Debora R. Hatch

Cochlear implantation in children with auditory neuropathy spectrum disorder

Objective: To report the patients characteristics, preoperative audiological profiles, surgical outcomes, and postoperative performance for children with auditory neuropathy spectrum disorder (ANSD) who ultimately received cochlear implants (CIs). Design: Prospective, longitudinal study of children with ANSD who received CIs after a stepwise management protocol that included electrophysiologic and medical assessment, documentation of behavioral audiometric thresholds and subsequent fitting of amplification according to Desired Sensation Level targets, auditory-based intervention with careful monitoring of skills development and communication milestones, and finally implantation when progress with the use of acoustic amplification was insufficient. Results: Of 140 children with ANSD, 52 (37%) received CIs in their affected ears (mean duration of use of 41 mos). Many of these children were born prematurely (42%) and impacted by a variety of medical comorbidities. More than one third (38%) had abnormal findings on preoperative magnetic resonance imaging of the brain and inner ear, and 81% had a greater than severe (>70 dB HL) degree of hearing loss before implantation. Although 50% of the implanted children with ANSD demonstrated open-set speech perception abilities after implantation, nearly 30% of them with >6 months of implant experience were unable to participate in this type of testing because of their young age or developmental delays. No child with cochlear nerve deficiency (CND) in their implanted ear achieved open-set speech perception abilities. In a subgroup of children, good open-set speech perception skills were associated with robust responses elicited on electrical-evoked intracochlear compound action potential testing when this assessment was possible. Conclusions: This report shows that children with ANSD who receive CIs are a heterogeneous group with a wide variety of impairments. Although many of these children may ultimately benefit from implantation, some will not, presumably because of a lack of electrical-induced neural synchronization, the detrimental effects of their other associated conditions, or a combination of factors. When preoperative magnetic resonance imaging reveals central nervous system pathology, this portends a poor prognosis for the development of open-set speech perception, particularly when CND is evident. These results also show that electrical-evoked intracochlear compound action potential testing may help identify those children who will develop good open-set speech perception. Instead of recommending CI for all children with electrophysiologic evidence of ANSD, the stepwise management procedure described herein allows for the identification of children who may benefit from amplification, those who are appropriate candidates for cochlear implantation, and those who, because of bilateral CND, may not be appropriate candidates for either intervention.

Cochlear implantation in children with labyrinthine anomalies and cochlear nerve deficiency: implications for auditory brainstem implantation.

Compare outcomes among children with inner ear malformations and/or cochlear nerve deficiency (CND) who have received a cochlear implant (CI).

Gap detection for similar and dissimilar gap markers

Detection thresholds for temporal gaps between markers of dissimilar frequency are usually elevated with respect to thresholds for gaps between markers of similar frequency. Because gaps between markers of dissimilar frequency represent both a spectrally based perceptual discontinuity as well as a temporal discontinuity, it is not clear what factors underlie the threshold elevation. This study sought to examine the effects of perceptual dissimilarities on gap detection. The first experiment measured gap detection for configurations of narrow-band gap markers comprised of pure tones, frequency-modulated tones, and amplitude-modulated tones. The results showed that gap thresholds for frequency-disparate pure-tone markers were elevated with respect to isofrequency tonal markers, but that perceptual discontinuities between markers restricted to the same frequency region did not uniformly elevate threshold. The second experiment measured gap detection for configurations of markers where the leading and trailing markers could differ along the dimensions of bandwidth, duration, and pitch. The results showed that, in most cases, gap detection deteriorated when the bandwidth of the two markers differed, even when the spectral content of the narrower-band marker was completely subsumed by the spectral content of the wider-band marker. This finding suggests that gap detection is sensitive to spectral dissimilarity between markers in addition to spectral discontinuity. The effects of marker duration depended on the marker bandwidth. Pitch differences across spectrally similar markers had no effect.

Perceptual consequences of peripheral hearing loss : do edge effects exist for abrupt cochlear lesions?

