Cochlear Implants
Consonant Production in Children Receiving a Multichannel Cochlear Implant*
Emily A. Tobey, PhD; Susan Pancamo, MCD; Steven J. Staller, PhD; Judy A. Brimacornbe, MA; Anne L. Beiter, MS
Department of Communication Disorders, Louisiana State University Medical Center, New Orleans, Louisiana [E.A. T., S.P.]; and Cochlear Corporation, Englewood, Colorado [S.J.S., J.A.B., A.L.B.]
ABSTRACT Consonant production was investigated in 29 children participating in the federal Food and Drug Administration's clinical trials of the Nucleus WSP-Ill cochlear implant. Speech samples were collected preimplant and 1 year postimplant. A significantly greater number of children produced stop, nasal, fricative, and glide consonants postimplant. Voiced stop consonants were used by more children than the voiceless cognates; however, voiceless fricatives were used more than voiced fricatives. Visible places of articulation were used more frequently than less visible places of articulation. Comparisons to Smith's data (J Speech Hear Res 1975;18:795-811) revealed qualitative similarities but postimplant, quantitative differences were observed. Post hoc analyses of the data revealed some sounds were influenced more by an implant than other sounds and suggest the role of an implant upon spontaneous speech is complex. (Ear Hear 12 1: 23-31)
A MAJOR CONSEQUENCE of deafness in children appears to be a reduced repertoire of sound segments, particularly consonants. The reduced segmental repertoire commonly includes errors such as substitutions of one sound for another, omissions, and distortions (Osberger & McGarr, 1983). Several studies report profoundly hearing impaired speakers use visible, front consonants more frequently than less visible, mid or back consonants (Carr, 1953; Gold, 1980; Lach, Ling, Ling, & Ship, 1970; Nober, 1967; Smith, 1975). Champagne ( 1975) for example, found profoundly hearingimpaired speakers produced 37% front and 14% back sounds correctly. Manner of articulation errors frequently appear as nasal-oral substitutions, that is, the speaker nasalizes a nonnasal sound (Hudgins & NumEar and Hearing, Vol. 12, No. 1, 1991
bers, 1942; Markides, 1970; Smith, 1975; Stevens, Nickerson, & Rollins, 1978). Reports of voicing errors are also common, although there does not appear to be a consensus regarding the exact pattern of such errors. Some studies report more errors on voiced sounds whereas others report more errors on voiceless sounds (Carr, 1953; Hudgins & Numbers, 1942: Mangan, 196 1 ; Markides, 1970: Millin, 197 1 ; Nober, 1967: Smith, 1975). Profoundly hearing impaired speakers also appear to omit many consonants (Geffner, 1980; Levitt & Stromberg, 1983). Omissions occur primarily in word-final positions and relatively infrequently in word-initial positions. Few omissions are observed for consonants produced near the front of the mouth but a relatively high rate of omissions occur for consonants produced in the middle region of the mouth (Levitt & Stromberg, 1983). Thus, it would appear that profoundly hearing-impaired speakers not only experience a reduced sound repertoire but the reduced sound repertoire may also be wrought with errors. Changes in suprasegmental and segmental aspects of speech production have been reported for profoundly hearing-impaired adults and adolescents receiving single and multichannel cochlear implants (Kirk & Edgerton, 1983: Leder et al, 1986; Oster, 1987; Plant & Oster, 1986; Tartter, Chute, & Hellman, 1989; Tobey & Mecklenberg, 1987). Improved segmental aspects of speech also have been noted in a few studies examining children with single channel cochlear implants. Osberger (1988) observed more accurate sound pronunciation in single channel implant users than in hearing-impaired subjects with hearing aids. Kirk and Hill-Brown ( 1985) reported significant improvement in the imitation of nonsense syllables in children receiving a single channel cochlear implant. Significant improvements occurred for the imitation of vowels, diphthongs, and simple consonants. Examination of the spontaneous production of speech sounds with the Phonologic Level Speech Evaluation (Ling, 1976) also revealed significant improvements for children using single-channel implants (IOrk & Hill-Brown, 1985). Observations such as these suggest single channel cochlear implants may represent " Portions of the analysis of this data were completed using equipment purchased from a Deafness Research Foundation grant awarded to the first author.
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0196/0202/91/1201-0023$03.00/0 * EARAND HEARING Copyright 0 1991 by The Williams & Wilkins Co. Printed in U.S.A.
Speech in Cochlear Implanted Children
23
a viable prosthetic aid for improving the sound repertoire in profoundly hearing impaired children unable to benefit from traditional hearing aids. In order to examine the possibility that the sound repertoire of profoundly hearing-impaired children also may be influenced by a multichannel cochlear implant, we examined consonant production in a subset of children participating in the federal Food and Drug Administration’s clinical trials of the Nucleus WSP-111 cochlear implant. The Nucleus multichannel cochlear implant is designed to extract several critical features in speech signals including fundamental frequency, a voiced/voiceless decision regarding the signal, acoustic amplitudes associated with spectral peaks, and estimates of the main spectral peaks at low- (approximately 300- 1000 Hz) and midfrequency ( 1000-4000 Hz) ranges. Given the varied number of parameters extracted by the Nucleus device, one might anticipate that young children may be able to use this information to assist them in monitoring and adjusting their speech production. To explore this possibility, we contrasted speech samples produced preimplant to samples produced after 1 year’s use with the implant. Four questions were addressed: first, what types of consonants are produced by children receiving cochlear implants; second, d o children of different ages produce different types of consonants: third, are consonant repertoires influenced by a multicha nel cochlear implant: and fourth, are the consonant I upertoires used by children using multichannel cochlear implants similar t o the repertoires of hearing-impaired children without cochlear implants? METHODS AND PROCEDURES
Subjects Twenty-nine profoundly hearing-impaired children, ranging in age from 3.8 to 17.8 years, participated in the study. The children were participants of the federal Food and Drug Administration’s clinical trials of a Nucleus multichannel cochlear implant. Table 1 describes pertinent background information on the individual subjects including gender, age at time of implant, duration of profound deafness, and etiology. Subjects are ordered in terms of age at time of implant. Mean age for the group is 9.5 years and mean duration of profound deafness for the group is 6.7 years, ranging from 0.8 to 15.3 years. Meningitis was responsible for deafness in 48.3% of the subject population and unknown etiologies contributed to the deafness in 4 1.4% of the subject pool. In order to provide a preliminary investigation examining consonant production as a function of age, subjects were broken into four age categories: 5 years and younger ( N = 6), 6 to 8 years ( N = 7), 9 to 1 1 years ( N = 8), and 12 years and older ( N = 8). Mean age of the 5 years and younger group at the time of implantation was 4.6 years and mean duration of profound deafness was 2.6 years. Mean implantation age of 6 to 8 years group was 6.8 years and mean duration of profound deafness was 5.1 years. Mean duration of profound deafness in the 9 to 1 1 years group was 8.9 years and mean age at implantation was 10.2 years. Average implantation age of the oldest group was 14.9 years and mean duration of profound hearing loss was 8.9 years. 24
Tobey et al.
Table 1. Description of individual subjects.
