RESIDUAL HEARING AND SPEECH PRODUCTION IN DEAF CHILDREN CLARISSA R. SMITH
tlunter College, CUNY, New York
Residual hearing, phoneme recognition, speech production errors, and selected background variables were examined in 40 congenitally deaf children of normal intelligence who had no apparent anomalies other than deafness, in an effort to identify factors most closely associated with speech intelligibility. Mean intelligibility of the recorded speech of the children, to inexperienced listeners, was 18.7g, corresponding closely with results of previous studies. Scores on the total and some portions of the phoneme recognition test showed significant correlations with both phoneme production and speech intelligibility. The correlation between phoneme production errors and intelligibility was -0.80. A sizable proportion of the dispersion could be accounted for by certain prosodic errors, such as those resulting from improper phonatory control. Errors of place of articulation and voicing remained in essentially the same proportion for all speakers. Errors of manner and combined place and manner of articulation showed a slight systematic decrease from the poorest to the best speakers. Omissions decreased sharply, but not systematically. Vowel errors showed the most marked and systematic decrease as intelligibility improved. Children of deaf parents were poorer in phoneme recognition and in speech intelligibility than children with comparable residual hearing but with hearing parents. The speech of many deaf children is not a viable instrument for verbal communication. It can be the cause of daily communication breakdown, a frustrating and unrewarding experience for the children and their listeners alike. Although it appears that speech intelligibility is poorer in children with less residual hearing, there is comparatively little detailed information on this relationship. Montgomery (1967) showed intelligible speech in deaf children to be strongly related to residual hearing at frequencies lower than those comprising the traditional average of 500, 1000, and 2000 Hz. Boothroyd (1970) found that among the students at an oral school for the deaf, three-quarters of those with hearing thresholds better than 90 dB (ISO) at 1000 or 2000 Hz had speech intelligibility scores better than 70% whereas only one-tenth of the students with poorer hearing at these frequencies had similar intelligibility scores. The classic investigation of errors in phoneme production by deaf children is that of Hudgins and Numbers (1942). Their main findings were nonfunction of the initial or final consonant, errors in clustered consonants, errors in voicing and nasality, substitutions, and either neutralization or diphthongiza795
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tion of vowels. Vowel production by deaf children shows overlap and poor definition of formant areas (Angelocci, Kopp, and Holbrook, 1964). There is a lack of correct timing in the movement from one articulatory position to another (Calvert, 1961; Martony, 1966). The speech is characterized by poor breath control (Hudgins, 1937, 1946) and errors of intonation, duration, and rhythm (Lafon et al., 1967; John and Howarth, 1965; Hood, 1966). These authors believed nonarticulatory or suprasegmental aspects of the children's speech to be a strong deterrent to intelligibility. A number of investigators have indicated the necessity for a detailed examination of the auditory capacity of the deaf child as it relates to speech production. The present study was undertaken in an effort to supply some of this information. A battery of measurements that included residual hearing for tones, phoneme recognition, articulatory and prosodic errors in speech production, and speech intelligibility scores was used. The relations among these variables were examined in an attempt to answer the following questions: 1. What are the relationships between a deaf child's hearing for pure tones and for speech sounds, and the articulatory and prosodic features of his speech production? 2. What variables in addition to hearing may account for divergence in individual children from the general trends that may be found? 3. What is the relative importance to speech intelligibility of various articulatory and prosodic features of the children's speech? PROCEDURE The subjects were 40 children with severe to profound congenital deafness, obtained from the population of a large day and residential oral school. They were chosen in the age ranges eight to 10 and 13 to 15 years. There were equal numbers of males and females in each age group. The children were of normal intelligence, as determined by standard tests, and presented no known anomalies other than deafness. One child in the older group and eight in the younger group were the children of deaf parents. Sign was designated as the principal language in the homes of seven of these nine children. Deafness had been diagnosed in the first year of life for 24 of the 40 children, in the second year for 12, and later than the second year for four. The age at obtaining the first hearing aid ranged from one to five years and at beginning special education 11 months to 11 years. For the largest number (16 children) special education was begun between two and three years. Additional information obtained for each child included hearing of siblings, language used in the home (English, sign, other), degree of parental cooperation with the school (as an indicator of parental motivation), apparent adequacy of the hearing aid, and adequacy of use of the hearing aid. Testing was performed in a sound-isolated two-room audiometric suite. 796 1ournal o[ Speech and Hearing Research
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18 795-811 1975
Audiological measures included pure-tone air conduction response levels (ISO, 1964) from 125 to 6000 Hz in half-octave steps; omitting bone-conduction measures because no child's previous audiograms showed any significant airbone gap; uncomfortable loudness levels for tones at 250 and 1000 Hz; speech defection level; and speech reception threshold, where obtainable. A test of phoneme recognition, consisting of 50 minimal-contrast triplet sets employing a very simple vocabulary, was designed for the study. The test presented a balanced set of contrasts for the articulatory features of place, manner, combined place and manner, and voicing vs nasality, as well as vowel contrasts. These were presented by earphone to one ear only of each subject. The ear selected was that in which the hearing aid was worn (25 children). If the child wore binaural aids (14 children) or no aid (one child), then the ear selected was the one with the better speech threshold (six children). If no speech threshold had been obtained, the ear selected was the one in which a pure-tone response had been obtained for a higher frequency (four children). If none of these criteria could be applied, the right ear was chosen (five children). A detailed description of the preparation and recording of the word lists appears in Smith (1972). To obtain a speech sample, a list of 20 sentences was recorded by each child. The sentences contained a transition to and from the v o w e l s / i / , / ~ e / , a n d / u ! for each place of consonant articulation. All consonants were represented in initial, medial, and final position, except where this does not occur in English and except for those with a frequency of occurrence in the spoken language of less than 0.1~ (Denes, 1963). These sentences were rerecorded on 40 listening tapes in such a manner that the order of sentences differed on every tape with each sentence spoken by a different child. Each tape was heard by three listeners (total of 120 listeners), all without significant previous experience in hearing the speech of deaf persons. The listeners, who each heard one tape only, wrote down as much as they could of what each child said with a maximum of two hearings of each recorded sentence. They then gave a rating of each child's intelligibility on a 1 (best) to 5 (poorest) scale. The responses of all listeners were scored word by word, and an intelligibility score was obtained for each child based on words correctly understood as a percentage of selected key words in each sentence. The tape recordings of the children's sentences were transcribed by skilled phoneticians of whom 11 in all participated. The resulting transcriptions were translated into a numerical code (Smith, 1972) for subsequent computer analysis. An additional set of tapes was prepared consisting of five consecutive utterances by each of the 40 children. These tapes were heard by three experienced speech pathologists who made binary judgments (present-not present) of errors in nonphonemic and suprasegmental aspects of the speech. The parameters judged included three error categories for voice quality, two for voice pitch, two for phonatory control, two for intonation, two for stress, four for fluency, and four for rate of speech. SMrrH: Residual Hearing 797
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RESULTS
Hearing Measures All but three children had an average hearing level in the better ear of 92 dB or poorer for 500, 1000, and 2000 Hz. Many deaf children, however, do not respond within conventional audiometric limits at 2000 Hz. In this group, 24 children of the 40 did not respond in either ear at 2000 Hz, while all b u t three children had a response in at least one ear to 1000 Hz. Because the aim was a meaningful description of hearing level as one variable affecting intelligibility of speech, it seemed appropriate to consider hearing levels at frequencies that were measurable with most of the children. Various frequencies were examined in correlations with the intelligibility data, and the average of 125, 500, and 1000 Hz was selected. Table 1 gives values of the correlation coefficient for pure-tone response TAnLE 1. Values of the correlation coefficient for various measures of hearing. PRT, phoneme recognition test. d[ = 38; p(0.05) = 0.31; p(0.01) = 0.40; p(0.001) = 0.51.
Related Measure Average of 125, 500, and 1000 Hz PRT errors Total Place Manner Placemanner Voicing Vowel
Highest Frequency1 Detectea
Average of 125, 500, and 1000 Hz
125
Hearing Level in dB (Hz) 250 500 750
1000
- 0.62
-- 0.43 - 0.22 - 0.46 -- 0.08 --0.20 - 0.33
-
0.57 0.02 0.44
0.39 - 0.05 0.40
0.39 0.04 0.29
0.42 - 0.06 0.18
0.39 0.55 0.38
0.17 0.40 0.24
0.33 0.34 0.23
0.43 0.50 0.25
0.57 0.07 0.44
0.62 0.10 0.47
0.37 0.48 0.38
0.40 0.42 0.48
levels and the various sections of the phoneme recognition test ( P R T ) . Data for frequencies above 1000 Hz were not included because of the small numbers of children responding. Because threshold at 1000 Hz was correlated significantly with several portions of the PRT, the responses were examined with subiects divided according to response at that frequency. There were eight children with hearing levels of 95 dB or better at 1000 Hz; 16 with hearing levels of 100-105 dB; 11 with hearing levels of 110 dB; and five with no response in the test ear at 110 dB, the highest level tested. For each section of the PRT, a mean score was obtained for each of these groups of children. These group means for percentage of correct response to each type of test item, together with the standard error of the mean, are shown in Table 2. Responses to items concerned with place of articulation are not included since they show little change as the result of hearing level at this frequency. 798 Journal of Speech and Hearing Research
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18 795-81l
1975
TABLE 2. Mean and standard error of percentage of correct responses to four types of items in the phoneme-recognition test, subjects grouped according to hearing at 1000 Hz in the test ear. 95 or better (N = 8) s~
Item
Manner Voicing Vowels Placemanner
Hearing Level (dB) 100-105 110 (N = 16) (N = 11) ~ s~ ~2 s~
> 110 (N = 5) 9 s~
64.0 56.2 58.0
9.5 4.9 6.8
50.0 51.6 41.0
4.5 3.7 3.4
45.4 44.7 33.8
5.6 5.1 4.0
40.0 33.3 44.2
4.6 3.7 4.7
45.3
7.4
35.1
3.6
32.9
4.2
22.5
4.6
With a single reversal for vowel items in the poorest hearing level group, the proportion of correct responses increased as the hearing level at 1000 Hz improved. The smallest improvement occurred between the two middle groups, which include children whose hearing level at 1000 Hz was 100 to 110 dB. The sharpest improvement was in the responses of the best-hearing group over the next group, on vowel items and those involving manner of articulation. Scores on voicing items are a little poorer than on manner items, and vowel items considerably poorer, for the two middle groups. These findings are generally consistent with those of Pickett et al. (1972). A comparison of total score was made between the older and younger children with hearing parents, and between the younger children with hearing and with deaf parents. Table 3 gives the mean and standard error of the TABLE 3. Mean and standard error of percent errors on phoneme recognition test, with children grouped according to age and parents' hearing. For younger and older children of hearing parents, t = 2.20, df = 29 (p < 0.05). For younger children of hearing and of deaf parents, t = 1.18, df = 18.
