ISSN:0196-0202    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveAs the need for objective measures with cochlear implant users increases, it is critical to understand how electrical potentials behave when stimulus parameters are systematically varied. The purpose of this study was to record and evaluate the effects of implanted electrode site and stimulus current level on latency, amplitude, and threshold measures of electrically evoked auditory potentials, representing brainstem and cortical levels of the auditory system.DesignThe electrical auditory brainstem response (EABR), electrical auditory middle latency response (EAMLR), and the electrical late auditory response (ELAR) were recorded from the same experimental subjects, 11 adult Clarion cochlear implant users. The Waves II, III, and V of the EABR, the Na-Pa complex of the EAMLR and the N1-P2 complex of the ELAR were investigated relative to electrode site (along the intra-cochlear electrode array) and stimulus current level. Evoked potential measures were examined for statistical significance using analysis of variance (ANOVA) for repeated measures.ResultsFor the EABR, Wave V latency was significantly longer for the basal electrode (7) compared with the mid (4) and apical (1) electrodes. For the EAMLR and ELAR, there were no significant differences in latency by electrode site. For all subjects and each of the evoked potentials, the apical electrodes tended to have the largest amplitude and the basal electrodes the smallest amplitude, although amplitude differences did not reach statistical significance. In general, decreases in stimulus current level resulted in statistically significant decreases in the amplitude of Wave V, Na-Pa and N1-P2. The evoked potential thresholds for Wave V, Na-Pa, and N1-P2 were significantly higher for the basal Electrode 7 than for Electrodes 4 and 1.ConclusionsElectrophysiologic responses of Waves II, III, and V of the EABR, Na-Pa of the EAMLR, and N1-P2 of the ELAR were characterized as functions of current level and electrode site. Data from this study may serve as a normative reference for expected latency, amplitude and threshold values for the recording of electrically evoked auditory brainstem and cortical potentials. Responses recorded from cochlear implant users show many similar patterns, yet important distinctions, compared with auditory potentials elicited with acoustic signals.

ISSN:0196-0202    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveThe overall objective of this study was to relate electrically evoked potentials recorded from different levels of the auditory pathway with behavioral measures obtained from adult cochlear implant subjects. The hypothesis was that adult recipients of cochlear implants who have open-set speech perception and those recipients with no open-set speech perception would differ in their neurophysiologic responses recorded at one or more levels of the auditory pathway.DesignThe subjects were 11 adults implanted with the Clarion cochlear implant. The electrical auditory brainstem response (EABR, Wave V), electrical auditory middle latency response (EAMLR, Na-Pa complex), and the electrical late auditory response (ELAR, N1-P2 complex), were recorded from three intra-cochlear electrodes. The stimuli used to record the evoked potentials varied in rate and amplitude. Behavioral measures (between threshold and upper limit of comfortable loudness) were used to define the subject's dynamic range at the different stimulus rates. Word and sentence recognition tests evaluated subjects’ speech perception in quiet and noise. Evoked potential and behavioral measures were examined for statistical significance using analysis of variance for repeated measures and correlational analyses.ResultsSubjects without open-set speech recognition demonstrated 1) poorly formed or absent evoked potential responses, 2) reduced behavioral dynamic ranges, 3) lack of change in the size of the dynamic range with a change in stimulus rate, and 4) longer periods of auditory deprivation. The variables that differentiated the best performers included 1) presence of responses at all three levels of the auditory pathway, with large normalized amplitudes for the EAMLR, 2) lower evoked potential thresholds for the Na-Pa complex, 3) relatively large dynamic ranges, and 4) changes in the size of the dynamic range with changes in stimulus rate.ConclusionsIn this study, the inability to follow changes in the temporal characteristics of the stimulus was associated with poor speech perception performance. Results also illustrate that variability in speech perception scores of cochlear implant recipients relates to neurophysiologic responses at higher cortical levels of the auditory pathway. Presumably, limited neural synchrony for elicitation of electrophysiologic responses underlies limited speech perception. Results confirm that neural encoding with electrical stimulation must provide sufficient physiologic responses of the central nervous system to perceive speech through a cochlear implant.

ISSN:0196-0202    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveThe aim of the present experiment was to assess the consequences of cochlear implantation at different ages on the development of the human central auditory system.DesignOur measure of the maturity of central auditory pathways was the latency of the P1 cortical auditory evoked potential. Because P1 latencies vary as a function of chronological age, they can be used to infer the maturational status of auditory pathways in congenitally deafened children who regain hearing after being fit with a cochlear implant. We examined the development of P1 response latencies in 104 congenitally deaf children who had been fit with cochlear implants at ages ranging from 1.3 yr to 17.5 yr and three congenitally deaf adults. The independent variable was the duration of deafness before cochlear implantation. The dependent variable was the latency of the P1 cortical auditory evoked potential.ResultsA comparison of P1 latencies in implanted children with those of age-matched normal-hearing peers revealed that implanted children with the longest period of auditory deprivation before implantation—7 or more yr—had abnormal cortical response latencies to speech. Implanted children with the shortest period of auditory deprivation—approximately 3.5 yr or less—evidenced age-appropriate latency responses within 6 mo after the onset of electrical stimulation.ConclusionsOur data suggest that in the absence of normal stimulation there is a sensitive period of about 3.5 yr during which the human central auditory system remains maximally plastic. Plasticity remains in some, but not all children until approximately age 7. After age 7, plasticity is greatly reduced. These data may be relevant to the issue of when best to place a cochlear implant in a congenitally deaf child.

ISSN:0196-0202    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

ObjectiveThe objective of the investigation described in this paper was the determination of the number of (widely spaced) active electrodes needed for users of a COMBI 40+ cochlear implant to achieve asymptotic performance in the recognition of speech against a background of wideband noise.DesignThis study measured the performance in speech tests of patients using the Med-El implementation of continuous interleaved sampling with widely spaced electrode pair subsets of 2, 3, 4, 6, 8, and 10 out of a possible maximum of 12. An eight-vowel test, a 16-consonant test, and BKB sentences were presented against a background of pink noise. Additionally, AB monosyllabic words were presented both in quiet and in noise to processors with 6, 8, and 11 widely spaced electrodes. 11 subjects participated in the study.ResultsUsing moderate signal-to-noise ratios, for these patients the curve relating percentage score to increasing numbers of active channels approached an asymptote before the 10-channel data point was reached. Asymptotic performance was achieved using four channels for consonants, and eight channels for sentences. Understanding of monosyllabic words reached a maximum value at a similar number of channels for both quiet conditions and against a background of pink noise, and the mean increase in test score between 6 and 11 channels was only 7%.ConclusionsThese results are similar to those of previous experiments carried out in quiet listening conditions. The data suggest that 12 frequency channels (the number implemented by the COMBI 40+ cochlear implant) are more than adequate for users to achieve asymptotic performance levels in clinical speech tests applied in the presence of wideband noise at moderate signal-to-noise ratios.

ISSN:0196-0202    

出版商:OVID    

年代:2002

数据来源: OVID