Mark S. Hedrick

Acute effect of nicotine on auditory gating in smokers and non-smokers

This paper investigates the role of cholinergic mechanisms in auditory gating by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on behavioral and electrophysiological measures of consonant-vowel (CV) discrimination in quiet and in broadband noise (BBN). In a single-blind procedure, categorical boundaries and mismatch negativity (MMN) in two conditions (quiet, BBN) were obtained from 10 non-smokers and 4 smokers with normal hearing under two drug conditions (nicotine, placebo). After the nicotine sessions, plasma tests revealed a subjects nicotine concentration and subjects reported any symptoms. Larger MMN areas and steeper slopes at the boundary were interpreted as reflecting better electrophysiological and behavioral CV discrimination, respectively. Results indicate that, in non-smokers, the effects of nicotine on electrophysiological CV discrimination in quiet increase with an increase in severity of symptoms. Specifically, asymptomatic non-smokers (N = 5) demonstrate little improvement (and sometimes decrements) in performance while symptomatic non-smokers (N = 5) exhibit nicotine-enhanced discrimination, as do smokers. In noise, all subjects demonstrate nicotine-enhanced behavioral and electrophysiological discrimination. Additionally, in noise, smokers exhibit a larger number of measurable categorical boundaries as well as larger MMN areas than non-smokers in both placebo and nicotine sessions. Results are consistent with the hypothesis that nicotinic cholinergic mechanisms play a role in the gating of auditory stimuli.

Effects of age and spectral shaping on perception and neural representation of stop consonant stimuli

OBJECTIVE To determine if (1) aging affects neural representation of a dynamic spectral speech cue and (2) spectrally-shaped gain applied to the cue reduces any aging effects. METHODS Psychometric functions and cortical evoked responses were compared in young and older listeners with normal hearing. Stimuli were consonant-vowels along a /bdg/ place-of-articulation continuum in an unshaped and shaped condition. Shaped stimuli enhanced audibility of the F2 formant transition relative to the rest of the stimulus. RESULTS Compared with younger listeners, older listeners had larger /d/ categories, longer P2 latencies, and larger N1 amplitudes to unshaped stimuli. To shaped stimuli, older listeners had /d/ categories and P2 latencies more similar to those measured from younger listeners, while N1 amplitudes were larger. CONCLUSIONS Aging significantly affects the processing of dynamic spectral information. For some measures, differences due to aging were minimized with spectrally-shaped stimuli. SIGNIFICANCE Aging reduces neural responsiveness to dynamic spectral cues. If the cue is enhanced, neural responsiveness is increased and perceptual measures are more like those from the younger listeners for some stimuli. This suggests that aging may decrease responsiveness of intact neurons as opposed to destroying neurons and/or distorting spectral coding.

EFFECT OF RELATIVE AND OVERALL AMPLITUDE ON PERCEPTION OF VOICELESS STOP CONSONANTS BY LISTENERS WITH NORMAL AND IMPAIRED HEARING

Previous studies of the /p/-/t/ contrast for normal-hearing listeners have shown that both manipulation of the amplitude of the burst relative to the vowel in the F4-F5 frequency region and overall presentation level can influence the perception of place of articulation [R. N. Ohde and K. N. Stevens, J. Acoust. Soc. Am. 74, 706-714 (1983); Gravel and Ohde, Asha 25, 101 (1983)], such that greater burst amplitude in the high frequencies and higher presentation levels result in more alveolar responses. The influence of relative amplitude and presentation level was tested for both normal-hearing (NH) and hearing-impaired (HI) listeners in the present study. Synthetic CV stimuli were used, and the amplitude of the burst relative to vowel-onset amplitude in the F4-F5 frequency region was manipulated across a 20-dB range. In addition, overall presentation level was varied across a 45-dB range. The findings revealed that the hearing-impaired listeners selected more alveolar responses than listeners with normal hearing when tested at equivalent SPLs. A group of five normal-hearing listeners were then presented the synthetic stimuli in a background of broadband noise at a level that produced thresholds at 4 kHz equivalent to the thresholds of five hearing-impaired listeners. Results from the noise-masked normal-hearing listeners did not consistently show more alveolar responses as presentation level of the stimuli was increased, thus failing to mimic the responses from the hearing-impaired listeners in quiet.