Datum
N Mean %error s~ .
.
.
.
.
.
.
.
All Children
older, Hearing Parents
Younger, Hearing Parents
Younger, Deaf Parents
40 56.0 1.7
19 51.0 2.8
12 59.0 2.6
8 63.0 2.0
.
percent errors in the 50-item test, according to age group and parents' hearing status. The reults of a t test for differences between means also is shown. There is a significant difference between the younger and older children of hearing parents, and some difference, not statisticallv significant, between the younger children of hearing and of deaf parents. Phoneme Analysis
From the phonemic transcriptions, a breakdown was obtained of the segSMITH: Residual Hearing
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799
TABLE 4. Rank order of percent correct production of consonant phonemes, data pooled over all children./n~/and/5/were not targets.
Phoneme
/b/ /w/ [m/ /p/ /f/ /1/ /v/ /n/ /r/ /j/ /d/ /k/ /h/ /0/ /5/ /t/ /g/ /n/ /s/ /~/ /z/ /ds/ /t~/ Mean
Total Occurrences
Correct Production (%)
400 400 520 280 360 480 240 680 360 40 600 640 400 200 240 560 160 120 280 120 600 120 160
85 79 72 70 70 70 64 61 55 53 40 40 39 38 38 37 36 30 24 22 21 18 16
Error (Including %Omission) in Each Word Position (~) Final Initial Medial
11 23 34 25 24 26 40 26 38 50 41 53 56 63 70 41 48 75 65 72 73 78 47
(1) ( 1) ( 1) (0 ) (2 ) (8) (3 ) (5) ( 1) (15) (8) (16) (33) (1) (5) (4) (1) (10) (5) (0) (5 ) (5)
10 (10) 30 ( 3 ) 25 (3 ) 26 (:/=0) 33 ( 5 ) 24 (10) 27 (6 ) 36 (20) 76 (20) 43 (24) 50 (20) 68 (35) 64 (13) 43 (5) 68 (55) 63 (15) 76 (44) 75 (10) 80 (15) 60 (8) 80 (16) 50.3
43
(15)
29 39
(10) (10)
45
(15)
37 49
(9.5) (25)
40
(30)
m
m
65 74
(39) (44)
58 55 73 I00
(13) (13) (41) (67)
9o
(8o)
76 90 83
(39) (32) (50)
88
(55)
95 (47) 64.7
mental errors made by the children. A summary of the consonant errors appears in Table 4. The consonants are ranked in order of percent correct production for all occurrences except occurrences in blends. The percentage of errors in initial, medial, and final position also is shown. The figures in parentheses are the percentages of omission in each position. Consonants with a bilabial place of articulation head the list of correct productions followed by all the glides, a n d / f / , / v / , a n d / n / . Stops in the alveolar and velar r e g i o n , / h / , and the lingua-dental fricatives follow. Near the bottom a r e / 1 3 / a n d the alveolar and palatal fricatives. Affricates have the greatest proportion of error. The single most frequent error for nearly all consonants was omission. Those for which omission was not the most frequent error were /p/ a n d / b / , which were substituted for each other; / f / , for w h i c h / v / was substituted; /0/ and /~)/, which were replaced by / t / and / d / ; and / w / , for which / b / was the most frequent substitution. While there is no difference in the mean proportion of errors in initial and medial position, there is a marked increase for errors in the final position, and a major proportion of these were omissions. The glottal stop was a frequent substitution for other stops (except the bilabials) and also f o r / h / . 800 1ournal of Speech and Hearing Research
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18 795-811 1975
"6
&
C~
2 b.
~
~
~
0
~
0
0
0
0
~
o
0
~
0
~
~
'
0
0 ~ 0 0 0 ~ 0 ~ 0 0 0 0 0 ~ 0 ~ ~ 0 b o ~
,~ 0
0
,~ 0
0
0
0
0
0
eq eq 0
eq 0
,-~ cO 0
,..~ cq ~ I 0
0
t~ , ~ , ~ cO
~ t
~
~-~
cOcD
CO
cq',~
0 0 0 ~ 0 0 0 0 0 ~ 0 ~ 0 ~ 0 ~ 0 0
o o o
"el
o
0 o b~ 0 0 0
o
.o r
N
0
0
c~
0
2
SMrrrt: Residual Hearing 801
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The total errors of each consonant phoneme were separated into the classes of single-feature errors (place, manner, or voicing), two-feature errors (place and manner, place and voice, or manner and voice), and three-feature errors (place, manner, and voicing). Table 5 summarizes the consonant errors in terms of these articulatory features. Among voiced-voiceless cognates, substitution toward the voiced member of the pair was more common than substitution toward the voiceless. Except for the glottal stop substitution, errors of manner and voicing predominated over errors of place of articulation. The low proportion of distortions should be noted. This was partly due to the fact that the phoneticians were encouraged to transcribe broadly, in order to obtain as much congruence between sets of transcriptions as possible. If a phoneme was recognizable as itself, they tended to give it its phonemic symbol with no diacritical modifications. Another factor was the high rate of omissions which reduced the probability of a phoneme being described as distorted./rj/, for example, was never heard as distorted because it was almost never produced. The fairly large proportion of distortions and unidentifiable substitutions for /b/, the phoneme most often produced correctly, is explained by the fact that /b/ was seldom omitted; the bilabial consonants all had low percentages of omission. The other consonant with a low proportion of omissions was //5/, which was replaced in most occurrences b y / d / . The percentages of error for vowel phonemes are shown in Table 6, with TASLV.6. Rank order of percent correct production of vowel phonemes, data pooled over all children. Vowel I^1
/o/ Icl lul la~l
/u/ /x/ /a/ /ou/ /i/ /aft /~/ /ex/ /~,/ /ju/ /~/
Total Occurrences
Correct Production (~)
40 360 280 3t]0 800 80 640 240 200 920 200 240 240 40 40 40
92.5 84.2 79.0 74.7 74.6 73.7 69.2 67.1 64.0 61.6 58.5 52.1 51.7 40.0 20.0 15.0
vowels ranked in order of correct production. All vowels and diphthongs that appeared in the selected words of the 20-sentence list are shown in the table. However, the sentence list was designed to display /i/, /~e/, and /u/; other 802 ]oumal of Speech and Hearing Research
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18 795-811 1975
vowels occurred randomly. For this reason, two English diphthongs, /at;/ and /3I/, do not appear at all. The low central vowels were produced correctly most often, and there was a tendency for all vowels to drop to a more neutral position./i/ a n d / i / w e r e the most frequent substitutions for each other, with /~/ being substituted for /i/ roughly twice as often as /i/ was substituted for /i/. /~r/ was the most frequent substitution f o r / u / , b u t / A / w a s substituted f o r / t r / m o r e often than was /u/. /A/ was also the most frequent substitution for /a/. /u/ became diphthongized frequently, as did /3/. The most common error in diphthong production was failure of the off glide, or, in the case o f / j u / , of the on glide. Many vowel phonemes could not be described in terms of any standard target, and were labeled as unidentifiable substitutions. Intel~gibi~ty
Speech intelligibility scores ranged from 76.1~ to 0~, with a mean of 18.7~. Table 7 shows the mean and standard error of the mean of intelligibility scores for all children and for the groups with hearing and with deaf parents. Since the children of deaf parents did not differ in any systematic manner from the others with respect to amount of residual hearing, the difference in their speech intelligibility is very striking. T~LE 7. Mean percent and standard error of speech intelligibility, children grouped according to age and parents' hearing.
