CEREBRAL LESIONS
Information transmission (bits) Group Veterans with flat hearing loss Veterans with high frequency hearing loss Recent cerebral infarcts
TESTS ON
Loss of information transmission compared with controls (bits)
Vowels
Consonants
Vowels
Consonants
2’.240
2.400
110
-200”
2.080
1.660
640
1.140
1.480
1.300
120
350
(1The controls showed somewhat poorer information transmission than the group of patients.
patients with recent cerebral infarcts to apply their intrinsic redundancies for language perception and to formulate meaningful words of correctly perceived phonemic units, i.e., their actual dysphasic symptom. CONCLUSIONS
The present studies on word and phoneme discrimination in three groups of patients with cerebral damage and hearing loss show that a highfrequency hearing loss and a recent cerebral infarct are factors which may distort word and phoneme perception and cause loss of transmission of information; the high-frequency loss appears to impair auditory word and phoneme perception more than cerebral damage only. The results obtained also show that minute disorders of auditory speech and speech sound perception can be recognized in normal speech audiometry tests close to the speech reception threshold, when detailed analysis of word and phoneme discrimination is undertaken in terms of place of articulation and distinctive features (Lafon, 1958). Phoneme discrimination impairment and the altered frequency distribution of phonemes used may reflect that internal auditory perceptual patterns of different phonemes are distorted and their intrinsic probabilities are changed as a result of cerebral lesion and high-frequency hearing loss, or that perceptual analysis of incoming signals is so distorted that errors of phoneme discrimination result. Comparing the high-frequency hearing loss and the cerebral damage components of the present material to each other, the
579
SPEECH PERCEPTION IN APHASIA
high-frequency loss seems to cause greater impairment of phoneme information transmission, whereas cerebral damage seems to distort auditory speech sound-feature reception to a greater extent. REFERENCES Aniansson, G. 1973. Methods for assessing high frequency hearing loss in every-day listening situations. Acta Ofo-Latyngologica Supplementurn, 311. Aten, J. L., Johns, D. F.. & Darley, F. L. 1971. Auditory perception of sequenced words in apraxia of speech. Journal of Speech and Hearing Research 14, 131-43. Carhart, K., & Porter, L. S. 1971. Audiometric configurations and prediction of threshold for spondees. Journal of Speech and Hearing Research 14,486-495. Carpenter, R. L., & Rutherford, D. R. 1973. Acoustic cue discrimination in adult aphasia. Journal
of Speech and Hearing
Research
16,534-544.
Farrimond, T. 1962. Factors influencing auditory perception of pure tones and speech. Journal of Speech and Hearing Research 5, 194-204. Garner, W. R., & Hake, H. W. 1951. The amount of information in absolute judgment. Psychological
Review
58, 446-459.
Jakobson, R. 1941. Kindersprache, Aphasie und allgemeine Lautgesetze. Den Haag: Mouton. Jauhiainen, T. 1974.An experimental study of the auditory perception of isolated bi-syllabic Finnish words. Unpublished dissertation, Helsinki. Kirikae, I. 1969. Auditory function in advanced age with reference to histological changes in the central auditory system. International Audiology 8, 221-230. Kirikae, I., Sato, T., & Shitara, T. 1963. A study of hearing in advanced age. International Audiology 2, 173- 175. Konig, E. 1969. Audiological tests in presbyacusis. International Audiology 8, 240-259. Korsan-Bengtsen, M. 1%8. The diagnosis of hearing loss in old people. In Liden (Ed.), Geriatric Audiology. Stockholm: Almqvist & Wiksell. Korsan-Bengtsen, M. 1973. Distorted speech audiometry. Acta Oto-Laryngologica Supplementum, 310. Labrun, Y. 1970. Sind die aphatischen Lautstorungen gesetzmassig? In A. Leischner (Ed.). Die Rehabilitation der Aphasie in den romanischen Liindern Aphasieforschung. Stuttgart: G. Thieme. Lafon, J.-C. 1958. Le test phonetique. Paris: Comp. Franc. d’Audiol.
nebst Beitriige
zur
Niemeyer, W. 1972. Studies on speech perception in dissociated hearing loss. In Fant (Ed.), Speech communication ability and profound deafness. International Symposium Stockholm, 1970. Palva, A., & Jokinen, K. 1970. Presbyacusis V: Filtered speech test. Acta Oto-Laryngologica
Supplementurn
70, 232-241.
