Cochlear Implants

Auditory Perception Changes After Reimplantation in a Child Cochlear Implant User Patricia M. Chute, MA; Sharon A. Hellman, MS; Simon C. Parisier, MD; Vivien C. Tartter, PhD; Alexandra Economou, MA Cochlear lmplant Center (P.M.C., S.A.H.) and Department of Otolaryngology (S.C.P.), Manhattan Eye, Ear and Throat Hospital, New York, New York and City College, CUNY, New York, New York (V.C.T., A.E.)

ABSTRACT The ability to remove cochlear implants from children and subsequently reimplant a more complex device in the same ear was the concern of this single case study. A postlinguistically deafened child, J.L., received a singlechannel cochlear implant 1 yr after contracting meningitis and suffering a profound bilateral sensorineural hearing loss. After 3 yr of successful implant use, J.L. suffered an internal coil tailure. She was then explanted and reimplanted with a multichannel cochlear implant in the same ear. This case report details her speech perception skills with her single-channel cochlear implant, a vibrotactile aid, and a multichannel cochlear implant. Results from auditory perceptual measures suggest that the explantation/reimplantation process was technically feasible with no adverse effects on J.L.’s ability to utilize a more sophisticated device and to exceed her previous performance levels. (Ear Hear 13 3:195-199)

THE NUCLEUS 22-CHANNEL cochlear implant (Cochlear Corporation) has been available to children as an approved device by the Food and Drug Administration since June, 1990. These devices have increasingly become an acceptable option for profoundly deaf children who receive minimal benefits from conventional hearing aids. However, there still remain questions regarding long-term implant use. One question relates to explantation/reimplantation due to device failure or technological improvements. This case study is a report of one center’s experience explanting and reimplanting a successful child cochlear implant user. Several generations of cochlear implants have been used in children since 1982. The early single-channel cochlear implants required several modifications because of problems encountered with the insulation capEar and Hearing, Vol. 13, No. 3,1992

sule and electrode flexibility. These changes were necessitated by electrical failures presumably due to seepage of fluid through the capsule of the internal receiver, which rendered the device nonfunctional. In addition, the earlier, less flexible electrodes cracked, resulting in similar device failure (personal communication, 3M Corporation). At the Cochlear Implant Center of Manhattan Eye, Ear and Throat Hospital, a total of 10 3M/ House internal receivers, representing 30.3% of the single-channel devices implanted at this facility, have failed (Parisier, Chute, Weiss, Hellman, & Wang, 199 1). This percentage is representative of the overall series (West & Money, 1990). In addition to device failure, children may also be explantedjreimplanted from single-channel implants to multichannel implants to take advantage of improved technology. With FDA approval of the Nucleus device, this is now a foreseeable option. Because of the likelihood of single-channeldevice failure and the option to upgrade to a multichannel system, the performance effects upon explanting a single-channel device and reimplanting a more complex device in the same ear is of great concern to professionals involved in cochlear implants. The single case study reported here explores the speech perception changes following reimplantation. METHOD

Subject In early 1984, the Cochlear Implant Center began participating in the investigational study of the 3M/House cochlear implant in children. Three yr later, after implanting 18 children with the single-channeldevice, the Center began study of the Nucleus 22-channel device. The subject, J.L., was implanted in July 1985. She was implanted at the age of 7.5 yr after suffering a profound bilateral sensorineural hearing loss, secondary to pneumoccocalmeningitis the previous year. She continued to attend her local elementary school along with a sign language interpreter/tutor. In October 1988, after 3 yr of single-channel cochlear implant use, J.L. suffered an internal receiver failure of her 3M/House system. A decision by the family, the implant team, and the child was made to replace J.L.3 failed 3M/ House cochlear implant with a Nucleus 22-channel implant. The surgery took place within 1 week of device failure. In order to maintain speech awareness during the process of reimplantation and surgical recuperation before activation 0196/0202/92/1303-0195$03.00/0EARAND HEARING Copyright Q 1992 by Williams 8 Wilkins Printed in the U.S.A.