Datum
N Mean intelligibility s~
All Children
Older, Hearing Parents
Younger, Younger, Hearing Deaf P a r e n t s Parents
40.0
19.0
12.0
8.0
18.7 3.2
28.5 5.6
14.2 2.6
4.2 1.5
Table 8 displays the mean percentage of phoneme production errors in various categories, for each quartile of intelligibility. The analyzed words in the sentence lists included 200 consonant and 110 vowel or diphthong tokens, for a total of 310 target phonemes per child. Based on this number of targets, the children as a group averaged 15.4~ consonant errors, an additional 14.5g omissions, 9g vowel and diphthong errors, and 4~ unidentifiable substitutions. Errors of combined place-voice, manner-voice, and place-manner-voice are not ineluded in Table 8 because their total percentage for all children was only 3.5~. Errors of place of articulation are virtually the same for all quartiles of intelligibility, and voicing errors also remain about the same, with a reversal in direction between the second and third quartile. There is a systematic decrease in percentage of manner errors and combined place-and-manner errors, and a S.~,IITH: Residual Hearing 803
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'I'AnLE 8. Mean and standard error of percentage of phoneme production errors in several categories, for each quartile of intelligibility. All percentages are based on 310 target phonemes. N = 10 in each quartile. Q1 Error Type
Place Voice Manner Place and manner Vowel and diphthong Omission Unidentifiable substitutions
Qe
X g,
s~
1.81 1.19 2.12 3.38 5.93
0.38 0.25 0.48 0.41 0.64
9.83 1.03
1.50 0.25
Qa
X~
Q4
s~
X~
s~
X~
s~r
1.84 2.90 2.22 3.90 8.35
0.22 0.71 0.30 0.44 0.80
2.74 2.58 3.06 4.83 10.22
0.37 0.31 0.39 0.55 0.59
2.50 2.90 3.93 5.03 11.45
0.37 0.65 0.47 0.54 1.02
17.60 2.45
1.50 0.44
15.96 3.06
1.06 0.73
18.64 9.29
1.10 2.77
m a r k e d but not systematic decrease ill p e r c e n t a g e of omissions, in going from the fourth to the first quartile. The rate of decrease in vowel errors b e c o m e s s u b s t a n t i a l l y greater b e t w e e n Quartiles 2 and 1, a n d there is a very large decrease in u n i d e n t i f i a b l e substitutions b e t w e e n Quartile 4 a n d Quartile 3. The extent to w h i c h intelligibility correlates with s e g m e n t a l errors (r = - 0.80) is shown b y the scatterplot of F i g u r e 1. On average, intelligibility
I
I
i
I
I
I
I
I
80
6~to v 4O o
0 0
20
40
6O
vt 80
PERCENT SEGMENTAL ERRORS F~c;tmE 1. Percent intelligibility as a function of the frequency of segmental errors. V : older group, hearing parents. V: older group, deaf parents. @: younger group, hearing parents, o: younger group, deaf parents. 804
Journal of Speech and Hearing Research
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18 795-811
1975
decreases with increasing frequency of segmental errors. The relationship is approximated quite well by the solid curve, a quadratic polynomial fitted by the method of least squares. This curve may be regarded as representing average performance for any given frequency of segmental errors. However, the data show a fair degree of dispersion, and children with roughly the same proportion of segmental errors can have speech intelligibility scores differing by as much as 30 percentage points. These differences appear to be related in part to certain suprasegmental errors. Prosodic Analysis
The errors' scores resulting from the judgments of suprasegmental aspects of the children's speech were subjected to factor analvsis. Two fairly significant factors emerged. One related in general to poor phonatory control, including intermittent phonation, inappropriate variations of pitch and loudness, and excessive variability of intonation. This factor, together with one related to rate of speech production, accounted for approximately 50% of the variance, the remaining factors accounting for small proportions. The solid curve of Figure 1 represents expected intelligibility based on segmental errors alone. The extent to which actual intelligibility scores deviated from this curve showed a moderate linkage (r = - 0.39) with the summed ratings of the judges for errors of phonatory control. Thus a child whose speech intelligibility is less than typical for a given frequency of segmental errors also is likely to have a greater frequency of the suprasegmental errors considered here. Relation of Hearing Mea, s~ures to Speech Production
The median hearing levels in the test ear for children in each quartile of speech intelligibility are shown in Table 9. Quartile 1, the most intelligible children, had slightly superior hearing at all frequences, and a median response a full octave higher (3000 [lz) than the children in Quartile 2. Those in Quartile 2 showed a median response to 1500 Hz, as against 1000 Hz for Quartiles 3 and 4. Table 10 presents values of the correlation coefficient for various hearing
TABLE 9. Median hearing levels in decibels in the test ear for children in each quartile of intelligibility. The audiometric reference is ISO 1964. Frequency (Hz) 1500 2000
Quartile
125
250
500
750
Q1 Q2
55 70
70 80 75
85 90 95
~ .... 10-0..... 1 0 5 100 105 110 105 110 >110
--110 .... 110....... ~ 1 ~ ...... >110 ~>110 >110 >110 >110 ~>110 ~>110 >110 >110
95
105
>11o
Q3
65
Q4
70
1000
110
>110
3000
>110
4000
>110
6000
>110
SMI'rH: Resqdual Hearing 805
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TABXm 10. Values of the correlation coefficient for hearing measures, speech-production errors, speech-intelligibility score, and rating. PRT, phoneme recognition test. df "-38; p (0.05) = 0.31; p (0.01) = 0.40; p (0.001) = 0.51.
Hearing Measure
Total Phoneme Errors
Intelligibility Score
Intelligibility Rating
Average of 125, 500, and 1000 Hz Highest frequency detected
0.46 - 0.13
-0.65 0.35
0.53 - 0.28
Itearing level 125 Hz 250 Hz 500 Hz 750 Hz 1000 Hz PRT Total score Place errors Manner errors Place-manner errors Voicing errors Vowel errors
0.28 0.17 0.41 0.48 0.46 - 0.64 - 0.03 0.42 0.35 0.60 0.53
-
0.54 0.40 0.48 0.57 0.55
0.35 0.18 0.42 0.56 0.56
0.78 0.03 -- 0.57 -0.49 -0.65 -0.63
-0.70 0.00 0.48 0.36 0.65 0.56
measures, total segmental errors, the intelligibility score, and the intelligibility rating. Since the listeners rated good intelligibility as 1 and poor intelligibility as 5, the signs in the last two columns are opposite. As before, frequencies above 1000 Hz are not tabled because of the small number of responses. There were, however, no older children with hearing above 1500 Hz in the two poorest quartiles of intelligibility. Of the 18 children who responded to any audiometric frequency above 1000 Hz, 13 were in Quartiles 1 and 2. These included nine older and four younger children. Chi square was computed on 2 • 2 contingency tables for response/no response at each frequency from 1500 to 4000 Hz, compared with above/below mean intelligibility. The chi square was significant at less than 0.05 for 2000, 3000, and 4000 Hz, although the expected cell values were very small. It appears that the hearing sensitivity of the deaf child, as it relates to the intelligibility of his speech, may be summarized reasonably well in terms of the average hearing at 125/500/1000 Hz and the extent of hearing into the higher frequencies. Such a description is similar in principle to the one proposed by Risberg and Martory (1972). Martony I has pointed out that the pure-tone audiogram can give only an indication of the deaf child's potential for auditory reception and for speech production, and that additional measures are necessary. Erber (1974) suggests classification of hearing impairment on the basis of perception of simple speech material (for example, spondaic words). 1j. Martony, personal communication (1972).