Sex
Age (Years)
Duration of Profound Hearing Loss
19 18 11 27 46 4 25 29 8 62 23 54 52 13 55 22 51 50 47 41 49 9 2 14 38 56
M M M F F M F M F M M F M F M M M F M F F F M F M F
3.8 4.1 4.4 4.4 5.0 5.8 6.1 6.2 6.4 6.8 7.1 7.3 8.0 9.2 9.4 9.8 10.0 10.2 10.8 10.9 11.3 12.5 12.9 14.1 15.3 15.3
3.2 2.3 2.6 1.8 5.0 0.8 2.6 3.4 2.4 5.2 6.8 7.3 8.0 2.5 9.4 6.8 10.0 10.2 10.8 10.9 11.3 12.5 4.9 8.1 15.3 15.3
6 17 30
M F F
15.4 16.0 17.8
9.4 1.5 11.3
Subject Number
Etioloav Unknown Meningitis Meningitis Meningitis Unknown Meningitis Meningitis Meningitis Meinere’s Meningitis Meningitis Unknown Unknown Meningitis Unknown Meningitis Unknown Unknown Unknown Unknown Unknown Meningitis Unknown Meningitis Usher’s Maternal Rubella Meningitis Unknown Meningitis
Speech Production Procedures Video tape recordings of speech samples were acquired preimplant and after 1 year’s experience with the implant by the individual Clinical Centers participating in the clinical trials. Speech samples were obtained by either having the child respond to a series of prompts, such as picture cards, or read a passage. Clinician prompts were used to elicit speech samples in younger children and reading a passage was used to elicit speech samples in the older children. Similar elicitation procedures for each subject were used in the pre- and postimplant conditions. Thirty pre- and postimplant utterances were phonetically transcribed using the International Phonetic Alphabet by two judges (the first two authors), one experienced in transcribing speech of the deaf and the other a master level student in speech-language pathology. Intratranscriber reliability measures were acquired by a second analysis of five speech samples. Three samples represented preimplant speech and two samples represented postimplant speech. Intrareliability scores were 0.98 and 0.97 for the two judges, respectively. Intertranscriber scores also were similar (0.89 preimplant and 0.92 postimplant). Frequency of occurrence matrices were constructed for each subject at each test period. Each row of the matrices corresponded to manner dimensions and each column corresponded to the voicing and place dimensions. Data were Ear and Hearing, Vol. 12, No. 1,1991
collapsed across the two judges and. in the event of judge disagreement, both judges reviewed the tapes until agreement was reached. Initial inspection of the matrices revealed the frequency of occurrences were confounded by the age of subjects: older subjects produced longer utterances (and thus, had more opportunities for phonemes to occur because of reading passages) and younger subjects produced shorter utterances (and thus. produced fewer phonemes elicited via clinician prompts). To eliminate this confounding factor. a second set of matrices was constructed by assigning a 1 when a phoneme occurred (regardless of the number of times it occurred) and a 0 when a phoneme never occurred. Data were statistically treated using analysis of variance techniques (BMDP2V). Several investigators (Lunney. 1970; Myers, DiCecco. White, & Borden, 1982: Seeger & Gabrielsson. 1968) have demonstrated dichotomous data for dependent samples may be appropriately analyzed using analysis of variance techniques. Myers et al (1982) also have demonstrated that analysis of variance techniques may yield "reasonably honest Type I error rates, even under conditions of extreme heterogeneity of covariance" (p. 5 17). Separate between-group. within-subject analyses were run for each manner category and examined age group (4). test condition (2). place (varied as a function of manner category) and voicing (2). Probability estimates were obtained using the Greenhouse Geisser corrections. Post hoc range tests were conducted using
40
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( 5 6-8 9-11 12)
( 5 6-89-11
12)
(5 6-89-11
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12)
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Figure 1. Mean percent of children in the four age groups producing stop, fricative, glide, and nasal consonants is shown collapsed across test condition, place of articulation,and voicing.
Newman-Kuels procedure. Such an analysis provided an estimate of the proportion of children producing consonants during each of the testing conditions. RESULTS
Figure 1 illustrates the percentage of children within the four age groups producing stop, nasal, glide, and fricative consonants. A significantly greater number of children within the 12 years and older group produced stop consonants than the three younger groups [F(3,25) = 2.87, p < 0.051. As depicted in the lower Icft puncl, fewer children in the youngest age group produced fricative consonants than the other groups. The greatest number of children producing fricatives were in the oldest age group [F(3,25)= 7.47, p < 0.0011. A significant age effect also was observed for the production of glides [F(3,25) = 3.44, p < 0.031: a greater proportion of the oldest age group produced glides relative to the other groups. Similarly. a greater proportion of the children in the oldest age group produced nasal consonants relative to the three younger groups [F(3,25) = 3.13, p < 0.041. Significant main condition effects were noted for each of the manner categories as illustrated in Figure 2. Significantly more children produced stop and fricative consonants within the spontaneous speech samples collected 1 year after implantation [F(1,25) = 14.95, p < 0.001 for stop consonants and F( 1,25) = 11.5 I , p < 0.002 for fricative consonants] than the preimplant condition. A similar picture also was observed for glide and nasal productions: a significantly greater proportion of children produced these consonants after one year's use with the implant [F(1,25) = 32.89, p < 0.001 for glides and F( 1,25) = 5.22, p < 0.03 for nasal consonants] than had before receiving the implant. A greater proportion of children produced voiced, stop consonants than their voiceless cognates during
Figure 2. Mean percent of children producing stop, fricative, glide, and nasal consonants pre- and 1 year postimplant is depicted.
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Ear and Hearing, Vol. 12, No. 1, 1991
0
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25
speech as depicted in Figure 3. The more visible place of articulation consonants (bilabials) were produced by a greater number of children than less visible, alveolar or velar stop consonants. These observations were confirmed by a place of articulation by voicing interactions [F(1,50) = 3.72, p < 0.031. In addition, a condition by place of articulation by age interaction was found [F(1,50) = 2.77, p < 0.021. Figure 4 portrays the threeway interaction. Post hoc analyses using a NewmanKeuls confirmed a ceiling effect for bilabial and alveolar stop consonants as a function of test session for the oldest age group: however, significantly fewer of these children produced velar stop consonants ( p < 0.001) than bilabial or alveolar sounds. In the remaining younger groups, significantly more bilabial and velar sounds were observed postimplant ( p < 0.00 1) than in the preimplant condition. No significant increases in the number of children producing alveolar stop consonants pre- and postimplant were observed for the 9 to 1 I year old group; however, a significant increases in alveolar stops were observed in the 5 years and younger and 6 to 8 year old groups ( p < 0.001). A significant interaction between place of articulation and voicing also was present for fricative consonants [F(1,75) = 4.90, p < 0.0041. As shown in Figure 5, voiceless fricatives were produced by significantly more children than the corresponding voiced cognates. Post hoc analyses indicated the voiceless labiodental, [fI, was produced by more children than alveolar, [s, J], or linguadental, [J] consonants ( p < 0.001). The voiced labiodental, [v], was produced by more children than the other voiced consonants ( p < 0.001). No significant differences appeared between the number of children producing [d] and [z]. Significantly fewer children produced [3], perhaps because of its relatively low frequency of occurrence in English. In addition, a significant condition by voicing by age interaction was observed for fricative consonants [F(1,25) = 3.61, p < 0.021 and is shown in Figure 6. Preimplant, voiced, and voiceless fricatives were produced by an equivalent number of children 5 years and younger; however, significantly more children produced voiceless fricatives than voiced fricatives postimplant ( p < 0.00 1). Preimplant, voiceless fricatives were produced by significantly more children in the 6 to 8 year old group than voiced fricatives ( p < 0.00 1). These differences were not pres-
z 100
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I-
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E
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L
O p b
t d
k g
Figure 3. Mean percent of children producing voiceless and voiced stop consonants as a function of place of articulation is illustrated.
26
Tobey et al.
,100,
loor
w 1
0 I-
Z
FRICATIVES 80.r-
60
40
:: 20
E
w
a
0 f v
a@
J j
S Z
Figure 5. Mean percent of children producing voiceless and voiced fricative consonants as a function of place of articulation is depicted.
z 100
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0
2
80 60
40
:: 20
E
w
a
0 VL
v (5
v1 v VL 6-8
v
9-11
VL
v
12)
Figure 6. A three-way interaction between age, condition,and voicing for the fricatives is shown. Open columns, represent preirnplant.Filled columns represent 1 year postimplant.
