Suzanne C. Purdy

Electrophysiological and speech perception measures of auditory processing in experienced adult cochlear implant users

OBJECTIVE This study determined the relationship between auditory evoked potential measures and speech perception in experienced adult cochlear implant (CI) users and compared the CI evoked potential results to those of a group of age- and sex-matched control subjects. METHODS CI subjects all used the Nucleus CI-22 implant. Middle latency response (MLR), obligatory cortical potentials (CAEP), mismatch negativity (MMN) and P3a auditory evoked potentials were recorded. Speech perception was evaluated using word and sentence tests. RESULTS Duration of deafness correlated with speech scores with poor scores reflecting greater years of deafness. Na amplitude correlated negatively with duration of deafness, with small amplitudes reflecting greater duration of deafness. Overall, N1 amplitude was smaller in CI than control subjects. Earlier P2 latencies were associated with shorter durations of deafness and higher speech scores. In general, MMN was absent or degraded in CI subjects with poor speech scores. CONCLUSIONS Auditory evoked potentials are related to speech perception ability and provide objective evidence of central auditory processing differences across experienced CI users. SIGNIFICANCE Since auditory evoked potentials relate to CI performance, they may be a useful tool for objectively evaluating the efficacy of speech processing strategies and/or auditory training approaches in both adults and children with cochlear implants.

Electrophysiological and behavioral evidence of auditory processing deficits in children with reading disorder

OBJECTIVE The aim of the research was to investigate auditory processing abilities in children with reading disorders using electrophysiological and behavioral tasks. METHODS Differences in auditory processing between control, compensated (age appropriate reading skills with a history of reading disorder), and reading disordered groups were systematically investigated. RESULTS The reading disorder group had significantly lower results than control and compensated reader groups for most tests in the reading and auditory processing test battery. All children with a reading disorder did not pass at least one behavioral test of auditory processing, and hence would be diagnosed clinically as having an auditory processing disorder (APD). The reading disorder group also had significantly smaller /ga/-evoked mismatch negativity (MMN) area than the control group. Compensated and control groups had similar results for the electrophysiological and behavioral auditory processing tests. Correlation analyses showed that reading fluency and accuracy and nonword scores (measured using Castle and Colthearts word/nonword test) correlated significantly with most APD measures. CONCLUSIONS The general profile of auditory processing deficits in children with reading disorder was a combination of deficits on frequency patterns (i.e. frequency pattern test) and absent or small /ga/-evoked MMN. Significant results from the correlation analyses support the co-morbidity of reading and auditory processing disorders. SIGNIFICANCE Children with reading disorders are likely to have auditory processing disorders.

Auditory Evoked Potentials as Measures of Plasticity in Humans

There is increasing evidence from animal studies for plasticity of auditory function. This has prompted research to determine whether such plastic changes occur in adults and children with hearing disorders. Behavioural measures such as speech perception scores do show improvements after hearing aid fitting and cochlear implantation. Several studies have also shown changes in cortical auditory evoked potentials after cochlear implantation and after auditory training. These studies indicate that improvements in speech perception ability are associated with changes in the central auditory system, particularly at the cortical level.

Frequency-Specific Auditory Brainstem Responses Relationship to Behavioural Thresholds in Cochlear-Impaired Adults

Auditory brainstem response (ABR) thresholds to ipsilaterally masked tone pip stimuli were obtained from three groups of hearing-impaired subjects. Using high-pass (for 500-Hz tone pips) and notched noise (for 1-, 2- and 4-kHz tone pips), ABR thresholds in subjects with low-frequency, high-frequency or flat cochlear hearing losses were compared to conventional pure-tone audiometric thresholds. A strong positive relationship was found between ABR and behavioural threshold elevation. Absolute ABR thresholds at 500 Hz were significantly higher than those at other frequencies. The results of this study indicate that frequency-specific ABR testing can provide an approximation of both degree and configuration of cochlear hearing losses in adults. Further refinements of testing and judging procedures are needed however to reduce the variation evident in our results and thus achieve the accuracy required for most clinical applications.