Pollack, E., & Rees, N. S. 1972. Disorders of articulation: Some critical applications of distinctive feature theory. Journal of Speech and Hearing Disorders 37, 451-461. Rees, N. S. 1973. Auditory processing factors in language disorders: The view from Procustes’ bed. Journal of Speech and Hearing Disorders 38, 304-315. Schultz, M. C. 1964. Suggested improvements in speech discrimination testing. Journal of Auditory Research 4, l- 14. Shankweiler, D., & Harris, K. S. 1966. An experimental approach to the problem of articulation in aphasia. Cortex 2, 277-292.
AND
LANGUAGE
Auditory
4, 572-579 (1977)
Perception of Speech and Speech Sounds Recent and Recovered Cases of Aphasia TAPANIJAUHIAINEN Helsinki
E.N.T.
Hospital
in
ANDARTO NUUTILA and Suitia Rehabilitation
Center
Auditory perception of speech and speech sounds was examined in three groups of patients with cerebral damage in the dominant hemisphere. Two groups consisted of brain-injured war veterans, one group of patients with high-frequency hearing loss and the other, a group of patients with a flat hearing loss. The third group consisted of patients with recent cerebral infarcts due to vascular occlusion of the middle cerebral and internal carotid artery. Word and phoneme discrimination as well as phoneme confusions in incorrect responses were analyzed from conventional speech audiometry tests with bisyllabic Finnish words fed close to the speech reception threshold of the patient. The results were compared with those of a control group with no cerebral disorders and normal hearing. The speech discrimination scores of veterans with high-frequency hearing loss and patients with recent cerebral infarcts were some 15-20% lower than those of controls or veterans with flat hearing loss. Speech sound feature discrimination, analyzed in terms of place of articulation and distinctive features, was distorted especially in cases of recent cerebral infarcts, whereas general information transmission of phonemes was more impaired in patients with high-frequency hearing loss.
In central disorders of speech communication, auditory perceptual processing of speech and speech sounds can be impaired, due either to disturbance in the analysis of the incoming signals or to distortion of the internal perceptual or motor patterns used for comparisons, for coding or decoding purposes (Labrun, 1970; Carpenter & Rutherford, 1973; Rees, 1973). Of course, auditory speech sound perception is also impaired in cases of different degrees and types of peripheral hearing loss (Schultz, 1964), and, furthermore, aging affects speech perception. This investigation was designed to collect some data on the problem of whether auditory perception of speech and speech sounds is distorted in three groups of patients with old and recent lesions of the dominant cerebral hemisphere. METHODS Two of the groups consisted of brain-injured war veterans, the first group having flat hearing loss, the second having high-frequency hearing loss due to age and exposure to noise. Requests for reprints should be sent to Dr. Tapani Jauhiainen, Department of Audiology, Helsinki University E.N.T. Hospital, 00290 Helsinki 29, Finland. 572 Copyright All rights
0 1977 by Academic Ress. Inc. of reoroduction in anv form reserved.
