Cochlear Implants: Fundamentals and Application - part 10 potx

Speech Production with Cochlear Implants 745 strategy on Nucleus 22 implant were reported by Tobey et al (1988, 1991) and Tobey and Hasenstab (1991). The speech production of children was categorized from the phonologic level evaluation (Ling 1976). Of the 61 children in the study, 31% had a significant improvement in imitative nonsegmental speech production, and 67% in segmental speech production 1 year after implantation (Tobey et al 1988, 1991; Tobey and Hasenstab 1991). Approximately half had significant im- provement in spontaneous speech production. The data suggested that children with increased auditory experience before implantation also developed better speech. It was subsequently shown by Tye-Murray et al (1995) that there was improved intelligibility in children who had used the Nucleus 22 system for 2 years or longer, and in those who had been implanted before the age of 5 years. Multipeak-MSP (Nucleus) As with the formant strategies, there was also considerable variability in perfor- mance. Osberger et al (1994) found speech intelligibility scores of 48% for chil- dren who had the Nucleus F0/F1/F2 WSP-III and Multipeak-MSP systems for at least 2 years. This score was well below that for hearing children of the same age. The ratings varied from 14% to 93% intelligible. Thus some children perform as well as hearing children. Over a 6-year period Blamey et al (2001a) assessed the progress in speech production of nine children with the Nucleus 22 system. Initially, two used the F0/F1/F2 strategy and seven the Multipeak. At 3 years postimplantation all were using the Multipeak, and by 6 years they had been converted to SPEAK. A broad transcription of the conversations was used to measure the percentage of correct productions of monophthongs, diphthongs, singleton consonants, consonant clus- ters, and whole words. A direct measure of intelligibility was also derived by counting the proportion of syllables that were unintelligible to the transcribers. The conversation was transcribed by a speech pathologist or linguist and analyzed by CASALA. Four years postimplantation, at least 90% of all syllables produced were intelligible (Fig. 12.5), although only one child had intelligibility over 19% prior to implantation. SPEAK and ACE Spectra-22 and Nucleus 24 Studies are required to follow the speech production of young children implanted at a young age with the Nucleus 24 device with the SPEAK and ACE strategies. The development of speech production in children who used a tonal language such as Cantonese has been assessed by Barry et al (2000) for the SPEAK strategy. It was thought the children with SPEAK should acquire a tonal inventory more rapidly than one for vowels (the latter depending on formants). But a study on three children by Barry et al (2000) showed that the acquisition of a tonal speech inventory was slower, with none acquiring a low-falling element. This could have been due to the fact that that the extraction of voicing as rate of stimulation with the Nucleus Multipeak and other formant strategies provides better pitch percep- tion and requires investigation. Ciocca et al (2002) found in 17 children, in whom 746 12. Results Time postimplant (y ears ) 012345678910 0 20 40 60 80 100 1 2 3 4 5 6 7 8 9 Percent unintelligible syllables F IGURE 12.5. The percentage of unintelligible syllables versus time postimplantation. Nine children’s results are graphed. (From Blamey 2002. Development of spoken language by deaf children. In: Marschark, M. and P. Spencer, eds. Handbook of deaf studies, language and education. With permission of Oxford University Press.) six used SPEAK and 11 ACE, that above-chance performance was obtained with three tonal contrasts but was poorer than a moderately impaired control. This suggests that the strategy is not providing the fine temporospatial patterns required for comparable hearing. Comparison with Hearing Aid and Tactile Vocoder It was also an important question to compare the speech production benefits from the F0/F1/F2 strategy on the Nucleus 22 implant with those from the 3M/House single channel and Tactaid II (two-channel vibrotactile aid). The speech was clas- sified as nonspeech, speech-like, and speech. The largest improvements were for the Nucleus 22 (F0/F1/F2) speech strategy. But only 67% of their utterances were judged to be phonetic approximations (Osberger et al 1991b). After 1 year the children with the Nucleus 22 (F0/F1/F2) speech strategies showed an increase in the number of stops, fricatives, and glides, and a reduction in nasal consonants. Osberger et al (1991c) compared the speech of children with the Nucleus 22 (F0/ F1/F2) speech strategies and children with hearing aids and different hearing thresholds. After 4 years the mean intelligibility of the children with the Nucleus 22 (F0/F1/F2 and Multipeak) speech strategies was 40% compared with 20% for the aided children with thresholds of 101 to 110 dB. The intelligibility