ent in the postimplant condition. Equal distributions of voiceless and voiced fricatives were produced preimplant by the 9 to 1 I year old group; however, more children produced voiceless fricatives than voiced fricatives postimplant ( p < 0.00 1). Production of voiceless fricatives contributed to the performance differences noted in the 12 year and older group: more children produced voiceless fricatives preimplant and postimplant than voiced fricatives ( p < 0.00 1). As shown in Figure 7, a significant condition by place of articulation by age interaction also occurred for glide consonants [F(1,100) = 2.22, p < 0.011. Post hoc analyses revealed no significant increase in the number of children in the 5 years and younger group producing Ear and Hearing, Vol. 12, No. 1, 1991
[wh] (41%) and [r] (0%) pre- and postimplant. It is possible that the younger children failed to increase their production of [r] for developmental reasons. Significantly fewer of these children produced the phonemes. [w] and b]. postimplant than preimplant ( p < 0.001) and significantly more of the children produced the phoneme [a] postimplant than preimplant ( p < 0.00 1). Similarly. no significant changes were observed in the number of children in the 6 to 8 year old group who produced either [wh] (53%) or [r] (0%)and significantly fewer of the children produced [w], [j], and [l] postimplant than preimplant ( p < 0.001). No significant changes in the number of children in the 9 to 1 1 year old group producing [w] (52%) or [j] (52%) were observed pre and postimplant. However, significantly more of the 9 to 1 1 year old children produced the phonemes, [r], [wh]. and [l], postimplant than preimplant ( p < 0.00 1 ). No significant changes in the number of children in the 12 year and older group producing [w] (0%)and [l] (35%) were observed postimplant and significantly fewer of the children produced [r] and [j] postimplant ( p < 0.00 1 ). DISCUSSION
Any discussion of consonant repertoires observed in children pre- and postimplant must be tempered by the limitations of the procedures used to determine the repertoires. First, the type of analysis used in this study does not distinguish between correct and incorrect utterances. The transcriptions used here describe the range and variety of sounds classified by raters but fail to determine the accuracy of such productions. Second, identical utterances often may be transcribed differently by different listeners, as many authors have pointed out (Gold, 1980; Levitt & Stromberg, 1983; Oller & Eilers, 1975). Although the inter- and intrajudge reliabilities within this study are high, reliabilities of transcriptions acquired during the preimplant sessions are lower than those acquired in the postimplant sessions and are related to less intelligible speech preimplant. With these limitations in mind, let us return to the present data set
PRE
POST
PRE
POST
Figure 7. A three-way interaction between age, condition, and place of articulation for glide consonants is illustrated. Open circles represent [wh], filled circles represent [w], open triangles represent [r], and open diamonds represent [Q]. filled triangles represent
u],
and examine the consonant repertoires of children receiving multichannel cochlear implants. Consonant Repertoires Significant age effects are observed for each of the manner classes examined: a greater proportion of children in the 12 years and older group produced consonants than in the three younger groups. These differences are particularly evident between the oldest and youngest age groups. A greater proportion of children in the three youngest groups produced stop and nasal consonants than glide or fricative consonants. The general pattern of a greater number of children producing stops and nasals followed by glides and fricatives is similar to other reports examining manner categories in profoundly hearing-impaired speakers. Smith ( 1975) and Nober ( 1967) report profoundly hearing-impaired children produce glides correctly most often, followed by stops, nasals, and fricatives. Although stop and nasal consonants are used by a greater proportion of the children in this study, these data must be viewed somewhat cautiously since numerous investigators report profoundly hearing-impaired speakers commonly make nasal-oral substitutions (Hudgins & Numbers, 1942; Markides, 1970; Smith, 1975). As remarked above, consonant repertoires based upon the type of analyses used in this study fail to uncover correct versus incorrect productions. Since nonnasal phonemes are substituted for nasal phonemes and vice versa in many profoundly hearing impaired speakers, it is highly likely that the high occurrence of these manner classes in this study may include nasal-oral substitutions. The remarkable similarity, however, between our data set and other studies suggest the range and type of sounds used by our subjects is reflective of the manner categories typically used by profoundly hearing impaired speakers. Voicing errors also are commonly reported for profoundly hearing-impaired speakers, although the direction of voicing error differs across various studies. Some studies report the errors occur to voiceless members (Markides, 1970; Nober, 1967) and other studies report the errors occur to the voiced cognate (Smith, 1975). Examination of voicing dimensions contained within the consonant repertoires observed in this study also are mixed. On the one hand, voiced stop consonants are produced by more children than the voiceless cognates. On the other hand, voiceless fricatives are transcribed by the raters more frequently than their voiced counterparts. Several factors may underlie these observations. First, fewer observations of voiceless stop consonants may be related to diffrculties in coordinating upper and laryngeal articulators. Voiced stop consonants may be produced by simultaneous action of these articulators but voiceless stop consonants require a more complex timing of upper and laryngeal articulators. Timing ofevents may also underlie the transcribers perceptions of more frequent voiceless fricatives: fricatives are perceived as voiceless when the frication is relatively long (Borden & Harris, 1980). Abnormal ~~
Ear and Hearing, Vol. 12, No. 1,1991
Speech in Cochlear Implanted Children
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timing relationships during speech are a commonly cited problem in profoundly hearing-impaired speech and may be factors contributing to the mixed pattern of voicing dimensions observed here. Children participating in this study also appear to use places of articulation that are similar to those previously reported for other profoundly hearing-impaired speakers. A greater proportion of the children use visible. anterior places of articulation than less visible, posterior configurations. For example, examination of Figures 3 and 5 reveals a greater proportion of children produced bilabial and labiodental consonants than consonants produced more posteriorly. Nober (1967). Smith (1975). and Gold (1980) report more accurate productions of visible consonants than consonants occurring in the mid or posterior regions of the mouth. Our data are in support of these previous observations.
Influence of Cochlear Implant upon Consonant Repertoires Previous comparisons of speech processing strategies with the Nucleus speech processor (Cochlear Proprietary LTD, U.S. patent No. 4,515,158) have focused upon the percentage of information transmitted for consonants in adult patients asked to identify consonants in vowel-consonant-vowel tokens (Blarney, Dowell, Clark, & Seligman, 1987b). In such tasks, listeners are asked to identify tokens and an analysis is completed comparing the correct and incorrect features perceived. The average percentage of information transmitted for consonants in a hearing only condition was 48% for eight subjects. Average percentages of information transmitted for various features included 55 % for voicing, 52% for duration, 49% for nasality, 43% for affrication, and 33% for place cues. HochmairDesoyer, Hochmair, Burian, and Fischer ( 198 1 ) also have reported voicing, manner, and nasality features constitute the greatest amount of information transmitted in German consonants. Thus, cochlear implants appear to provide greater information regarding voicing, durational, and nasality cues than for place cues, per se, and these cues might be more evident in speech produced by children using such a device. Production data contrasting consonants produced before and after implantation reveal a complex picture. Although it is clearly difficult to separate out the contributions of a cochlear implant upon consonant repertoires versus the contributions provided by maturational or aural rehabilitation factors, a review of the data suggests the implant, perhaps in conjunction with these other factors, may provide useful information for speech production. Significantly more children produce consonants after using the implant for a year and several age interactions appear in the data. Significantly more children in the youngest group produced stop consonants postimplant, with the greatest changes occurring for bilabial and alveolar places of articulation. Significantly more children in the 6 to 8 and 9 to 1 1 year old 28
Tobey et al.
groups produced velar stop consonants in the postimplant session. Fewer changes are evident in the oldest age group because of ceiling effects. This effect highlights the difficulties inherent in preforming group comparisons among children with disparate production abilities. Such ceiling effects may have been eliminated if more stringent criteria had been applied to the children with more advanced speech skills (i.e., more than one occurrence). The data do suggest, however, that manner and place features for stop consonants are being used in speech by a greater proportion of children after receiving cochlear implants. As discussed in detail by Blarney. Dowell, Clark. and Seligman ( 1987a), information regarding voicing of stop consonants may be carried by the coded amplitude contours and FO information which is steady for voiced and random for unvoiced consonants. Front cavity resonance information, a source of place of articulation (Kuhn, 1975) appears to be coded by the F2 values. One possible approach to separating out the contributions of maturation versus the implant, albeit limited, is to compare the number of children in the youngest age group producing consonants postimplant to the preimplant performance measures of the older groups. Significantly more children in the youngest group produce stop consonants postimplant when compared to the number of children in next two older groups preimplant ( p < 0.01). If only maturational issues were a factor, one would only anticipate that the youngest group after a year would more nearly resemble the next age group, preimplant. Instead, significantly more children in the youngest group produced stop consonants postimplant than the 9 to 1 1 year old group, preimplant ( p < 0.0 1). Similar age and condition interactions also are apparent in the fricatives and glides. Significant increases are observed in the youngest group for voiced and voiceless fricatives postimplant. However, comparisons to the 6 to 8 year group suggest the implant may have influenced the incidence of voiced fricatives but not necessarily voiceless fricatives since the number of young children producing voiceless fricatives postimplant is comparable to the number of 6 to 8 year olds preimplant. Comparisons of postimplant to preimplant performance in the 6 to 8 and 9 to 1 1 year old groups suggest the implant may influence the incidence of voiceless and voiced fricatives in the 6 to 8 year olds. Similar comparisons between the two oldest groups suggest the implant may play only a minimal role. Amplitude and frequency contours are coded differently from stop consonants and high frequency fricatives may be accompanied with an increase in amplitude due to the preemphasis of the high-frequency part of the spectrum in the processor (Blarney et al, 1987a). Data from our study suggest that information from the implant, in conjunction with developmental trends for fricative acquisition, may contribute to the proportion of children using fricatives postimplant. Ear and Hearing, Vol. 12, No. 1, 1991
