Speech discrimination tests in investigation of sensorineural hearing loss By VILIJA M. PRIEDE and R. R. A. COLES (Southampton) ALTHOUGH speech tests in the form of live-voice tests must be the oldest technique of all for detection and estimation of deafness and VIII nerve lesions, comparatively little progress has been made until quite recently in the quantitative application of speech audiometry to the differential diagnosis of the type and site of disorder causing sensorineural hearing loss. References to the potential use of speech tests of hearing for this purpose are to be found in a number of published works, for example the following statement by Owens (1971) '. . . extremely low speech discrimination scores may provide a strong indication of retrocochlear involvement, especially in cases where pure-tone impairment is relatively mild.' However, a satisfactory criterion denning the values beyond which speech discrimination is reduced in such cases was not available. Jerger and Jerger (1971) stated that the exact shape of the performance-intensity function for PB words, 'would appear to have potential
2>? > where
diagnostic significance.' They used an index of — ^ max
PBjjjj,, is the lowest discrimination score measured at levels above the PBmax up to n o dB, if tolerated. This index, when plotted as a function of the average pure-tone threshold, gave a complete separation between the two diagnostic categories in a sample consisting of 41 cochlear cases and 10 VIII nerve tumours. Calculation of the index relies on the performance-intensity curve showing a substantial reduction of speech discrimination scores at higher intensity levels, which Jerger et al. first described in 1966 and subsequently referred to as the 'rollover phenomenon'. However, Jerger and Jerger (1971) admitted that their sample was rather limited and that 'the rollover effect is somewhat confused and conflicting'. To illustrate this uncertainty, they quoted nine references where the rollover has been reported as occurring in various diagnostic categories or not at all. More recently, Hood and Poole (1971) failed to find much distinction in the shape of the speech discrimination curves between patients with Meniere's disorder and those with VIII nerve lesions; the rollover effect occurred in their sample in both diagnostic categories. Moreover, the present authors' experience, using PB words over much the same intensity 1081
V. M. Priede and R. R. A. Coles range, is that the rollover effect does not provide a satisfactory distinction between the majority of sensory and neural cases. A preliminary study of the speech audiograms of 235 ears with acquired sensorineural hearing loss tested in our own clinics was made by Priede in 1971. The optimal discrimination scores (ODS, a measure similar to the PB max used by Jerger et al., 1966) were correlated with the average puretone thresholds calculated according to a formula based on that of Fletcher (1950) {vide infra). The results showed good separation of the two diagnostic categories, the primary cochlear lesions from the primary neural lesions. A criterion line, at that time drawn 'by eye', indicated only a 10% overlap. A further analysis of ODS values was carried out by Priede in 1973 on a larger sample comprising 327 ears with cochlear disorders and 50 ears with neural ones. A criterion line derived from the lower 10 percentile ODS values in cochlear cases was found to exclude 90% of neural cases. The line itself was essentially the same as that of the 1971 preliminary criterion. Another principal measurement of great potential value is the 'speech threshold' (or HPLE, Half-Peak Level Elevation, vide infra). Additional to the clinical series noted above, Priede (1973) compared HPLE values of 107 ears with non-organic hearing loss with 448 having cochlear disorder. This confirmed our earlier observations (Coles and Priede, 1971) of the great value of speech audiometry in detecting the presence of non-organic hearing loss and, often, of measuring the real hearing loss. This paper presents these analyses in condensed form, draws conclusions as to the value of the diagnostic criteria derived which are supported by further years of clinical experience with them, and indicates the means by which they may be put into clinical application. Methods and terminology
An important objective in any clinical test is to obtain as much diagnostic information as possible within as short a time as possible. Considerable effort has been given in our clinic over the last decade to develop a speech audiometric method which combines sufficient reliability with a clinically acceptable test duration. The method which has ultimately been derived is outlined in Appendix 1, and is similar to that used earlier in obtaining the clinical data presented in this paper. Phonetically-balanced word lists, scored by phonemes, were used to measure both the 'speech threshold' and the optimal discrimination score (ODS). The conventional term Speech Reception Threshold is not used here, since it really refers to the level at which 50% of spondee words are correctly recognized. Not only are PB words often used instead of spondees, but also in many cases of sensorineural hearing loss the discrimination score does not even reach 50%: nevertheless, most of those patients do have a threshold for recognition of speech. 1082
Speech discrimination tests Therefore, it was decided (Coles et al., 1973) that a more appropriate term would be the Half-Peak Level (HPL). The HPL is estimated from the speech discrimination curve* as the (nominal) intensity level at which the speech discrimination would be half of that corresponding to the peak of the curve. The Half-Peak Level Elevation (HPLE) is the difference between the measured HPL and the normal HPL for the particular test material and equipment. The ODS is the score specially measured at the intensity level corresponding to the peak of the speech discrimination curve**. Such a method of measurement avoids the errors, due to use of an incorrect intensity, which frequently occur when the test level is at some fixed value, e.g. 40 dB above an estimated or measured 'speech threshold'. The terminology and measurements relating to the method of speech audiometry described here are illustrated in Figure 1. The tape-recorded Ampliation of speech material ( dial readings in decibels )
1 E
0
m
10
20
30
20 30 40 Corrected pure-tone average (dB) Primorilv eochleor le.ion, ( N - 3 2 7 eon in 208 potient.) Confirmed VIII nerve tumon ( N = ! ? . • early cosei with possible inadequacy of masking) Other VIII nerve lesions ( N - 9 ) Vascular VIII nerve lesions ( N = 8) Unclassified VIII nerve lesions( N « 14) 10
• 0 a V A
= 5
|
P» intt p^nt
FIG. 3. Relationship between pure-tone thresholds and speech discrimination scores in patients with cochlear and VIII nerve lesions. Note: The above data refer to use of one of Fry's PB word lists. For three AB(S) word lists the criterion line is at 91% (instead of 93%) at o db, at 54% (instead of 59%) at 50 dB, and at 42% (instead of 47%) at 70 dB. (The values for AB(S) lists were derived from data on 60 cochlear cases tested with both speech materials).