806 Journal of Speech and Hearing Research
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18 795-811
1975
Effect of Additional Variables A considerable amount of background information on the children was collected at the time of selecting the subjects for testing. In addition to the parents" hearing status, the factors that seemed to have a possible bearing on speech intelligibility were the quality of parental cooperation with the school (as a reflection of parental motivation), the age when the child obtained his first hearing aid and when he began special education, and the adequacy of use of the hearing aid. There was a modest positive correlation between the age of obtaining the first hearing aid and speech intelligibility (r = 0.32) and between intelligibility and age of beginning special education (r = 0.32, p = 0.05 for both). That is, there was some tendency for the better speakers to have received hearing aids and begun special education later than the poorer speakers. This is explainable by the fact that most of the poorer speakers were among the children with either the least amount of residual hearing, the children of deaf parents, or both. These disadvantages frequently were not offset by early attention. Eight children received hearing aids or special education before the age of two years; none received both before this age. Therefore, too few of the children received early help to allow a real measure of the effect of this variable. Of these eight children, six were in the lower two quartiles of intelligibility. More children in the upper two quartiles were good hearing aid users, in the opinion of the school, than in the lower two quartiles. In the matter of parent cooperation, again according to the school's judgment, Quartiles i and 4 were identical. Good vs poor use of hearing aid and good vs poor parent cooperation were compared by means of chi square with mean speech intelligibility, mean prosodic score, and mean proportion of total phoneme errors. In none of these tests did the chi square demonstrate a difference approaching the 0.05 level of significance. There was no tendency for a difference in speech intelligibility to be associated with the hearing status of the deaf child's siblings. A recent score on either the Wechsler or the Leiter Scale was available for all children. A correlation coefficient obtained beween these test scores and speech intelligibility was -0.17, or essentially no relationship at all. This agrees with the findings of previous investigations that, at least within the range of "normal" intelligence, such test scores are unrelated to speech skills. DISCUSSION The purpose of this investigation was to examine relationships between speech intelligibility and various measures of hearing and speech skills in deaf children. Intelligibility was related to hearing level for pure tones, but the measure most closelv related to intelligibility was the test of phoneme recognition. For most of the children, the auditorv recognition of speech features was SMrrn: Residual Hearing 807
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reflected in the ability to produce intelligible speech. This could occur even in the absence of ability to recognize whole words; there were some children for whom no speech reception threshold could be obtained with spondee words, who nevertheless scored above the mean on the phoneme-recognition test and who were in the upper two quartiles of intelligibility. As would be anticipated, performance on most portions of the phonemerecognition test, and most aspects of phoneme production, were directly related to hearing sensitivity. The hearing sensitivity index used here was the average of 125/500/1000 Hz. Much of the information on manner of articulation, voicing, and vowel differences is carried below 1000 Hz, and ability to recognize these differences was significantly related to speech intelligibility. However, voicing errors in consonant production, while very numerous, had a rather low correlation with speech intelligibility (r = - 0 . 3 6 ) . There was no evidence of a relationship between errors involving place of articulation, either in recognition or production, and any hearing abilities, or between place of articulation errors and intelligibility of speech (r = - 0 . 2 0 ) . The poorest groups in intelligibility made about the same proportion of place errors as the best (Table 8). This is reasonable from the standpoint that children with the least amount of hearing, particularly in the low frequencies, may learn earlier in life to watch the faces of those around them who are speaking. Place of articulation, the one reasonably visible element of speech production, may thus be the earliest learned of their speech behaviors. Much acoustic information oil place of articulation is carried in the higher frequencies of the speech spectrum and requires integration of rapid spectral and intensity changes. The deaf child, even if he has sensitivity in these frequency regions, may not be able to use this information in the same manner as a normal-hearing listener. It is apparent ill Table 8 that identifiable consonant errors in speech production remain in much the same proportion from one quartile of intelligibility to the next. Vowel and diphthong errors, omissions, and unidentifiable substitutions decreased quite systematically from the poorest to the best speakers. The poor identification of the vowels of deaf children has been described by Angelocci, et al. (I964) and quantified ill terms of atypical formant ratios. The major physiological correlate of these improper ratios is inaccurate placement of the tongue. It may be questioned in deaf children whether poor vowel placement is the result of improper consonant targets, or whether the children, having poor appreciation of the quality of most vowels, never aim for a true vowel target and tend to produce a neutral vowel as a substitute for all others, regardless of consonant environment. Examination of the data on speech production reveals some similarities and differences with respect to the study of Hudgins and Numbers (1942). Omission of the initial consonant was less frequent in the present study than omission of the final consonant. Voiced-voiceless confusions were frequent in both studies. However our correlation of -0.36 between these confusions and speech intelligibility is somewhat lower than the -0.44 reported by Hudgins 808 Journal o[ Speech and Hearing Research
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18 795-811 1975
and Numbers. The correlation coefficient for consonant phoneme errors and intelligibility in the earlier work is the same as reported here for identifiable consonant errors: -0.70. The present data agree exactly with the earlier data on types of vowel errors, but show a higher correlation, -0.75, for vowel errors and intelligibility than the --0.61 reported by Hudgins and Numbers (1942). The present findings, those of Nober (1967), and those of Markides (1970) are in essential agreement on the order of correct consonant production: the bilabial consonants, the glides, and / f , v / a r e most often correct, and the palatal and alveolar fricatives, the affricates, and /I3/ are the poorest. The mean intelligibility, to naive listeners, of the recorded speech of the deaf children studied here (18.7~) is remarkably similar to that found in previous investigations (Brannon, 1964, 20.7~; John and Howarth, 1965, 19~; Markides, 1970, 19.1%), where age groups, hearing of the children, and method of deriving the scores all were comparable. One influence on the scores we obtained was, of course, that these deaf children were attending a school for the deaf; that is, their general communication skills, including speech, were not such as to permit their attendance at a regular school. The percent intelligibility, obtained was also directly related to the proportion of children of deaf and of hearing parents in the group. Had there been fewer children of deaf parents, the mean intelligibility of the group might have been higher. It was not possible in selecting the sample of children for our population to match exactly the numbers of children with deaf and with hearing parents. Eight of the nine children with deaf parents were in the younger group, thus all the tests between children of deaf and of hearing parents were restricted to this age group. Nevertheless, there was considerable consistency in the performance of the two groups of younger children on each comparative measure, with those of deaf parents performing more poorly. This may be due to the lack of early and ongoing experience of speech in the home, affecting the children's ability to make use of the information their residual hearing will permit them to receive. Previous investigators have shown the extent to which the intelligibility of deaf children's speech can be interfered with by errors of duration (John and Howarth, 1965), intonation and phrasing (Lafon et al, 1967), and speech rhythm (Hudgins and Numbers, 1942; Hood, 1966.) There was some evidence in the present data of an interaction between prosodic errors and speech intelligibility, but a clear pattern did not emerge. However, the most frequent comment of the inexperienced listeners from whose responses the intelligibility scores were derived, was that what they were hearing sounded like a foreign language. Hearing an unfamiliar pattern, to which his experience of English prosody does not apply, a listener cannot bring his knowledge of the statistics of his language to bear in an attempt to synthesize the meaning of an utterance. Speech training of deaf children has traditionally put most of its attention on articulation. It appears that this concentration may be misplaced. Training toward improvement in the stress and intonation patterns of the deaf SMITH: Residt, al Hearing 809
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child's speech should enable a listener to compensate for omitted and substituted elements and should result in better intelligibility.
ACKNOWLEDGMENT 9Research was partially supported by Grant 09252 from the National Institute of Neurological Diseases and Stroke. This material is drawn from a doctoral dissertation completed under the direction of Harry Levitt while the author was a U.S. Office of Education Fellow in the City University of New York. Requests for reprints should be sent to Clarissa R. Smith, School of Health Sciences, Department of Communication Sciences, 105 East 106th Street, New York, New York 10029.
REFERENCES
ANGELOCCI,A., KoPP, G., and HOLBROOK,A., The vowel formants of deaf and normal hearing eleven to fourteen-year-old boys. 1. Speech Hearing Dis., 29, 156-170 (1964). Bo(yrrmoYo, A., Distribution of hearing levels in the student population of Clarke School for the Deaf. Sensory Aids Research Project Rept. #3. Northampton, Mass.: C. V. Hudgins Diagnostic and Research Center, Clarke School for the Deaf (1970). BRANNON, J. B., Jr., Visual feedback of glossal motions and its influence on the speech of deaf children. Doctoral dissertation, Northwestern Univ. (1964). CALVERT, D. R., Some acoustic characteristics of the speech of profoundly deaf individuals. Doctoral dissertation, Stanford Univ. (1961). DENES, P. B., On the statistics of spoken English. 1. acoust. Soc. Am., 35, 892-904 (1963). E~.R, N. P., Pure-tone thresholds and word-recognition abilities of hearing-impaired children. J. Speech Hearing Res., 17, 194-202 (1974). HooD, R. B., Some physical concomitants of the perception of speech rhythm of the deaf. Doctoral dissertation, Stanford Univ. (1966). HutX~INS, C. V., Voice production and breath control in the speech of the deaf. Am. A. Deaf, 82, 338-363 (1937). HtrDGZNS, C. V., Speech breathing and speech intelligibility. Volta Rev., 48, 642-644 (1946). HtrI~INS, C. V., and NrJMnERS, F. C., An investigation of the intelligibility of the speech of the deaf. Genet. Psychol. Monogr., 25, 289-392 (1942). JOHN, J. E. J., and HOWAnTH, J. N., The effect of time distortions on the intelligibility of deaf children's speech. Lang. Speech, 8, 127-134 (1965). LAFON, J. c., DULAC,A. M., LACROIX,F., and PLANTIER, A., La melodie de la parole et la surdite. Rev. Lar. Otol. RhinoI., 88, 179-187 (1967). MARrJOES, A., The speech of deaf and partially hearing children with special reference to factors affecting intelligibility. Brit. J. Dis. Commun., 5, 126-140 (1970). MARTONY, J., Studies on the speech of the deaf. Q. Prog. Status Rept. Stockholm, Sweden: Speech Transmission Laboratory, Royal Institute of Technology (January 1966). MONTCOMVaY, G. W. G., Analysis of pure tone audiometric responses in relation to speech development in the profoundly deaf. 1. acoust. Soc. Am., 41, 53-59 (1967). NoaEa, E. H., Articulation of the deaf. Except. Child, 33, 611-621 (1967). PICKETT, J. M., MARTIN, E. S., JOHNSON, D., SMITH, S. B., DANIEL, Z., WILLIS, D., and OTIS, W., Patterns of speech feature reception by deaf listeners. In, C. G. M. Fant (Ed.), International Symposium on Speech Communication Ability and Profound Deafness, 1970. Washington: A. G. Bell Association (1972). RISB~RC, A., and M.~RTONY, J., A method for the classification of audiograms. In, C. G. M. Fant (Ed.), International Symposium on Speech Communication Ability and Profound Deafness, 1970. Washington: A. G. Bell Association (1972). SMITH, C. R., Residual hearing and speech production in deaf children. Doctoral dissertation, City Univ. of New York (1972). Received October 1, 1973. Accepted May 17, 1975. 810 1ournal of Speech and Hearing Research