Frequency-Specific Auditory Brainstem Responses: Effective Masking Levels and Relationship to Behavioural Thresholds in Normal Hearing Adults

Ipsilateral masking levels and normal thresholds for tone pip auditory brainstem responses (ABRs) were investigated in normal subjects for the purpose of establishing recording parameters and norms for frequency-specific tone pip ABR testing. White noise was found to effectively mask ABRs to tone pips at mean signal-to-noise ratios of between -1 and -5.5 dB [dB peak-equivalent (pe) SPL/dB SPL] depending on the tone pip frequency. ABR thresholds were established for tone pips in the presence of ipsilateral masking with high-pass filtered noise for 50-Hz tone pips and notched noise for tone pips from 1,000 to 4,000 Hz, at a nominal signal-to-noise ratio of -5 dB (i.e. with the noise SPL measured prior to filtering). Thresholds occurred between 28.6 and 36.6 dB pe SPL, equivalent to 4.4-8.8 dB nHL. ABR thresholds for masked and unmasked tone pips did not differ significantly.

A randomized control trial of interventions in school-aged children with auditory processing disorders

Objective: The primary purpose of the study was to compare intervention approaches for children with auditory processing disorder (APD): bottom-up training including activities focused on auditory perception, discrimination, and phonological awareness, and top-down training including a range of language activities. Another purpose was to determine the benefits of personal FM systems. Design: The study is a randomized control trial where participants were allocated to groups receiving one of the two interventions, with and without personal FM, or to the no intervention group. The six-week intervention included weekly one-hour sessions with a therapist in the clinic, plus 1–2 hours per week of parent-directed homework. Study sample: 55 children (7 to 13 years) with APD participated in the study. Intervention outcomes included reading, language, and auditory processing. Results: Positive outcomes were observed for both training approaches and personal FM systems on several measures. Pre-intervention nonverbal IQ, age, and severity of APD did not influence outcomes. Performance of control group participants did not change when retested after the intervention period. Conclusions: Both intervention approaches were beneficial and there were additional benefits with the use of personal FM. Positive results were not limited to the areas specifically targeted by the interventions.

Abr Thresholds to Tonebursts Gated with Blackman and Linear Windows in Adults with High-frequency Sensorineural Hearing Loss

Objective The goal of this study was to determine whether tonebursts gated on and off using a nonlinear, exact-Blackman-gating function would be a more frequency-specific stimulus for auditory brain stem response audiometry than the more traditional 2-1-2 cycle linearly gated toneburst. Design Toneburst ABRs were recorded in 10 adults with normal hearing and in 18 adults with sloping high-frequency sensorineural hearing loss. It was hypothesized that any advantage of the Blackman stimuli for frequency-specific threshold assessment should be evident in hearing-impaired subjects with hearing loss confined to the 2000 to 4000 Hz frequency region since spectral splatter in the toneburst stimuli could lead to an underestimation of hearing loss based on the ABR thresholds. ABR stimuli consisted of 2000- and 4000-Hz 2-1-2 (rise-plateau-fall) cycle linearly gated tonebursts and 1-0-1 msec exact-Blackman-gated tonebursts. An additional 0.5-0-0.5 msec 4000-Hz Blackman-gated toneburst was used to investigate whether the difference in rise/fall characteristics of the linearly and Blackman-gated tonebursts could account for any differences in ABR results at 4000 Hz. The ABR toneburst stimuli were calibrated behaviorally in 15 adults with normal hearing. Results In the normal-hearing listeners toneburst-ABR thresholds generally exceeded behavioral thresholds by 10 to 13 dB for all stimuli. Correlations of 0.85 to 0.96 were obtained between 2000 and 4000 Hz toneburst ABR thresholds and pure-tone audiometric thresholds in the hearing-impaired listeners. Results were similar for Blackman- and linearly gated stimuli. Conclusions There were no clear differences between Blackman- and linearly gated tonebursts in terms of how well ABR thresholds predicted pure-tone thresholds at 2000 and 4000 Hz. In general audiometric thresholds were predicted with good accuracy (±15 dB) by the toneburst ABR thresholds. The 4000-Hz audiometric threshold was underestimated in one subject with a very steeply sloping hearing loss by both Blackman- and linearly gated toneburst ABR thresholds, indicating that ipsilateral masking such as notched noise would be needed to ensure frequency specificity in this and similar cases.