These results are in good agreement with the general clinical experience that speech discrimination is particularly poor in neural cases. It is evident that the speech discrimination loss is proportional to the hearing loss in cochlear cases, whereas it is disproportionately great in the neural cases. Whilst there is not an absolute separation between the two groups, criterion line comprising the goth percentile curve for the cochlear cases approximates to the 10th percentile curve for the neural cases. Thus go% of the results from patients with sensory disorders came above this line and a similar proportion of the results from neural cases lay below it. 1086
Speech discrimination tests Test/retest reliability studies of the ODS in 10 cochlear cases (tested with single ioo-phoneme word lists on five separate occasions) showed that the intra-patient standard deviation is about 2 to 3%, the highest individual standard deviation being 6% (Priede, 1973). This might account for some of the overlap between the two groups, but more probably it is additional to a true diagnostic overlap. Therefore, for practical purposes, the diagnostic significance of an individual result occurring on or near the criterion line has to be interpreted with caution, taking account of the limitation of test accuracy and the overlap between the two groups. It should also be recalled that an VIII nerve lesion causing a disproportionally great degree of speech discrimination loss may also cause, secondarily, a cochlear lesion resulting in a marked degree of recruitment. Conversely, some neural cases with borderline speech scores have markedly neural patterns of loudness growth, i.e. with no recruitment or rather little recruitment. Measurements of speech discrimination and of recruitment must, therefore, be regarded as complementary rather than as alternatives. C. Relationships between pure-tone and speech thresholds in patients non-organic hearing loss
with
In Figure 2 it can be seen that these threshold measurements are within ±10 dB of one another in about 90% of cases with end-organ disorder; only 10% have pure-tone thresholds that are more than 10 dB greater than the HPLE, and then by up to 20 dB only in nearly all instances. Neural cases tend to err in the other direction. The majority of conductive cases would be expected to be within the i i o dB limits. The non-organic cases are shown in Figure 4, and it can be seen that the ±10 dB band includes only 18% of the 107 results, whilst in 58% the pure-tone thresholds are more than 20 dB greater than the HPLE. Thus, the value of speech audiometry in revealing such cases, noted previously by Coles and Priede (1971), is confirmed by this larger series. Once non-organic hearing loss is suspected, the method of applying speech audiometry is best changed to that of Fournier (1956). In this, a word list, (a), is presented about 20 bB below the lowest level at which a good discrimination score has previously been achieved. A low score is likely to result, and the next list, (b), is presented at a level 10 or 15 dB higher than list (a). If a reasonable score then results, the next list, (c), is presented about 20 dB below that of list (b). A further list, (d), is then presented 10 or 15 dB above the level of list (c); and so on. This confuses the patient in his self-set task of maintaining an imaginary threshold and cajoles him into responses at progressively lower intensities. This takes much longer to perform than ordinary speech audiometry, but does not take as long as electrophysiological tests and yields a more relevant measure of auditory function for general clinical purposes. The time is 1087
V. M. Priede and R. R. A. Coles
!
well spent since further subjective auditory tests are a waste of effort in presence of non-organic hearing loss, and decisions on medical, surgical or prosthetic management are liable to be erroneous until the real hearing state is reliably assessed. no t
no
no t
100 ,
y./Y
• •' '
90 -
//
80 —
I 70
'
/ / /
% 8
8
'
30 20 10 0
- 10
t'/ yy
L :••
-. ¥/ / Y/
i 10
20
30
40 50 40 70 80 Half - peak level elevation (dB)
I 90
i 100
110
FIG. 4. Relationship between pure-tone and speech 'thresholds' in patients with non-organic hearing loss (N=iO7 ears).