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of the Nucleus device, a Tactaid I1 vibrotactile device was used. J.L. returned to her regular school environment and continued in her rehabilitation program with her school-based therapist using the Tactaid I1 on a daily basis. J.L. was fit with a Nucleus 22 WSP I11 speech processor approximately 1 mo postsurgery. At that time, 18 active electrodes were programmed in a bipolar+3 stimulation mode. The coding scheme was FO, F1, F2. This coding scheme extracts the fundamental frequency (coded as rate of electrical stimulation) and first and second formant cues (coded as place of electrical stimulation). Table 1 displays J.L.’s current MAP. Test Materials Speech perception testing was performed using closed set and open set tasks in an auditory-only mode. All tests were presented using recorded materials in the sound field at 70 dB SPL. The battery of audiological tests included pure-tone thresholds, aided warble tone thresholds, the Test of Auditory Comprehension (TAC), the Discrimination After Training Test (DAT), the Glendonald Auditory Screening Procedure (GASP), the Northwestern University-6 (NU-6) Monosyllable Word Lists, Central Institute for the Deaf (CID) Everyday Sentences Test and the Three Interval Forced Choice Test (THRIFT). The TAC (Los Angeles, 1980) measures a variety of skills necessary for the auditory processing of speech. It includes performance in discriminating words and phrases, memory sequencing and figure ground. There is a hierarchy of 10 subtests with each area assessed using a closed set of picture stimuli. The DAT test was initially developed by Thielemeir, Tonokawa, Peterson, and Eisenberg (1985) for use with prelinguisticallydeafened adults. There is a hierarchy of 12 subtests ranging from simple visual discrimination between two stimuli (level 1) to discrimination among four spondaic words (level 12). The GASP (Erber, 1982) was adapted by the House Ear Institute as an open set test of word recognition and sentence comprehension for children using cochlear implants. It consists of 12 basic children’s vocabulary words and 10 everyday questions. The NU-6 monosyllabic word lists are phonemically balanced word lists routinely used to assess word recognition in adults. The CID Everyday Sentences are used to assess word recognition at the sentence level with adults. Each sentence has a number of key words, which are generally the content words in the sentence. Scores are reported as the percentage of key words correct. The THRIFT (Boothroyd, Spring, Smith, & Schulman, 1988)was developed to measure listeners’ access to phonologically significant cues. The 10 contrasts sampled are duration (1 sec/ 0.5 sec), intonation (constant FO/changing FO), vowel height (e.g., boo/baw), vowel place (e.g., oosh/eesh), initial consonant voicing (e.g., see/zee), final consonant voicing (e.g., ood/ oot), initial consonant continuance (e.g., too/soo), final consonant continuance (e.g., awb/awm) and final consonant place (e.g., ood/oob).

Procedure On the day of suspected 3M/House failure, J.L. was seen at the cochlear implant facility for evaluation. Temporary function of her cochlear implant was obtained by delivering high current levels to her internal receiver. J.L. reported that she was hearing as well as before. At this time, J.L. received the complete speech perception battery (see Table 3). J.L.3 performance on these measures was again assessed with a Tactaid I1 Vibrotactile aid after approximately 6 weeks of Tactaid use. This testing was completed the day before J.L. was fit with her Nucleus WSP 111 speech processor (see Table 4). J.L. was again given this battery of tests at 6 mo, 1 yr, 2 190

Chute et crl

Table 1. Current map for subject J.L. Stimulation mode: Bipolar + 3; frequency spacing: Lin-Log; encoder strategy: FOFl F2. Electrode

Threshold

Comfort Level

Pulse Width

ia 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2

60 70 60 60 60 60 60 60 55 60 55 80 91 95 95 96 90 109

155 154 152 150 155 157 157 150 157 150 155 158 163 151 148 143 136 140

204 204 204 204 204 204 204 204 204 204 204 204 204 204 204 204 204 204

1

Frequency Range

0-408 408-518 518-643 643-753 753-878 878-1004 1004-1098 1098-1224 1224-1349 1349-1490 1490-1647 1647-1820 1820-2008 2008-2212 2212-247 2447-2698 2698-2980 2980andabove

yr, and 3 yr post-Nucleus 22 cochlear implant use (see Table 5).