Applying a similar approach to the glide consonants. one finds the implant may have positively influenced the incidence of [I] in the youngest group and played a minimal role. if any, in the other groups. This is rather surprising. given that acoustically glides are composed of resonant patterns which may be coded by the implant. However, the acoustic patterns for glides also are very similar. Blarney et a1 (1987a) reported Fl and F2 values of 190 and 1810 Hz for b]. 320 and 860 Hz for [r], and 420 and 950 Hz for [I] for the glides produced in a vowel-consonant-vowel context. It may be possible that additional training and experience is needed in order to distinguish them. One of the key controversies involved in assessing the contributions of cochlear implants upon children’s performance centers upon the issue of appropriate control groups. That is, should the performance of implanted children be contrasted to normal-hearing children of similar ages or to profoundly hearing-impaired children with or without other types of prosthetic devices? As a first step in contrasting the performance of implant children to other types of populations. we compared the proportion of children producing the various consonants in this study to the proportion of profoundly hearing-impaired children producing consonants correctly in sentences previously reported by Smith (1975). Figure 8 depicts the rank order of percent correct productions of consonants pooled across 40 subjects, ages 8 to 15 years, tested by Smith ( 1975) and represented by the line. Seventeen children in our population are similar in age to Smith’s population and the percentage of these children producing consonants preand postimplant also are shown. Remarkable similarities are evident between the percentage of children producing [O, 6, k, j, v, f, m, w] preimplant to those data presented by Smith (1975). Postimplant, a greater proportion of children are producing a wider range of consonants with only three phonemes [n, r, 11 produced by fewer children than those observed by Smith (1975). It is important to note the limitations of these comparisons since Smith’s data reflects the proportion of children correctly producing sounds and our pre/post com-
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z J s r ~ g t 3 0 k d rj n v l f p r n w b PHONEMES
Figure 8. Mean percent of children (from Smith, 1975) producing consonants is depicted by the line. Filled and striped columns represent a subset of the children (N = 17) in this study who overlapped in age with Smith’s population. Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
Ear and Hearing, Vol. 12, No. 1, 1991
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Figure 9. Mean percent of children 5 years and younger producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
z 100
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z ~ s ~ g t 8 O k d j r n v l f p r n w b PHONEMES Figure 10. Mean percent of children 6 to 8 years old producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
parisons reflect the proportion of children producing sounds which may or may not be correctly produced. Figure 9 shows a similar comparison between Smith’s findings and those of our youngest group (5 years and younger). A larger percentage of children in Smith’s study produced consonants relative to the preimplant percentages observed for the youngest group: however, more children preimplant in our study were observed to produced the phonemes, [b, m, d]. With few exceptions ([r, z, k, qJ),the number of young children producing consonants postimplant more closely approximates those observed by Smith ( 1975), despite the large age and methodological differences in the two populations. Figures 10 and 1 1 show comparable comparisons between Smith’s data and the data collected for the 6 to 8 year old and 9 to 1 1 year old groups of the present study. These figures break down the data described in Figure 8 into the two age categories and add the responses of the 6 and 7 year old subjects. Again, the patterns of performance between the three sets of data are similar in terms of the range of consonants used. Figure 12 depicts a similar portrayal of the data for the 12 years and older group. These comparisons suggest our data is qualitatively similar to Smith ( 1975) in terms of the types of sounds produced but quantitatively different. Quantitative differences are particularly evident in comparisons of postSpeech in Cochlear Implanted Children
29
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s qg
t 5 I3 k d j r n v I f p r n w b
PHONEMES Figure 11. Mean percent of children 9 to 11 years old producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
z 100
12) YEARS
W
LT
n -I 0
$
80
60 40
W
2
20
W
0 - 0
z j s g g t a 0 k d j r n v l fprnwb PHONEMES
Figure 12. Mean percent of children 12 years and older producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
implant performance to Smith’s data. Postimplant, even the youngest group appears to have more children producing sounds but quantitative comparisons and conclusions must be tempered by the differences within the methodologies used. That is, comparisons between sounds judged as correct relative to targets (Smith, 1975) versus a repertoire of sounds produced regardless of target. Although it is tempting to suggest the quantitative differences observed in these comparisons reflect direct contributions by the implant. further investigations separating incorrect versus correct tokens produced with cochlear implants are needed. Take overall, data from this study suggest that the speech patterns of children participating in the federal Food and Drug Administration’s clinical trials of the Nucleus multichannel cochlear implant resemble other profoundly hearing-impaired speakers. Although significantly more children produced consonants after using an implant for a year, the role of the implant is complex and may influence some consonants more than others. Additional studies are needed in order to further explore these complex relationships. REFERENCES Blamey P. Dowell R. Clark G, and Seligman P. Acoustic parameters measured by a formant-estimating speech processor for a multiple-
30
Tobey e t al.
channel cochlear implant. J Acoust SOCAm 1987a:82:38-47. Blarney P. Dowell R. Clark G. and Seligman P. Vowel and consonant recognition of cochlear implant patients using formant-estimating speech processors. J Acoust SOCAm 1987b:82:48-57. Borden G. and Harrih K. Speech Science Primer: Physiology, Acoustics. and Perception of Speech. Baltimore: Williams & Wilkins. 1980. Carr J. An investigation of the spontaneous speech sounds of fiveyear-old deaf born children. J Speech Hear Disord 1953: I8:22-29. Champagne S. A study on the relationship between articulatory ability and spoken language of deaf and hard-of-hearing adolescent children [Unpublished Master’s Thesis]. Columbus. OH: The Ohio State University. 1975. Geffner D. Feature characteristics of spontaneous speech production in young deaf children. J Commun Disord 1980:13:443-454. Gold T. Speech production in hearing impaired children. J Commun Disord 1980: l0:397-4 18. Hochmair-Desoyer I. Hochmair E. Burian K. and Fischer R. Four years experience with cochlear prosthesis. Med Prog Techno1 1981~8:107-119. Hudgins C and Numbers F. An investigation of the intelligibility of the speech of the deaf. Genet Psychol Monographs 1942;38:289392. Kirk K and Edgerton F. The effects of cochlear implant use on voice parameters. Symposium Inner Ear Surg 1983: 16:28 1-292. Kirk K and Hill-Brown C. Speech and language results in children with a cochlear implant. Ear Hear 1985:6(Supp1)36S-47S. Kuhn G. On the front cavity resonance and its possible role in speech perception. J Acoust SOCAm I975:77:428-433. Lach R. Ling D. Ling A. and Ship N. Early speech development in deaf infants. Am Ann Deaf 1970:15:522-526. Leder S, Spitzer J, Milner P, Flevaris-Phillips C, Richardson F, and Kirchner J. Reacquisition of contrastive stress in an adventitiously deaf speaker using a single-channel cochlear implant. J Acoust SOC Am 1986:84:1967-1974. Levitt H and Stromberg H. Speech ofthe Hearing Impaired: Research, Training, and Personnel Preparation. Baltimore: University Press, 1983; 53-73. Ling D. Speech and the Hearing Impaired Child: Theory and Practice. Washington, DC: Alexander Graham Bell Association. 1976. Lunney G. Using analysis of variance with dichotomous dependent variables: an empirical study. J Educ Meas 1970: 12:263-269. Mangan K. Speech improvement through articulation testing. Am Ann Deaf 1961;106:3-39. Markides A. The speech of deaf and partially hearing children with special reference to factors affecting intelligibility. Br J Disord Commun 19705: 126- 140. Myers J, DiCecco J, White J, and Borden V. Repeated measurements on dichotomous variables. Q and F tests. Am Psychol Assoc 1982;10:517-525. Millin J. Therapy for reduction of continuous phonation in the hardof-hearing population. J Speech Hear Disord 197 1;36:496-498. Nober H. Articulation of the deaf. Except Child 1967;33:6 I 1-62 1. Oller K and Eilers R. Phonetic expectation and transcription validity. Phonetica 1975: 11:288-304. Osberger M. The speech of implanted children. In Owens E, Kessler D, Eds. Cochlear Implants in Children. Boston: College Hill, Press 1988: 257-281. Osberger M and McGarr N. Speech production characteristics of the hearing impaired. In Lass N, Ed. Speech and Language: Advances in basic science and research. New York: Academic Press, 1983: 223-233. Oster A-M. Some effects of cochlear implantation on speech production. Speech Transmission Laboratory: Q Progr Rep 1987;01:8I89. Plant G and Oster A-M. The effects of cochlear implantation upon speech production. Speech Transmission Laboratory: Q Progr Rep 1986:01:65-84. Seeger P and Gabrielsson A. Applicability of the Cochran Q test and the F test for statistical analysis of dichotomous data for dependent samples. Psychol Bull 1968;I3:269-277. Smith C. Residual hearing and speech production in deaf children. J
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Speech Hear Res 1975;18:795-8 I I . Stevens K, Nickerson R, and Rollins A. On describing the suprasegmental properties of the speech of deaf children. In McPherson D, Davids M, Eds. Advances in Prosthetic Devices for the Deaf: A Technical Workshop. Rochester, NY: National Technical Institute for the Deaf, 1978: 383-416. Tartter V, Chute P, and Hellman S. The speech of postlingually deafened teenager during the first year of use of a multichannel cochlear implant. J Acoust SOCAm 1989;12:2113-2122. Tobey E and Mecklenberg D. Fundamental frequency in persons with cochlear prostheses. Proceedings of the XXth Congress of the Tobey E and Mecklenberg D. Fundamental frequency in persons
Ear and Hearing, Vol. 12, No. 1,1991
with cochlear prostheses. Proceedings of the XXth Congress of the International Association for Logopedics and Phoniatrics. Tokyo, 1987: 145-146. Acknowledgments: We wish to express our appreciation to all the Clinical Centers for their participation and to especially thank the children and their parents for their cooperation in this project. Address reprint requests to Dr. Emily A. Tobey, Department of Communication Disorders, LSU Medical Center, 1900 Gravier St., New Orleans, LA 701 12. Received May 1,1990; accepted September 26, 1990.