,
573
SPEECH PERCEPTION IN APHASIA
These groups were examined at Suitia Rehabilitation Center. In the acute phase, 29-34 years earlier, all patients had had aphasic symptoms of at least of 1 month’s duration. The third group consisted of patients with recent occlusions of the internal carotid artery or middle cerebral artery of the dominant hemisphere. They were examined at the Department of Audiology, Helsinki University E.N.T. Hospital. All of them had clear aphasic symptoms during the period of auditory tests. Mean ages and times elapsed from injury as well as mean hearing levels and acoustic levels at which the speech discrimination test was conducted are given in Table 1. The table also includes data on the control group of 20 subjects with normal hearing and no case history of cerebral disease. The test-word material consisted of 180 bisyllabic Finnish words used in clinical speech audiometry and presented monaurally to the patients at the ear contralateral to the injured hemisphere, at a signal level somewhat above the speech reception threshold (Table 1). A low signal level was used in order to obtain incorrect response words which could be subjected to further analysis. The patients were asked to repeat the test words as they heard them. The responses, which were either correct, incorrect, or omitted, were analyzed for correct test-word discrimination, correct phoneme discrimination, use of phonemes in incorrect response words, as well as phoneme confusions (Jauhiainen, 1974).
RESULTS
AND DISCUSSION
Correct Test- Word Discrimination The results are shown in Table 1. Although a number of different factors are involved in speech perception measurements at low sensation levels, the results indicate that statistically significant differences could be found between controls and veterans with high-frequency hearing loss and between controls and patients with recent cerebral infarcts. No significant difference was observed between controls and veterans with flat hearing loss. TABLE 1 SPEECH DISCRIMINATION
VetCillS wth flat hearmg loss Vet.CrZinS with high frequency hearing loss Recent cerebral Infarcts Controlx
GROUPS OF PATIENTS
age lyeFIrs)
Mean tm~e elapsed from l”J”ry (years)
MGVl hearmg level (db ISO)
12
s4
30
37
12
57
30
I9 20
46 29
1 -
Mea,! GKWp
IN THREE
N
n Standard error of the mean. D The number m parentheses gives the extrapolated
Mean level of speech test (db SL)
WITH
CEREBRAL
Correct discrlmmatmn
LESIONS
Discrimination loss compared with controls
(RI Meall
SEM’
8
x3
2.1
3
37
I4
72
2.x
22
II 3
4 4 x I4
55 70 X6
2.5 3.0 1.6
I5
cw
-
-
value.
WI
574
JAUHIAINEN
AND NUUTILA
The discrimination loss of about 15-20% found in the present study is comparable with the results reported by Aten, Johns, and Darley (1971), who showed that patients with apraxia of speech had only about a 10% discrimination loss at a comfortable listening level. In other studies concerning cases of temporal lobe damage involving the contralateral auditory cortex, conventional speech audiometric tests revealed a discrimination loss of about IO%, unless time- or frequency-distorted speech tests were used (Korsan-Bengtsen, 1973). Since the peripheral hearing loss was the only essential difference between the two groups of veterans, it is likely that the high-frequency hearing loss was responsible for the discrimination loss in the second group. High-frequency loss is known to be combined with impairment of word discrimination (Carhart &Porter, 1971; Niemeyer, 1972; Aniansson, 1973). It can further be concluded that the veterans had almost recovered from their aphasic disorders. In comparison with the control series, there is, in addition, a marked difference in age. However, speech hearing loss which exceeds that predicted by pure tone hearing loss should not be evident until the sixth and seventh decades (Farrimond, 1962; Kirikae,
t
mean
mean
•l
front/labial
q half front /dental n back/palatal + velar FIG. 1. Mean discrimination, expressed as a percentage, for phonemes grouped according to the place of articulation, as a difference from the mean of all vowels (V) and consonants (C), respectively. Arabic numerals give the different groups of subjects: normal controls (I), veterans with flat hearing loss (2), veterans with high-frequency hearing loss (3), and recent cerebral infarcts (4).
SPEECH PERCEPTION IN APHASIA
575
0
Cl Compact/diffuse n grave/acute FIG. 2. Mean discrimination, expressed as a percentage, for phonemes grouped according to distinctive features, as a difference from the mean of all vowels (V) and consonants (C), respectively. Arabic numerals give the different groups of subjects: normal controls (l), veterans with flat hearing loss (2) veterans with high-frequency hearing loss (3) and recent cerebral infarcts (4).