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18 795-811 1975
APPENDIX Phoneme recognition test items. The italicized words were the stimuli used in the experiment. Items were randomized for presentation. Place Contrasts fat
sat
pea bum
tea gum see /et lead s/t bib
he wet weed sip bid
Place-Manner Contrasts hat key dumb
chair
fair
mumps
she
then
dumps D den
yet sick
moo when bum
big
mass
read
Manner Contrasts zoo
bill /ot
zip bet me pad bud
do mill dot dip met be
pan buzz,
we
do ten buzz map
Voicing Contrasts (cont.) seat but
pair jumps
new
mat mark mill new tip some rim cup
wet we al ~un
pat knee
seen bud
gee men you hen
Vowel Contrasts bit
Pete
bug
pat park
bat
pill two
bill do
hot neat lock sick heat feet feel pool
dip sub rip cub pan D
nip
~eel
match
Voicing Contrasts will not lip
seed bun
bark
sup r/b
fall pet
come
boot it ~t nut
luck suck hit foot full
pull pal lid
beet ot ~oot not look sock hut fit
fool pill
fool
~e~ 1 full
pot
put
pad tea
SMrrri: Residual Hearing
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811
tlunter College, CUNY, New York
Residual hearing, phoneme recognition, speech production errors, and selected background variables were examined in 40 congenitally deaf children of normal intelligence who had no apparent anomalies other than deafness, in an effort to identify factors most closely associated with speech intelligibility. Mean intelligibility of the recorded speech of the children, to inexperienced listeners, was 18.7g, corresponding closely with results of previous studies. Scores on the total and some portions of the phoneme recognition test showed significant correlations with both phoneme production and speech intelligibility. The correlation between phoneme production errors and intelligibility was -0.80. A sizable proportion of the dispersion could be accounted for by certain prosodic errors, such as those resulting from improper phonatory control. Errors of place of articulation and voicing remained in essentially the same proportion for all speakers. Errors of manner and combined place and manner of articulation showed a slight systematic decrease from the poorest to the best speakers. Omissions decreased sharply, but not systematically. Vowel errors showed the most marked and systematic decrease as intelligibility improved. Children of deaf parents were poorer in phoneme recognition and in speech intelligibility than children with comparable residual hearing but with hearing parents. The speech of many deaf children is not a viable instrument for verbal communication. It can be the cause of daily communication breakdown, a frustrating and unrewarding experience for the children and their listeners alike. Although it appears that speech intelligibility is poorer in children with less residual hearing, there is comparatively little detailed information on this relationship. Montgomery (1967) showed intelligible speech in deaf children to be strongly related to residual hearing at frequencies lower than those comprising the traditional average of 500, 1000, and 2000 Hz. Boothroyd (1970) found that among the students at an oral school for the deaf, three-quarters of those with hearing thresholds better than 90 dB (ISO) at 1000 or 2000 Hz had speech intelligibility scores better than 70% whereas only one-tenth of the students with poorer hearing at these frequencies had similar intelligibility scores. The classic investigation of errors in phoneme production by deaf children is that of Hudgins and Numbers (1942). Their main findings were nonfunction of the initial or final consonant, errors in clustered consonants, errors in voicing and nasality, substitutions, and either neutralization or diphthongiza795
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tion of vowels. Vowel production by deaf children shows overlap and poor definition of formant areas (Angelocci, Kopp, and Holbrook, 1964). There is a lack of correct timing in the movement from one articulatory position to another (Calvert, 1961; Martony, 1966). The speech is characterized by poor breath control (Hudgins, 1937, 1946) and errors of intonation, duration, and rhythm (Lafon et al., 1967; John and Howarth, 1965; Hood, 1966). These authors believed nonarticulatory or suprasegmental aspects of the children's speech to be a strong deterrent to intelligibility. A number of investigators have indicated the necessity for a detailed examination of the auditory capacity of the deaf child as it relates to speech production. The present study was undertaken in an effort to supply some of this information. A battery of measurements that included residual hearing for tones, phoneme recognition, articulatory and prosodic errors in speech production, and speech intelligibility scores was used. The relations among these variables were examined in an attempt to answer the following questions: 1. What are the relationships between a deaf child's hearing for pure tones and for speech sounds, and the articulatory and prosodic features of his speech production? 2. What variables in addition to hearing may account for divergence in individual children from the general trends that may be found? 3. What is the relative importance to speech intelligibility of various articulatory and prosodic features of the children's speech? PROCEDURE The subjects were 40 children with severe to profound congenital deafness, obtained from the population of a large day and residential oral school. They were chosen in the age ranges eight to 10 and 13 to 15 years. There were equal numbers of males and females in each age group. The children were of normal intelligence, as determined by standard tests, and presented no known anomalies other than deafness. One child in the older group and eight in the younger group were the children of deaf parents. Sign was designated as the principal language in the homes of seven of these nine children. Deafness had been diagnosed in the first year of life for 24 of the 40 children, in the second year for 12, and later than the second year for four. The age at obtaining the first hearing aid ranged from one to five years and at beginning special education 11 months to 11 years. For the largest number (16 children) special education was begun between two and three years. Additional information obtained for each child included hearing of siblings, language used in the home (English, sign, other), degree of parental cooperation with the school (as an indicator of parental motivation), apparent adequacy of the hearing aid, and adequacy of use of the hearing aid. Testing was performed in a sound-isolated two-room audiometric suite. 796 1ournal o[ Speech and Hearing Research
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18 795-811 1975
Audiological measures included pure-tone air conduction response levels (ISO, 1964) from 125 to 6000 Hz in half-octave steps; omitting bone-conduction measures because no child's previous audiograms showed any significant airbone gap; uncomfortable loudness levels for tones at 250 and 1000 Hz; speech defection level; and speech reception threshold, where obtainable. A test of phoneme recognition, consisting of 50 minimal-contrast triplet sets employing a very simple vocabulary, was designed for the study. The test presented a balanced set of contrasts for the articulatory features of place, manner, combined place and manner, and voicing vs nasality, as well as vowel contrasts. These were presented by earphone to one ear only of each subject. The ear selected was that in which the hearing aid was worn (25 children). If the child wore binaural aids (14 children) or no aid (one child), then the ear selected was the one with the better speech threshold (six children). If no speech threshold had been obtained, the ear selected was the one in which a pure-tone response had been obtained for a higher frequency (four children). If none of these criteria could be applied, the right ear was chosen (five children). A detailed description of the preparation and recording of the word lists appears in Smith (1972). To obtain a speech sample, a list of 20 sentences was recorded by each child. The sentences contained a transition to and from the v o w e l s / i / , / ~ e / , a n d / u ! for each place of consonant articulation. All consonants were represented in initial, medial, and final position, except where this does not occur in English and except for those with a frequency of occurrence in the spoken language of less than 0.1~ (Denes, 1963). These sentences were rerecorded on 40 listening tapes in such a manner that the order of sentences differed on every tape with each sentence spoken by a different child. Each tape was heard by three listeners (total of 120 listeners), all without significant previous experience in hearing the speech of deaf persons. The listeners, who each heard one tape only, wrote down as much as they could of what each child said with a maximum of two hearings of each recorded sentence. They then gave a rating of each child's intelligibility on a 1 (best) to 5 (poorest) scale. The responses of all listeners were scored word by word, and an intelligibility score was obtained for each child based on words correctly understood as a percentage of selected key words in each sentence. The tape recordings of the children's sentences were transcribed by skilled phoneticians of whom 11 in all participated. The resulting transcriptions were translated into a numerical code (Smith, 1972) for subsequent computer analysis. An additional set of tapes was prepared consisting of five consecutive utterances by each of the 40 children. These tapes were heard by three experienced speech pathologists who made binary judgments (present-not present) of errors in nonphonemic and suprasegmental aspects of the speech. The parameters judged included three error categories for voice quality, two for voice pitch, two for phonatory control, two for intonation, two for stress, four for fluency, and four for rate of speech. SMrrH: Residual Hearing 797
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RESULTS
Hearing Measures All but three children had an average hearing level in the better ear of 92 dB or poorer for 500, 1000, and 2000 Hz. Many deaf children, however, do not respond within conventional audiometric limits at 2000 Hz. In this group, 24 children of the 40 did not respond in either ear at 2000 Hz, while all b u t three children had a response in at least one ear to 1000 Hz. Because the aim was a meaningful description of hearing level as one variable affecting intelligibility of speech, it seemed appropriate to consider hearing levels at frequencies that were measurable with most of the children. Various frequencies were examined in correlations with the intelligibility data, and the average of 125, 500, and 1000 Hz was selected. Table 1 gives values of the correlation coefficient for pure-tone response TAnLE 1. Values of the correlation coefficient for various measures of hearing. PRT, phoneme recognition test. d[ = 38; p(0.05) = 0.31; p(0.01) = 0.40; p(0.001) = 0.51.