Speech in Cochlear Implanted Children
31
Consonant Production in Children Receiving a Multichannel Cochlear Implant*
Emily A. Tobey, PhD; Susan Pancamo, MCD; Steven J. Staller, PhD; Judy A. Brimacornbe, MA; Anne L. Beiter, MS
Department of Communication Disorders, Louisiana State University Medical Center, New Orleans, Louisiana [E.A. T., S.P.]; and Cochlear Corporation, Englewood, Colorado [S.J.S., J.A.B., A.L.B.]
ABSTRACT Consonant production was investigated in 29 children participating in the federal Food and Drug Administration's clinical trials of the Nucleus WSP-Ill cochlear implant. Speech samples were collected preimplant and 1 year postimplant. A significantly greater number of children produced stop, nasal, fricative, and glide consonants postimplant. Voiced stop consonants were used by more children than the voiceless cognates; however, voiceless fricatives were used more than voiced fricatives. Visible places of articulation were used more frequently than less visible places of articulation. Comparisons to Smith's data (J Speech Hear Res 1975;18:795-811) revealed qualitative similarities but postimplant, quantitative differences were observed. Post hoc analyses of the data revealed some sounds were influenced more by an implant than other sounds and suggest the role of an implant upon spontaneous speech is complex. (Ear Hear 12 1: 23-31)
A MAJOR CONSEQUENCE of deafness in children appears to be a reduced repertoire of sound segments, particularly consonants. The reduced segmental repertoire commonly includes errors such as substitutions of one sound for another, omissions, and distortions (Osberger & McGarr, 1983). Several studies report profoundly hearing impaired speakers use visible, front consonants more frequently than less visible, mid or back consonants (Carr, 1953; Gold, 1980; Lach, Ling, Ling, & Ship, 1970; Nober, 1967; Smith, 1975). Champagne ( 1975) for example, found profoundly hearingimpaired speakers produced 37% front and 14% back sounds correctly. Manner of articulation errors frequently appear as nasal-oral substitutions, that is, the speaker nasalizes a nonnasal sound (Hudgins & NumEar and Hearing, Vol. 12, No. 1, 1991
bers, 1942; Markides, 1970; Smith, 1975; Stevens, Nickerson, & Rollins, 1978). Reports of voicing errors are also common, although there does not appear to be a consensus regarding the exact pattern of such errors. Some studies report more errors on voiced sounds whereas others report more errors on voiceless sounds (Carr, 1953; Hudgins & Numbers, 1942: Mangan, 196 1 ; Markides, 1970: Millin, 197 1 ; Nober, 1967: Smith, 1975). Profoundly hearing impaired speakers also appear to omit many consonants (Geffner, 1980; Levitt & Stromberg, 1983). Omissions occur primarily in word-final positions and relatively infrequently in word-initial positions. Few omissions are observed for consonants produced near the front of the mouth but a relatively high rate of omissions occur for consonants produced in the middle region of the mouth (Levitt & Stromberg, 1983). Thus, it would appear that profoundly hearing-impaired speakers not only experience a reduced sound repertoire but the reduced sound repertoire may also be wrought with errors. Changes in suprasegmental and segmental aspects of speech production have been reported for profoundly hearing-impaired adults and adolescents receiving single and multichannel cochlear implants (Kirk & Edgerton, 1983: Leder et al, 1986; Oster, 1987; Plant & Oster, 1986; Tartter, Chute, & Hellman, 1989; Tobey & Mecklenberg, 1987). Improved segmental aspects of speech also have been noted in a few studies examining children with single channel cochlear implants. Osberger (1988) observed more accurate sound pronunciation in single channel implant users than in hearing-impaired subjects with hearing aids. Kirk and Hill-Brown ( 1985) reported significant improvement in the imitation of nonsense syllables in children receiving a single channel cochlear implant. Significant improvements occurred for the imitation of vowels, diphthongs, and simple consonants. Examination of the spontaneous production of speech sounds with the Phonologic Level Speech Evaluation (Ling, 1976) also revealed significant improvements for children using single-channel implants (IOrk & Hill-Brown, 1985). Observations such as these suggest single channel cochlear implants may represent " Portions of the analysis of this data were completed using equipment purchased from a Deafness Research Foundation grant awarded to the first author.
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0196/0202/91/1201-0023$03.00/0 * EARAND HEARING Copyright 0 1991 by The Williams & Wilkins Co. Printed in U.S.A.
Speech in Cochlear Implanted Children
23
a viable prosthetic aid for improving the sound repertoire in profoundly hearing impaired children unable to benefit from traditional hearing aids. In order to examine the possibility that the sound repertoire of profoundly hearing-impaired children also may be influenced by a multichannel cochlear implant, we examined consonant production in a subset of children participating in the federal Food and Drug Administration’s clinical trials of the Nucleus WSP-111 cochlear implant. The Nucleus multichannel cochlear implant is designed to extract several critical features in speech signals including fundamental frequency, a voiced/voiceless decision regarding the signal, acoustic amplitudes associated with spectral peaks, and estimates of the main spectral peaks at low- (approximately 300- 1000 Hz) and midfrequency ( 1000-4000 Hz) ranges. Given the varied number of parameters extracted by the Nucleus device, one might anticipate that young children may be able to use this information to assist them in monitoring and adjusting their speech production. To explore this possibility, we contrasted speech samples produced preimplant to samples produced after 1 year’s use with the implant. Four questions were addressed: first, what types of consonants are produced by children receiving cochlear implants; second, d o children of different ages produce different types of consonants: third, are consonant repertoires influenced by a multicha nel cochlear implant: and fourth, are the consonant I upertoires used by children using multichannel cochlear implants similar t o the repertoires of hearing-impaired children without cochlear implants? METHODS AND PROCEDURES
Subjects Twenty-nine profoundly hearing-impaired children, ranging in age from 3.8 to 17.8 years, participated in the study. The children were participants of the federal Food and Drug Administration’s clinical trials of a Nucleus multichannel cochlear implant. Table 1 describes pertinent background information on the individual subjects including gender, age at time of implant, duration of profound deafness, and etiology. Subjects are ordered in terms of age at time of implant. Mean age for the group is 9.5 years and mean duration of profound deafness for the group is 6.7 years, ranging from 0.8 to 15.3 years. Meningitis was responsible for deafness in 48.3% of the subject population and unknown etiologies contributed to the deafness in 4 1.4% of the subject pool. In order to provide a preliminary investigation examining consonant production as a function of age, subjects were broken into four age categories: 5 years and younger ( N = 6), 6 to 8 years ( N = 7), 9 to 1 1 years ( N = 8), and 12 years and older ( N = 8). Mean age of the 5 years and younger group at the time of implantation was 4.6 years and mean duration of profound deafness was 2.6 years. Mean implantation age of 6 to 8 years group was 6.8 years and mean duration of profound deafness was 5.1 years. Mean duration of profound deafness in the 9 to 1 1 years group was 8.9 years and mean age at implantation was 10.2 years. Average implantation age of the oldest group was 14.9 years and mean duration of profound hearing loss was 8.9 years. 24
Tobey et al.
Table 1. Description of individual subjects.
