Loudness Growth Research Articles

Toward parametric Bayesian adaptive procedures for multi-frequency categorical loudness scaling.

A series of Bayesian adaptive procedures to estimate loudness growth across a wide frequency range from individual listeners was developed, and these procedures were compared. Simulation experiments were conducted based on multinomial psychometric functions for categorical loudness scaling across ten test frequencies estimated from 61 listeners with normal hearing and 87 listeners with sensorineural hearing loss. Adaptive procedures that optimized the stimulus selection based on the interim estimates of two types of category-boundary models were tested. The first type of model was a phenomenological model of category boundaries adopted from previous research studies, while the other type was a data-driven model derived from a previously collected set of categorical loudness scaling data. An adaptive procedure without Bayesian active learning was also implemented. Results showed that all adaptive procedures provided convergent estimates of the loudness category boundaries and equal-loudness contours between 250 and 8000 Hz. Performing post hoc model fitting, using the data-driven model, on the collected data led to satisfactory accuracies, such that all adaptive procedures tested in the current study, independent of modeling approach and stimulus-selection rules, were able to provide estimates of the equal-loudness-level contours between 20 and 100 phons with root-mean-square errors typically under 6 dB after 100 trials.

Tinnitus as central noise revealed by increased loudness at thresholds

Tinnitus is an auditory sensation in the absence of external sounds; its neural mechanisms remain unclear. An active loudness model suggests that tinnitus is a result of increased central noise while hyperacusis is that of increased central gain. To the extent that loudness reflects the system-level neural activities, this active model predicts that tinnitus increases loudness at thresholds but does not increase the slope of loudness function. To test this prediction, the present study compared loudness growth of various stimuli between tinnitus and non-tinnitus subjects. The stimuli were tested at frequencies without hearing loss and both tinnitus and non-tinnitus subjects had unremarkable hyperacusis. Consistent with the prediction, the loudness at threshold in tinnitus subjects were 2.3 times greater than that in non-tinnitus subjects; there was no significant difference in the slope of loudness growth between these two groups of subjects. The present result shows that traditional psychophysics, originally developed to investigate relationships between subjective sensation and physical stimulation, can also help delineate neural mechanisms underlying tinnitus and other disorders.

Vocal intensity control challenges in bilateral cochlear implant users

Bilateral cochlear implantation offers benefits but poses challenges for vocal intensity control. This study explored how differences in loudness growth between ears contribute to poor vocal intensity control in BiCI users. Experiment 1 tested 13 BiCI users with sustained vowel vocalization using both cochlear implant devices together and each one separately to measure their ability to control long-term vocal intensity variation (vAm). To determine if deficits in vAm when using both ears reflected mismatched loudness growth across ears, Experiment 2 examined loudness growth from each ear for a subset of participants and Experiment 3 manipulated the loudness growth function of the processor to change the shape of loudness growth function while measuring vAm for a subset of participants. Experiment 1 showed decreased vocal intensity control with BiCI devices compared to unilateral CIs. Experiment 2 revealed different loudness growth perceptions between ears for most BiCI users, possibly explaining their poor vocal performance with both implants. Experiment 3 demonstrated that changing loudness growth functions of the processor altered the ability to control vAm, indicating that changes in loudness growth affect vAm. The results suggest unmatched loudness growth perception between ears likely contributes to poor vocal intensity control in BiCI users.

Brain’s Frequency Following Responses to Low-Frequency and Infrasound

Complaints and awareness about environmental low-frequency (LF) noise and infrasound (IS) have increased in recent years, but knowledge about perceptual mechanisms is limited. To evaluate the use of the brain’s frequency-following response (FFR) as an objective correlate of individual sensitivity to IS and LF, we recorded the FFR to monaurally presented IS (11 Hz) and LF (38 Hz) tones over a 30-phon range for 11 subjects. It was found that 11-Hz FFRs were often significant already at ~0 phon, steeply grew to 20 phon, and saturated above. In contrast, the 38-Hz FFR growth was relatively shallow and continued to 60 phon. Furthermore, at the same loudness level (30 phon), the 11-Hz FFR strength was significantly larger (4.5 dB) than for 38 Hz, possibly reflecting a higher phase synchronization across the auditory pathway. Overall, unexpected inter-individual variability as well as qualitative differences between the measured FFR growth functions and typical loudness growth make interpretation of the FFR as objective correlate of IS and LF sensitivity difficult.