Discussion and conclusions It has been shown that the discrimination loss (DL) in cases of cochlear disorder increases in an orderly manner with increased hearing loss. However, in cases with VIII nerve lesions the DLis disproportionately greater than would be expected from the pure-tone audiometric threshold elevation. A possible explanation for this is that the conduction velocity in some of the nerve fibres may be reduced by the effects of pressure from a tumour or by interference with the neuron's metabolism, perhaps with demyelinization. Such changes would modify the temporal relationships in transmission of different 'phonetic' elements in the neural signal, and would result in temporal distortion of the neural signal reaching the brainstem. One would expect greater impairment in a speech discrimination 1088
Speech discrimination tests test, where temporal relationships are important, than in a detection test such as pure-tone audiometry. A tendency towards demyelinization would also reduce the electrical insulation properties of the myelin sheath. In turn, this might lead to 'crosstalk' between adjacent nerve fibres, and thereby to distortion of the coding in the neural signal. Whatever the cause may be, measurement of the ODS provides a most useful diagnostic test in cases of sensorineural hearing loss, provided the non-test ear is carefully and adquately masked. Since the preliminary analyses were published (in 1971), and the present ones were carried out (in 1973) to verify them, we have continued to use this test procedure regularly in our clinical work at the Wessex Regional Audiology Centre and in the neuro-otology clinic at the Wessex Neurological Centre. Nothing has occurred to cause us any qualms concerning its value and accuracy, provided allowances are made for the rather lower scores to be expected from very young persons (under 7), from persons who do not speak English, and from persons who have suffered either very recent and sudden unilateral hearing loss or who have had unilateral hearing loss of very long standing: both of the latter groups may have lost confidence in hearing speech in what they believe to be a useless ear. A word of caution is needed also in cases where the hearing loss is steeply falling or rising, when correlations between speech and pure-tone data at 500 Hz, 1000 Hz and 2000 Hz are liable to be less close. Presumably this is because islands of relatively good hearing, at 250 Hz or 4000 Hz, may sometimes contribute significantly to speech discrimination; in other instances, the speech discrimination is worse than might be expected. It is relevant here to consider the relationship between discrimination loss and tone decay. Although VIII nerve lesions often cause both to be excessive, it is believed that tone decay is a manifestation of a quite different aspect of dysfunction. Excessive tone decay probably results from an interference with the metabolism of the nerve fibres such that, although fully polarized in its resting state and able to pass short-duration signals, it is unable to sustain the metabolic activity involved in the rapid series of depolarizations and repolarizations that are necessary for transmission of long-duration signals. One would not, therefore, expect abnormal discrimination loss and tone decay to occur simultaneously or to the same degree in all neural lesions. Indeed, our clinical experience, with some 2000 cases of sensorineural hearing loss investigated with both types of test indicates that enough VIII nerve cases occur in which there is abnormal discrimination loss but little tone decay, or vice versa, for it to be mandatory to test for both types of dysfunction (as well as to measure the amount of any recruitment present). There is a second great benefit to be obtained from carrying out speech audiometry in cases of (apparent) sensorineural hearing loss. This is in the 1089
V. M. Priede and R. R. A. Coles detection of non-organic hearing loss, which is far from uncommon* and is almost invariably present as a sensorineural or mixed hearing loss. Speech audiometry is useful in nearly all such cases, whether ultimately shown to be non-organic or organic. The HPLE is needed for the former and the ODS for the latter, but in order to obtain the ODS it is necessary to plot out the general shape of the speech discrimination function and this yields, in passing, the HPLE. The speech audiogram also, of course, gives a most helpful indication of the patient's potential speech discrimination ability with amplification or intended middle-ear surgery. Why persons with non-organic hearing loss indicate more acute thresholds with speech audiometry than with pure-tone audiometry is not clear. Perhaps because of the transients and level fluctuations of speech, the subjective impression of a suprathreshold signal is louder with speech test material than with pure tones: certainly it seems more difficult for a patient to assign an artificial threshold with speech test material, and the Fournier method of test deliberately takes advantage of this difficulty. In children, the differences between thresholds for pure-tone and speech audiometry are apt to be gross: probably the cause is in their much greater attentiveness to the relatively interesting task involved in speech audiometry. Several