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Hearing Disorders: HELP
Articles by David W. Purcell
Based on 3 articles published since 2010
(Why 3 articles?)
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Between 2010 and 2020, David W. Purcell wrote the following 3 articles about Hearing Disorders.
 
+ Citations + Abstracts
1 Article Effect of Stimulus Level and Bandwidth on Speech-Evoked Envelope Following Responses in Adults With Normal Hearing. 2015

Easwar, Vijayalakshmi / Purcell, David W / Aiken, Steven J / Parsa, Vijay / Scollie, Susan D. ·1National Centre for Audiology, Western University, London, Ontario, Canada; 2School of Communication Sciences and Disorders, Western University, London, Ontario, Canada; and 3School of Human Communication Disorders, Dalhousie University, Halifax, Nova Scotia, Canada. ·Ear Hear · Pubmed #26226607.

ABSTRACT: OBJECTIVE: The use of auditory evoked potentials as an objective outcome measure in infants fitted with hearing aids has gained interest in recent years. This article proposes a test paradigm using speech-evoked envelope following responses (EFRs) for use as an objective-aided outcome measure. The method uses a running speech-like, naturally spoken stimulus token /susa∫i/ (fundamental frequency [f0] = 98 Hz; duration 2.05 sec), to elicit EFRs by eight carriers representing low, mid, and high frequencies. Each vowel elicited two EFRs simultaneously, one from the region of formant one (F1) and one from the higher formants region (F2+). The simultaneous recording of two EFRs was enabled by lowering f0 in the region of F1 alone. Fricatives were amplitude modulated to enable recording of EFRs from high-frequency spectral regions. The present study aimed to evaluate the effect of level and bandwidth on speech-evoked EFRs in adults with normal hearing. As well, the study aimed to test convergent validity of the EFR paradigm by comparing it with changes in behavioral tasks due to bandwidth. DESIGN: Single-channel electroencephalogram was recorded from the vertex to the nape of the neck over 300 sweeps in two polarities from 20 young adults with normal hearing. To evaluate the effects of level in experiment I, EFRs were recorded at test levels of 50 and 65 dB SPL. To evaluate the effects of bandwidth in experiment II, EFRs were elicited by /susa∫i/ low-pass filtered at 1, 2, and 4 kHz, presented at 65 dB SPL. The 65 dB SPL condition from experiment I represented the full bandwidth condition. EFRs were averaged across the two polarities and estimated using a Fourier analyzer. An F test was used to determine whether an EFR was detected. Speech discrimination using the University of Western Ontario Distinctive Feature Differences test and sound quality rating using the Multiple Stimulus Hidden Reference and Anchors paradigm were measured in identical bandwidth conditions. RESULTS: In experiment I, the increase in level resulted in a significant increase in response amplitudes for all eight carriers (mean increase of 14 to 50 nV) and the number of detections (mean increase of 1.4 detections). In experiment II, an increase in bandwidth resulted in a significant increase in the number of EFRs detected until the low-pass filtered 4 kHz condition and carrier-specific changes in response amplitude until the full bandwidth condition. Scores in both behavioral tasks increased with bandwidth up to the full bandwidth condition. The number of detections and composite amplitude (sum of all eight EFR amplitudes) significantly correlated with changes in behavioral test scores. CONCLUSIONS: Results suggest that the EFR paradigm is sensitive to changes in level and audible bandwidth. This may be a useful tool as an objective-aided outcome measure considering its running speech-like stimulus, representation of spectral regions important for speech understanding, level and bandwidth sensitivity, and clinically feasible test times. This paradigm requires further validation in individuals with hearing loss, with and without hearing aids.

2 Article Evaluation of Speech-Evoked Envelope Following Responses as an Objective Aided Outcome Measure: Effect of Stimulus Level, Bandwidth, and Amplification in Adults With Hearing Loss. 2015

Easwar, Vijayalakshmi / Purcell, David W / Aiken, Steven J / Parsa, Vijay / Scollie, Susan D. ·1National Centre for Audiology, Western University, London, Ontario, Canada; 2School of Communication Sciences and Disorders, Western University, London, Ontario, Canada; and 3School of Human Communication Disorders, Dalhousie University, Halifax, Nova Scotia, Canada. ·Ear Hear · Pubmed #26226606.