Extending the audiogram with loudness growth: The complementarity of electric and acoustic hearing in bimodal patients.

Clinically, recording hearing detection thresholds and representing them in an audiogram is the most common way of evaluating hearing loss and starting the fitting of hearing devices. As an extension, we present the loudness audiogram, which does not only show auditory thresholds but also visualizes the full course of loudness growth across frequencies. The benefit of this approach was evaluated in subjects who rely on both electric (cochlear implant) and acoustic (hearing aid) hearing. In a group of 15 bimodal users, loudness growth was measured with the cochlear implant and hearing aid separately using a loudness scaling procedure. Loudness growth curves were constructed, using a novel loudness function, for each modality and then integrated in a graph plotting frequency, stimulus intensity level, and loudness perception. Bimodal benefit, defined as the difference between wearing a cochlear implant and hearing aid together versus wearing only a cochlear implant, was assessed for multiple speech outcomes. Loudness growth was related to bimodal benefit for speech recognition in noise and to some aspects of speech quality. No correlations between loudness and speech in quiet were found. Patients who had predominantly unequal loudness input from the hearing aid, gained more bimodal benefit for speech recognition in noise compared to those patients whose hearing aid provided mainly equivalent input. Results show that loudness growth is related to bimodal benefit for speech recognition in noise and to some aspects of speech quality. Subjects who had different input from the hearing aid compared to CI, generally gained more bimodal benefit compared to those patients whose hearing aid provided mainly equivalent input. This suggests that bimodal fitting to create equal loudness at all frequencies may not always be beneficial for speech recognition.

Comparing Fixed and Individualized Channel Interaction Coefficients for Speech Perception With Dynamic Focusing Cochlear Implant Strategies.

Dynamic focusing cochlear implant strategies aim to emulate normal cochlear excitation patterns by varying the degree of current focusing as a function of input level. Results on the speech perception benefits of these strategies have been mixed. In previous studies, channel interaction coefficients (K), which mediate the relationship between current level and degree of focusing, were fixed across channels and participants. Fixing K without accounting for channel interaction and the current required to accurately stimulate target neurons may elicit suboptimal loudness growth and speech perception. This study tested whether individualizing K improved speech perception relative to fixed-K and monopolar strategies. Fourteen ears of implanted adults were programmed with 14-channel strategies matched on pulse duration, pulse rate, filtering, and loudness. Sentence recognition and vowel identification was measured at 60 dB SPL equivalent in quiet and four-talker babble. On the group level, speech recognition in quiet and noise was similar between strategies. On the individual level, there were participants who benefitted with dynamic focusing strategies for speech perception in noise. Patterns of benefit were generally unclear, beyond associations between focused thresholds, duration of hearing loss, and individual-K benefit. Participants rated dynamic focusing like monopolar in clarity and ease of listening. Almost all participants expressed their willingness to use the strategies in a take-home trial. These results suggest that while individualizing K does not benefit all, there are individuals who benefit, for which the electrode-neuron interface may play a role. Future studies will evaluate acclimatization of dynamic focusing strategies using take-home trials.

Electrical Determinants of Tinnitus Extinction in a Cochlear Implant Patient

Electrical tinnitus suppression by cochlear implants requires stimulation of a subset of neural elements in the cochlea. Tinnitus is the phantom perception of sound in the ears and is a known correlate of hearing loss. Cochlear implants restore hearing and are known to lessen or extinguish tinnitus. The amount of electrical charge required and the number and location of electrodes required to extinguish tinnitus with a cochlear implant are factors that remain poorly understood. In a subject with single-sided deafness, with tinnitus in the deaf ear, we enabled single electrodes and groups of electrodes along the cochlea and increased the current until tinnitus was diminished or extinguished. We recorded the subject's perception of these changes using loudness scaling of both the electrical stimuli and the tinnitus. Tinnitus could be extinguished with individual electrodes and more effectively extinguished by activating a greater number of electrodes. Tinnitus suppression and loudness growth of the electrical stimuli were imperfectly correlated. Tinnitus suppression in this cochlear implant patient was achieved by electrically stimulating multiple distinct portions of the cochlea, and the cochlear neural substrate for tinnitus suppression may be distinct from that for auditory perception.