Sex
Age (Years)
Duration of Profound Hearing Loss
19 18 11 27 46 4 25 29 8 62 23 54 52 13 55 22 51 50 47 41 49 9 2 14 38 56
M M M F F M F M F M M F M F M M M F M F F F M F M F
3.8 4.1 4.4 4.4 5.0 5.8 6.1 6.2 6.4 6.8 7.1 7.3 8.0 9.2 9.4 9.8 10.0 10.2 10.8 10.9 11.3 12.5 12.9 14.1 15.3 15.3
3.2 2.3 2.6 1.8 5.0 0.8 2.6 3.4 2.4 5.2 6.8 7.3 8.0 2.5 9.4 6.8 10.0 10.2 10.8 10.9 11.3 12.5 4.9 8.1 15.3 15.3
6 17 30
M F F
15.4 16.0 17.8
9.4 1.5 11.3
Subject Number
Etioloav Unknown Meningitis Meningitis Meningitis Unknown Meningitis Meningitis Meningitis Meinere’s Meningitis Meningitis Unknown Unknown Meningitis Unknown Meningitis Unknown Unknown Unknown Unknown Unknown Meningitis Unknown Meningitis Usher’s Maternal Rubella Meningitis Unknown Meningitis
Speech Production Procedures Video tape recordings of speech samples were acquired preimplant and after 1 year’s experience with the implant by the individual Clinical Centers participating in the clinical trials. Speech samples were obtained by either having the child respond to a series of prompts, such as picture cards, or read a passage. Clinician prompts were used to elicit speech samples in younger children and reading a passage was used to elicit speech samples in the older children. Similar elicitation procedures for each subject were used in the pre- and postimplant conditions. Thirty pre- and postimplant utterances were phonetically transcribed using the International Phonetic Alphabet by two judges (the first two authors), one experienced in transcribing speech of the deaf and the other a master level student in speech-language pathology. Intratranscriber reliability measures were acquired by a second analysis of five speech samples. Three samples represented preimplant speech and two samples represented postimplant speech. Intrareliability scores were 0.98 and 0.97 for the two judges, respectively. Intertranscriber scores also were similar (0.89 preimplant and 0.92 postimplant). Frequency of occurrence matrices were constructed for each subject at each test period. Each row of the matrices corresponded to manner dimensions and each column corresponded to the voicing and place dimensions. Data were Ear and Hearing, Vol. 12, No. 1,1991
collapsed across the two judges and. in the event of judge disagreement, both judges reviewed the tapes until agreement was reached. Initial inspection of the matrices revealed the frequency of occurrences were confounded by the age of subjects: older subjects produced longer utterances (and thus, had more opportunities for phonemes to occur because of reading passages) and younger subjects produced shorter utterances (and thus. produced fewer phonemes elicited via clinician prompts). To eliminate this confounding factor. a second set of matrices was constructed by assigning a 1 when a phoneme occurred (regardless of the number of times it occurred) and a 0 when a phoneme never occurred. Data were statistically treated using analysis of variance techniques (BMDP2V). Several investigators (Lunney. 1970; Myers, DiCecco. White, & Borden, 1982: Seeger & Gabrielsson. 1968) have demonstrated dichotomous data for dependent samples may be appropriately analyzed using analysis of variance techniques. Myers et al (1982) also have demonstrated that analysis of variance techniques may yield "reasonably honest Type I error rates, even under conditions of extreme heterogeneity of covariance" (p. 5 17). Separate between-group. within-subject analyses were run for each manner category and examined age group (4). test condition (2). place (varied as a function of manner category) and voicing (2). Probability estimates were obtained using the Greenhouse Geisser corrections. Post hoc range tests were conducted using
40
0
n
( 5 6-8 9-11 12)
( 5 6-89-11
12)
(5 6-89-11
(5 6 - 8 9 - 1 1
12)
40
20
12)
Figure 1. Mean percent of children in the four age groups producing stop, fricative, glide, and nasal consonants is shown collapsed across test condition, place of articulation,and voicing.
Newman-Kuels procedure. Such an analysis provided an estimate of the proportion of children producing consonants during each of the testing conditions. RESULTS
Figure 1 illustrates the percentage of children within the four age groups producing stop, nasal, glide, and fricative consonants. A significantly greater number of children within the 12 years and older group produced stop consonants than the three younger groups [F(3,25) = 2.87, p < 0.051. As depicted in the lower Icft puncl, fewer children in the youngest age group produced fricative consonants than the other groups. The greatest number of children producing fricatives were in the oldest age group [F(3,25)= 7.47, p < 0.0011. A significant age effect also was observed for the production of glides [F(3,25) = 3.44, p < 0.031: a greater proportion of the oldest age group produced glides relative to the other groups. Similarly. a greater proportion of the children in the oldest age group produced nasal consonants relative to the three younger groups [F(3,25) = 3.13, p < 0.041. Significant main condition effects were noted for each of the manner categories as illustrated in Figure 2. Significantly more children produced stop and fricative consonants within the spontaneous speech samples collected 1 year after implantation [F(1,25) = 14.95, p < 0.001 for stop consonants and F( 1,25) = 11.5 I , p < 0.002 for fricative consonants] than the preimplant condition. A similar picture also was observed for glide and nasal productions: a significantly greater proportion of children produced these consonants after one year's use with the implant [F(1,25) = 32.89, p < 0.001 for glides and F( 1,25) = 5.22, p < 0.03 for nasal consonants] than had before receiving the implant. A greater proportion of children produced voiced, stop consonants than their voiceless cognates during
Figure 2. Mean percent of children producing stop, fricative, glide, and nasal consonants pre- and 1 year postimplant is depicted.
Z
w 100
100
K
80
I 0 6 0
c
60
g 40 a 2 20
40
z
0
20
PRE
1 YR POST
Ear and Hearing, Vol. 12, No. 1, 1991
0
PRE
1 YR POST Speech in Cochlear Implanted Children
25
speech as depicted in Figure 3. The more visible place of articulation consonants (bilabials) were produced by a greater number of children than less visible, alveolar or velar stop consonants. These observations were confirmed by a place of articulation by voicing interactions [F(1,50) = 3.72, p < 0.031. In addition, a condition by place of articulation by age interaction was found [F(1,50) = 2.77, p < 0.021. Figure 4 portrays the threeway interaction. Post hoc analyses using a NewmanKeuls confirmed a ceiling effect for bilabial and alveolar stop consonants as a function of test session for the oldest age group: however, significantly fewer of these children produced velar stop consonants ( p < 0.001) than bilabial or alveolar sounds. In the remaining younger groups, significantly more bilabial and velar sounds were observed postimplant ( p < 0.00 1) than in the preimplant condition. No significant increases in the number of children producing alveolar stop consonants pre- and postimplant were observed for the 9 to 1 I year old group; however, a significant increases in alveolar stops were observed in the 5 years and younger and 6 to 8 year old groups ( p < 0.001). A significant interaction between place of articulation and voicing also was present for fricative consonants [F(1,75) = 4.90, p < 0.0041. As shown in Figure 5, voiceless fricatives were produced by significantly more children than the corresponding voiced cognates. Post hoc analyses indicated the voiceless labiodental, [fI, was produced by more children than alveolar, [s, J], or linguadental, [J] consonants ( p < 0.001). The voiced labiodental, [v], was produced by more children than the other voiced consonants ( p < 0.001). No significant differences appeared between the number of children producing [d] and [z]. Significantly fewer children produced [3], perhaps because of its relatively low frequency of occurrence in English. In addition, a significant condition by voicing by age interaction was observed for fricative consonants [F(1,25) = 3.61, p < 0.021 and is shown in Figure 6. Preimplant, voiced, and voiceless fricatives were produced by an equivalent number of children 5 years and younger; however, significantly more children produced voiceless fricatives than voiced fricatives postimplant ( p < 0.00 1). Preimplant, voiceless fricatives were produced by significantly more children in the 6 to 8 year old group than voiced fricatives ( p < 0.00 1). These differences were not pres-
z 100
W
5
80 60
I-
40
s
20
Z
E
W
L
O p b
t d
k g
Figure 3. Mean percent of children producing voiceless and voiced stop consonants as a function of place of articulation is illustrated.
26
Tobey et al.
,100,
loor
w 1
0 I-
Z
FRICATIVES 80.r-
60
40
:: 20
E
w
a
0 f v
a@
J j
S Z
Figure 5. Mean percent of children producing voiceless and voiced fricative consonants as a function of place of articulation is depicted.
z 100
W
5
0
2
80 60
40
:: 20
E
w
a
0 VL
v (5
v1 v VL 6-8
v
9-11
VL
v
12)
Figure 6. A three-way interaction between age, condition,and voicing for the fricatives is shown. Open columns, represent preirnplant.Filled columns represent 1 year postimplant.