ABSTRACT: OBJECTIVES: The present study evaluated a novel test paradigm based on speech-evoked envelope following responses (EFRs) as an objective aided outcome measure for individuals fitted with hearing aids. Although intended for use in infants with hearing loss, this study evaluated the paradigm in adults with hearing loss, as a precursor to further evaluation in infants. The test stimulus was a naturally male-spoken token /susa∫i/, modified to enable recording of eight individual EFRs, two from each vowel for different formants and one from each fricative. In experiment I, sensitivity of the paradigm to changes in audibility due to varying stimulus level and use of hearing aids was tested. In experiment II, sensitivity of the paradigm to changes in aided audible bandwidth was evaluated. As well, experiment II aimed to test convergent validity of the EFR paradigm by comparing the effect of bandwidth on EFRs and behavioral outcome measures of hearing aid fitting. DESIGN: Twenty-one adult hearing aid users with mild to moderately severe sensorineural hearing loss participated in the study. To evaluate the effects of level and amplification in experiment I, the stimulus was presented at 50 and 65 dB SPL through an ER-2 insert earphone in unaided conditions and through individually verified hearing aids in aided conditions. Behavioral thresholds of EFR carriers were obtained using an ER-2 insert earphone to estimate sensation level of EFR carriers. To evaluate the effect of aided audible bandwidth in experiment II, EFRs were elicited by /susa∫i/ low-pass filtered at 1, 2, and 4 kHz and presented through the programmed hearing aid. EFRs recorded in the 65 dB SPL aided condition in experiment I represented the full bandwidth condition. EEG was recorded from the vertex to the nape of the neck over 300 sweeps. Speech discrimination using the University of Western Ontario Distinctive Feature Differences test and sound quality rating using the Multiple-Stimulus Hidden Reference and Anchor paradigm were measured in the same bandwidth conditions. RESULTS: In experiment I, an increase in stimulus level above threshold and the use of amplification resulted in a significant increase in the number of EFRs detected per condition. At positive sensation levels, an increase in level demonstrated a significant increase in response amplitude in unaided and aided conditions. At 50 and 65 dB SPL, the use of amplification led to a significant increase in response amplitude for the majority of carriers. In experiment II, the number of EFR detections and the combined response amplitude of all eight EFRs improved with an increase in bandwidth up to 4 kHz. In contrast, behavioral measures continued to improve at wider bandwidths. Further change in EFR parameters was possibly limited by the hearing aid bandwidth. Significant positive correlations were found between EFR parameters and behavioral test scores in experiment II. CONCLUSIONS: The EFR paradigm demonstrates sensitivity to changes in audibility due to a change in stimulus level, bandwidth, and use of amplification in clinically feasible test times. The paradigm may thus have potential applications as an objective aided outcome measure. Further investigations exploring stimulus-response relationships in aided conditions and validation studies in children are warranted.

3 Article Phase stability of auditory steady state responses in newborn infants. 2011

Choi, Jong Min / Purcell, David W / John, M Sasha. ·National Centre for Audiology, The University of Western Ontario, Ontario, Canada. ·Ear Hear · Pubmed #21422930.

ABSTRACT: OBJECTIVES: This study examined the phases of auditory steady state responses (ASSRs) evoked by exponentially amplitude-modulated (AM) tones in 44 newborn infants (within 3 days of birth) and in 15 older infants (within 3 to 15 wks of birth). Our hypothesis was that the phases of the ASSRs would show orderly changes with modulation rate/carrier frequency and that this stability could be used with phase-biasing statistical techniques to augment response detection. DESIGN: Multiple ASSRs were recorded to four modulated tonal carriers with intensities of 50 dB SPL, which were combined and presented simultaneously. The carriers of 0.5, 1, 2, and 4 kHz were modulated at rates between 78 and 95 Hz. Recordings lasted 12.3 mins. Data were analyzed offline with particular attention to phase and its possible exploitation in response detection using a phase-weighted t test (PWT). Population normative phase values were compared with self-normative values. The latter uses phase estimates from ASSRs that are detected at an earlier time to estimate expected phases of ASSRs, which have not yet been detected. This was implemented as an interstimulus phase-weighted t test (iPWT). A secondary analysis compared using fixed test durations where data were evaluated once at the end of the recording with variable test durations where data were evaluated after every sweep. RESULTS: Average phases were not statistically different between the newborn and older infants. The mean ASSR phases across both infant groups were 10°, 36°, 83°, and 110° in the left ear and 78°, 97°, 135°, and 138° in the right ear for the four modulated carriers, respectively. Of a total of 172 detected ASSRs across the four carriers, 63% (109/172), 84% (144/172), and 99% (170/172) of the phase values fell within ±30°, ±45°, and ±90° of the population mean values, respectively. Self-normative phase values were slightly closer to actual measured phases, than population normative values. Compared with the F test, with a fixed duration, the iPWT technique did slightly better (71.7% versus 77.1% detected). Compared with the F test, with variable test duration, test time was reduced using the iPWT technique for normal and weighted averaging by 4 and 2.9 sweeps (66 and 48 secs), respectively, while false-positive rates were maintained. Compared with tests that relied on the F-ratio and a fixed time of 12.3 mins, using variable test times and the iPWT approach resulted in a halving of test time, while slightly improving comparable ASSR detection rates (66.7% versus 72.5%). An inter-ear average phase difference of 52° was found, which was not accounted for by modulation rates used for left/right ears. Converting phase to latency yielded similar results to prior studies. CONCLUSIONS: The phase responses of ASSRs evoked by AM tones are stable in newborn and young infants. When using the multiple auditory steady state response (MASTER) technique, it is possible to employ phase-biasing methods to reduce test time and increase detection rates. Using self-normative intrastimulus phase difference values provides better estimated phases than average population phases for purposes of response detection.