Genetic Hearing Loss Affects Cochlear Processing.

The relationship between speech recognition and hereditary hearing loss is not straightforward. Underlying genetic defects might determine an impaired cochlear processing of sound. We obtained data from nine groups of patients with a specific type of genetic hearing loss. For each group, the affected cochlear site-of-lesion was determined based on previously published animal studies. Retrospectively obtained speech recognition scores in noise were related to several aspects of supra-threshold cochlear processing as assessed by psychophysical measurements. The differences in speech perception in noise between these patient groups could be explained by these factors and partially by the hypothesized affected structure of the cochlea, suggesting that speech recognition in noise was associated with a genetics-related malfunctioning of the cochlea. In particular, regression models indicate that loudness growth and spectral resolution best describe the cochlear distortions and are thus a good biomarker for speech understanding in noise.

Behavioural and Electrophysiological Evaluation of Loudness Growth in Clinically Normal Hearing Tinnitus Patients with and without Hyperacusis

Introduction: The common mechanism of tinnitus, hyperacusis, and loudness perception is hypothesized to be related to central gain. Although central gain increases with attempts to compensate hearing loss, reduced input can also be observed in those with clinically normal hearing. This study aimed to evaluate the loudness growth function of tinnitus patients with and without hyperacusis using behavioural and electrophysiological methods. Methods: The study consists of three groups with a total of 60 clinically normal hearing subjects, including the control group (10 men and 10 women; mean age 39.8, SD 11.8 years), tinnitus group (10 men and 10 women; mean age 40.9, SD 12.2 years), and hyperacusis group (also have tinnitus) (7 men and 13 women; mean age 38.7, SD 14.6 years). Loudness discomfort levels (LDLs), categorical loudness scaling (CLS), and cortical auditory evoked potentials were used for the evaluation of loudness growth. N1-P2 component amplitudes and latencies were measured. Results: LDL results of 500, 1,000, 2,000, 4,000, and 8,000 Hz showed a significant difference between the hyperacusis group and the other two groups (p < 0.001). In the loudness scale test performed with 500 Hz and 2,000 Hz narrow-band noise (NBN) stimulus, a significant difference was observed between the hyperacusis group and the other two groups in the “medium,” “loud,” and “very loud” categories (p < 0.001). In the cortical examination performed with 500 Hz and 2,000 Hz NBN stimulus at 40, 60, and 80 dB nHL intensities, no significant difference was observed between the groups in the N1, P2 latency, and N1-P2 peak-to-peak amplitude. Conclusion: Although the hyperacusis group is significantly different between groups in behavioural tests, the same cannot be said for electrophysiological tests. In our attempt to differentiate tinnitus and hyperacusis with electrophysiological tests over the loudness growth function, N1 and P2 responses were not seen as suitable methods. However, it appears to be beneficial to use CLS in addition to LDLs in behavioural tests.

Perceptual Loudness Growth in Cochlear Implant Users

Purpose: Despite a growing number of cochlear implant (CI) studies, little attention has been given to loudness perception. The overall purpose of this study is to obtain the perceptual loudness growth from CI users and systematically investigate it with other relevant variables.Methods: Fourteen CI users and 14 normal hearing (NH) adults participated in this study. Loudness growth functions were obtained using three warble tones presented at 500 Hz, 1 kHz, and 4 kHz. Sentence recognition tests were implemented under favorable and adverse noise conditions. Mapping parameters including T-level, C-level, and electrical dynamic range were analyzed in conjunction with outcomes from the loudness growth.Results: The loudness growth curves for CI group were sharper than those for NH group. CI group showed a narrower acoustic dynamic range than NH group. There was no significant relationship between acoustic dynamic range and electrical dynamic range for CI users. Sentence recognition scores in adverse noise conditions were associated with electrical dynamic range in CI users. In NH group, a significant positive relationship was found between sentence recognition scores in adverse condition and acoustic dynamic range.Conclusion: This study showed that the perceptual loudness growth of CI users is not identical to that of NH adults, due to the unique way of signal processing mechanisms. Acoustic dynamic range for CI users seems affected by gain control algorithms. The adjusting mapping parameters associated with loudness may improve speech perception performance regardless of the dynamic range of CIs.