audiologists from this country and overseas with whom we have discussed this subject have suggested that about 50% of children with sensorineural hearing loss apparently acquired at ages of about 8-14 prove in fact to be non-organic. Certainly in our own clinics we see several dozens of cases of non-organic hearing loss in such children every year, some of whom have previously been subjected to multiple investigations, hearing-aid fitting and even operations: in the vast majority, a speech audiogram speedily resolves the issue and frequently demonstrates the underlying normality of hearing. Apart from the Stenger test, which is only applicable to cases of unilateral or asymmetrical hearing loss, speech audiometry is considered to be by far the most valuable single test for detection and measurement of non-organic hearing loss. Acknowledgements The authors are indebted to the Wessex Regional Health Authority and to the Medical Research Council (grant 970/512/C) for financial support of this work. REFERENCES BOOTHROYD, D. B. (1968). Sound, 2, 3. COLES, R. R. A. and PRIEDE, V. M. (1971) Proceedings of the Royal Society of Medicine, 64, 194. * It is estimated that in the 'deaf patients referred to the Wessex Regional Audiology Centre about 4% have non-organic hearing loss: it occurs in about 10% of the adults and in about 30% of the schoolchildren with (apparent) acquired or newly-detected sensorineural hearing loss, and in about 40% of the potential litigation or compensation cases. 1090
Speech discrimination tests R. R. A., MARKIDES, A. and PRIEDE, V. M. (1973) Pages 181-202 in 'Disorders of Auditory Function', ed. W. Taylor, Academic Press, London. COLES, R. R. A. and PRIEDE, V. M. (1975) Journal of Laryngology and Otology, 90, COLES,
217. FLETCHER, FOURNIER,
H. (1950) Journal of the Acoustical Society of America, 22, 1. J. E. (1956) Exposes Annuels d'Oto-Rhino-Laryngologie, 107, Masson et Cie, Paris. (Also published as Beltone Institute Translation No. 8, 1958). FRY, D. B. (1961) Lancet, ii, 197. HOOD, J. D. and POOLE, J. P. (1971) Sound, 5, 30.
J., JERGER, S., AINSWORTH, J. and CARAM, P. (1966) Journal of Speech and Hearing Disorders, 31, 377. JERGER, J. and JERGER, S. (1971) Archives of Otolaryngology, 93, 573. OWENS, E. (1971) Ada otolaryngologica, Supplement 283. PRIEDE, V. M. (1971) Personal communication, quoted by Coles, R. R. A. (1972) in Journal of Laryngology and Otology, 86, 191. PRIEDE, V. M. (1973) Ph.D. Thesis, University of Southampton. JERGER,
APPENDIX
I.S.V.R. Method for Clinical Speech Audiometry (using AB(S) short isophonemic word lists : 10 words/30 phonemes per list) 1. Calculate the speech dial level for the Estimated HPL in the test ear. This is done from the pure-tone audiogram, taking the average of the best two thresholds at 500, 1000 and 2000 Hz-[-speech audiometer calibration factor (=HPL of normals with the particular equipment, test-tapes, etc.) 2. Measure Actual HPL using one list per level, scored by phonemes and presented at the following test levels: at Estimated HPL+3odB at Estimated HPL+2odB at Estimated HPL+iodB at Estimated HPL+ odB at Estimated HPL—iodB and so on until a score of less than 10% is reached. 3. Where non-organic hearing loss is suspected, add lists at a variety of further levels (including replications and intermediate ones) in order to 'work the threshold down'. 4. Complete the speech discrimination curve by testing at higher levels: at Estimated HPL+5odB (if not too loud) at Estimated HPL+yodB (if not too loud) and so on, to outline the speech discrimination curve over the whole dynamic range available (if tolerable). 5. Except where the discrimination score averaged over three adjacent test levels is 95% or more, measure the ODS separately. To do this, select the intensity level (judged from the 'best-fit' curve of the measured results of stages 2-4) as most likely to be the optimal one for speech discrimination. Then, present three word lists at this level, and score by phonemes to obtain the optimal discrimination score (ODS). With AB(S) word lists, word lists 12, 13 and 14 should be used for ODS determinations. 1091
V. M. Priede and R. R. A. Coles NOTES: A. Phoneme Scoring. Example for word 'CAT' Response* CAT CAP BAT *Write down the response. KIT if the word cannot be scored quickly. Comment COP SCOT on any particular (? nonCATS organic) pattern of GOD response. (nil)
Record as CAT CAT" £AT CXT
C0 0/T
CAZ*
Score 3 2 2 2 I I 2 0
6AT
0
B. Instructions to Patient (appropriate for phoneme scoring and to those who can hear, or read, and understand the following): 'You are going to listen to someone speaking single words through the earphones. These words are spoken rhythmically like this . . . SHOP . . . BUS . . . FUN . . . TOY. To start, these words will be fairly loud, but eventually I'll make them very quiet. Please listen carefully and repeat after each word whatever you think you heard. Even if you hear only part of the word, or a word that doesn't seem to make sense, or even a single sound, like /a/, /o/, or /ch/, please repeat it because it adds to your score. Do you have any questions?' Institute of Sound and Vibration Research, The University, Southampton SOg 5NH. Operational Acoustics and Audiology Group, Institute of Sound and Vibration Research, University of Southampton, England.