Related Measure Average of 125, 500, and 1000 Hz PRT errors Total Place Manner Placemanner Voicing Vowel
Highest Frequency1 Detectea
Average of 125, 500, and 1000 Hz
125
Hearing Level in dB (Hz) 250 500 750
1000
- 0.62
-- 0.43 - 0.22 - 0.46 -- 0.08 --0.20 - 0.33
-
0.57 0.02 0.44
0.39 - 0.05 0.40
0.39 0.04 0.29
0.42 - 0.06 0.18
0.39 0.55 0.38
0.17 0.40 0.24
0.33 0.34 0.23
0.43 0.50 0.25
0.57 0.07 0.44
0.62 0.10 0.47
0.37 0.48 0.38
0.40 0.42 0.48
levels and the various sections of the phoneme recognition test ( P R T ) . Data for frequencies above 1000 Hz were not included because of the small numbers of children responding. Because threshold at 1000 Hz was correlated significantly with several portions of the PRT, the responses were examined with subiects divided according to response at that frequency. There were eight children with hearing levels of 95 dB or better at 1000 Hz; 16 with hearing levels of 100-105 dB; 11 with hearing levels of 110 dB; and five with no response in the test ear at 110 dB, the highest level tested. For each section of the PRT, a mean score was obtained for each of these groups of children. These group means for percentage of correct response to each type of test item, together with the standard error of the mean, are shown in Table 2. Responses to items concerned with place of articulation are not included since they show little change as the result of hearing level at this frequency. 798 Journal of Speech and Hearing Research
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18 795-81l
1975
TABLE 2. Mean and standard error of percentage of correct responses to four types of items in the phoneme-recognition test, subjects grouped according to hearing at 1000 Hz in the test ear. 95 or better (N = 8) s~
Item
Manner Voicing Vowels Placemanner
Hearing Level (dB) 100-105 110 (N = 16) (N = 11) ~ s~ ~2 s~
> 110 (N = 5) 9 s~
64.0 56.2 58.0
9.5 4.9 6.8
50.0 51.6 41.0
4.5 3.7 3.4
45.4 44.7 33.8
5.6 5.1 4.0
40.0 33.3 44.2
4.6 3.7 4.7
45.3
7.4
35.1
3.6
32.9
4.2
22.5
4.6
With a single reversal for vowel items in the poorest hearing level group, the proportion of correct responses increased as the hearing level at 1000 Hz improved. The smallest improvement occurred between the two middle groups, which include children whose hearing level at 1000 Hz was 100 to 110 dB. The sharpest improvement was in the responses of the best-hearing group over the next group, on vowel items and those involving manner of articulation. Scores on voicing items are a little poorer than on manner items, and vowel items considerably poorer, for the two middle groups. These findings are generally consistent with those of Pickett et al. (1972). A comparison of total score was made between the older and younger children with hearing parents, and between the younger children with hearing and with deaf parents. Table 3 gives the mean and standard error of the TABLE 3. Mean and standard error of percent errors on phoneme recognition test, with children grouped according to age and parents' hearing. For younger and older children of hearing parents, t = 2.20, df = 29 (p < 0.05). For younger children of hearing and of deaf parents, t = 1.18, df = 18.
Datum
N Mean %error s~ .
.
.
.
.
.
.
.
All Children
older, Hearing Parents
Younger, Hearing Parents
Younger, Deaf Parents
40 56.0 1.7
19 51.0 2.8
12 59.0 2.6
8 63.0 2.0
.
percent errors in the 50-item test, according to age group and parents' hearing status. The reults of a t test for differences between means also is shown. There is a significant difference between the younger and older children of hearing parents, and some difference, not statisticallv significant, between the younger children of hearing and of deaf parents. Phoneme Analysis
From the phonemic transcriptions, a breakdown was obtained of the segSMITH: Residual Hearing
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799
TABLE 4. Rank order of percent correct production of consonant phonemes, data pooled over all children./n~/and/5/were not targets.
Phoneme
/b/ /w/ [m/ /p/ /f/ /1/ /v/ /n/ /r/ /j/ /d/ /k/ /h/ /0/ /5/ /t/ /g/ /n/ /s/ /~/ /z/ /ds/ /t~/ Mean
Total Occurrences
Correct Production (%)
400 400 520 280 360 480 240 680 360 40 600 640 400 200 240 560 160 120 280 120 600 120 160
85 79 72 70 70 70 64 61 55 53 40 40 39 38 38 37 36 30 24 22 21 18 16
Error (Including %Omission) in Each Word Position (~) Final Initial Medial
11 23 34 25 24 26 40 26 38 50 41 53 56 63 70 41 48 75 65 72 73 78 47
(1) ( 1) ( 1) (0 ) (2 ) (8) (3 ) (5) ( 1) (15) (8) (16) (33) (1) (5) (4) (1) (10) (5) (0) (5 ) (5)
10 (10) 30 ( 3 ) 25 (3 ) 26 (:/=0) 33 ( 5 ) 24 (10) 27 (6 ) 36 (20) 76 (20) 43 (24) 50 (20) 68 (35) 64 (13) 43 (5) 68 (55) 63 (15) 76 (44) 75 (10) 80 (15) 60 (8) 80 (16) 50.3
43
(15)
29 39
(10) (10)
45
(15)
37 49
(9.5) (25)
40
(30)
m
m
65 74
(39) (44)
58 55 73 I00
(13) (13) (41) (67)
9o
(8o)
76 90 83
(39) (32) (50)
88
(55)
95 (47) 64.7
mental errors made by the children. A summary of the consonant errors appears in Table 4. The consonants are ranked in order of percent correct production for all occurrences except occurrences in blends. The percentage of errors in initial, medial, and final position also is shown. The figures in parentheses are the percentages of omission in each position. Consonants with a bilabial place of articulation head the list of correct productions followed by all the glides, a n d / f / , / v / , a n d / n / . Stops in the alveolar and velar r e g i o n , / h / , and the lingua-dental fricatives follow. Near the bottom a r e / 1 3 / a n d the alveolar and palatal fricatives. Affricates have the greatest proportion of error. The single most frequent error for nearly all consonants was omission. Those for which omission was not the most frequent error were /p/ a n d / b / , which were substituted for each other; / f / , for w h i c h / v / was substituted; /0/ and /~)/, which were replaced by / t / and / d / ; and / w / , for which / b / was the most frequent substitution. While there is no difference in the mean proportion of errors in initial and medial position, there is a marked increase for errors in the final position, and a major proportion of these were omissions. The glottal stop was a frequent substitution for other stops (except the bilabials) and also f o r / h / . 800 1ournal of Speech and Hearing Research
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18 795-811 1975
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0
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o
.o r
N
0
0
c~
0
2
SMrrrt: Residual Hearing 801
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The total errors of each consonant phoneme were separated into the classes of single-feature errors (place, manner, or voicing), two-feature errors (place and manner, place and voice, or manner and voice), and three-feature errors (place, manner, and voicing). Table 5 summarizes the consonant errors in terms of these articulatory features. Among voiced-voiceless cognates, substitution toward the voiced member of the pair was more common than substitution toward the voiceless. Except for the glottal stop substitution, errors of manner and voicing predominated over errors of place of articulation. The low proportion of distortions should be noted. This was partly due to the fact that the phoneticians were encouraged to transcribe broadly, in order to obtain as much congruence between sets of transcriptions as possible. If a phoneme was recognizable as itself, they tended to give it its phonemic symbol with no diacritical modifications. Another factor was the high rate of omissions which reduced the probability of a phoneme being described as distorted./rj/, for example, was never heard as distorted because it was almost never produced. The fairly large proportion of distortions and unidentifiable substitutions for /b/, the phoneme most often produced correctly, is explained by the fact that /b/ was seldom omitted; the bilabial consonants all had low percentages of omission. The other consonant with a low proportion of omissions was //5/, which was replaced in most occurrences b y / d / . The percentages of error for vowel phonemes are shown in Table 6, with TASLV.6. Rank order of percent correct production of vowel phonemes, data pooled over all children. Vowel I^1
/o/ Icl lul la~l
/u/ /x/ /a/ /ou/ /i/ /aft /~/ /ex/ /~,/ /ju/ /~/
Total Occurrences
Correct Production (~)
40 360 280 3t]0 800 80 640 240 200 920 200 240 240 40 40 40
92.5 84.2 79.0 74.7 74.6 73.7 69.2 67.1 64.0 61.6 58.5 52.1 51.7 40.0 20.0 15.0
vowels ranked in order of correct production. All vowels and diphthongs that appeared in the selected words of the 20-sentence list are shown in the table. However, the sentence list was designed to display /i/, /~e/, and /u/; other 802 ]oumal of Speech and Hearing Research
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18 795-811 1975
vowels occurred randomly. For this reason, two English diphthongs, /at;/ and /3I/, do not appear at all. The low central vowels were produced correctly most often, and there was a tendency for all vowels to drop to a more neutral position./i/ a n d / i / w e r e the most frequent substitutions for each other, with /~/ being substituted for /i/ roughly twice as often as /i/ was substituted for /i/. /~r/ was the most frequent substitution f o r / u / , b u t / A / w a s substituted f o r / t r / m o r e often than was /u/. /A/ was also the most frequent substitution for /a/. /u/ became diphthongized frequently, as did /3/. The most common error in diphthong production was failure of the off glide, or, in the case o f / j u / , of the on glide. Many vowel phonemes could not be described in terms of any standard target, and were labeled as unidentifiable substitutions. Intel~gibi~ty
Speech intelligibility scores ranged from 76.1~ to 0~, with a mean of 18.7~. Table 7 shows the mean and standard error of the mean of intelligibility scores for all children and for the groups with hearing and with deaf parents. Since the children of deaf parents did not differ in any systematic manner from the others with respect to amount of residual hearing, the difference in their speech intelligibility is very striking. T~LE 7. Mean percent and standard error of speech intelligibility, children grouped according to age and parents' hearing.
