Semantic processing in children with cochlear implants: Evidence from event-related potentials.

Introduction: Existing research has shown that children with significant hearing loss who use cochlear implants (CIs) perform worse than their hearing peers on behavioral measures of spoken language. The present study sought to examine how children with CIs process lexical-semantic incongruence, as indexed by electrophysiological evidence of the N400 effect. Method: Twelve children with CIs, aged between 6 and 9 years, participated in a spoken word-picture matching task while event-related potentials (ERPs) were recorded. To determine whether the N400 effect elicited in this group deviated from normal, independent samples t tests and analysis of variance (ANOVA) analyses were used to compare the results of children with CIs against those of a similarly aged typically hearing (TH) group (n = 30). Correlational analyses were also conducted within each group to gauge the degree to which the N400 effect related to behavioral measures of spoken language. Results: An N400 effect was elicited in both groups of CI and TH children. The amplitude and latency of the N400 effect did not differ significantly between groups. Despite the similarity in ERP responses, children with CIs scored significantly lower on behavioral measures of spoken word- and sentence-level comprehension. No significant correlations between ERP and behavioral measures were found, although there was a trending relationship between sentence-level spoken language comprehension and the TH group's N400 effect mean amplitude (p = .060). Conclusions: The results suggest that, at a neural level, children with CIs can process lexical-semantic incongruence, and that other underlying processes not measured by the N400 effect contribute to this population's spoken language difficulties.

Towards the preferred stimulus parameters for distortion product otoacoustic emissions in adults: A preliminary study.

BACKGROUND:  Although distortion product otoacoustic emissions (DPOAEs) are useful in evaluating cochlear outer hair cell function, determining the optimal stimulus parameters could result in a more reliable, sensitive and specific diagnostic tool across the range of DPOAE applications. Objectives: To identify which stimulus parameters warrant further investigation for eliciting the largest and most reliable DPOAEs in adult humans. Method: A single group, repeated measures design involving a convenience sample of 20 normal-hearing participants between 19 and 24 years of age. Results: Descriptive statistics and mixed model analyses suggested L1/L2 intensity levels of 65/65 dB sound pressure level (SPL) and 65/55 dB SPL, and f2/f1 ratios of 1.18, 1.20 and 1.22 elicited larger and more reliable DPOAEs in both ears. Conclusion: Further investigation of the 65/65 dB SPL and 65/55 dB SPL intensity levels and the 1.18, 1.20 and 1.22 f2/f1 ratios is warranted to determine the stimulus parameters for eliciting the largest and most reliable DPOAEs in adult humans across the range of DPOAE applications.

No evidence for enhanced processing of speech that is low-pass filtered near the edge frequency of cochlear dead regions in children.

OBJECTIVES: Cochlear dead regions (DRs) are regions in the cochlea where the inner hair cells and/or neurons are not functioning. Adults with extensive high-frequency DRs have enhanced abilities in processing sounds with frequencies just below the edge frequency, fedge, of the DR. It was assessed whether the same is true for children. DESIGN: Performance was compared for children aged 8 to 13 years with: DRs (group DR), hearing impairment but without DRs (group NODR), and normal hearing (group NH). Seven ears in each group were tested. Each ear in the DR group was matched in age and low-frequency hearing with an ear in the NODR group, and in age with an ear in the NH group, giving seven "triplets". Within each triplet, the percent correct identification of vowel-consonant-vowel stimuli was measured using stimuli that were low-pass filtered at fedge and 0.67fedge, based on the ear with a DR. For the hearing-impaired ears, stimuli were given frequency-selective amplification as prescribed by DSL 4.1. RESULTS: No significant differences in performance were found between groups for either low-pass cut-off frequency. CONCLUSION: Unlike adults, the children with DRs did not show enhanced discrimination of speech stimuli with frequencies below fedge.

The impact of auditory white noise on semantic priming.

It has been proposed that white noise can improve cognitive performance for some individuals, particularly those with lower attention, and that this effect may be mediated by dopaminergic circuitry. Given existing evidence that semantic priming is modulated by dopamine, this study investigated whether white noise can facilitate semantic priming. Seventy-eight adults completed an auditory semantic priming task with and without white noise, at either a short or long inter-stimulus interval (ISI). Measures of both direct and indirect semantic priming were examined. Analysis of the results revealed significant direct and indirect priming effects at each ISI in noise and silence, however noise significantly reduced the magnitude of indirect priming. Analyses of subgroups with higher versus lower attention revealed a reduction to indirect priming in noise relative to silence for participants with lower executive and orienting attention. These findings suggest that white noise focuses automatic spreading activation, which may be driven by modulation of dopaminergic circuitry.

A systematic review of stimulus parameters for eliciting distortion product otoacoustic emissions from adult humans.

