Advanced Combination Encoder Research Articles

Otimização da percepção da fala em deficientes auditivos usuários do sistema de implante coclear multicanal

OBJETIVO: realizar um estudo intra-sujeito, avaliando o reconhecimento da fala e a preferência subjetiva em deficientes auditivos usuários do sistema de implante coclear (IC) Nucleus 24, nas diferentes estratégias de codificação disponíveis nesse sistema (Spectral Peak - SPEAK, Continuous Interleaved Sampler - CIS e Advanced Combination Encoders - ACE), a fim de promover a otimização da percepção da fala em cada sujeito. FORMA DE ESTUDO: Clínico prospectivo. MATERIAL E MÉTODO: Sete adultos com deficiência auditiva pós-lingual foram divididos aleatoriamente em 2 grupos, determinados A e B para a realização do protocolo de avaliação. CIS foi adaptada inicialmente aos sujeitos do grupo A e ACE aos do grupo B. SPEAK foi a linha de base para todos os sujeitos. Foram realizadas avaliações do reconhecimento da fala no silêncio e no ruído (S/R + 10dB), ajustes nas estratégias de codificação e aplicação de questionários de auto-avaliação. RESULTADOS: Altos níveis de reconhecimento da fala foram obtidos para as três estratégias. Os resultados médios dos sete sujeitos atingidos para o reconhecimento de sentenças no silêncio foram de 69,1%, 76,2% e 80,2% para CIS, SPEAK e ACE respectivamente. Na situação de ruído foram de 38,0%, 40,8% e 53,1% para SPEAK, CIS e ACE, respectivamente. Não houve diferença estatisticamente significante entre as estratégias avaliadas. Escores de reconhecimento da fala mais altos foram notados sujeito a sujeito, com a estratégia otimizada. CONCLUSÃO: A utilização de estratégias múltiplas de codificação da fala e escolhas de parâmetros flexíveis permitem ao clínico individualizar um programa de adaptação e resulta em maiores benefícios aos usuários de IC.

Speech coding strategies and revised cochlear implant candidacy: an analysis of post-implant performance.

Technological advances in cochlear implant systems on which a sequence of speech coding strategies have been implemented seem to have resulted in improved speech perception. However, changing selection criteria for implantation have coincided with evolving technology and may confound post-implantation speech perception performance. This study compares speech coding strategy with speech perception performance in severe and profound postlingually deafened adults using one of three successive generations of Nucleus Cochlear Implant speech processors (i.e., Mini Speech Processor, Spectra 22, and SPrint) implementing three speech coding strategies (i.e., MPEAK, SPEAK, and Advanced Combination Encoders; Cochlear Corporation, Englewood, CO, U.S.A.). Four cohorts of patients were retrospectively reviewed. Multicenter, tertiary referral cochlear implant programs in Ontario, Canada. Four cohorts of patients (n = 139) were identified based on preimplant audiological measures, duration of deafness, device type, and speech coding strategy. Word and sentence recognition scores at 12 months after implantation were compared using MPEAK with SPEAK22 implemented on the Nucleus 22 speech processors (Mini Speech Processor and Spectra22, respectively) and SPEAK24 as well as Advanced Combination Encoders implemented on the Nucleus 24 SPrint processor. Open-set speech recognition batteries revealed significant improvements in word and sentence scores as advancing technology implemented new speech coding strategies. Subgroup analysis of profoundly deafened patients supported this. Analysis of covariance confirmed that the measured differences could not be accounted for by changing selection criteria for implantation. Improvements in performance can be attributed to evolving speech coding strategies and speech processors rather than to differences in preimplant candidacy.

Effects of stimulation rate with the Nucleus 24 ACE speech coding strategy.

The primary objective of the study was to determine whether individual cochlear implant recipients recognize speech better with an electrical stimulation rate of 720 or 1800 pulses per second per channel (pps/ch) using the Nucleus 24 Advanced Combination Encoder (ACE) speech coding strategy. The secondary objective was to determine, for each active electrode, the relation between psychophysical measures and MAP minimum and maximum stimulation levels for each rate, as well as the stability of MAP minimum and maximum levels during the study. Eight postlinguistically deaf adults implanted with the Nucleus 24 device participated in this study comparing the effect of a moderate (720 pps/ch) and a fast (1800 pps/ch) rate of electrical stimulation on speech recognition of words in quiet and sentences in noise presented at 50, 60, and 70 dB SPL in the laboratory and on listening to sound in everyday life over a 14-wk time period. At the beginning of the study, psychophysical measures (i.e., counted threshold and maximum acceptable loudness [MAL] levels) were obtained for each active electrode with each of the two rates to initially set MAP minimum and maximum stimulation levels. These levels were then adjusted to make speech and environmental sound clear and comfortable in everyday life. Threshold and MAL levels were obtained again half way through the study to monitor possible hearing changes. A four-phase test design for evaluation of speech recognition was followed; an equal number of subjects started with each of the two rates and alternated rates for each phase. In the last 2 wk of each phase, word and sentence scores were obtained, and subjects responded to a questionnaire. For the group, factorial analyses of variance were conducted for subject, stimulation rate, and time period (first two phases versus second two phases) for words, phonemes within words, and sentences at each level. Additional analyses were obtained for individual subjects. Group mean scores across time periods were significantly higher for 1800 pps/ch than 720 pps/ch for phonemes and sentences in noise at 50 dB SPL. There was no significant difference in scores for phonemes and sentences at 60 and 70 dB SPL or for words at any of the three levels. Group mean scores across stimulation rate were significantly higher during the second half than the first half of the study for words, phonemes, and sentences at 50 dB SPL. This result is consistent with subjects learning to recognize speech cues near threshold. A subject by rate interaction was seen for sentences at 70 dB SPL and for all three speech measures at 50 dB SPL. These interactions reflect the fact that two subjects performed significantly better with 720 pps/ch, whereas two other subjects performed significantly better with 1800 pps/ch. Responses to the questionnaire indicated that two subjects preferred 720 pps/ch, three preferred 1800 pps/ch, and three had no preference. The minimum and/or maximum levels in most subjects' final MAPs differed from the psychophysical measures for both rates. Changes in Current Level at threshold and MAL were minimal from the first to the second half of the study for each rate. More than half the subjects preferred one of the two rates for use in everyday life, and four subjects performed significantly better with one of the two rates on at least one test measure. These findings underscore the clinical importance of creating MAPs for each implant recipient that include at least a moderate and a fast rate within ACE during the first months of device use. Given the significant learning effects for soft speech that occurred over several weeks use of each rate in this study, it is suggested that each rate be used alone for a week or two before comparing them and deciding which provides more benefit. In addition, adjustments in an individual's MAP minimum and maximum levels are needed at each rate so soft and normal conversational speech as well as loud sound are clear and comfortable in everyday life.