Effects of hearing loss and spectral shaping on identification and neural response patterns of stop-consonant stimuli

In order to determine the effects of hearing loss and spectral shaping on a dynamic spectral speech cue, behavioral identification and neural response patterns of stop-consonant stimuli varying along the /b-d-g/ place-of-articulation continuum were measured from 11 young adults (mean age = 27 years) and 10 older adults (mean age = 55.2 years) with normal hearing, and compared to those from 10 older adults (mean age = 61.3 years) with mild-to-moderate hearing impairment. Psychometric functions and N1-P2 cortical evoked responses were obtained using consonant-vowel (CV) stimuli with frequency-independent (unshaped) amplification as well as with frequency-dependent (shaped) amplification that enhanced F2 relative to the rest of the stimulus. Results indicated that behavioral identification and neural response patterns of stop-consonant CVs were affected primarily by aging and secondarily by age-related hearing loss. Further, enhancing the audibility of the F2 transition cue with spectrally shaped amplification partially reduced the effects of age-related hearing loss on categorization ability but not neural response patterns of stop-consonant CVs. These findings suggest that aging affects excitatory and inhibitory processes and may contribute to the perceptual differences of dynamic spectral cues seen in older versus young adults. Additionally, age and age-related hearing loss may have separate influences on neural function.

Effect of an Auditory Training Program on Reading, Phoneme Awareness, and Language:

This investigation examined the effect of an auditory training program, Fast ForWord-Language, with 26 children ages 7 to 10 years. As two subgroups based on reading ability, all children received 6 wk. of intervention. Thresholds for three conditions of backward masking were obtained pre- and postintervention, and 6 mo. afterward. Immediately following the intervention period, backward masking thresholds improved for all backward masking conditions. Participants also showed increases in language skills and in phoneme awareness but not in reading skills. Six months after intervention, there were improvements in thresholds for backward masking but no improvements in language or reading skills for either group. This study calls into question the efficacy of an intensive auditory training program to improve reading skills.

Effects of hearing loss and spectral shaping on identification and neural response patterns of stop-consonant stimuli in young adults

Objectives: The primary purpose of this study was to more clearly define the effects of hearing loss, separate from age, on perception, and neural response patterns of dynamic spectral cues. To do this, the study was designed to determine whether (1) hearing loss affects the neural representation and/or categorical perception of stop-consonant stimuli among young adults and (2) spectrally shaped amplification aimed at increasing the audibility of the F2 formant transition cue reduces any effects of hearing loss. It was predicted that (1) young adults with hearing loss would differ from young adults with normal hearing in their behavioral and neural responses to stop-consonant stimuli and (2) enhancing the audibility of the F2 formant transition cue relative to the rest of the stimulus would not overcome the effects of hearing loss on behavioral performance or neural response patterns. Design: Behavioral identification and neural response patterns of stop-consonant stimuli varying along the /b-d-g/ place-of-articulation continuum were measured from seven young adults with mild-to-moderate hearing impairment (mean age = 21.4 yr) and compared with responses from 11 young adults with normal hearing (mean age = 27 yr). Psychometric functions and N1-P2 cortical-evoked responses were evoked by consonant-vowel (CV) stimuli without (unshaped) and with (shaped) frequency-dependent amplification that enhanced F2 relative to the rest of the stimulus. Results: Behavioral identification and neural response patterns of stop-consonant CVs differed between the two groups. Specifically, to the unshaped stimuli, listeners with hearing loss tended to make low-frequency judgments more often (more /b/, fewer /g/) than listeners with normal hearing when categorizing along the /b-d-g/ continuum. Additionally, N1 amplitudes were larger and P2 latencies were longer to all phonemes in young adults with hearing impairment versus normal hearing. Enhancing the audibility of the F2 transition cue with spectrally shaped amplification did not alter the neural representation of the stop-consonant CVs in the young listeners with hearing loss. It did modify categorical perception such that listeners with hearing loss tended to make high-frequency judgments more often (more /g/, fewer /b/). However, shaping the stimuli did not make their psychometric functions more like those of the normal controls. Instead, young adults with hearing loss went from one extreme (low-frequency judgments with unshaped stimuli) to the other (high-frequency judgments with shaped stimuli), whereas judgments from the normal controls were more balanced. Conclusions: Hearing loss, separate from aging, seems to negatively impact identification and neural representation of time-varying spectral cues like the F2 formant transition. Enhancing the audibility of the F2 formant transition cue relative to the rest of the stimulus does not overcome the effects of hearing loss on behavioral performance or neural response patterns in young adults. Thus, the deleterious effects of hearing loss on stop-consonant perception along the place-of-articulation continuum may not only be due solely to decreased audibility but also due to improper coding by residual neurons, resulting in distortion of the time-varying spectral cue. This may explain, in part, why amplification cannot completely compensate for the effects of sensorineural hearing loss.