To explore the acoustical changes in J.L.’s speech associated with single-channel implant use, implant failure (no auditory stimulation), and subsequent multichannel implant use, a series of speech recordings were made following the procedures outlined in Tartter, Chute, and Hellman (1989). For detailed analyses of these results, the reader is referred to Economou, Chute, Hellman, and Tartter ( 1991). Reimplantation Surgery At the time of the surgery, the 3M/House”Iplant was removed. Working through the facial recess area, the round window which had been found to be ossified at the original procedure was identified and the basal turn of the cochlea skeletonized. A trephination needed to be made into the scala tympani by drilling away some soft new bone that occluded this area. Only 15 of the 22 electrodes could be inserted into the scala tympani. The remaining electrodes were placed in a bony trough that had been created in the area of ossification adjacent to the round window. Postoperatively, the patient’s wound healed well. RESULTS

Performances with each of the devices at varying time periods were obtained in order to assess their comparative eficacy. Pure-tone thresholds under headphones obtained before the original 3M/House surgery revealed responses through 1 kHz and a speech detection threshold of 100 d B HL in the ear to be implanted. After the 3M/House device had failed and before the revision surgery, a repeat audiometric evaluation revealed that there were no measureable acoustic responses to pure tones. However, a speech detection threshold of 114 dB HL was obtained. Table 2 displays these results along with the sound field results measured using her 3M/House implant and her Nucleus 22 implant. Ear and Hearing, Vol. 13, NO. 3,1992

J.L.’s longitudinal auditory perceptual performance with the 3M/House device is displayed in Table 3. J.L. was a highly successful user of her 3M/House singlechannel system. Within the first 6 weeks of singlechannel implant use, J.L. obtained pattern perception of speech (i.e., the ability to discriminate words and phrases using duration, intensity, and timing cues). By 1 yr postsurgery, J.L. was beginning to recognize words using segmental cues. She acheived level 12 of the DAT (discrimination among four spondaic words) and level 5 of the TAC (discrimination of two critical items requiring word recognition skills). After 2 yr of use, J.L. was approximately 10.5 yr old. She obtained some open set speech recognition abilities. After 3 yr of singlechannel implant use, J.L. correctly recognized 50% of the words and comprehended 70% of the questions on the GASP. In a report by Thielemeir et a1 (1 985) of 126 implanted children, only 1.5% of this sample obtained some sentence and word recognition on the GASP. However, the words sampled by the GASP are simple vocabulary items familiar to most children (e.g., popcorn, airplane, ball, fish). The sentences are also routine. They consist of 10 everyday questions (e.g., “What is your name?”, “How old are you?”, “What number comes after seven?”). On a more difficult word recognition task such as the NU-6 lists, J.L. was unable to Table 2. Unaided and aided audiometric results. Results were collected under headphones before the initial surgery and before the explantation/reimplantationsurgery. Unaided results are reported in dB HTL. Aided results were gathered using warble tones in the sound field with the subject‘s cochlear implant on. Aided results are reported in dB SPL.

recognize any words even after 3 yr of experience. Recognition of these words may require a higher vocabulary level as well as a greater ability to extract phonemic information at an acoustic level. Because of the nature of the single-channel processor, this information is not likely available to its users. The 3M/ House system delivers an analog coding of the speech signal to a single-ball electrode. It is assumed that the implant user receives timing and intensity cues of the speech waveform, but no formant specific information. J.L.3 ability to extract phonemic information can further be seen in Figure l . Figure l illustrates J.L.’sresults on the THRIFT. After 3 yr of 3M/House cochlear implant use, J.L. was unable to discriminate above chance levels any of the phonological contrasts tested. However, this is a difficult test, and her particularly poor performance may be related more to J.L.3 age at the time of testing and the cognitive/linguistic skill necessary for this test than the implant itself. AAer approximately 1 mo experience with the Tactaid 11, J.L. was again assessed. Table 4 displays the results obtained using a Tactaid 11. Her performance with this device reveals pattern perception abilities, but no word recognition. Note that her performance at this time was approximately the same as that obtained after 6 weeks of single-channel cochlear implant use. J.L. was retested at 6 mo, 1 yr, 2 yr, and 3 yr postNucleus surgery. At the 6 mo interval, J.L. was starting to reach the performance levels obtained with her 3M/ House device. In addition, at that time she was beginning to recognize words and sentences on both the NU6 test and the CID Everyday Sentences test. J.L. also demonstrated an ability to extract phonemic informa-