Speech recognition in background noise of cochlear implant patients.

The performances of adult patients using Spectral peak (Nucleus 22 or Nucleus 24 patients) or Continuous Interleaved Sampling or Advanced Combination Encoder (Clarion patients) were evaluated in their ability to perform in quiet and in 2 levels of background noise. Ninety-six patients were tested with the City University of New York Sentences presented at 70 dB in quiet and at signal-to-noise ratios (SNR) of +10 and +5 dB. Patients were scored on the number of words perceived correctly. Scores were different at each condition (P < 0.05): 88% words correct in quiet, 73% correct at an SNR of +10 dB, and 47% correct at an SNR of +5 dB. Linear regression analysis found no significant correlation between test score and age at implantation or time using the implant. A weak negative correlation was found between years of hearing loss and score. Competing noise interferes with comprehension of connected speech for most cochlear implant patients.

Conversion from the SPEAK to the ACE strategy in children using the nucleus 24 cochlear implant system: speech perception and speech production outcomes.

The main objective of this study was to assess whether speech perception and speech production in children using the Nucleus 24 cochlear implant system improved with a change in speech processing strategy from the SPEAK to the Advanced Combination Encoder (ACE) strategy. The major difference between the two strategies is that ACE uses a higher stimulation rate (in this study the stimulation rate was 900 Hz per channel) compared with the SPEAK strategy, where the stimulation rate is 250 Hz per channel. Information also was obtained regarding the adjustment period after conversion to the ACE strategy. An ABA experimental design was used where scores were initially obtained using the SPEAK strategy' (in the initial A time interval), and subsequently performance was assessed using the ACE strategy (B time interval) and then again with the SPEAK strategy (second A time interval). The duration of the B interval was 10 wk, and the duration for the second A interval was 4 wk. Seven children aged between 9 and 16 yr who had at least 6 mo experience with the SPEAK strategy participated. Open-set monosyllabic CNC word perception in quiet and Speech Intelligibility Test sentence perception in noise was evaluated at the end of each of the time intervals. Word perception was also monitored at fortnightly intervals during the B time interval. Speech production was assessed at the end of the initial A time interval and at the end of the B time interval. Mean word and phoneme scores for open-set words in quiet for the group of seven children were significantly higher with the ACE strategy as compared with the SPEAK strategy scores obtained in both of the A time intervals. For sentences in noise, mean scores using the ACE strategy as well as the SPEAK strategy at the second A evaluation point were significantly higher than the scores using the SPEAK strategy measured at the first A time interval. This suggests that learning effects may have influenced outcomes. For some subjects, an initial decrease in scores was found during the initial 2-wk period after fitting the ACE strategy; however, scores subsequently were found to be similar to or higher than those when using the initial SPEAK strategy. Analysis of speech production assessments showed an improvement in the medial consonant scores after using the ACE strategy. This study demonstrated that some children were able to benefit from the additional information provided by the ACE strategy as compared with the SPEAK strategy. However, the differences in overall performance between the two strategies appear to be relatively small.

Effect of Stimulation Rate on Cochlear Implant Recipients' Thresholds and Maximum Acceptable Loudness Levels

Clinically, speech processor programs are created using electrical thresholds and maximum acceptable loudness levels (MALs) at several different stimulation rates to determine what rate will provide cochlear implant recipients with the best speech recognition when using fast-rate speech coding strategies. This study was designed to determine the difference in thresholds and MALs (expressed in the clinical unit, Current Level [CL]) for pairs of six rates spanning those available with the Nucleus 24 device (i.e., 250 to 2,400 pps/ch) using monopolar, 25 microsec/phase stimulation. Test-retest measures of threshold and MAL for each rate were obtained from seven adult Nucleus 24 recipients on each of 11 electrodes. The difference in threshold and in MAL between pairs of rates was dependent on the absolute CL. Below approximately 190 CL, thresholds and MALs decreased with increasing rate; above 210 CL, there was little change in threshold or MAL with increasing rate. Based on these findings, an approach to estimating threshold and MAL from one rate to another is suggested, pending further research.