OBJECTIVE: The objective of this study is to review the scientific literature to determine if a set of stimulus parameters can be described to elicit distortion product otoacoustic emissions (DPOAEs) of higher absolute level and/or greater reliability in healthy adult humans and higher sensitivity and specificity in adults with cochlear lesions. DESIGN: Systematic review. STUDY SAMPLE: Searches of four electronic databases yielded 47 studies that had used different parameters to elicit DPOAEs from within or between-groups of adult humans. RESULTS: The wide range of stimulus parameters used in the reviewed studies saw a wide range of reported values for DPOAE level, reliability, and sensitivity and specificity to cochlear lesions. CONCLUSION: The most commonly used stimulus parameters for eliciting DPOAEs from adult humans have included frequency ratios for the two primary tones (f2/f1) of between 1.04 and 1.4 and levels (L1/L2) of 65/55 dB SPL. The most commonly used parameters for eliciting DPOAEs of higher level in healthy adults appear to be linked to f2/f1 values between 1.20 and 1.22 and L1/L2 levels of 75/75 dB SPL. The stimulus parameters for eliciting DPOAEs of greater reliability in healthy adults and higher sensitivity and specificity in adults with cochlear lesions have yet to be clearly determined.

Identifying a context-effective school hearing screening test: An emic/etic framework.

OBJECTIVE: To identify a context-effective hearing screening test for primary schools in the Western Cape, South Africa using an emic-etic framework for test selection. DESIGN: A sequential mixed methods design was used to: (1) Identify test properties needed to successfully screen hearing in primary school children in the Western Cape, (2) select the hearing screening test most likely to succeed in this context, and (3) assess the use of the test in context. STUDY SAMPLE: Three nurses, two nursing assistants, two paediatric audiologists, and 100 grade-one children participated. RESULTS: Distortion product otoacoustic emissions (DPOAEs) were identified as the test most likely to succeed as a hearing screening test in primary school children in the Western Cape. While school nurses were able to successfully apply OAE testing in this context, its sensitivity to hearing loss in these children was 57.14%. CONCLUSIONS: The sensitivity would need to be improved before OAE testing could be used as a context-effective screening test for primary school children in the Western Cape. The study demonstrated the value of collaborative program planning using an emic-etic framework to ensure that screening tests are contextually appropriate.

A systematic review of electrophysiological outcomes following auditory training in school-age children with auditory processing deficits.

OBJECTIVE: To systematically review the peer-reviewed literature on electrophysiological outcomes following auditory training (AT) in school-age children with (central) auditory processing disorder ([C]APD). DESIGN: A systematic review. STUDY SAMPLE: Searches of 16 electronic databases yielded four studies involving school-aged children whose auditory processing deficits had been confirmed in a manner consistent with ASHA (2005) and AAA (2010) and compared to a treated and/or an untreated control group before and after AT. A further three studies were identified with one lacking a control group and two measuring auditory processing in a manner not consistent with ASHA (2005) and AAA (2010). RESULTS: There is limited evidence that AT leads to measurable electrophysiological changes in children with auditory processing deficits. CONCLUSION: The evidence base is too small and weak to provide clear guidance on the use of electrophysiological outcomes as a measure of AT outcomes in children with auditory processing problems. The currently limited data can only be used to suggest that click-evoked AMLR and tone-burst evoked auditory P300 might be more likely to detect such outcomes in children diagnosed with (C)APD, and that speech-evoked ALLR might be more likely to detect phonological processing changes in children without a specific diagnosis of (C)APD.

Fast assessment of canine hearing using high click-rate BAER.

The aim of this study was to determine if high stimulus repetition rates could reduce the time taken to obtain brainstem auditory evoked response (BAER) waveforms of equivalent quality in dogs. Click-evoked BAER waveforms were obtained from nine healthy, adult, mixed-breed dogs at stimulus intensities of 70, 60, 50 and 40 decibels (normal hearing level) (dBnHL) and stimulus repetition rates of 11, 33 and 91 clicks-per-second (cps). The quality of the BAER waveforms was kept constant by ensuring all waveforms achieved the same signal-to-noise (SNR), as shown by their F(sp) value of 3.1. Increasing the stimulus repetition rate from 11 to 91Hz significantly (P<0.01) reduced the median time to obtain BAER waveforms of equivalent quality by 3.29-14.07s per waveform, or alternatively, increased the recording speed by 4.6-13.7 times per waveform (depending on the stimulus intensity). The use of high stimulus repetition rate BAER shows significant promise for the rapid assessment of auditory function in dogs.

Spectral and synchrony differences in auditory brainstem responses evoked by chirps of varying durations.