1092
2>? > where
diagnostic significance.' They used an index of — ^ max
PBjjjj,, is the lowest discrimination score measured at levels above the PBmax up to n o dB, if tolerated. This index, when plotted as a function of the average pure-tone threshold, gave a complete separation between the two diagnostic categories in a sample consisting of 41 cochlear cases and 10 VIII nerve tumours. Calculation of the index relies on the performance-intensity curve showing a substantial reduction of speech discrimination scores at higher intensity levels, which Jerger et al. first described in 1966 and subsequently referred to as the 'rollover phenomenon'. However, Jerger and Jerger (1971) admitted that their sample was rather limited and that 'the rollover effect is somewhat confused and conflicting'. To illustrate this uncertainty, they quoted nine references where the rollover has been reported as occurring in various diagnostic categories or not at all. More recently, Hood and Poole (1971) failed to find much distinction in the shape of the speech discrimination curves between patients with Meniere's disorder and those with VIII nerve lesions; the rollover effect occurred in their sample in both diagnostic categories. Moreover, the present authors' experience, using PB words over much the same intensity 1081
V. M. Priede and R. R. A. Coles range, is that the rollover effect does not provide a satisfactory distinction between the majority of sensory and neural cases. A preliminary study of the speech audiograms of 235 ears with acquired sensorineural hearing loss tested in our own clinics was made by Priede in 1971. The optimal discrimination scores (ODS, a measure similar to the PB max used by Jerger et al., 1966) were correlated with the average puretone thresholds calculated according to a formula based on that of Fletcher (1950) {vide infra). The results showed good separation of the two diagnostic categories, the primary cochlear lesions from the primary neural lesions. A criterion line, at that time drawn 'by eye', indicated only a 10% overlap. A further analysis of ODS values was carried out by Priede in 1973 on a larger sample comprising 327 ears with cochlear disorders and 50 ears with neural ones. A criterion line derived from the lower 10 percentile ODS values in cochlear cases was found to exclude 90% of neural cases. The line itself was essentially the same as that of the 1971 preliminary criterion. Another principal measurement of great potential value is the 'speech threshold' (or HPLE, Half-Peak Level Elevation, vide infra). Additional to the clinical series noted above, Priede (1973) compared HPLE values of 107 ears with non-organic hearing loss with 448 having cochlear disorder. This confirmed our earlier observations (Coles and Priede, 1971) of the great value of speech audiometry in detecting the presence of non-organic hearing loss and, often, of measuring the real hearing loss. This paper presents these analyses in condensed form, draws conclusions as to the value of the diagnostic criteria derived which are supported by further years of clinical experience with them, and indicates the means by which they may be put into clinical application. Methods and terminology
An important objective in any clinical test is to obtain as much diagnostic information as possible within as short a time as possible. Considerable effort has been given in our clinic over the last decade to develop a speech audiometric method which combines sufficient reliability with a clinically acceptable test duration. The method which has ultimately been derived is outlined in Appendix 1, and is similar to that used earlier in obtaining the clinical data presented in this paper. Phonetically-balanced word lists, scored by phonemes, were used to measure both the 'speech threshold' and the optimal discrimination score (ODS). The conventional term Speech Reception Threshold is not used here, since it really refers to the level at which 50% of spondee words are correctly recognized. Not only are PB words often used instead of spondees, but also in many cases of sensorineural hearing loss the discrimination score does not even reach 50%: nevertheless, most of those patients do have a threshold for recognition of speech. 1082
Speech discrimination tests Therefore, it was decided (Coles et al., 1973) that a more appropriate term would be the Half-Peak Level (HPL). The HPL is estimated from the speech discrimination curve* as the (nominal) intensity level at which the speech discrimination would be half of that corresponding to the peak of the curve. The Half-Peak Level Elevation (HPLE) is the difference between the measured HPL and the normal HPL for the particular test material and equipment. The ODS is the score specially measured at the intensity level corresponding to the peak of the speech discrimination curve**. Such a method of measurement avoids the errors, due to use of an incorrect intensity, which frequently occur when the test level is at some fixed value, e.g. 40 dB above an estimated or measured 'speech threshold'. The terminology and measurements relating to the method of speech audiometry described here are illustrated in Figure 1. The tape-recorded Ampliation of speech material ( dial readings in decibels )
1 E
0
m
10
20
30
20 30 40 Corrected pure-tone average (dB) Primorilv eochleor le.ion, ( N - 3 2 7 eon in 208 potient.) Confirmed VIII nerve tumon ( N = ! ? . • early cosei with possible inadequacy of masking) Other VIII nerve lesions ( N - 9 ) Vascular VIII nerve lesions ( N = 8) Unclassified VIII nerve lesions( N « 14) 10
• 0 a V A
= 5
|
P» intt p^nt
FIG. 3. Relationship between pure-tone thresholds and speech discrimination scores in patients with cochlear and VIII nerve lesions. Note: The above data refer to use of one of Fry's PB word lists. For three AB(S) word lists the criterion line is at 91% (instead of 93%) at o db, at 54% (instead of 59%) at 50 dB, and at 42% (instead of 47%) at 70 dB. (The values for AB(S) lists were derived from data on 60 cochlear cases tested with both speech materials).