ent in the postimplant condition. Equal distributions of voiceless and voiced fricatives were produced preimplant by the 9 to 1 I year old group; however, more children produced voiceless fricatives than voiced fricatives postimplant ( p < 0.00 1). Production of voiceless fricatives contributed to the performance differences noted in the 12 year and older group: more children produced voiceless fricatives preimplant and postimplant than voiced fricatives ( p < 0.00 1). As shown in Figure 7, a significant condition by place of articulation by age interaction also occurred for glide consonants [F(1,100) = 2.22, p < 0.011. Post hoc analyses revealed no significant increase in the number of children in the 5 years and younger group producing Ear and Hearing, Vol. 12, No. 1, 1991
[wh] (41%) and [r] (0%) pre- and postimplant. It is possible that the younger children failed to increase their production of [r] for developmental reasons. Significantly fewer of these children produced the phonemes. [w] and b]. postimplant than preimplant ( p < 0.001) and significantly more of the children produced the phoneme [a] postimplant than preimplant ( p < 0.00 1). Similarly. no significant changes were observed in the number of children in the 6 to 8 year old group who produced either [wh] (53%) or [r] (0%)and significantly fewer of the children produced [w], [j], and [l] postimplant than preimplant ( p < 0.001). No significant changes in the number of children in the 9 to 1 1 year old group producing [w] (52%) or [j] (52%) were observed pre and postimplant. However, significantly more of the 9 to 1 1 year old children produced the phonemes, [r], [wh]. and [l], postimplant than preimplant ( p < 0.00 1 ). No significant changes in the number of children in the 12 year and older group producing [w] (0%)and [l] (35%) were observed postimplant and significantly fewer of the children produced [r] and [j] postimplant ( p < 0.00 1 ). DISCUSSION
Any discussion of consonant repertoires observed in children pre- and postimplant must be tempered by the limitations of the procedures used to determine the repertoires. First, the type of analysis used in this study does not distinguish between correct and incorrect utterances. The transcriptions used here describe the range and variety of sounds classified by raters but fail to determine the accuracy of such productions. Second, identical utterances often may be transcribed differently by different listeners, as many authors have pointed out (Gold, 1980; Levitt & Stromberg, 1983; Oller & Eilers, 1975). Although the inter- and intrajudge reliabilities within this study are high, reliabilities of transcriptions acquired during the preimplant sessions are lower than those acquired in the postimplant sessions and are related to less intelligible speech preimplant. With these limitations in mind, let us return to the present data set
PRE
POST
PRE
POST
Figure 7. A three-way interaction between age, condition, and place of articulation for glide consonants is illustrated. Open circles represent [wh], filled circles represent [w], open triangles represent [r], and open diamonds represent [Q]. filled triangles represent
u],
and examine the consonant repertoires of children receiving multichannel cochlear implants. Consonant Repertoires Significant age effects are observed for each of the manner classes examined: a greater proportion of children in the 12 years and older group produced consonants than in the three younger groups. These differences are particularly evident between the oldest and youngest age groups. A greater proportion of children in the three youngest groups produced stop and nasal consonants than glide or fricative consonants. The general pattern of a greater number of children producing stops and nasals followed by glides and fricatives is similar to other reports examining manner categories in profoundly hearing-impaired speakers. Smith ( 1975) and Nober ( 1967) report profoundly hearing-impaired children produce glides correctly most often, followed by stops, nasals, and fricatives. Although stop and nasal consonants are used by a greater proportion of the children in this study, these data must be viewed somewhat cautiously since numerous investigators report profoundly hearing-impaired speakers commonly make nasal-oral substitutions (Hudgins & Numbers, 1942; Markides, 1970; Smith, 1975). As remarked above, consonant repertoires based upon the type of analyses used in this study fail to uncover correct versus incorrect productions. Since nonnasal phonemes are substituted for nasal phonemes and vice versa in many profoundly hearing impaired speakers, it is highly likely that the high occurrence of these manner classes in this study may include nasal-oral substitutions. The remarkable similarity, however, between our data set and other studies suggest the range and type of sounds used by our subjects is reflective of the manner categories typically used by profoundly hearing impaired speakers. Voicing errors also are commonly reported for profoundly hearing-impaired speakers, although the direction of voicing error differs across various studies. Some studies report the errors occur to voiceless members (Markides, 1970; Nober, 1967) and other studies report the errors occur to the voiced cognate (Smith, 1975). Examination of voicing dimensions contained within the consonant repertoires observed in this study also are mixed. On the one hand, voiced stop consonants are produced by more children than the voiceless cognates. On the other hand, voiceless fricatives are transcribed by the raters more frequently than their voiced counterparts. Several factors may underlie these observations. First, fewer observations of voiceless stop consonants may be related to diffrculties in coordinating upper and laryngeal articulators. Voiced stop consonants may be produced by simultaneous action of these articulators but voiceless stop consonants require a more complex timing of upper and laryngeal articulators. Timing ofevents may also underlie the transcribers perceptions of more frequent voiceless fricatives: fricatives are perceived as voiceless when the frication is relatively long (Borden & Harris, 1980). Abnormal ~~
Ear and Hearing, Vol. 12, No. 1,1991
Speech in Cochlear Implanted Children
27
timing relationships during speech are a commonly cited problem in profoundly hearing-impaired speech and may be factors contributing to the mixed pattern of voicing dimensions observed here. Children participating in this study also appear to use places of articulation that are similar to those previously reported for other profoundly hearing-impaired speakers. A greater proportion of the children use visible. anterior places of articulation than less visible, posterior configurations. For example, examination of Figures 3 and 5 reveals a greater proportion of children produced bilabial and labiodental consonants than consonants produced more posteriorly. Nober (1967). Smith (1975). and Gold (1980) report more accurate productions of visible consonants than consonants occurring in the mid or posterior regions of the mouth. Our data are in support of these previous observations.
Influence of Cochlear Implant upon Consonant Repertoires Previous comparisons of speech processing strategies with the Nucleus speech processor (Cochlear Proprietary LTD, U.S. patent No. 4,515,158) have focused upon the percentage of information transmitted for consonants in adult patients asked to identify consonants in vowel-consonant-vowel tokens (Blarney, Dowell, Clark, & Seligman, 1987b). In such tasks, listeners are asked to identify tokens and an analysis is completed comparing the correct and incorrect features perceived. The average percentage of information transmitted for consonants in a hearing only condition was 48% for eight subjects. Average percentages of information transmitted for various features included 55 % for voicing, 52% for duration, 49% for nasality, 43% for affrication, and 33% for place cues. HochmairDesoyer, Hochmair, Burian, and Fischer ( 198 1 ) also have reported voicing, manner, and nasality features constitute the greatest amount of information transmitted in German consonants. Thus, cochlear implants appear to provide greater information regarding voicing, durational, and nasality cues than for place cues, per se, and these cues might be more evident in speech produced by children using such a device. Production data contrasting consonants produced before and after implantation reveal a complex picture. Although it is clearly difficult to separate out the contributions of a cochlear implant upon consonant repertoires versus the contributions provided by maturational or aural rehabilitation factors, a review of the data suggests the implant, perhaps in conjunction with these other factors, may provide useful information for speech production. Significantly more children produce consonants after using the implant for a year and several age interactions appear in the data. Significantly more children in the youngest group produced stop consonants postimplant, with the greatest changes occurring for bilabial and alveolar places of articulation. Significantly more children in the 6 to 8 and 9 to 1 1 year old 28
Tobey et al.
groups produced velar stop consonants in the postimplant session. Fewer changes are evident in the oldest age group because of ceiling effects. This effect highlights the difficulties inherent in preforming group comparisons among children with disparate production abilities. Such ceiling effects may have been eliminated if more stringent criteria had been applied to the children with more advanced speech skills (i.e., more than one occurrence). The data do suggest, however, that manner and place features for stop consonants are being used in speech by a greater proportion of children after receiving cochlear implants. As discussed in detail by Blarney. Dowell, Clark. and Seligman ( 1987a), information regarding voicing of stop consonants may be carried by the coded amplitude contours and FO information which is steady for voiced and random for unvoiced consonants. Front cavity resonance information, a source of place of articulation (Kuhn, 1975) appears to be coded by the F2 values. One possible approach to separating out the contributions of maturation versus the implant, albeit limited, is to compare the number of children in the youngest age group producing consonants postimplant to the preimplant performance measures of the older groups. Significantly more children in the youngest group produce stop consonants postimplant when compared to the number of children in next two older groups preimplant ( p < 0.01). If only maturational issues were a factor, one would only anticipate that the youngest group after a year would more nearly resemble the next age group, preimplant. Instead, significantly more children in the youngest group produced stop consonants postimplant than the 9 to 1 1 year old group, preimplant ( p < 0.0 1). Similar age and condition interactions also are apparent in the fricatives and glides. Significant increases are observed in the youngest group for voiced and voiceless fricatives postimplant. However, comparisons to the 6 to 8 year group suggest the implant may have influenced the incidence of voiced fricatives but not necessarily voiceless fricatives since the number of young children producing voiceless fricatives postimplant is comparable to the number of 6 to 8 year olds preimplant. Comparisons of postimplant to preimplant performance in the 6 to 8 and 9 to 1 1 year old groups suggest the implant may influence the incidence of voiceless and voiced fricatives in the 6 to 8 year olds. Similar comparisons between the two oldest groups suggest the implant may play only a minimal role. Amplitude and frequency contours are coded differently from stop consonants and high frequency fricatives may be accompanied with an increase in amplitude due to the preemphasis of the high-frequency part of the spectrum in the processor (Blarney et al, 1987a). Data from our study suggest that information from the implant, in conjunction with developmental trends for fricative acquisition, may contribute to the proportion of children using fricatives postimplant. Ear and Hearing, Vol. 12, No. 1, 1991