Frequency (Hz) 250 500 750 1000 2000 3000 4000 8000 Pre-SM/House(dB 95 105 120 120 NR HL) Sound field 3M/ 42 49 44 House (dB SPL) Pre-Nucleus(dBHL) NR NR NR NR NR Soundfield Nucleus 53 46 41 45 41 22 (dB SPL)

NR

NR

55

55

NR 41

NR 55

NR

DISCRIMINATION OF PHONOLOGICAL CONTRASTS THREE INTERVAL FORCED CHOICE TEST

NR

NR = no response.

Table 3. Auditory speech perception abilities using a 3M/House single-channel cochlear implant.

Time Interval Test DAT TAC GASP Word recognition Sentence comprehension NU6 Word recognition CID sentence recognition a

Pretest 6 Weeks 6 mo 1 yr 2 yr 3 yr 1 CNE*

8 2

DNT DNT

DNT DNT

DNT DNT 40% 50% DNT DNT 60% 70%

DNT DNT

DNT DNT

DNT DNT 0% 0% DNT DNT 0% 0%

128

2

Highest possible score. CNE, could not evaluate; DNT,did nor rest

Ear and Hearing, Vol. 13, No. 3,1992

12 12 5 4

12 7

Figure 1. Results of the THRIFT 3 yr post-3M/House, 6 mo postNucleus, and 3 yr post-Nucleus. The x-axis represents the 10 phonological contrasts tested. They are: DUR, duration; INT, intonation; VH, vowel height; VP, vowel place; ICV, initial consonant voicing; FCV, final consonant voicing; ICC, initial consonant continuance; FCC, final consonant continuance; ICP, initial consonant place; and FCP, final consonant place. The y-axis representsthe percent correct score. All scores have been corrected for guessing. The 95% confidence interval is visualized as a solid line at approximately 18% correct.

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tion as measured by the THRIFT. Figure 1 also illustrates these results. It can be seen in Figure 1 that at 6 mo post-Nucleus, J.L. was making good use of timing and intensity cues as well as lower formant information. She was near 100% correct discrimination for the contrasts differing in duration, vowel height, vowel place, and final consonant voicing. Using a difference in proportion statistic (Shearer, 1982),these changes were found to be significant at p < 0.001. A significant change was also seen for the phonological contrast initial consonant continuance at p < 0.05. For contrasts varying in initial or final place of articulation, initial consonant voicing, or final consonant continuance, her performance was still poor even with 6 mo of multichannel experience. This measure was repeated at the 3 yr post-Nucleus interval. Her performance, as shown in Figure 1, was not strikingly different from the 6 mo interval. Those changes between 6 mo post-Nucleus and 3 yr post-Nucleus were not significant. However, her performance 3 yr post-Nucleus, compared with her 3M/House data, was significantly different for the phonological features, duration, intonation, vowel height, vowel place, and final consonant voicing ( p < 0.001). In addition, changes in initial consonant voicing, initial consonant continuance, and final consonant continuance were all significant at p < 0.05. These improvements in J.L.’s ability to extract phonemic information can be seen in her word and sentence recognition in Table 5. Three yr of Nucleus 22 cochlear implant use did indeed improve her auditory word and sentence recognition. Closed set measures of auditory memory and