These results are in good agreement with the general clinical experience that speech discrimination is particularly poor in neural cases. It is evident that the speech discrimination loss is proportional to the hearing loss in cochlear cases, whereas it is disproportionately great in the neural cases. Whilst there is not an absolute separation between the two groups, criterion line comprising the goth percentile curve for the cochlear cases approximates to the 10th percentile curve for the neural cases. Thus go% of the results from patients with sensory disorders came above this line and a similar proportion of the results from neural cases lay below it. 1086
Speech discrimination tests Test/retest reliability studies of the ODS in 10 cochlear cases (tested with single ioo-phoneme word lists on five separate occasions) showed that the intra-patient standard deviation is about 2 to 3%, the highest individual standard deviation being 6% (Priede, 1973). This might account for some of the overlap between the two groups, but more probably it is additional to a true diagnostic overlap. Therefore, for practical purposes, the diagnostic significance of an individual result occurring on or near the criterion line has to be interpreted with caution, taking account of the limitation of test accuracy and the overlap between the two groups. It should also be recalled that an VIII nerve lesion causing a disproportionally great degree of speech discrimination loss may also cause, secondarily, a cochlear lesion resulting in a marked degree of recruitment. Conversely, some neural cases with borderline speech scores have markedly neural patterns of loudness growth, i.e. with no recruitment or rather little recruitment. Measurements of speech discrimination and of recruitment must, therefore, be regarded as complementary rather than as alternatives. C. Relationships between pure-tone and speech thresholds in patients non-organic hearing loss
with
In Figure 2 it can be seen that these threshold measurements are within ±10 dB of one another in about 90% of cases with end-organ disorder; only 10% have pure-tone thresholds that are more than 10 dB greater than the HPLE, and then by up to 20 dB only in nearly all instances. Neural cases tend to err in the other direction. The majority of conductive cases would be expected to be within the i i o dB limits. The non-organic cases are shown in Figure 4, and it can be seen that the ±10 dB band includes only 18% of the 107 results, whilst in 58% the pure-tone thresholds are more than 20 dB greater than the HPLE. Thus, the value of speech audiometry in revealing such cases, noted previously by Coles and Priede (1971), is confirmed by this larger series. Once non-organic hearing loss is suspected, the method of applying speech audiometry is best changed to that of Fournier (1956). In this, a word list, (a), is presented about 20 bB below the lowest level at which a good discrimination score has previously been achieved. A low score is likely to result, and the next list, (b), is presented at a level 10 or 15 dB higher than list (a). If a reasonable score then results, the next list, (c), is presented about 20 dB below that of list (b). A further list, (d), is then presented 10 or 15 dB above the level of list (c); and so on. This confuses the patient in his self-set task of maintaining an imaginary threshold and cajoles him into responses at progressively lower intensities. This takes much longer to perform than ordinary speech audiometry, but does not take as long as electrophysiological tests and yields a more relevant measure of auditory function for general clinical purposes. The time is 1087
V. M. Priede and R. R. A. Coles
!
well spent since further subjective auditory tests are a waste of effort in presence of non-organic hearing loss, and decisions on medical, surgical or prosthetic management are liable to be erroneous until the real hearing state is reliably assessed. no t
no
no t
100 ,
y./Y
• •' '
90 -
//
80 —
I 70
'
/ / /
% 8
8
'
30 20 10 0
- 10
t'/ yy
L :••
-. ¥/ / Y/
i 10
20
30
40 50 40 70 80 Half - peak level elevation (dB)
I 90
i 100
110
FIG. 4. Relationship between pure-tone and speech 'thresholds' in patients with non-organic hearing loss (N=iO7 ears).