Applying a similar approach to the glide consonants. one finds the implant may have positively influenced the incidence of [I] in the youngest group and played a minimal role. if any, in the other groups. This is rather surprising. given that acoustically glides are composed of resonant patterns which may be coded by the implant. However, the acoustic patterns for glides also are very similar. Blarney et a1 (1987a) reported Fl and F2 values of 190 and 1810 Hz for b]. 320 and 860 Hz for [r], and 420 and 950 Hz for [I] for the glides produced in a vowel-consonant-vowel context. It may be possible that additional training and experience is needed in order to distinguish them. One of the key controversies involved in assessing the contributions of cochlear implants upon children’s performance centers upon the issue of appropriate control groups. That is, should the performance of implanted children be contrasted to normal-hearing children of similar ages or to profoundly hearing-impaired children with or without other types of prosthetic devices? As a first step in contrasting the performance of implant children to other types of populations. we compared the proportion of children producing the various consonants in this study to the proportion of profoundly hearing-impaired children producing consonants correctly in sentences previously reported by Smith (1975). Figure 8 depicts the rank order of percent correct productions of consonants pooled across 40 subjects, ages 8 to 15 years, tested by Smith ( 1975) and represented by the line. Seventeen children in our population are similar in age to Smith’s population and the percentage of these children producing consonants preand postimplant also are shown. Remarkable similarities are evident between the percentage of children producing [O, 6, k, j, v, f, m, w] preimplant to those data presented by Smith (1975). Postimplant, a greater proportion of children are producing a wider range of consonants with only three phonemes [n, r, 11 produced by fewer children than those observed by Smith (1975). It is important to note the limitations of these comparisons since Smith’s data reflects the proportion of children correctly producing sounds and our pre/post com-
z W
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Figure 8. Mean percent of children (from Smith, 1975) producing consonants is depicted by the line. Filled and striped columns represent a subset of the children (N = 17) in this study who overlapped in age with Smith’s population. Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
Ear and Hearing, Vol. 12, No. 1, 1991
t-
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Figure 9. Mean percent of children 5 years and younger producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
z 100
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z ~ s ~ g t 8 O k d j r n v l f p r n w b PHONEMES Figure 10. Mean percent of children 6 to 8 years old producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
parisons reflect the proportion of children producing sounds which may or may not be correctly produced. Figure 9 shows a similar comparison between Smith’s findings and those of our youngest group (5 years and younger). A larger percentage of children in Smith’s study produced consonants relative to the preimplant percentages observed for the youngest group: however, more children preimplant in our study were observed to produced the phonemes, [b, m, d]. With few exceptions ([r, z, k, qJ),the number of young children producing consonants postimplant more closely approximates those observed by Smith ( 1975), despite the large age and methodological differences in the two populations. Figures 10 and 1 1 show comparable comparisons between Smith’s data and the data collected for the 6 to 8 year old and 9 to 1 1 year old groups of the present study. These figures break down the data described in Figure 8 into the two age categories and add the responses of the 6 and 7 year old subjects. Again, the patterns of performance between the three sets of data are similar in terms of the range of consonants used. Figure 12 depicts a similar portrayal of the data for the 12 years and older group. These comparisons suggest our data is qualitatively similar to Smith ( 1975) in terms of the types of sounds produced but quantitatively different. Quantitative differences are particularly evident in comparisons of postSpeech in Cochlear Implanted Children
29
z 100
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6
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PHONEMES Figure 11. Mean percent of children 9 to 11 years old producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
z 100
12) YEARS
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Figure 12. Mean percent of children 12 years and older producing consonants is compared to data from Smith (1975) (line). Filled columns represent the percent number of children producing consonants preimplant and striped columns represent postimplant.
implant performance to Smith’s data. Postimplant, even the youngest group appears to have more children producing sounds but quantitative comparisons and conclusions must be tempered by the differences within the methodologies used. That is, comparisons between sounds judged as correct relative to targets (Smith, 1975) versus a repertoire of sounds produced regardless of target. Although it is tempting to suggest the quantitative differences observed in these comparisons reflect direct contributions by the implant. further investigations separating incorrect versus correct tokens produced with cochlear implants are needed. Take overall, data from this study suggest that the speech patterns of children participating in the federal Food and Drug Administration’s clinical trials of the Nucleus multichannel cochlear implant resemble other profoundly hearing-impaired speakers. Although significantly more children produced consonants after using an implant for a year, the role of the implant is complex and may influence some consonants more than others. Additional studies are needed in order to further explore these complex relationships. REFERENCES Blamey P. Dowell R. Clark G, and Seligman P. Acoustic parameters measured by a formant-estimating speech processor for a multiple-
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channel cochlear implant. J Acoust SOCAm 1987a:82:38-47. Blarney P. Dowell R. Clark G. and Seligman P. Vowel and consonant recognition of cochlear implant patients using formant-estimating speech processors. J Acoust SOCAm 1987b:82:48-57. Borden G. and Harrih K. Speech Science Primer: Physiology, Acoustics. and Perception of Speech. Baltimore: Williams & Wilkins. 1980. Carr J. An investigation of the spontaneous speech sounds of fiveyear-old deaf born children. J Speech Hear Disord 1953: I8:22-29. Champagne S. A study on the relationship between articulatory ability and spoken language of deaf and hard-of-hearing adolescent children [Unpublished Master’s Thesis]. Columbus. OH: The Ohio State University. 1975. Geffner D. Feature characteristics of spontaneous speech production in young deaf children. J Commun Disord 1980:13:443-454. Gold T. Speech production in hearing impaired children. J Commun Disord 1980: l0:397-4 18. Hochmair-Desoyer I. Hochmair E. Burian K. and Fischer R. Four years experience with cochlear prosthesis. Med Prog Techno1 1981~8:107-119. Hudgins C and Numbers F. An investigation of the intelligibility of the speech of the deaf. Genet Psychol Monographs 1942;38:289392. Kirk K and Edgerton F. The effects of cochlear implant use on voice parameters. Symposium Inner Ear Surg 1983: 16:28 1-292. Kirk K and Hill-Brown C. Speech and language results in children with a cochlear implant. Ear Hear 1985:6(Supp1)36S-47S. Kuhn G. On the front cavity resonance and its possible role in speech perception. J Acoust SOCAm I975:77:428-433. Lach R. Ling D. Ling A. and Ship N. Early speech development in deaf infants. Am Ann Deaf 1970:15:522-526. Leder S, Spitzer J, Milner P, Flevaris-Phillips C, Richardson F, and Kirchner J. Reacquisition of contrastive stress in an adventitiously deaf speaker using a single-channel cochlear implant. J Acoust SOC Am 1986:84:1967-1974. Levitt H and Stromberg H. Speech ofthe Hearing Impaired: Research, Training, and Personnel Preparation. Baltimore: University Press, 1983; 53-73. Ling D. Speech and the Hearing Impaired Child: Theory and Practice. Washington, DC: Alexander Graham Bell Association. 1976. Lunney G. Using analysis of variance with dichotomous dependent variables: an empirical study. J Educ Meas 1970: 12:263-269. Mangan K. Speech improvement through articulation testing. Am Ann Deaf 1961;106:3-39. Markides A. The speech of deaf and partially hearing children with special reference to factors affecting intelligibility. Br J Disord Commun 19705: 126- 140. Myers J, DiCecco J, White J, and Borden V. Repeated measurements on dichotomous variables. Q and F tests. Am Psychol Assoc 1982;10:517-525. Millin J. Therapy for reduction of continuous phonation in the hardof-hearing population. J Speech Hear Disord 197 1;36:496-498. Nober H. Articulation of the deaf. Except Child 1967;33:6 I 1-62 1. Oller K and Eilers R. Phonetic expectation and transcription validity. Phonetica 1975: 11:288-304. Osberger M. The speech of implanted children. In Owens E, Kessler D, Eds. Cochlear Implants in Children. Boston: College Hill, Press 1988: 257-281. Osberger M and McGarr N. Speech production characteristics of the hearing impaired. In Lass N, Ed. Speech and Language: Advances in basic science and research. New York: Academic Press, 1983: 223-233. Oster A-M. Some effects of cochlear implantation on speech production. Speech Transmission Laboratory: Q Progr Rep 1987;01:8I89. Plant G and Oster A-M. The effects of cochlear implantation upon speech production. Speech Transmission Laboratory: Q Progr Rep 1986:01:65-84. Seeger P and Gabrielsson A. Applicability of the Cochran Q test and the F test for statistical analysis of dichotomous data for dependent samples. Psychol Bull 1968;I3:269-277. Smith C. Residual hearing and speech production in deaf children. J
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Speech Hear Res 1975;18:795-8 I I . Stevens K, Nickerson R, and Rollins A. On describing the suprasegmental properties of the speech of deaf children. In McPherson D, Davids M, Eds. Advances in Prosthetic Devices for the Deaf: A Technical Workshop. Rochester, NY: National Technical Institute for the Deaf, 1978: 383-416. Tartter V, Chute P, and Hellman S. The speech of postlingually deafened teenager during the first year of use of a multichannel cochlear implant. J Acoust SOCAm 1989;12:2113-2122. Tobey E and Mecklenberg D. Fundamental frequency in persons with cochlear prostheses. Proceedings of the XXth Congress of the Tobey E and Mecklenberg D. Fundamental frequency in persons
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with cochlear prostheses. Proceedings of the XXth Congress of the International Association for Logopedics and Phoniatrics. Tokyo, 1987: 145-146. Acknowledgments: We wish to express our appreciation to all the Clinical Centers for their participation and to especially thank the children and their parents for their cooperation in this project. Address reprint requests to Dr. Emily A. Tobey, Department of Communication Disorders, LSU Medical Center, 1900 Gravier St., New Orleans, LA 701 12. Received May 1,1990; accepted September 26, 1990.
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