did not reach those children with a threshold of 90 to 100 dB when using a hearing aid. In a comparative study by Tobey et al (1994), triads of children with the Nu- cleus 22 implant, hearing aids, and the Tactaid II and IV were compared. They were matched for age, unaided thresholds, family support, intelligence, and Language Development for Pre- and Postlinguistically Deaf Children 747 speech and language skills. After 3 years the children with the Nucleus implant had increases in imitative speech production of 36% compared to 20% for both the hearing aid and Tactaid groups. Svirsky et al (1998) compared the speech intelligibility of 44 children using the Nucleus SPEAK and Clarion CIS strategies, and after 1.5 to 2.5 years’ usage the speech of the implant children was the same as for those with a threshold in the 90- to 100-dB range. Language Development for Pre- and Postlinguistically Deaf Children The development of receptive and spoken language by deaf children is very im- portant for their education, social development, and career opportunities. This can now be achieved through early diagnosis with procedures that include steady- state evoked potentials (Rickards and Clark 1984; Cohen et al 1991; Rance et al 1993, 1995), auditory brainstem responses (ABRs) with a “notched-noise” masker (Stapells et al 1995), and otoacoustic emissions (Kemp 1978), as well as with early intervention and training programs (Ling 1976, 1984; Ling and Ling 1978; Ling and Nienhuys 1983). The elements of spoken language as discussed above (see Language: Test Principles) are (1) receptive and expressive; (2) cognitive, motor, and sensory; and (3) phonology, morphology, syntax, and pragmatics. The language of children with a cochlear implant is related to their speech perception. Cochlear implants provide information in the middle to high speech frequency range not available to the children, as they usually have only low- frequency hearing. Their speech perception can be predicted to a reasonable de- gree, as discussed in some detail above (see Predictive Factors) and in Chapters 9 and 11, and thus their language ability can also be predicted. In developing language it is important to consider the nature of the child, family, and habilitation or education programs (Spencer 2002). The benefits of cochlear implants in developing language have been summa- rized by Spencer (2002) as follows: “Cochlear implants provide many, but not all, deaf children with access to information that can help them develop under- standing and production of spoken language. However, the range of benefits ex- perienced is large and the factors that influence the benefits received by an indi- vidual child are still being investigated.” Receptive Language There is a normal distribution of equivalent language age for children with good hearing, as for example measured with the CELF test. Children with a hearing loss and a hearing aid or a cochlear implant have language that fallspredominantly outside this distribution (Blamey 2002). Studies on hearing-impaired children indicated that extrinsic factors leading to language delays are age of intervention (Davis et al 1986; Ramkalawan and Davis 1992; Gilbertson and Kamhi 1995; 748 12. Results Limbrick et al 1992; Dodd et al 1998; Yoshinaga-Itano et al 1998) and time spent reading (Limbrick et al 1992). Intrinsic factors are specific language impairment seen in 10 of 20 (50%) of hearing-impaired children by Gilbertson and Kamhi (1995) and speech-reading ability (Dodd et al 1998). It is important to distinguish between these extrinsic and intrinsic factors. Initial studies on small groups of children showed receptive language improved with the Nucleus 22 (F0/F1/F2 and Multipeak) (Kirk and Hill-Brown 1985; Busby et al 1989; Dowell et al 1991; Geers and Moog 1991; Hasenstab and Tobey 1991). This trend was confirmed by Dawson et al (1995a,b) from the data on a larger group of 32 children. On average they had a language-learning rate of 0.87 based on the PPVT that was approximately double the 0.4 to 0.6 rate for children with hearing aids (Geers and Moog 1988; Boothroyd 1991b). Comparing the learning rates for the implant and hearing aid groups made allowance for maturation by assuming it was the same for both. To further isolate maturation, Robbins et al (1995, 1997) predicted the effects on the Reynell scale (Reynell and Gruber 1990), and found that for the Nucleus 22 implant the lan- guage increase was 7 to 10 months ahead of expected after 12 to 15 months. The factors responsible for differences in receptive language were examined by Dawson et al (1995a,b). They first confirmed the findings of Osberger et al (1991a), Staller (1990), and Staller et al (1991a,b) for the Nucleus 22 system that age at onset of deafness and duration of the profound hearing loss correlated negatively with speech perception. Second, the variance among children for the growth of vocabulary was not significantly accounted for by these factors as well as duration of