Toward an adaptive procedure for multi-frequency categorical loudness scaling: A Monte Carlo simulation study

To capture a listener’s loudness perception profile, categorical loudness scaling (CLS) is typically repeated at various frequencies. The current study aims to develop psychophysical procedures that enable simultaneous estimation of loudness growth across frequencies. For these procedures, the listener hears a pure-tone stimulus provides a categorical rating (“Soft,” “Loud,” etc.) on each trial. After a response is collected, the procedures update a model of the loudness profile and leverage the model to optimize the stimulus (i.e., level and frequency) for the next trial. The modified slope-adaptive procedure selects the stimulus from a uniform distribution spanning the model-predicted dynamic range, while the modified maximum expected information (MEI) procedure optimizes the stimulus based on an entropy metric. Monte Carlo simulations were conducted to evaluate the two procedures using a database that consists of CLS data collected from 148 listeners at Boys Town National Research Hospital. For each listener, the two procedures were run based on responses simulated using their known loudness profiles (i.e., the ground truth). Both procedures were able to estimate the loudness profile close to the ground truth, with a root-mean-square error (RMSE) of about 6 dB after 100 trials. Below 100 trials, the modified MEI procedure showed a lower RMSE.

Audibility emphasis of low-level sounds improves consonant identification while preserving vowel identification for cochlear implant users

Consonant perception is challenging for listeners with hearing loss, and transmission of speech over communication channels further deteriorates the acoustics of consonants. Part of the challenge arises from the short-term low energy spectro-temporal profile of consonants (for example, relative to vowels). We hypothesized that an audibility enhancement approach aimed at boosting the energy of low-level sounds would improve identification of consonants without diminishing vowel identification. We tested this hypothesis with 11 cochlear implant users, who completed an online listening experiment remotely using the media device and implant settings that they most commonly use when making video calls. Loudness growth and detection thresholds were measured for pure tone stimuli to characterize the relative loudness of test conditions. Consonant and vowel identification were measured in quiet and in speech-shaped noise for progressively difficult signal-to-noise ratios (+12, +6, 0, -6 dB SNR). These conditions were tested with and without an audibility-emphasis algorithm designed to enhance consonant identification at the source. The results show that the algorithm improves consonant identification in noise for cochlear implant users without diminishing vowel identification. We conclude that low-level emphasis of audio can improve speech recognition for cochlear implant users in the case of video calls or other telecommunications where the target speech can be preprocessed separately from environmental noise.

Auditory hypersensitivity and processing deficits in a rat model of fragile X syndrome

Fragile X (FX) syndrome is one of the leading inherited causes of autism spectrum disorder (ASD). A majority of FX and ASD patients exhibit sensory hypersensitivity, including auditory hypersensitivity or hyperacusis, a condition in which everyday sounds are perceived as much louder than normal. Auditory processing deficits in FX and ASD also afford the opportunity to develop objective and quantifiable outcome measures that are likely to translate between humans and animal models due to the well-conserved nature of the auditory system and well-developed behavioral read-outs of sound perception. Therefore, in this study we characterized auditory hypersensitivity in a Fmr1 knockout (KO) transgenic rat model of FX using an operant conditioning task to assess sound detection thresholds and suprathreshold auditory reaction time-intensity (RT-I) functions, a reliable psychoacoustic measure of loudness growth, at a variety of stimulus frequencies, bandwidths, and durations. Male Fmr1 KO and littermate WT rats both learned the task at the same rate and exhibited normal hearing thresholds. However, Fmr1 KO rats had faster auditory RTs over a broad range of intensities and steeper RT-I slopes than WT controls, perceptual evidence of excessive loudness growth in Fmr1 KO rats. Furthermore, we found that Fmr1 KO animals exhibited abnormal perceptual integration of sound duration and bandwidth, with diminished temporal but enhanced spectral integration of sound intensity. Because temporal and spectral integration of sound stimuli were altered in opposite directions in Fmr1 KO rats, this suggests that abnormal RTs in these animals are evidence of aberrant auditory processing rather than generalized hyperactivity or altered motor responses. Together, these results are indicative of fundamental changes to low-level auditory processing in Fmr1 KO animals. Finally, we demonstrated that antagonism of metabotropic glutamate receptor 5 (mGlu5) selectively and dose-dependently restored normal loudness growth in Fmr1 KO rats, suggesting a pharmacologic approach for alleviating sensory hypersensitivity associated with FX. This study leverages the tractable nature of the auditory system and the unique behavioral advantages of rats to provide important insights into the nature of a centrally important yet understudied aspect of FX and ASD.