Do children with reading delay benefit from the use of personal FM systems in the classroom

Abstract FM systems have been used to compensate for poor signal-to-noise ratios in classrooms. This study evaluates benefits of a 6-week trial of personal FM systems used during the school day for children with reading delay aged 6–11 years, using a randomized control design. Teachers and children completed the LIFE-UK questionnaire. Test-retest reliability of the LIFE-UK childrens version was confirmed in a separate group of 18 children from the same school. The 23 children in the FM group had significantly improved teacher ratings, and the childrens ratings of classroom listening for difficult situations were significantly better after the trial. These changes did not occur for the 23 control-group children. Most children (92%) commented positively about the FM after the trial. It is likely that a longer FM trial or a specific reading intervention combined with FM will be required for the benefits of enhanced listening to affect performance on standardized reading tests. Sumario Los sistemas FM han sido utilizados para compensar las tasas pobres de señal-ruido en el salón de clases. Este estudio evalúa los beneficios de un ensayo de 6 semanas usando sistemas personales FM durante el día escolar en niños con retardo en la lectura, en edades de 6 a 11 años, usando un diseño de control aleatorio. Tantos los niños como los maestros llenaron un cuestionario LIFE-UK. La confiabilidad test-retest de la versión infantil del LIFE-UK fue confirmada en un grupo separado de 18 niños de la misma escuela. Los 23 niños del grupo FM lograron apreciaciones significativamente mejoradas de sus maestros, y la apreciación de los propios niños sobre su audición en clase para situaciones difíciles fue significativamente mejor después del ensayo. Estos cambios no ocurrieron para el grupo control de 23 niños. La mayoría de los niños (92%) comentaron positivamente después del estudio acerca del sistema FM. Es posible que una prueba más larga con un sistema FM o una intervención específica en cuanto a la lectura combinada con un sistema FM se requiera para que los beneficios de una lectura mejorada afecten el desempeño en pruebas estandarizadas de lectura.

Evidence for adaptive plasticity in elderly monaural hearing aid users

Hearing aids can induce perceptual changes in some elderly listeners but few studies have investigated physiological changes in this population. Loudness discomfort levels and acoustic reflex thresholds were measured in long-term users of a single hearing aid. The results show an asymmetry of +2 to +9 dB between ears in the sound level that (i) causes loudness discomfort and (ii) elicits a reflex contraction of the middle ear muscles. The elevation of the acoustic reflex threshold occurs in the ear with hearing aid experience, irrespective of the ear of stimulation. Therefore, there is evidence of adaptive plasticity and this can be measured at the level of the auditory brainstem.

Asymmetry in the auditory brainstem response following experience of monaural amplification.

Hearing aids can induce perceptual changes in some elderly listeners and there is recent evidence that this might be associated with reorganization within the auditory system. We compared the click-evoked auditory brainstem response in adults with and without monaural hearing aid experience. In listeners with monaural hearing aid experience, the mean peak-to-peak amplitude between wave V and SN10 was approximately 100 nV larger in the ear with hearing aid experience and this difference was statistically significant (P<0.01). The response was symmetrical in adults with no hearing aid experience. This suggests that hearing aids can induce physiological changes at the level of the auditory brainstem in elderly monaural hearing aid users.