The chirp-evoked ABR has been termed a more synchronous response, referring to the fact that rising-frequency chirp stimuli theoretically compensate for temporal dispersions down the basilar membrane. This compensation is made possible by delaying the higher frequency content of the stimulus until the lower frequency traveling waves are closer to the cochlea apex. However, it is not yet clear how sensitive this temporal compensation is to variation in the delay interval. This study analyzed chirp- and click-evoked ABRs at low intensity, using a variety of tools in the time, frequency, and phase domains, to measure synchrony in the response. Additionally, this study also examined the relationship between chirp sweep rate and response synchrony by varying the delay between high- and low-frequency portions of chirp stimuli. The results suggest that the chirp-evoked ABRs in this study exhibited more synchrony than the click-evoked ABRs and that slight gender-based differences exist in the synchrony of chirp-evoked ABRs. The study concludes that a tailoring of chirp parameters to gender may be beneficial in pathologies that severely affect neural synchrony, but that such a customization may not be necessary in routine clinical applications.

On chirp stimuli and neural synchrony in the suprathreshold auditory brainstem response.

The chirp-evoked ABR has been regarded as a more synchronous response than the click-evoked ABR, referring to the belief that the chirp stimulates lower-, mid-, and higher-frequency regions of the cochlea simultaneously. In this study a variety of tools were used to analyze the synchronicity of ABRs evoked by chirp- and click-stimuli at 40 dB HL in 32 normal hearing subjects aged 18 to 55 years (mean=24.8 years, SD=7.1 years). Compared to the click-evoked ABRs, the chirp-evoked ABRs showed larger wave V amplitudes, but an absence of earlier waves in the grand averages, larger wave V latency variance, smaller FFT magnitudes at the higher component frequencies, and larger phase variance at the higher component frequencies. These results strongly suggest that the chirp-evoked ABRs exhibited less synchrony than the click-evoked ABRs in this study. It is proposed that the temporal compensation offered by chirp stimuli is sufficient to increase neural recruitment (as measured by wave V amplitude), but that destructive phase interactions still exist along the cochlea partition, particularly in the low frequency portions of the cochlea where more latency jitter is expected. The clinical implications of these findings are discussed.

The effects of electrode montage on the amplitude of wave V in the auditory brainstem response to maximum length sequence stimuli.

The use of maximum length sequence (MLS) stimuli to elicit an auditory brainstem response (ABR) has been limited, in part, by the observation that these stimuli reduce ABR wave amplitudes. This study recorded ABR waveforms from 14 normally hearing adults using MLS click stimuli (maximum stimulus rate = 250 clicks per second) at stimulus levels of 70, 60, 50, 40, 30 and 20 dB nHL, with a vertical and then an ipsilateral electrode montage. The vertical electrode montage produced significantly larger (p < 0.05) wave V amplitudes, with no change in wave V latencies (p > 0.05), at all stimulus levels. This result suggests a vertical electrode montage could be used to counter some of the loss in wave V amplitude observed when using MLS stimuli.

A system to generate patient-specific stimuli for use with the auditory brainstem response test.

The short-pulsed "click" stimuli most commonly used to evoke an Auditory Brainstem Response (ABR) do not account for temporal shifts along the basilar membrane and do not produce ABRs of maximal amplitude. This paper describes a system that maps these temporal shifts and generates patient-specific stimuli to compensate. This is of interest both to enhance the ABR and as a potential way to map the physiology of the basilar membrane.

Over-complete discrete wavelet transformation of the normal auditory brainstem response improves prediction of outcome following severe acute closed head injury.

Previous research has shown that complex statistical analysis (discriminant function analysis) of a 'normal' auditory brainstem response (ABR) result can improve this measure's ability to predict subject outcome following severe acute closed head injury (ACHI). We hypothesized that adding the ABR's time-frequency information to such an analysis would improve this predictive value even further. 'Normal' ABR results were sampled from 69 severe ACHI subjects (22 of whom died and 47 of whom lived) and their time-frequency information extracted using an over-complete discrete wavelet transformation (OCDWT). A series of logistic regression analyses then showed correct predictions of death and survival as follows: ABR measures only 72 and 89% (respectively), ABR OCDWT measures only 82 and 89% (respectively), and ABR and ABR OCDWT measures combined 86 and 93% (respectively). These results showed that the addition of time-frequency information can improve the ability of the 'normal' ABR result to predict outcome following severe ACHI.

The effects of high stimulus rate on the electrocochleogram in normal-hearing subjects.

The use of high stimulus rates has the potential to improve the electrocochleogram's (ECochG) sensitivity and specificity in endolymphatic hydrops and Menière's disease, but is currently hindered by the absence of an acceptable normative database. In response, this study recorded click-evoked ECochG tracings from 51 normal-hearing subjects (102 ears), between 18 and 60 years of age, at 7.1, 51.1, 101.1 and 151.1 clicks/s using a tympanic membrane electrode. As stimulus rate increased, various statistically significant (p < 0.05) changes were observed. In general, summating potential (SP) latency and amplitude and action potential (AP) latency increased, SP/AP amplitude ratio and waveform width increased but then plateaued, and AP amplitude fluctuated. While providing the largest contribution to a high-stimulus-rate ECochG normative database published to date, potential clinical limitations were identified and a possible solution proposed.