Sato, and Shitara, 1963; Korsan-Bengtsen, 1968; Kirikae, 1969; Konig, 1969; Palva & Jokinen, 1970). The speech discrimination loss in the group of patients with recent occlusions of the cerebral arteries mentioned above can be attributed to the cerebral lesion itself rather than to age. In this group, too, the mean pure tone hearing loss was within normal limits. Further, in this group, correct word discrimination showed no correlation with the results of the Token test according to Spearman’s rank-order correlation, with the location of the vascular insult to the middle cerebral or internal carotid artery, with the severity of the EEG disturbance recorded, or with the quality of speech production of the patients. The last finding agrees with the results obtained by Shankweiler and Harris (1966) and Aten et al. (1971). An analysis of phoneme discrimination in the different groups of patients shows that, in all groups including the controls, vowels and consonants with back place of articulation are discriminated more easily than other phonemes (Fig. 1). This tendency, however, is especially prominent for consonants among patients with recent cerebral infarcts and in the group of veterans with high-frequency hearing loss. No clear tendencies could be seen when phoneme discrimination was analyzed in terms of
576
JAUHIAINEN
AND NUUTILA
manner of articulation. Vowels with the distinctive feature grave, /a/, /o/, and /u/, were also easily discriminated by patients with recent cerebral infarcts, since they are the back vowels (Fig. 2) and the same applies for consonants with compact features such as /k/. Actually, the controls discriminated diffuse consonants, /m/, In/, /p/, and It/, more easily than compact ones. These results only present tendencies obtained in phoneme discrimination, and no statistical analyses are given, because the results are calculated from meaningful bisyllabic words instead of logathomes. Use of Phonemes in Incorrect Response Words (Fig. 3) This showed that the veterans with flat hearing loss tended to use back vowels as substitutes more often than would be expected from their frequency of occurrence. Veterans with high-frequency hearing loss used vowels with half-front place of articulation instead, and front vowels dominated in incorrect responses in patients with recent cerebral infarcts. In the case of consonants (Fig. 3), veterans with flat hearing loss showed a pattern similar to that of controls, i.e., front and back place of articulation dominated in incorrect response words. Labial consonants, however,
[_I
front/labial
n
half back
I
front/dental / palatal
+velar
FIG. 3. Phoneme responses, expressed as a percentage, grouped according to the place of articulation as a difference from the predicted values, calculated from the frequency of occurrence of phonemes in Finnish. Arabic numerals give the different groups of subjects: normal controls (I), veterans with flat hearing loss (2), veterans with high-frequency hearing loss (3), and recent cerebral infarcts (4).