Investigating the role of temporal lobe activation in speech perception accuracy with normal hearing adults: An event-related fNIRS study

Abstract Functional near infrared spectroscopy (fNIRS) is a safe, non‐invasive, relatively quiet imaging technique that is tolerant of movement artifact making it uniquely ideal for the assessment of hearing mechanisms. Previous research demonstrates the capacity for fNIRS to detect cortical changes to varying speech intelligibility, revealing a positive relationship between cortical activation amplitude and speech perception score. In the present study, we use an event‐related design to investigate the hemodynamic response in the temporal lobe across different listening conditions. We presented participants with a speech recognition task using sentences in quiet, sentences in noise, and vocoded sentences. Hemodynamic responses were examined across conditions and then compared when speech perception was accurate compared to when speech perception was inaccurate in the context of noisy speech. Repeated measures, two‐way ANOVAs revealed that the speech in noise condition (−2.8 dB signal‐to‐noise ratio/SNR) demonstrated significantly greater activation than the easier listening conditions on multiple channels bilaterally. Further analyses comparing correct recognition trials to incorrect recognition trials (during the presentation phase of the trial) revealed that activation was significantly greater during correct trials. Lastly, during the repetition phase of the trial, where participants correctly repeated the sentence, the hemodynamic response demonstrated significantly higher deoxyhemoglobin than oxyhemoglobin, indicating a difference between the effects of perception and production on the cortical response. Using fNIRS, the present study adds meaningful evidence to the body of knowledge that describes the brain/behavior relationship related to speech perception. HighlightsTo our knowledge, this is the first study to employ an event‐related design using fNIRS to investigate neural responses time‐locked to a speech perception task to compare differences across conditions and trial types of speech perception and production.Compared to easier listening conditions, the temporal lobe exhibits significantly greater activity to extract speech in background noise.Neural activation is significantly higher when speech is accurately perceived compared to when speech perception is inaccurate.A reversal in the hemodynamic pattern was observed during the repetition phase of the task, demonstrating that speech perception and speech production evoke distinct responses in the temporal lobe.

Noise levels during recreational flight of a Cessna 172 Skyhawk

Recreational and private pilots are regularly exposed to potentially hazardous noise levels during flight training sessions and recreational flying. For the first part of this study, light airplane noise was recorded during recurrent 1.5-hour flight training sessions. Measurements were made at the level of the pilot’s left and right shoulders (using dosimeters). Data demonstrated that changing inflight operations and power adjustments were associated with specific acoustic patterns. Noise levels (Leq) ranged from 76 dBA to 96 dBA during flight. The second part of this study examined the effect of the noise on subjective and objective measures of the pilot’s auditory function. Measurements were made before and immediately after flight training sessions. Pure-tone audiometric thresholds, middle-ear absorbance and click-evoked otoacoustic emissions did not show significant changes from pre- to post-flight. Although inflight noise levels are potentially hazardous, the use of an aviation headset acted to mitig...