Measurements From Ears With Endolymphatic Hydrops and 2-Hydroxypropyl-Beta-Cyclodextrin Provide Evidence That Loudness Recruitment Can Have a Cochlear Origin.

Background: Loudness recruitment is commonly experienced by patients with putative endolymphatic hydrops. Loudness recruitment is abnormal loudness growth with high-level sounds being perceived as having normal loudness even though hearing thresholds are elevated. The traditional interpretation of recruitment is that cochlear amplification has been reduced. Since the cochlear amplifier acts primarily at low sound levels, an ear with elevated thresholds from reduced cochlear amplification can have normal processing at high sound levels. In humans, recruitment can be studied using perceptual loudness but in animals physiological measurements are used. Recruitment in animal auditory-nerve responses has never been unequivocally demonstrated because the animals used had damage to sensory and neural cells, not solely a reduction of cochlear amplification. Investigators have thus looked for, and found, evidence of recruitment in the auditory central nervous system (CNS). While studies on CNS recruitment are informative, they cannot rule out the traditional interpretation of recruitment originating in the cochlea.Design: We used techniques that could assess hearing function throughout entire frequency- and dynamic-range of hearing. Measurements were made from two animal models: guinea-pig ears with endolymphatic-sac-ablation surgery to produce endolymphatic hydrops, and naïve guinea-pig ears with cochlear perfusions of 13 mM 2-Hydroxypropyl-Beta-Cyclodextrin (HPBCD) in artificial perilymph. Endolymphatic sac ablation caused low-frequency loss. Animals treated with HPBCD had hearing loss at all frequencies. None of these animals had loss of hair cells or synapses on auditory nerve fibers.Results: In ears with endolymphatic hydrops and those perfused with HPBCD, auditory-nerve based measurements at low frequencies showed recruitment compared to controls. Recruitment was not found at high frequencies (> 4 kHz) where hearing thresholds were normal in ears with endolymphatic hydrops and elevated in ears treated with HPBCD.Conclusions: We found compelling evidence of recruitment in auditory-nerve data. Such clear evidence has never been shown before. Our findings suggest that, in patients suspected of having endolymphatic hydrops, loudness recruitment may be a good indication that the associated low-frequency hearing loss originates from a reduction of cochlear amplification, and that measurements of recruitment could be used in differential diagnosis and treatment monitoring of Ménière's disease.

Weakened Cochlear Nonlinearity During Human Aging and Perceptual Correlates.