Discussion and conclusions It has been shown that the discrimination loss (DL) in cases of cochlear disorder increases in an orderly manner with increased hearing loss. However, in cases with VIII nerve lesions the DLis disproportionately greater than would be expected from the pure-tone audiometric threshold elevation. A possible explanation for this is that the conduction velocity in some of the nerve fibres may be reduced by the effects of pressure from a tumour or by interference with the neuron's metabolism, perhaps with demyelinization. Such changes would modify the temporal relationships in transmission of different 'phonetic' elements in the neural signal, and would result in temporal distortion of the neural signal reaching the brainstem. One would expect greater impairment in a speech discrimination 1088
Speech discrimination tests test, where temporal relationships are important, than in a detection test such as pure-tone audiometry. A tendency towards demyelinization would also reduce the electrical insulation properties of the myelin sheath. In turn, this might lead to 'crosstalk' between adjacent nerve fibres, and thereby to distortion of the coding in the neural signal. Whatever the cause may be, measurement of the ODS provides a most useful diagnostic test in cases of sensorineural hearing loss, provided the non-test ear is carefully and adquately masked. Since the preliminary analyses were published (in 1971), and the present ones were carried out (in 1973) to verify them, we have continued to use this test procedure regularly in our clinical work at the Wessex Regional Audiology Centre and in the neuro-otology clinic at the Wessex Neurological Centre. Nothing has occurred to cause us any qualms concerning its value and accuracy, provided allowances are made for the rather lower scores to be expected from very young persons (under 7), from persons who do not speak English, and from persons who have suffered either very recent and sudden unilateral hearing loss or who have had unilateral hearing loss of very long standing: both of the latter groups may have lost confidence in hearing speech in what they believe to be a useless ear. A word of caution is needed also in cases where the hearing loss is steeply falling or rising, when correlations between speech and pure-tone data at 500 Hz, 1000 Hz and 2000 Hz are liable to be less close. Presumably this is because islands of relatively good hearing, at 250 Hz or 4000 Hz, may sometimes contribute significantly to speech discrimination; in other instances, the speech discrimination is worse than might be expected. It is relevant here to consider the relationship between discrimination loss and tone decay. Although VIII nerve lesions often cause both to be excessive, it is believed that tone decay is a manifestation of a quite different aspect of dysfunction. Excessive tone decay probably results from an interference with the metabolism of the nerve fibres such that, although fully polarized in its resting state and able to pass short-duration signals, it is unable to sustain the metabolic activity involved in the rapid series of depolarizations and repolarizations that are necessary for transmission of long-duration signals. One would not, therefore, expect abnormal discrimination loss and tone decay to occur simultaneously or to the same degree in all neural lesions. Indeed, our clinical experience, with some 2000 cases of sensorineural hearing loss investigated with both types of test indicates that enough VIII nerve cases occur in which there is abnormal discrimination loss but little tone decay, or vice versa, for it to be mandatory to test for both types of dysfunction (as well as to measure the amount of any recruitment present). There is a second great benefit to be obtained from carrying out speech audiometry in cases of (apparent) sensorineural hearing loss. This is in the 1089
V. M. Priede and R. R. A. Coles detection of non-organic hearing loss, which is far from uncommon* and is almost invariably present as a sensorineural or mixed hearing loss. Speech audiometry is useful in nearly all such cases, whether ultimately shown to be non-organic or organic. The HPLE is needed for the former and the ODS for the latter, but in order to obtain the ODS it is necessary to plot out the general shape of the speech discrimination function and this yields, in passing, the HPLE. The speech audiogram also, of course, gives a most helpful indication of the patient's potential speech discrimination ability with amplification or intended middle-ear surgery. Why persons with non-organic hearing loss indicate more acute thresholds with speech audiometry than with pure-tone audiometry is not clear. Perhaps because of the transients and level fluctuations of speech, the subjective impression of a suprathreshold signal is louder with speech test material than with pure tones: certainly it seems more difficult for a patient to assign an artificial threshold with speech test material, and the Fournier method of test deliberately takes advantage of this difficulty. In children, the differences between thresholds for pure-tone and speech audiometry are apt to be gross: probably the cause is in their much greater attentiveness to the relatively interesting task involved in speech audiometry. Several audiologists from this country