Datum
N Mean intelligibility s~
All Children
Older, Hearing Parents
Younger, Younger, Hearing Deaf P a r e n t s Parents
40.0
19.0
12.0
8.0
18.7 3.2
28.5 5.6
14.2 2.6
4.2 1.5
Table 8 displays the mean percentage of phoneme production errors in various categories, for each quartile of intelligibility. The analyzed words in the sentence lists included 200 consonant and 110 vowel or diphthong tokens, for a total of 310 target phonemes per child. Based on this number of targets, the children as a group averaged 15.4~ consonant errors, an additional 14.5g omissions, 9g vowel and diphthong errors, and 4~ unidentifiable substitutions. Errors of combined place-voice, manner-voice, and place-manner-voice are not ineluded in Table 8 because their total percentage for all children was only 3.5~. Errors of place of articulation are virtually the same for all quartiles of intelligibility, and voicing errors also remain about the same, with a reversal in direction between the second and third quartile. There is a systematic decrease in percentage of manner errors and combined place-and-manner errors, and a S.~,IITH: Residual Hearing 803
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'I'AnLE 8. Mean and standard error of percentage of phoneme production errors in several categories, for each quartile of intelligibility. All percentages are based on 310 target phonemes. N = 10 in each quartile. Q1 Error Type
Place Voice Manner Place and manner Vowel and diphthong Omission Unidentifiable substitutions
Qe
X g,
s~
1.81 1.19 2.12 3.38 5.93
0.38 0.25 0.48 0.41 0.64
9.83 1.03
1.50 0.25
Qa
X~
Q4
s~
X~
s~
X~
s~r
1.84 2.90 2.22 3.90 8.35
0.22 0.71 0.30 0.44 0.80
2.74 2.58 3.06 4.83 10.22
0.37 0.31 0.39 0.55 0.59
2.50 2.90 3.93 5.03 11.45
0.37 0.65 0.47 0.54 1.02
17.60 2.45
1.50 0.44
15.96 3.06
1.06 0.73
18.64 9.29
1.10 2.77
m a r k e d but not systematic decrease ill p e r c e n t a g e of omissions, in going from the fourth to the first quartile. The rate of decrease in vowel errors b e c o m e s s u b s t a n t i a l l y greater b e t w e e n Quartiles 2 and 1, a n d there is a very large decrease in u n i d e n t i f i a b l e substitutions b e t w e e n Quartile 4 a n d Quartile 3. The extent to w h i c h intelligibility correlates with s e g m e n t a l errors (r = - 0.80) is shown b y the scatterplot of F i g u r e 1. On average, intelligibility
I
I
i
I
I
I
I
I
80
6~to v 4O o
0 0
20
40
6O
vt 80
PERCENT SEGMENTAL ERRORS F~c;tmE 1. Percent intelligibility as a function of the frequency of segmental errors. V : older group, hearing parents. V: older group, deaf parents. @: younger group, hearing parents, o: younger group, deaf parents. 804
Journal of Speech and Hearing Research
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18 795-811
1975
decreases with increasing frequency of segmental errors. The relationship is approximated quite well by the solid curve, a quadratic polynomial fitted by the method of least squares. This curve may be regarded as representing average performance for any given frequency of segmental errors. However, the data show a fair degree of dispersion, and children with roughly the same proportion of segmental errors can have speech intelligibility scores differing by as much as 30 percentage points. These differences appear to be related in part to certain suprasegmental errors. Prosodic Analysis
The errors' scores resulting from the judgments of suprasegmental aspects of the children's speech were subjected to factor analvsis. Two fairly significant factors emerged. One related in general to poor phonatory control, including intermittent phonation, inappropriate variations of pitch and loudness, and excessive variability of intonation. This factor, together with one related to rate of speech production, accounted for approximately 50% of the variance, the remaining factors accounting for small proportions. The solid curve of Figure 1 represents expected intelligibility based on segmental errors alone. The extent to which actual intelligibility scores deviated from this curve showed a moderate linkage (r = - 0.39) with the summed ratings of the judges for errors of phonatory control. Thus a child whose speech intelligibility is less than typical for a given frequency of segmental errors also is likely to have a greater frequency of the suprasegmental errors considered here. Relation of Hearing Mea, s~ures to Speech Production
The median hearing levels in the test ear for children in each quartile of speech intelligibility are shown in Table 9. Quartile 1, the most intelligible children, had slightly superior hearing at all frequences, and a median response a full octave higher (3000 [lz) than the children in Quartile 2. Those in Quartile 2 showed a median response to 1500 Hz, as against 1000 Hz for Quartiles 3 and 4. Table 10 presents values of the correlation coefficient for various hearing
TABLE 9. Median hearing levels in decibels in the test ear for children in each quartile of intelligibility. The audiometric reference is ISO 1964. Frequency (Hz) 1500 2000
Quartile
125
250
500
750
Q1 Q2
55 70
70 80 75
85 90 95
~ .... 10-0..... 1 0 5 100 105 110 105 110 >110
--110 .... 110....... ~ 1 ~ ...... >110 ~>110 >110 >110 >110 ~>110 ~>110 >110 >110
95
105
>11o
Q3
65
Q4
70
1000
110
>110
3000
>110
4000
>110
6000
>110
SMI'rH: Resqdual Hearing 805
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TABXm 10. Values of the correlation coefficient for hearing measures, speech-production errors, speech-intelligibility score, and rating. PRT, phoneme recognition test. df "-38; p (0.05) = 0.31; p (0.01) = 0.40; p (0.001) = 0.51.
Hearing Measure
Total Phoneme Errors
Intelligibility Score
Intelligibility Rating
Average of 125, 500, and 1000 Hz Highest frequency detected
0.46 - 0.13
-0.65 0.35
0.53 - 0.28
Itearing level 125 Hz 250 Hz 500 Hz 750 Hz 1000 Hz PRT Total score Place errors Manner errors Place-manner errors Voicing errors Vowel errors
0.28 0.17 0.41 0.48 0.46 - 0.64 - 0.03 0.42 0.35 0.60 0.53
-
0.54 0.40 0.48 0.57 0.55
0.35 0.18 0.42 0.56 0.56
0.78 0.03 -- 0.57 -0.49 -0.65 -0.63
-0.70 0.00 0.48 0.36 0.65 0.56
measures, total segmental errors, the intelligibility score, and the intelligibility rating. Since the listeners rated good intelligibility as 1 and poor intelligibility as 5, the signs in the last two columns are opposite. As before, frequencies above 1000 Hz are not tabled because of the small number of responses. There were, however, no older children with hearing above 1500 Hz in the two poorest quartiles of intelligibility. Of the 18 children who responded to any audiometric frequency above 1000 Hz, 13 were in Quartiles 1 and 2. These included nine older and four younger children. Chi square was computed on 2 • 2 contingency tables for response/no response at each frequency from 1500 to 4000 Hz, compared with above/below mean intelligibility. The chi square was significant at less than 0.05 for 2000, 3000, and 4000 Hz, although the expected cell values were very small. It appears that the hearing sensitivity of the deaf child, as it relates to the intelligibility of his speech, may be summarized reasonably well in terms of the average hearing at 125/500/1000 Hz and the extent of hearing into the higher frequencies. Such a description is similar in principle to the one proposed by Risberg and Martory (1972). Martony I has pointed out that the pure-tone audiogram can give only an indication of the deaf child's potential for auditory reception and for speech production, and that additional measures are necessary. Erber (1974) suggests classification of hearing impairment on the basis of perception of simple speech material (for example, spondaic words). 1j. Martony, personal communication (1972).
806 Journal of Speech and Hearing Research
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18 795-811
1975
Effect of Additional Variables A considerable amount of background information on the children was collected at the time of selecting the subjects for testing. In addition to the parents" hearing status, the factors that seemed to have a possible bearing on speech intelligibility were the quality of parental cooperation with the school (as a reflection of parental motivation), the age when the child obtained his first hearing aid and when he began special education, and the adequacy of use of the hearing aid. There was a modest positive correlation between the age of obtaining the first hearing aid and speech intelligibility (r = 0.32) and between intelligibility and age of beginning special education (r = 0.32, p = 0.05 for both). That is, there was some tendency for the better speakers to have received hearing aids and begun special education later than the poorer speakers. This is explainable by the fact that most of the poorer speakers were among the children with either the least amount of residual hearing, the children of deaf parents, or both. These disadvantages frequently were not offset by early attention. Eight children received hearing aids or special education before the age of two years; none received both before this age. Therefore, too few of the children received early help to allow a real measure of the effect of this variable. Of these eight children, six were in the lower two quartiles of intelligibility. More children in the upper two quartiles were good hearing aid users, in the opinion of the school, than in the lower two quartiles. In the matter of parent cooperation, again according to the school's judgment, Quartiles i and 4 were identical. Good vs poor use of hearing aid and good vs poor parent cooperation were compared by means of chi square with mean speech intelligibility, mean prosodic score, and mean proportion of total phoneme errors. In none of these tests did the chi square demonstrate a difference approaching the 0.05 level of significance. There was no tendency for a difference in speech intelligibility to be associated with the hearing status of the deaf child's siblings. A recent score on either the Wechsler or the Leiter Scale was available for all children. A correlation coefficient obtained beween these test scores and speech intelligibility was -0.17, or essentially no relationship at all. This agrees with the findings of previous investigations that, at least within the range of "normal" intelligence, such test scores are unrelated to speech skills. DISCUSSION The purpose of this investigation was to examine relationships between speech intelligibility and various measures of hearing and speech skills in deaf children. Intelligibility was related to hearing level for pure tones, but the measure most closelv related to intelligibility was the test of phoneme recognition. For most of the children, the auditorv recognition of speech features was SMrrn: Residual Hearing 807