sequencing using complex language (i.e., as measured by levels 7 and 8 of the TAC) and open set measures of word and sentence recognition (GASP, NU-6, and CID Sentences) all show improvements which surpassed her previous impressive performance with the 3M/House system. J.L.’s word recognition scores significantly improved, as measured by both the GASP words and NU-6 word lists [ X (3) = 38.75, p < 0.001, x (4) = 32.6 1, p c 0.00 1, respectively]. Her longitudinal performance on both the GASP sentences and CID Everyday Sentences also showed significant improveqent [ x (3) = 49.40, p < 0.001, X (3) = 49.40, p < 0.001, respectively]. It should also be noted that J.L. has begun to use the telephone interactively and is currently attending her local junior high school without a sign language interpreter. J.L. is now receiving itinerant services from a teacher of the hearing impaired. Academically she is doing well and is an honor student. Her speech is highly intelligible as measured by the Speech Intelligibility Evaluation (Monsen, 1981). She received a score of 9 1%, which suggests that her speech is highly intelligible even to the naive listener. DISCUSSION

J.L.’s performance with a variety of sensory aids over a substantial time period suggests several important things. First, it is apparent from the results comparing the Nucleus and 3M/House devices that the explantation/reimplantation process did not hamper J.L.’s abilities to take advantage of a more complex processing scheme. Although it did appear to take J.L. approximately 6 mo to learn to use the speech code delivered by her new multichannel device, by that time she was functioning at least as well as with her 3M/House single-channel implant. After 1 yr of Nucleus multichannel implant use, J.L. began to display greater abilities in using spectral information to discriminate phonological contrasts and recognize unfamiliar CVC words and words in complex sentences. After 3 yr of Nucleus use, J.L.’s performance had still not plateaued. This is very encouraging. These data suggest that J.L. has been able to take advantage of the FO, Fl, F2 feature extraction coding scheme of the Nucleus cochlear implant at least as well as those who have received this implant as their first device.

Table 4. Speech perception abilities with a two-channel tactile aid (Tactaid 11).

Test TAC DAT GASP Word recognition Sentence comprehension NU6 Word recognition CID sentence recognition NUCHIPS

Results Level 2 Level 8 0% 0%

0% 0% 20%

Table 5. Auditory speech perception abilities with a 3M/House single-channel cochlear implant and a Nucleus 22-channel cochlear implant.

Time Interval Test TAC DAT GASP Word recognition Sentence comprehension NU6 Word recognition CID sentence recognition

3 yr 3M/House

6 mo Nucleus

1 yr Nucleus

2 yr Nucleus

3 yr Nucleus

Level 7 Level 12”

Level 6 Level 12

Level 7 Level 12

Level 8 Level 12

Level 8 Level 12

50% 70%

18% 20%

67% 70%

100%

0% DNTb

2Yo 6%

12% 31yo

75%

22% 60%

75% 70% 20% 46% ~~

a

Highest possible score. DNT, did not rest.

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Chute et al

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In a multicenter, independent evaluation of the Nucleus implant, Osberger, Miyamoto, Zimmerman-Phillips, Kemick, Stoer, Firszt, and Novak ( 1991) evaluated 28 implanted children. The PBK-50 list was used as a measure of open set speech recognition. Seventeen children were able to complete this test. The mean score was 11% (SD = 8%; range = 0-36%). Thus, J.L.3 performance on a similar measure (i.e., NU-6) was comparable to this group. Staller, Dowell, Beiter, and Brimacombe (1 99 1) reported on the perceptual abilities of 142 child cochlear implant users from 23 investigational sites. Five tests of open set speech recognition were administered, including the GASP. Postoperatively, the group mean at 12 mo was 23.6% on the GASP words and 23.1 % on the GASP sentences. This places J.L.’s performance at a similar time interval well above this group mean. There are issues regarding electrode insertion, however, that need to be carefully considered. In J.L.’s case, 15 electrodes could be inserted, but in other cases with more advanced ossification, this may not be possible. The shorter 3M/House electrode is only inserted 6 mm into the cochlea, and in those cases of advanced ossification, the longer electrode insertion necessary with the Nucleus device may not be possible. This may tend to compromise the performance with the multichannel device. For this reason, parents and children need to be carefully counseled regarding the reimplantation results so that they are realistic about their expectations. The results of the pure-tone testing are of interest and suggest that although J.L.’s unaided hearing sensitivity was compromised due to explantation/reimplantation and/or previous cochlear implant use, this did not preclude her obtaining auditory-only comprehension of speech. Finally, her performance with the Tactaid I1 during the period between implant failure and reactivation indicates the utility of vibrotactile devices in delivering basic envelope cues. It should be noted that J.L.’s results with this device are similar to her responses after an equivalent amount of time using the 3M/House device. Because J.L. only used the Tactaid I1 for 1 mo, it is unfair to make any further projections. However, as an interim device for a child who was faced with the prospect of once again being without sound, it helped her through an extremely stressful period. Vibrotactile aids should be strongly considered during this time for those individuals who have sustained an internal receiver failure. CONCLUSION