There is a growing body of research that shows evidence of central neural reorganization in response to lesions in the auditory periphery, even if the lesions occur in maturity. This reorganization consists of an increased neural representation of frequencies corresponding to the edge frequency of the lesion. Data were collected to determine whether this over-representation might have consequences for human perception. The hypothesis was that increased central representation might increase acuity on some psychophysical tasks performed at the edge frequency. Tasks included frequency sweep detection (for tones), intensity discrimination (for 100-Hz-wide bands of noise and tones), gap detection and gap discrimination (both for 100-Hz-wide bands of noise). Results from observers with steeply sloping hearing losses were compared with results from normal-hearing observers performing these tasks with masking noise generated to simulate steeply sloping hearing loss. None of these data provide compelling evidence for the hypothesized edge effect. A 40-Hz following response to tone bursts was collected from a subset of the hearing-impaired observers in an attempt to confirm the animal physiology findings of neural over-representation of the edge frequency. No edge-frequency effect was noted in the results, though there was a non-significant tendency for one of the hearing-impaired observers to show shorter latency of response.

Comodulation masking release (CMR): Effects of gating as a function of number of flanking bands and masker bandwidth

Normal-hearing subjects participated in two CMR experiments. For experiment 1, two, three, five or nine 20-Hz-wide comodulated flanking bands were presented continuously or gated simultaneously with a 2000-Hz signal. The signal had a duration of 400 ms. Larger CMRs were obtained as the number of flanking bands increased for both the continuous and gated conditions. For fewer number of bands, the average CMR for continuous noise was substantially larger than for gated noise. As the number of bands increased, CMR increased more for gated than for continuous noise, and the difference between CMRs for gated and continuous noise decreased. Experiment 2 involved detecting a 400-ms 1000-Hz pure-tone signal in a seven-band comodulated noise complex. The noise bands, presented continuously or gated with the signal, were either 10, 20, 40, or 80 Hz wide. Larger CMRs were observed for continuous maskers and for smaller masker bandwidths; however, the effect of gating did not change significantly across bandwidth. The results of the first experiment indicate that the effects of gating on CMR are minimized when the number of auditory channels providing information is large. The results of the second experiment indicate that this effect is not simply a function of the large CMR magnitude obtained with a large number of flanking bands.

Gap detection measured with electrically evoked auditory event-related potentials and speech-perception abilities in children with auditory neuropathy spectrum disorder.

Objectives: This study aimed (1) to investigate the feasibility of recording the electrically evoked auditory event–related potential (eERP), including the onset P1-N1-P2 complex and the electrically evoked auditory change complex (EACC) in response to temporal gaps, in children with auditory neuropathy spectrum disorder (ANSD); and (2) to evaluate the relationship between these measures and speech-perception abilities in these subjects. Design: Fifteen ANSD children who are Cochlear Nucleus device users participated in this study. For each subject, the speech-processor microphone was bypassed and the eERPs were elicited by direct stimulation of one mid-array electrode (electrode 12). The stimulus was a train of biphasic current pulses 800 msec in duration. Two basic stimulation conditions were used to elicit the eERP. In the no-gap condition, the entire pulse train was delivered uninterrupted to electrode 12, and the onset P1-N1-P2 complex was measured relative to the stimulus onset. In the gapped condition, the stimulus consisted of two pulse train bursts, each being 400 msec in duration, presented sequentially on the same electrode and separated by one of five gaps (i.e., 5, 10, 20, 50, and 100 msec). Open-set speech-perception ability of these subjects with ANSD was assessed using the phonetically balanced kindergarten (PBK) word lists presented at 60 dB SPL, using monitored live voice in a sound booth. Results: The eERPs were recorded from all subjects with ANSD who participated in this study. There were no significant differences in test–retest reliability, root mean square amplitude or P1 latency for the onset P1-N1-P2 complex between subjects with good (>70% correct on PBK words) and poorer speech-perception performance. In general, the EACC showed less mature morphological characteristics than the onset P1-N1-P2 response recorded from the same subject. There was a robust correlation between the PBK word scores and the EACC thresholds for gap detection. Subjects with poorer speech-perception performance showed larger EACC thresholds in this study. Conclusions: These results demonstrate the feasibility of recording eERPs from implanted children with ANSD, using direct electrical stimulation. Temporal-processing deficits, as demonstrated by large EACC thresholds for gap detection, might account in part for the poor speech-perception performances observed in a subgroup of implanted subjects with ANSD. This finding suggests that the EACC elicited by changes in temporal continuity (i.e., gap) holds promise as a predictor of speech-perception ability among implanted children with ANSD.

