LaGuinn P. Sherlock

Adaptive plasticity of loudness induced by chronic attenuation and enhancement of the acoustic background (L)

Strategies for treating hyperacusis, an anomolous condition of loudness perception, paradoxically seek either to minimize or enhance listeners’ sound exposures. We show that these reciprocal treatment approaches, implemented with similar amounts of background sound attenuation and enhancement, produce diametrically opposite perceptual effects in normal listeners. Specifically, we show after continuous, 2-week earplugging and low-level noise treatments that listeners become more and less sensitive, respectively, to the loudness of sounds. This simple demonstration of adaptive plasticity is consistent with modification of a theoretical gain control process, which is the basis for desensitizing sound therapies used in treating hyperacusis and related sound tolerance problems.

Temporal gap detection measured with multiple sinusoidal markers: Effects of marker number, frequency, and temporal position

Detection thresholds were measured for silent temporal gaps within combinations of two, three, or four sinusoidal markers (i.e., combinations of one or two pre-gap markers with one or two post-gap markers). The markers were selected from the frequency range 2000-3100 Hz. Sinusoidal frequencies F1 and F4 were used as pre-gap markers, while F2 and F3 served as post-gap markers. Temporal gap detection (TGD) thresholds were measured from sets of three normal-hearing adults who tracked 70.7% correct detection thresholds adaptively across blocks of 50 two-interval, two-alternative, forced-choice trials. For symmetric marker conditions, where pre- and post-gap markers were equivalent in frequency (e.g., F1 = F2 or F1 = F2 and F3 = F4), TGD thresholds were < 10 ms. However, for asymmetric marker frequency alignments across the silent gap, including stimulus configurations where only three markers were presented on a trial (e.g., F1 = F2, F2 not equal to F3, no F4), performance was highly variable and was dramatically disrupted by the presentation of a second post-gap marker. The multiple-marker results reveal that TGD depends greatly on the number of markers presented, both in terms of the marker temporal position before and after the silent gap signal and the marker frequency alignment (symmetry) across the gap. These results, which cannot be predicted from models of the auditory periphery, may reflect perceptual mechanisms that are important in grouping and organizing auditory images.

Enhancement of the edges of temporal masking functions by complex patterns of overshoot and undershoot

The purpose of this report is to present new data that provide a novel perspective on temporal masking, different from that found in the classical auditory literature on this topic. Specifically, measurement conditions are presented that minimize rather than maximize temporal spread of masking for a gated (200-ms) narrow-band (405-Hz-wide) noise masker logarithmically centered at 2500 Hz. Masked detection thresholds were measured for brief sinusoids in a two-interval, forced-choice (21FC) task. Detection was measured at each of 43 temporal positions within the signal observation interval for the sinusoidal signal presented either preceding, during, or following the gating of the masker, which was centered temporally within each 500-ms observation interval. Results are presented for three listeners; first, for detection of a 1900-Hz signal across a range of masker component levels (0-70 dB SPL) and, second, for masked detection as a function of signal frequency (fs = 500-5000 Hz) for a fixed masker component level (40 dB SPL). For signals presented off-frequency from the masker, and at low-to-moderate masker levels, the resulting temporal masking functions are characterized by sharp temporal edges. The sharpness of the edges is accentuated by complex patterns of temporal overshoot and undershoot, corresponding with diminished and enhanced detection, respectively, at both masker onset and offset. This information about the onset and offset timing of the gated masker is faithfully represented in the temporal masking functions over the full decade range of signal frequencies (except for fs=2500 Hz presented at the center frequency of the masker). The precise representation of the timing information is remarkable considering that the temporal envelope characteristics of the gated masker are evident in the remote masking response at least two octaves below the frequencies of the masker at a cochlear place where little or no masker activity would be expected. This general enhancement of the temporal edges of the masking response is reminiscent of spectral edge enhancement by lateral suppression/inhibition.