SPEECH PERCEPTION
IN APHASIA
577
were not used as frequently as in the other two groups of patients: those with recent cerebral infarcts and veterans with high-frequency hearing loss. Analysis of the use of consonants in incorrect response words in terms of manner of articulation showed a similar pattern in all three groups of patients as well as in controls, i.e., a tendency for the frequent use of plosives. Analysis of the use of phonemes in incorrect response words in terms of distinctive features revealed, in addition, that acute vowels, /e/, /iI, lyl, /a~/,/ii/, were dominant in contrast to the grave ones, /a/, /o/,/u/, especially in recent cerebral infarcts. Replacement of acute phonemes for grave ones also seems to be a characteristic feature of young children (Jakobson, 1941; Pollack & Rees, 1972). Thus, speech sound confusions in cerebral lesions may be a symptom of regression. Analysis ofphoneme confusions revealed no distinct differences as compared with normals in any of the three groups of patients, except for the veterans with high-frequency hearing loss who showed the following tendencies: In the case of consonants, a voiceless stop ltl replaced a voiced stop /d/, the converse being the case in controls. Tremulant lrl is replaced by stops lkl and It/ as well as by labiodental fricative Iv/, instead of by Ill or lhl as in controls. These differences may be due to the hearing loss component of this group. Among vowels, the veterans with high-frequency loss also showed substitutions due to difficulties in discriminating the second formant frequency differences, as for example between lul and lel. In the group of veterans with flat hearing loss, however, a certain tendency appears: demonstration of some difficulty in discrimination of the first formant frequency in confusions between /el and Ii/, for example. Otherwise, phoneme confusions parallel those observed in controls. Information
Transmitted
The information transmitted by vowels and consonants was calculated from phoneme confusion matrices according to Garner and Hake (1951) (Table 2). The greatest differences were found in the group of veterans with high-frequency hearing loss, whereas veterans with flat hearing loss were equal to the controls, and those with recent cerebral infarcts were close to the controls. Thus, the results indicate that the greatest loss in information transmission of phonemes is due to the loss of hearing at high frequencies rather than to cerebral damage causing aphasia. The recent cerebral infarcts had, however, a 15% discrimination loss compared to controls, when correct word discrimination is considered, whereas, according to phoneme information transmission analysis, the difference in bits was not as great. This discrepancy may be due to the disability of the
578
JAUHIAINEN
AND NUUTILA
TABLE 2 INFORMATION
TRANSMISSION BY PHONEMES THREE GROUPS OF PATIENTS
IN SPEECH SOUND PERCEPTION WITH CEREBRAL LESIONS
Information transmission (bits) Group Veterans with flat hearing loss Veterans with high frequency hearing loss Recent cerebral infarcts
TESTS ON
Loss of information transmission compared with controls (bits)
Vowels
Consonants
Vowels
Consonants
2’.240
2.400
110
-200”
2.080
1.660
640
1.140
1.480
1.300
120
350
(1The controls showed somewhat poorer information transmission than the group of patients.
patients with recent cerebral infarcts to apply their intrinsic redundancies for language perception and to formulate meaningful words of correctly perceived phonemic units, i.e., their actual dysphasic symptom. CONCLUSIONS
The present studies on word and phoneme discrimination in three groups of patients with cerebral damage and hearing loss show that a highfrequency hearing loss and a recent cerebral infarct are factors which may distort word and phoneme perception and cause loss of transmission of information; the high-frequency loss appears to impair auditory word and phoneme perception more than cerebral damage only. The results obtained also show that minute disorders of auditory speech and speech sound perception can be recognized in normal speech audiometry tests close to the speech reception threshold, when detailed analysis of word and phoneme discrimination is undertaken in terms of place of articulation and distinctive features (Lafon, 1958). Phoneme discrimination impairment and the altered frequency distribution of phonemes used may reflect that internal auditory perceptual patterns of different phonemes are distorted and their intrinsic probabilities are changed as a result of cerebral lesion and high-frequency hearing loss, or that perceptual analysis of incoming signals is so distorted that errors of phoneme discrimination result. Comparing the high-frequency hearing loss and the cerebral damage components of the present material to each other, the
579
SPEECH PERCEPTION IN APHASIA
high-frequency loss seems to cause greater impairment of phoneme information transmission, whereas cerebral damage seems to distort auditory speech sound-feature reception to a greater extent. REFERENCES Aniansson, G. 1973. Methods for assessing high frequency hearing loss in every-day listening situations. Acta Ofo-Latyngologica Supplementurn, 311. Aten, J. L., Johns, D. F.. & Darley, F. L. 1971. Auditory perception of sequenced words in apraxia of speech. Journal of Speech and Hearing Research 14, 131-43. Carhart, K., & Porter, L. S. 1971. Audiometric configurations and prediction of threshold for spondees. Journal of Speech and Hearing Research 14,486-495. Carpenter, R. L., & Rutherford, D. R. 1973. Acoustic cue discrimination in adult aphasia. Journal
of Speech and Hearing
Research
16,534-544.
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