Acoustically Evoked Auditory Change Complex in Children with Auditory Neuropathy Spectrum Disorder: A Potential Objective Tool for Identifying Cochlear Implant Candidates

Objectives: The overall aim of the study was to evaluate the feasibility of using electrophysiological measures of the auditory change complex (ACC) to identify candidates for cochlear implantation in children with auditory neuropathy spectrum disorder (ANSD). To achieve this overall aim, this study (1) assessed the feasibility of measuring the ACC evoked by temporal gaps in a group of children with ANSD across a wide age range and (2) investigated the association between gap detection thresholds (GDTs) measured by the ACC recordings and open-set speech-perception performance in these subjects. Design: Nineteen children with bilateral ANSD ranging in age between 1.9 and 14.9 years (mean: 7.8 years) participated in this study. Electrophysiological recordings of the auditory event-related potential (ERP), including the onset ERP response and the ACC, were completed in all subjects and open-set speech perception was evaluated for a subgroup of 16 subjects. For the ERP recordings, the stimulus was a Gaussian noise presented through ER-3A insert earphones to the test ear. Two stimulation conditions were used. In the “control condition,” the stimulus was an 800-msec Gaussian noise. In the “gapped condition,” the stimuli were two noise segments, each being 400 msec in duration, separated by one of five gaps (i.e., 5, 10, 20, 50, or 100 msec). The interstimulation interval was 1200 msec. The aided open-set speech perception ability was assessed using the Phonetically Balanced Kindergarten (PBK) word lists presented at 60 dB SPL using recorded testing material in a sound booth. For speech perception tests, subjects wore their hearing aids at the settings recommended by their clinical audiologists. For a subgroup of five subjects, psychophysical GDTs for the Gaussian noise were also assessed using a three-interval, three-alternative forced-choice procedure. Results: Responses evoked by the onset of the Gaussian noise (i.e., onset responses) were recorded in all stimulation conditions from all subjects tested in this study. The presence/absence, peak latency and amplitude, and response width of the onset response did not correlate with aided PBK word scores. The objective GDTs measured with the ACC recordings from 17 subjects ranged from 10 to 100 msec. The ACC was not recorded from two subjects for any gap durations tested in this study. There was a robust negative correlation between objective GDTs and aided PBK word scores. In general, subjects with prolonged objective GDTs showed low-aided PBK word scores. GDTs measured using electrophysiological recordings of the ACC correlated well with those measured using psychophysical procedures in four of five subjects who were evaluated using both procedures. Conclusions: The clinical application of the onset response in predicting open-set speech-perception ability is relatively limited in children with ANSD. The ACC recordings can be used to objectively evaluate temporal resolution abilities in children with ANSD having no severe comorbidities, and who are older than 1.9 years. The ACC can potentially be used as an objective tool to identify poor performers among children with ANSD using properly fit amplification, and who are thus, cochlear implant candidates.

Gating effects in CMR

CMR is sometimes smaller for gated than continuous maskers. Our current work on CMR for multiple, comodulated narrow noise bands indicates that the gating effect is minimized when the number of comodulated bands is large. The present study extends this work to the CMR paradigm where pure tone signal thresholds are obtained as function of modulated and unmodulated noise bandwidth. Results indicate that in unmodulated noise, gated and continuous thresholds do not differ, regardless of noise bandwidth. In modulated noise, thresholds are often higher for gated noise than continuous noise when noise bandwidth is narrow, but not when the noise bandwidth is considerably wider than the auditory filter bandwidth. These results may suggest that gating effects on CMR are generally small when comodulation information is available across a large number of auditory channels. Results will be discussed in terms of competing cues for auditory grouping. [Research supported by AFOSR.]