Intervention for restricted dynamic range and reduced sound tolerance: Clinical trial using a Tinnitus Retraining Therapy protocol for hyperacusis

Hyperacusis is the intolerance to sound levels that normally are judged acceptable to others. The presence of hyperacusis (diagnosed or undiagnosed) can be an important reason that some persons reject their hearing aids. Tinnitus Retraining Therapy (TRT), a treatment approach for debilitating tinnitus and hyperacusis, routinely gives rise to increased loudness discomfort levels (LDLs) and improved sound tolerance. TRT involves both counseling and the daily exposure to soft sound from bilateral noise generator devices (NGs). We implemented a randomized, double-blind, placebo-controlled clinical trial to assess the efficacy of TRT as an intervention for reduced sound tolerance in hearing-aid eligible persons with hyperacusis and/or restricted dynamic ranges. Subjects were assigned to one of four treatment groups (2x2): Devices: NGs or placebo NGs and Counseling: Yes or No. They were evaluated at least monthly on a variety of audiometric tests, including LDLs, the Contour Test for Loudness for tones and spee...

A Sound Therapy-Based Intervention to Expand the Auditory Dynamic Range for Loudness among Persons with Sensorineural Hearing Losses: Case Evidence Showcasing Treatment Efficacy

Case evidence is presented that highlights the clinical relevance and significance of a novel sound therapy-based treatment. This intervention has been shown to be efficacious in a randomized controlled trial for promoting expansion of the dynamic range for loudness and increased sound tolerance among persons with sensorineural hearing losses. Prior to treatment, these individuals were unable to use aided sound effectively because of their limited dynamic ranges. These promising treatment effects are shown in this article to be functionally significant, giving rise to improved speech understanding and enhanced hearing aid benefit and satisfaction, and, in turn, to enhanced quality of life posttreatment. These posttreatment sound therapy effects also are shown to be sustained, in whole or part, with aided environmental sound and to be dependent on specialized counseling to maximize treatment benefit. Importantly, the treatment appears to be efficacious for hearing-impaired persons with primary hyperacusis (i.e., abnormally reduced loudness discomfort levels [LDLs]) and for persons with loudness recruitment (i.e., LDLs within the typical range), which suggests the intervention should generalize across most individuals with reduced dynamic ranges owing to sensorineural hearing loss. An exception presented in this article is for a person describing the perceptual experience of pronounced loudness adaptation, which apparently rendered the sound therapy inaudible and ineffectual for this individual. Ultimately, these case examples showcase the enormous potential of a surprisingly simple sound therapy intervention, which has utility for virtually all audiologists to master and empower the adaptive plasticity of the auditory system to achieve remarkable treatment benefits for large numbers of individuals with sensorineural hearing losses.

A descriptive model of under‐ and over‐shoot patterns in the temporal masking function of a narrow‐band noise

Complex temporal patterns of under‐ and over‐shoot (i.e., enhanced and diminished detection) at onset and offset of a 200‐ms, 400‐Hz‐wide noise masker (2500 Hz center frequency) have been reported for a temporal masking paradigm [Formby et al.., J. Acoust. Soc. Am. 102, 3161(A) (1997)]. The paradigm measured detection of a 5‐ms sinusoidal signal (1900 or 2100 Hz) at 43 temporal positions preceding, during, and following the masker. Efforts to model under‐ and over‐shoot patterns in the temporal masking functions will be considered. The modeling strategy is similar to that used in the study of vestibular adaptation [Formby et al., 21st Meeting of Association for Research in Otolaryngology, 1988], and allows for quantification of the relative amplitudes, time constants, and delays of excitatory and adaptive processes. Linear combinations of exponential functions are used to represent the effects of excitatory masking and adaptation. Suppression and adaptation of suppression may also play roles in the masking process. These effects can be evaluated in our scheme by including corresponding exponential functions to represent the processes. The least‐squares fitting model will be described and parameter estimates for the model will be presented for a range of masker levels. [Work supported by ONR.]