upgrading and replacement of cochlear implants. The fact that the child was reimplanted in the same ear with no loss of auditory/speech perception abilities is reassuring. There is a caveat that needs to be addressed by all centers performing reimplant surgery. Although the data would suggest an increase in performance when changing from a single-channel to a multichannel device, this cannot be guaranteed. Level of ossification and electrode insertion depth may play important roles in the final performance of the child or adult. Careful counseling of both parents and children undergoing reimplantation is still a necessary part of the presurgical testing. This should not be overlooked in the rush to give the child back some sound. REFERENCES Boothroyd A, Spring N, Smith L, and Schulman J. Amplitude compression and profound hearing loss. J Speech Hear Res 1988; 311362-376. Erber NP. Auditory Training. Washington, D.C.: Alexander Graham Bell Association for the Deaf, 1982. Los Angeles County Office of the Superintendent of Schools. Audiologic Services and Southwest School for the Hearing Impaired. Test of Auditory Comprehension. North Hollywood, CA: Foreworks, 1980. Monsen RB. A usable test for the speech intelligibility of deaf talkers. Am Ann Deaf 1981;126:845-852. Osberger MJ, Miyamoto RT, Zimmerman-Phillips MS, Kemick JL, Stoer BS Firszt JB, and Novak MA. Independent evaluation of the speech perception abilities of children with the Nucleus 22-channel cochlear implant system. Ear Hear I99 l;(suppl):66S-8OS. Parisier SC, Chute PM, Weiss MH, Hellman SA, and Wang RC. Results of cochlear implant reinsertion. Laryngoscope 1991;101: 1013- I0 15. Shearer WM. Research Procedures in Speech, Language and Hearing. Baltimore: Williams & Wilkins, 1982. Staller SJ, Dowell RC, Beiter AL, and Brimacombe JA. Perceptual abilities of children with the Nucleus 22-channel cochlear implant. Ear Hear 1991;(suppl):34S-47S. Tartter V, Chute P, and Hellman S. The speech of a post-linguistically deafened teenager during the first year of use of a multichannel cochlear implant. J Acoust SOCAm 1989;86:2 1 13-2 12 I. Thielemeir MA. The Discrimination After Training Test. Los Angeles: House Ear Institute, 1984. Thielemeir MA, Tonokawa LL, Peterson B, and Eisenberg LS. Audiological results in children with a cochlear implant, Ear Hear 1985;(suppl):27S-35S. West R and Money D. Comparative reliability of cochlear implants. Paper presented at the annual Colorado Otology Audiology Conference, Snowmass, CO, March 1990.

Address reprint requests to Patricia M. Chute, M.A., Cochlear Implant Center, Manhattan Eye, Ear and Throat Hospital, 210 East 64 Street, New York, NY 10021. Received January 8,1991 ; accepted January 2, 1992.

In summary, J.L. represents a child who illustrates a growing concern among hearing professionals regarding

Ear and Hearing, Vol. 13, No. 3,1992

Portions of this paper were presented at the annual meeting of the American Auditory Society, Boston, MA, September 1989.

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