As humans age, compressive nonlinearity-a hallmark of healthy cochlear function-changes. The nonlinear distortion-component of the distortion product otoacoustic emission (DPOAE) provides a noninvasive gauge of cochlear nonlinearity. Earlier published work has suggested that weakened nonlinearity begins in middle age; the current work extends this investigation into the eight decade of life using advanced DPOAE data collection and analysis methods as well as multiple metrics of nonlinearity, including a test of loudness scaling. The 2f1-f2 DPOAE was recorded in 20 young adults, 25 middle-aged adults and 32 older adults from f2 = 0.78 to 9.4 kHz with primary tones (f2/f1 = 1.22) swept upward at a rate of 0.5 octave/sec. Only frequencies with audiometric thresholds ≤20 dB HL were included in the analysis and to the extent possible, ears were audiometrically matched to eliminate hearing threshold as a contributing factor to the observed age effects. Input/output functions were generated for the separated distortion-component of the DPOAE to probe compressive nonlinearity of the cochlea, and ipsilateral suppression of the DPOAE was conducted to probe two-tone suppression. To investigate the perceptual effects of weakening nonlinearity on loudness perception, the same subjects performed categorical loudness scaling. Age effects on both DPOAE and loudness scaling variables were assessed, and correlations were conducted between key OAE and perceptual metrics. Age × Frequency ANOVAs revealed that the compression knee of the DPOAE I/O function occurred at higher stimulus levels in both groups of older adults compared to young adults, suggesting an expanded linear range with aging; also, the compressive slope (growth beyond the knee point) was steeper in older-adults compared to young adults. These results were most notable at high frequencies. ANOVAs including age and auditory threshold as factors confirmed that the age effect observed was independent of threshold. Additionally, in smaller subsets of subjects with audiometrically matched data, these same trends persisted, further ruling out hearing threshold as an influential factor. The growth of DPOAE ipsilateral suppression was shallower near 4 kHz in middle-aged and older adults compared to young adults and elevated suppression thresholds were observed. Results of categorical loudness scaling showed steeper growth of loudness for older adults and, at fixed sensation levels (dB SL), the older-adult group rated tones as louder than did their young-adult counterparts, suggesting abnormal loudness growth and perception. Several correlations between the compression knee of the DPOAE I/O function and key metrics of loudness scaling were significant and accounted for up to one-third of the variance. Results indicate that the aging cochlea begins to show weakened nonlinearity in middle age and it progressively weakens further into senescence. The perceptual impact of weakened nonlinearity during aging is manifested as abnormal loudness judgments; that is, in older-adult ears, a tone considered comfortable or medium in young-adult ears can be considered loud. The biophysical origin of this weakened nonlinearity is not known. It is hypothesized to reflect aging-related damage to, or loss of, outer hair cells and their stereocilia. More work is warranted to better define the perceptual impact of a linearized cochlear response in older adults and to consider how this deficit might impact the fitting of hearing aids and other intervention strategies.

Variability of fitting parameters across cochlear implant centres.

As a follow-up to the studies by Vaerenberg et al. (Sci World J 501738:1-12, 2014) and Browning et al. (Cochlear Implant Int 21(3):1-13, 2020), who used questionnaires, we determined whether there are between-centre variations in the fitting of cochlear implants by analysing the methodology, fitting parameters and hearing results of patients from four centres with real data. The purpose of this study is to highlight the lack of streamlined mapping guides and outcome measures with respect to cochlear implant (CI) fittings. A retrospective study with ninety-seven post-lingual adults with a nucleus cochlear implant placed between 2003 and 2013 was included to ensure at least 5years of follow-up. The studied data were as follows: the methodology, including the fitter's professional background, the method of activation, the sequence of fitting sessions, the objectives measures and hearing outcomes; and the fitting parameters, including the speech processors, programming strategy, stimulation mode, T and C levels, T-SPL and C-SPL, maxima, pulse width, loudness growth and hearing results. This investigation highlights some common practices across professionals and CI centres: the activation of a CI is behavioural; impedances are systematically measured at each fitting; and some parameters are rarely modified. However, there are also differences, either between centres, such as the sequences of fitting sessions (p < 0.05) or their approach to spectral bands (p < 0.05), or even within centres, such as the policy regarding T and C levels at high frequencies compared to those at low and mid-frequencies. There are important variations between and within centres that reflect a lack of CI-related policies and outcome measures in the fitting of CI. NCT03700268.