Intra- and Intersubject Variability in Audiometric Measures and Loudness Judgments in Older Listeners with Normal Hearing

This research was to document intra- and intersubject variability in measures of pure tone thresholds, loudness discomfort levels, and the Contour test of loudness for tonal and speech stimuli across 8 to 10 repeated test sessions over a period of almost 1 year in a group of 11 normal-hearing, older middle-aged adults (39 to 73 years, mean of 56 years). The measured pure tone thresholds and loudness discomfort levels were determined to be stable across sessions, with variability on the order of 5 dB. The categorical judgments for the Contour test for both warbled tones and spondaic speech stimuli decreased over time in level required for categories greater than comfortable. This result contrasts with reports of a slight increase over time when young, normal-hearing adults were tested in comparable measures. The intrasubject variability in the Contour test results was greatest for the 4,000-Hz tonal stimulus for which the largest time effects were observed. The intersubject variability was typically greater than the intrasubject variability and typically increased as the loudness category increased, with some exceptions. The results from this study can be used to aid in power and sample size analyses using these measures in future studies designed to compare effects of treatments based on changes in loudness judgments over time.

Clinical trials of a hybrid adaptive beamformer (HAB) for improved speech understanding in noise

A wearable, hybrid adaptive beamformer (HAB) device has been developed using a four‐microphone array and a combination of adaptive and fixed‐weight beamforming. The HAB is being evaluated with hard‐of‐hearing (HoH) listeners in a variety of environments. Pilot tests used HINT test sentences and noise from separate loudspeakers (106‐deg angle) in an audiological booth (AI‐weighted direct‐to‐reverberant ratio 9.1 dB). Measured sentence reception thresholds (SRTs) indicated that the HAB provided 14.5, 16.1, and 12.8 dB improvement over the single microphone for two normal‐hearing and one HoH listener. Results will be reported for ongoing objective and subjective testing of elderly listeners with mild to moderate hearing losses. Subjects are fitted monaurally with a commercially available behind‐the‐ear hearing aid with a dual microphone array following the NAL‐R fitting algorithm. Comparisons are made between listeners’ SRTs in noise, using: (a) conventional single‐microphone, (b) dual microphone, and (c) fo...

Considerations in the Development of a Sound Tolerance Interview and Questionnaire Instrument

Most clinicians approach the objective fitting of hearing aids with three goals in mind: audibility, comfort, and tolerance. When these three amplification goals have been met, the hearing aid user is more likely to adapt to and perceive benefit from hearing aid use. However, problems related to the loudness of sounds and reduced sound tolerance, which may or may not be reported by the aided user, can adversely impact adaptation to amplification and the individuals quality of life. Although there are several standardized questionnaires available to evaluate hearing aid benefit and satisfaction, there is no standardized questionnaire or interview tool for evaluating reduced sound tolerance and the related impact on hearing aid use. We describe a 36-item tool, the Sound Tolerance Questionnaire (STQ), consisting of six sections, including experience with hearing aids, sound sensitivity/intolerance, medical and noise exposure histories, coexisting tinnitus problems, and a final question to differentiate the primary and secondary problems related to sound intolerance, tinnitus, and hearing loss. In its current format as a research tool, the STQ was sensitive in pinpointing vague sound tolerance complaints not reported by the study participants in eligibility screening by Formby et al. A refined version of the STQ, the Sound Tolerance Interview and Questionnaire Instrument (STIQI), structured as a two-part tool, is presented in the appendix for prospective clinical use. The STIQI has potential utility to delineate factors contributing to loudness complaints and/or reduced sound tolerance in individuals considering hearing aid use, as well as those who have been unsuccessful hearing aid users secondary to loudness complaints or sound intolerance. The STIQI, when validated and refined, also may hold promise for predicting hearing aid benefit and/or assessing treatment-related change over time of hearing aid use or interventions designed to remediate problems of loudness and/or sound intolerance among hearing aid candidates or users.

Evaluation of extended-wear earplug technology as a transparent hearing-protection device

One of the greatest challenges in hearing conservation is providing adequate protection for those listeners who spend most of their time in quiet environments, but are occasionally exposed to high levels of noise that occur at unpredictable times. A classic example of this problem occurs for dismounted soldiers, who rely heavily on their natural hearing acuity to detect threats and opportunities on the battlefield but always face the risk of becoming engaged in a dangerously noisy firefight with little or no warning. One emerging technology that might have application in this domain is the extended-wear hearing aid, which is capable of remaining deep in the ear canal for weeks or months before being removed. Preliminary results suggest that the extended wear earplug can provide protection from blast or continuous noise that is comparable to a conventional earplug or muff, and that it can provide detection and localization performance comparable to that achieved with the open ear. Its form factor also make...