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reflected in the ability to produce intelligible speech. This could occur even in the absence of ability to recognize whole words; there were some children for whom no speech reception threshold could be obtained with spondee words, who nevertheless scored above the mean on the phoneme-recognition test and who were in the upper two quartiles of intelligibility. As would be anticipated, performance on most portions of the phonemerecognition test, and most aspects of phoneme production, were directly related to hearing sensitivity. The hearing sensitivity index used here was the average of 125/500/1000 Hz. Much of the information on manner of articulation, voicing, and vowel differences is carried below 1000 Hz, and ability to recognize these differences was significantly related to speech intelligibility. However, voicing errors in consonant production, while very numerous, had a rather low correlation with speech intelligibility (r = - 0 . 3 6 ) . There was no evidence of a relationship between errors involving place of articulation, either in recognition or production, and any hearing abilities, or between place of articulation errors and intelligibility of speech (r = - 0 . 2 0 ) . The poorest groups in intelligibility made about the same proportion of place errors as the best (Table 8). This is reasonable from the standpoint that children with the least amount of hearing, particularly in the low frequencies, may learn earlier in life to watch the faces of those around them who are speaking. Place of articulation, the one reasonably visible element of speech production, may thus be the earliest learned of their speech behaviors. Much acoustic information oil place of articulation is carried in the higher frequencies of the speech spectrum and requires integration of rapid spectral and intensity changes. The deaf child, even if he has sensitivity in these frequency regions, may not be able to use this information in the same manner as a normal-hearing listener. It is apparent ill Table 8 that identifiable consonant errors in speech production remain in much the same proportion from one quartile of intelligibility to the next. Vowel and diphthong errors, omissions, and unidentifiable substitutions decreased quite systematically from the poorest to the best speakers. The poor identification of the vowels of deaf children has been described by Angelocci, et al. (I964) and quantified ill terms of atypical formant ratios. The major physiological correlate of these improper ratios is inaccurate placement of the tongue. It may be questioned in deaf children whether poor vowel placement is the result of improper consonant targets, or whether the children, having poor appreciation of the quality of most vowels, never aim for a true vowel target and tend to produce a neutral vowel as a substitute for all others, regardless of consonant environment. Examination of the data on speech production reveals some similarities and differences with respect to the study of Hudgins and Numbers (1942). Omission of the initial consonant was less frequent in the present study than omission of the final consonant. Voiced-voiceless confusions were frequent in both studies. However our correlation of -0.36 between these confusions and speech intelligibility is somewhat lower than the -0.44 reported by Hudgins 808 Journal o[ Speech and Hearing Research
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18 795-811 1975
and Numbers. The correlation coefficient for consonant phoneme errors and intelligibility in the earlier work is the same as reported here for identifiable consonant errors: -0.70. The present data agree exactly with the earlier data on types of vowel errors, but show a higher correlation, -0.75, for vowel errors and intelligibility than the --0.61 reported by Hudgins and Numbers (1942). The present findings, those of Nober (1967), and those of Markides (1970) are in essential agreement on the order of correct consonant production: the bilabial consonants, the glides, and / f , v / a r e most often correct, and the palatal and alveolar fricatives, the affricates, and /I3/ are the poorest. The mean intelligibility, to naive listeners, of the recorded speech of the deaf children studied here (18.7~) is remarkably similar to that found in previous investigations (Brannon, 1964, 20.7~; John and Howarth, 1965, 19~; Markides, 1970, 19.1%), where age groups, hearing of the children, and method of deriving the scores all were comparable. One influence on the scores we obtained was, of course, that these deaf children were attending a school for the deaf; that is, their general communication skills, including speech, were not such as to permit their attendance at a regular school. The percent intelligibility, obtained was also directly related to the proportion of children of deaf and of hearing parents in the group. Had there been fewer children of deaf parents, the mean intelligibility of the group might have been higher. It was not possible in selecting the sample of children for our population to match exactly the numbers of children with deaf and with hearing parents. Eight of the nine children with deaf parents were in the younger group, thus all the tests between children of deaf and of hearing parents were restricted to this age group. Nevertheless, there was considerable consistency in the performance of the two groups of younger children on each comparative measure, with those of deaf parents performing more poorly. This may be due to the lack of early and ongoing experience of speech in the home, affecting the children's ability to make use of the information their residual hearing will permit them to receive. Previous investigators have shown the extent to which the intelligibility of deaf children's speech can be interfered with by errors of duration (John and Howarth, 1965), intonation and phrasing (Lafon et al, 1967), and speech rhythm (Hudgins and Numbers, 1942; Hood, 1966.) There was some evidence in the present data of an interaction between prosodic errors and speech intelligibility, but a clear pattern did not emerge. However, the most frequent comment of the inexperienced listeners from whose responses the intelligibility scores were derived, was that what they were hearing sounded like a foreign language. Hearing an unfamiliar pattern, to which his experience of English prosody does not apply, a listener cannot bring his knowledge of the statistics of his language to bear in an attempt to synthesize the meaning of an utterance. Speech training of deaf children has traditionally put most of its attention on articulation. It appears that this concentration may be misplaced. Training toward improvement in the stress and intonation patterns of the deaf SMITH: Residt, al Hearing 809
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child's speech should enable a listener to compensate for omitted and substituted elements and should result in better intelligibility.
ACKNOWLEDGMENT 9Research was partially supported by Grant 09252 from the National Institute of Neurological Diseases and Stroke. This material is drawn from a doctoral dissertation completed under the direction of Harry Levitt while the author was a U.S. Office of Education Fellow in the City University of New York. Requests for reprints should be sent to Clarissa R. Smith, School of Health Sciences, Department of Communication Sciences, 105 East 106th Street, New York, New York 10029.
REFERENCES
ANGELOCCI,A., KoPP, G., and HOLBROOK,A., The vowel formants of deaf and normal hearing eleven to fourteen-year-old boys. 1. Speech Hearing Dis., 29, 156-170 (1964). Bo(yrrmoYo, A., Distribution of hearing levels in the student population of Clarke School for the Deaf. Sensory Aids Research Project Rept. #3. Northampton, Mass.: C. V. Hudgins Diagnostic and Research Center, Clarke School for the Deaf (1970). BRANNON, J. B., Jr., Visual feedback of glossal motions and its influence on the speech of deaf children. Doctoral dissertation, Northwestern Univ. (1964). CALVERT, D. R., Some acoustic characteristics of the speech of profoundly deaf individuals. Doctoral dissertation, Stanford Univ. (1961). DENES, P. B., On the statistics of spoken English. 1. acoust. Soc. Am., 35, 892-904 (1963). E~.R, N. P., Pure-tone thresholds and word-recognition abilities of hearing-impaired children. J. Speech Hearing Res., 17, 194-202 (1974). HooD, R. B., Some physical concomitants of the perception of speech rhythm of the deaf. Doctoral dissertation, Stanford Univ. (1966). HutX~INS, C. V., Voice production and breath control in the speech of the deaf. Am. A. Deaf, 82, 338-363 (1937). HtrDGZNS, C. V., Speech breathing and speech intelligibility. Volta Rev., 48, 642-644 (1946). HtrI~INS, C. V., and NrJMnERS, F. C., An investigation of the intelligibility of the speech of the deaf. Genet. Psychol. Monogr., 25, 289-392 (1942). JOHN, J. E. J., and HOWAnTH, J. N., The effect of time distortions on the intelligibility of deaf children's speech. Lang. Speech, 8, 127-134 (1965). LAFON, J. c., DULAC,A. M., LACROIX,F., and PLANTIER, A., La melodie de la parole et la surdite. Rev. Lar. Otol. RhinoI., 88, 179-187 (1967). MARrJOES, A., The speech of deaf and partially hearing children with special reference to factors affecting intelligibility. Brit. J. Dis. Commun., 5, 126-140 (1970). MARTONY, J., Studies on the speech of the deaf. Q. Prog. Status Rept. Stockholm, Sweden: Speech Transmission Laboratory, Royal Institute of Technology (January 1966). MONTCOMVaY, G. W. G., Analysis of pure tone audiometric responses in relation to speech development in the profoundly deaf. 1. acoust. Soc. Am., 41, 53-59 (1967). NoaEa, E. H., Articulation of the deaf. Except. Child, 33, 611-621 (1967). PICKETT, J. M., MARTIN, E. S., JOHNSON, D., SMITH, S. B., DANIEL, Z., WILLIS, D., and OTIS, W., Patterns of speech feature reception by deaf listeners. In, C. G. M. Fant (Ed.), International Symposium on Speech Communication Ability and Profound Deafness, 1970. Washington: A. G. Bell Association (1972). RISB~RC, A., and M.~RTONY, J., A method for the classification of audiograms. In, C. G. M. Fant (Ed.), International Symposium on Speech Communication Ability and Profound Deafness, 1970. Washington: A. G. Bell Association (1972). SMITH, C. R., Residual hearing and speech production in deaf children. Doctoral dissertation, City Univ. of New York (1972). Received October 1, 1973. Accepted May 17, 1975. 810 1ournal of Speech and Hearing Research
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18 795-811 1975
APPENDIX Phoneme recognition test items. The italicized words were the stimuli used in the experiment. Items were randomized for presentation. Place Contrasts fat
sat
pea bum
tea gum see /et lead s/t bib
he wet weed sip bid
Place-Manner Contrasts hat key dumb
chair
fair
mumps
she
then
dumps D den
yet sick
moo when bum
big
mass
read
Manner Contrasts zoo
bill /ot
zip bet me pad bud
do mill dot dip met be
pan buzz,
we
do ten buzz map
Voicing Contrasts (cont.) seat but
pair jumps
new
mat mark mill new tip some rim cup
wet we al ~un
pat knee
seen bud
gee men you hen
Vowel Contrasts bit
Pete
bug
pat park
bat
pill two
bill do
hot neat lock sick heat feet feel pool
dip sub rip cub pan D
nip
~eel
match
Voicing Contrasts will not lip
seed bun
bark
sup r/b
fall pet
come
boot it ~t nut
luck suck hit foot full
pull pal lid
beet ot ~oot not look sock hut fit
fool pill
fool
~e~ 1 full
pot
put
pad tea
SMrrri: Residual Hearing
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811