and overseas with whom we have discussed this subject have suggested that about 50% of children with sensorineural hearing loss apparently acquired at ages of about 8-14 prove in fact to be non-organic. Certainly in our own clinics we see several dozens of cases of non-organic hearing loss in such children every year, some of whom have previously been subjected to multiple investigations, hearing-aid fitting and even operations: in the vast majority, a speech audiogram speedily resolves the issue and frequently demonstrates the underlying normality of hearing. Apart from the Stenger test, which is only applicable to cases of unilateral or asymmetrical hearing loss, speech audiometry is considered to be by far the most valuable single test for detection and measurement of non-organic hearing loss. Acknowledgements The authors are indebted to the Wessex Regional Health Authority and to the Medical Research Council (grant 970/512/C) for financial support of this work. REFERENCES BOOTHROYD, D. B. (1968). Sound, 2, 3. COLES, R. R. A. and PRIEDE, V. M. (1971) Proceedings of the Royal Society of Medicine, 64, 194. * It is estimated that in the 'deaf patients referred to the Wessex Regional Audiology Centre about 4% have non-organic hearing loss: it occurs in about 10% of the adults and in about 30% of the schoolchildren with (apparent) acquired or newly-detected sensorineural hearing loss, and in about 40% of the potential litigation or compensation cases. 1090
Speech discrimination tests R. R. A., MARKIDES, A. and PRIEDE, V. M. (1973) Pages 181-202 in 'Disorders of Auditory Function', ed. W. Taylor, Academic Press, London. COLES, R. R. A. and PRIEDE, V. M. (1975) Journal of Laryngology and Otology, 90, COLES,
217. FLETCHER, FOURNIER,
H. (1950) Journal of the Acoustical Society of America, 22, 1. J. E. (1956) Exposes Annuels d'Oto-Rhino-Laryngologie, 107, Masson et Cie, Paris. (Also published as Beltone Institute Translation No. 8, 1958). FRY, D. B. (1961) Lancet, ii, 197. HOOD, J. D. and POOLE, J. P. (1971) Sound, 5, 30.
J., JERGER, S., AINSWORTH, J. and CARAM, P. (1966) Journal of Speech and Hearing Disorders, 31, 377. JERGER, J. and JERGER, S. (1971) Archives of Otolaryngology, 93, 573. OWENS, E. (1971) Ada otolaryngologica, Supplement 283. PRIEDE, V. M. (1971) Personal communication, quoted by Coles, R. R. A. (1972) in Journal of Laryngology and Otology, 86, 191. PRIEDE, V. M. (1973) Ph.D. Thesis, University of Southampton. JERGER,
APPENDIX
I.S.V.R. Method for Clinical Speech Audiometry (using AB(S) short isophonemic word lists : 10 words/30 phonemes per list) 1. Calculate the speech dial level for the Estimated HPL in the test ear. This is done from the pure-tone audiogram, taking the average of the best two thresholds at 500, 1000 and 2000 Hz-[-speech audiometer calibration factor (=HPL of normals with the particular equipment, test-tapes, etc.) 2. Measure Actual HPL using one list per level, scored by phonemes and presented at the following test levels: at Estimated HPL+3odB at Estimated HPL+2odB at Estimated HPL+iodB at Estimated HPL+ odB at Estimated HPL—iodB and so on until a score of less than 10% is reached. 3. Where non-organic hearing loss is suspected, add lists at a variety of further levels (including replications and intermediate ones) in order to 'work the threshold down'. 4. Complete the speech discrimination curve by testing at higher levels: at Estimated HPL+5odB (if not too loud) at Estimated HPL+yodB (if not too loud) and so on, to outline the speech discrimination curve over the whole dynamic range available (if tolerable). 5. Except where the discrimination score averaged over three adjacent test levels is 95% or more, measure the ODS separately. To do this, select the intensity level (judged from the 'best-fit' curve of the measured results of stages 2-4) as most likely to be the optimal one for speech discrimination. Then, present three word lists at this level, and score by phonemes to obtain the optimal discrimination score (ODS). With AB(S) word lists, word lists 12, 13 and 14 should be used for ODS determinations. 1091
V. M. Priede and R. R. A. Coles NOTES: A. Phoneme Scoring. Example for word 'CAT' Response* CAT CAP BAT *Write down the response. KIT if the word cannot be scored quickly. Comment COP SCOT on any particular (? nonCATS organic) pattern of GOD response. (nil)
Record as CAT CAT" £AT CXT
C0 0/T
CAZ*
Score 3 2 2 2 I I 2 0
6AT
0
B. Instructions to Patient (appropriate for phoneme scoring and to those who can hear, or read, and understand the following): 'You are going to listen to someone speaking single words through the earphones. These words are spoken rhythmically like this . . . SHOP . . . BUS . . . FUN . . . TOY. To start, these words will be fairly loud, but eventually I'll make them very quiet. Please listen carefully and repeat after each word whatever you think you heard. Even if you hear only part of the word, or a word that doesn't seem to make sense, or even a single sound, like /a/, /o/, or /ch/, please repeat it because it adds to your score. Do you have any questions?' Institute of Sound and Vibration Research, The University, Southampton SOg 5NH. Operational Acoustics and Audiology Group, Institute of Sound and Vibration Research, University of Southampton, England.
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