use, perception performance, and communication mode. A later study by Connor et al (2000) found a receptive vocabulary growth of 0.63 for children implanted at 2 years compared to 0.45 for children implanted at age 6.5 years. It was also necessary to monitor language acquisition over time to determine the longer term effects of the Nucleus 22 multiple-channel cochlear implant and F0/F1/F2 and Multipeak strategies. Sarant et al (1996, 2001) and Blamey et al (1998) studied 57 children aged between 4 and 12 years with a bilateral severe or profound hearing loss over a 4-year period. There were 33 hearing aid and 24 implant users. Receptive language measured with the PPVT was on average 62% of the expected level for hearing children. There were considerable differences in performance, and some were at the normal level. The results for children with implants were comparable to those for children with hearing who had a mean threshold of 81 dB. The structural complexity of language as well as vocabulary developed on average faster than predicted for deaf children without cochlear implants. This was assessed with the RDLS test (Svirsky et al 2000). Nevertheless, after 18 months some of the 23 children in the study continued to have severely delayed expressive language compared to children with unimpaired hearing. Some, how- ever, progressed at a rate typical for hearing children. Bollard et al (1999) also reported scores on vocabulary and language comprehension in 10 young children that increased at a rate equal to or faster than hearing children at an equivalent Language Development for Pre- and Postlinguistically Deaf Children 749 BKB AV score (%) 0 10 20 30 40 50 60 70 80 90 100 1 61116 PPVT equivalent age (years) Implant Hearing aid F IGURE 12.6. Speech perception (Bamford-Kowal-Bench (BKB) words in sentences) with audition and speech reading versus Peabody Picture Vocabulary Test (PPVT) equivalent language age for implanted and aided children (Sarant et al 1996, 2001; Blamey et al 1998). (Reprinted with permission from Blamey et al 1998. Speech perception and spoken language in children with impaired hearing. In: Mannell, R. H. and J. Robert-Ribes, eds. ICSLP ’98 Proceedings: 2615–2618.) language level. Nevertheless, after 18 months their language was behind the same children with hearing. The above studies showed considerable variability in receptive language, and in general children were not reaching age-appropriate language. The data indi- cated the variability did not depend only on percepts such as place pitch percep- tion (Busby and Clark 2000a,b) or the general factors leading to good speech perception (Dawson et al 1995a,b). A study was therefore undertaken to evaluate how strong a relationship existed between speech perception and language. The speech perception word and sentence scores for audition (A), speech reading (V), and audition plus speech reading (AV) were plotted against the PPVT or CELF equivalent language. As discussed in Chapter 11, a very close relationship was seen. The AV word score reached 100% at a PPVT or CELF age of approximately 8 to 10 years and the A score at 10 to 11 years (Fig. 12.6). So although language age did not increase at quite the same rate as for normal children, it rose rapidly in proportion to speech perception in quiet. However, it was not clear to what extent perception and language were interdependent. It was hypothesized that open-set speech perception was limited by vocabulary and that remediation of vocabulary and syntax would increase open-set speech perception scores. A study was undertaken on three implanted children from 9 to 15 years of age (Sarant et al 1996). The perception scores were recorded for words that were both known and unknown. They were retested after the meanings of all words had been learned. Two of the children had statistically significant improvements in the unknown word scores rather than for the known words, suggesting that it was not a practice effect but due to the effect of “top-down” 750 12. Results processing on “bottom-up” perception. The BKB sentence test was then used to assess specific grammatical constructs, again after the children had been taught the rules governing their use. There was benefit for two of the three children. Improvements in receptive language as reported above for the Nucleus 22 F0/ F1/F2 and Multipeak strategies are also being seen for the Clarion CIS strategy, which was approved by the FDA in 1997. In a study on 23 young children, they were found to have a greater than normal increase in language (Robbins et al 1991). Expressive Language The expressive language of children, as discussed above, can be analyzed at a phonological level using articulation tests and phonetic transcripts of spoken lan- guage. The results are presented as phonetic inventories, percent correct pho- nemes, or phonological processes. The order of occurrence of the phonemes is thought due to linguistic, acoustic, and articulatory factors. It was shown by Bla- mey et al (2001b) in a study on nine children using the Nucleus multiple-channel cochlear implant that the order of development was the same as for children with unimpaired hearing, although delayed. In addition, conversational speech samples were analyzed from nine children who received the Nucleus 22 implant and F0/F1/F2 and Multipeak speech-pro- cessing strategies between the ages of 2 and 5 years (Blamey et al 2001a). There was a significant increase in the complexity of the spoken language of the im- planted children seen in the study by Blamey et al (2001a). The mean number of syllables both intelligible and unintelligible rose from 1.7 to 5.2. The PPVT can be used to evaluate expressive language with the expressive subtest of the Woodcock Johnson Tests of Cognitive Ability. Woodcock and Mather (1989) and Blamey et al (2001c) found using the test that the implant and hearing aid users progressed at about 65% of the normal rate. This was similar to the rate for receptive language in children implanted at age 2 years. A marked improvement in language with implant children was reported by Svirsky et al (2000), who found the rate of language development was comparable to that of children with unimpaired hearing. The production of English grammar for 57 children implanted between 4 and 12 years of age and who used the Nucleus 22 F0/F1/F2 and Multipeak systems was measured with the CELF-3 and CELF-Preschool tests (Blamey et al 1998). The results were on average 45% of the expected level. The development of grammar skills in 29 children in a total communication (simultaneous speech and signed language) program using the Nucleus 22 F0/F1/F2 and Multipeak speech- processing strategies or hearing aids was studied by Tomblin et al (1999). The children’s ability to use expressive grammar (syntax) in this study was measured with story retelling. A control group of unimplanted deaf children was involved in the study. The children were 3 to 13 years postimplantation. The children’s understanding of sentence structure was assessed by their performance on the Rhode Island Test of Language Structure. The sentences were presented in speech plus signed English. The results showed that all but one of the children with the Language Development for Pre- and Postlinguistically Deaf Children 751 Nucleus 22 cochlear implants scored very high, and well above the expected results for deaf children. The scores improved from 30% to 65% in the first 5 years of cochlear implant use, while children with unimpaired hearing improved from 30% to 90% between the ages of 2 and 4 years. In addition, the children with implants tended to use speech (without signs) for a larger percentage of their words than did deaf children without implants, although both groups continued to use both modalities simultaneously for the majority of their productions. Grammatical morphemes are difficult for deaf children to recognize and pro- duce. Spencer et al (1998) found that 25 children with cochlear implants used grammatical morphemes more often than 13 children with hearing aids in a total communication program. The children with implants did not use signs for ex- pressing these morphemes, although speech and signs were used together for the majority of other words. This indicated the children with implants could perceive the morphemes and incorporate them into their expressive language. Furthermore, despite the language delays, they integrated the morphemes into their language in the same order as hearing children. Cognition As discussed above, there were considerable differences in the speech perception, speech production, and language results for children with the multiple-channel cochlear implant, and only about one third to one half of the variance of the speech perception scores could be accounted for (Dowell et al 1995; Sarant et al 2001). Furthermore, the receptive language scores did not match those for normal- hearing children (Blamey et al 1998; Sarant et al 2001). For the above reasons, cognitive studies were commenced to help determine the factors that contribute to the development of language. Cognition involves perception, attention, learn- ing, and memory. Information processing theory emphasizes that these processes should be viewed as a continuum and that all involve some kind of storage system or memory (Pisoni 2000). The effect of restoring some hearing with a multiple- channel cochlear implant on visual attention was first studied, as deaf children had been shown to have deficits in visual matching tasks (Moores et al 1973). Deaf children with cochlear implants performed better than those without, and also developed visual selective attention at a faster rate (Quittner et al 1994). But in another study no substantial difference was found between children with hear- ing, prelinguistically deaf without a cochlear implant, and deaf with a cochlear implant on a continuous performance visual attention task and a letter cancellation task. 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