The Effects of Nonlinear Frequency Compression and Digital Noise Reduction on Word Recognition and Satisfaction Ratings in Noise in Adult Hearing Aid Users

BACKGROUND Nonlinear frequency compression (NLFC) and digital noise reduction (DNR) are hearing aid features often used simultaneously in the adult population with hearing loss. Although each feature has been studied extensively in isolation, the effects of using them in combination are unclear. PURPOSE The effects of NLFC and DNR in noise on word recognition and satisfaction ratings in noise in adult hearing aid users were evaluated. RESEARCH DESIGN A repeated measures design was used. STUDY SAMPLE Two females and 13 males between the ages of 55 and 83 yr who were experienced hearing aid users participated. Thirteen were experienced with NLFC and all were experienced with DNR. Each participant was fit with Phonak Bolero Q90-P hearing instruments using their specific audiometric data and the Desired Sensation Level v5.0 (adult) fitting strategy. Fittings were verified with probe microphone measurements using speech at 65-dB sound pressure level (SPL). NLFC verification was performed using the Protocol for the Provision of Amplification, Version 2014.01. DATA COLLECTION AND ANALYSIS All testing was conducted in a double-walled sound booth. Four hearing aid conditions were used for all testing: Baseline (NLFC off, DNR off), NLFC only, DNR only, and Combination (NLFC on, DNR on). A modified version of the Pascoes High-Frequency Word List was presented at 65-dB SPL with speech spectrum noise at 6-dB signal-to-noise ratio (SNR) and 1-dB SNR for each hearing aid condition. Listener satisfaction ratings were obtained after each listening condition in terms of word comfort, word clarity, and average satisfaction. Two-way repeated measures analyses of variance were conducted to assess listener performance. Pairwise comparisons were then completed for significant main effects. RESULTS Word recognition results indicated a significant SNR effect only (6 dB SNR > 1 dB SNR). Satisfaction ratings results indicated a significant SNR and hearing aid condition effect for clarity, comfort, and average satisfaction. Clarity ratings were significantly higher for DNR and Combination than NLFC. Comfort ratings were significantly higher for DNR than NLFC. Average satisfaction was significantly higher for DNR and Combination than for NLFC. Also, average ratings were significantly higher for Combination than Baseline. CONCLUSIONS Activating NLFC or DNR in isolation or in combination did not significantly impact word recognition in noise. Activating NLFC in isolation reduced satisfaction ratings relative to the DNR or Combination conditions. The isolated use of DNR significantly improved all satisfaction ratings when compared with the isolated use of NLFC. These findings suggest NLFC should not be used in isolation and should be coupled with DNR for best results. Future research should include a field trial as this was a limitation of the study.

Comparison of Multichannel Wide Dynamic Range Compression and ChannelFree Processing Strategies on Consonant Recognition.

BACKGROUND Both wide dynamic range compression (WDRC) and ChannelFree (CF) processing strategies in hearing aids were designed to improve listener comfort and consonant identification, yet few studies have actually compared them. PURPOSE To determine whether CF processing provides equal or better consonant identification and subjective preference than WDRC. RESEARCH DESIGN A repeated-measures randomized design was used in which each participant identified consonants from prerecorded nonsense vowel-consonant-vowel syllables in three conditions: unaided, aided using CF processing, and aided using WDRC processing. For each of the three conditions, syllables were presented in quiet and in a speech-noise background. Participants were also asked to rate the two processing schemes according to overall preference, preference in quiet and noise, and sound quality. STUDY SAMPLE Twenty adults (seven females; mean age 69.7 yr) with ≥1 yr of hearing aid use participated. Ten participants had previous experience wearing aids with WDRC, and 10 had previous experience with CF processing. Participants were tested with both WDRC and CF processing. DATA COLLECTION AND ANALYSIS Number of consonants correct were measured and used as the dependent variable in analyses of variance with subsequent post hoc testing. For subjective preference, a listener rating form was employed with subsequent χ² analysis. RESULTS Overall results showed that signal-processing strategy did not significantly affect consonant identification or subjective preference, nor did previous hearing aid use influence results. Listeners with audiometric slopes exceeding 11 dB per octave, however, preferred CF processing and performed better in noise with CF processing. CONCLUSION CF processing is a viable alternative to WDRC for listeners with more severely sloping audiometric contours.