Ventral cochlear nucleus bushy cells encode hyperacusis in guinea pigs

Psychophysical studies characterize hyperacusis as increased loudness growth over a wide-frequency range, decreased tolerance to loud sounds and reduced behavioral reaction time latencies to high-intensity sounds. While commonly associated with hearing loss, hyperacusis can also occur without hearing loss, implicating the central nervous system in the generation of hyperacusis. Previous studies suggest that ventral cochlear nucleus bushy cells may be putative neural contributors to hyperacusis. Compared to other ventral cochlear nucleus output neurons, bushy cells show high firing rates as well as lower and less variable first-spike latencies at suprathreshold intensities. Following cochlear damage, bushy cells show increased spontaneous firing rates across a wide-frequency range, suggesting that they might also show increased sound-evoked responses and reduced latencies to higher-intensity sounds. However, no studies have examined bushy cells in relationship to hyperacusis. Herein, we test the hypothesis that bushy cells may contribute to the neural basis of hyperacusis by employing noise-overexposure and single-unit electrophysiology. We find that bushy cells exhibit hyperacusis-like neural firing patterns, which are comprised of enhanced sound-driven firing rates, reduced first-spike latencies and wideband increases in excitability.

Enhanced loudness perception in ears with reduced peripheral function: A remote psychoacoustic investigation

Central gain models of hyperacusis propose that a loss of afferent input drives over-amplification of sound-evoked activity in the central auditory system, leading to enhanced loudness perception. We conducted a remote study aimed at quantifying variation in loudness perception as a function of peripheral auditory status [i.e., summating potential (SP)/action potential (AP) ratio]. To control for the contributions of age and other individual differences, twelve adults with normal hearing and strongly asymmetric SP/AP ratios between ears were recruited from a prior study. Participants completed a battery of self-directed psychoacoustic tests at home using calibrated headphones and tablet computers running custom software. Loudness perception was assessed at a variety of frequencies in each ear using standard clinical assessments [e.g., loudness discomfort levels (LDLs), dynamic range] and more fine-grained assessments of loudness growth as a function of stimulus intensity. While traditional measures of LDL and dynamic range varied widely both within and between subjects, ears with evidence of possible cochlear synaptopathy (high SP/AP ratios) demonstrated elevated loudness perception for intensities in-between threshold and LDL. Detailed assessments of loudness growth across sensation levels may be more sensitive to variation in underlying peripheral neural status than traditional, single-point clinical measures of loudness discomfort.

Perceptual Benefits of Extended Bandwidth Hearing Aids With Children: A Within-Subject Design Using Clinically Available Hearing Aids

Purpose The aim of the study was to investigate the achieved audibility with clinically available, modern, high-end, behind-the-ear hearing aids fitted using the Desired Sensation Level v5.0 child prescription for a clinical sample of children with hearing impairment and the effect of the extended bandwidth provided by the hearing aids on several outcome measures. Method The achieved audibility was measured using the maximum audible output frequency method. Twenty-eight children (7-17 years old) with mild to severe hearing losses completed this study. Two hearing aid conditions were fitted for each participant: an extended bandwidth condition, which was fitted to targets as closely as possible, and a restricted bandwidth condition, for which aided output was restricted above 4.5 kHz. Consonant discrimination in noise, subjective preference, aided loudness growth, and preferred listening levels were evaluated in both conditions. Results The extended bandwidth hearing aid fittings provided speech audibility above 4.5 kHz for all children, with an average maximum audible output frequency of 7376 Hz (SD = 1669 Hz). When compared to a restricted bandwidth, the extended bandwidth condition led to an improvement of 5.4% for consonant discrimination in noise scores, mostly attributable to /s/, /z/, and /t/ phoneme perception. Aided loudness results and preferred listening levels were not significantly different across bandwidth conditions; however, 65% of the children indicated a subjective preference for the extended bandwidth. Conclusion The study suggests that providing the full bandwidth available, with modern, behind-the-ear hearing aids, leads to improved audibility, when compared to restricted bandwidth hearing aids, and that it leads to beneficial outcomes for children who use hearing aids, fitted to the Desired Sensation Level v5.0 child prescription, without causing significant increases in their loudness perception.

Using auditory reaction time to measure loudness growth in rats

Previous studies have demonstrated that auditory reaction time (RT) is a reliable surrogate of loudness perception in humans. Reaction time-intensity (RT-I) functions faithfully recapitulate equal loudness contours in humans while being easier to obtain than equal loudness judgments, especially in animals. In humans, loudness estimation not only depends on sound intensity, but on a variety of other acoustic factors. Stimulus duration and bandwidth are known to impact loudness perception. In addition, the presence of background noise mimics loudness recruitment; loudness growth is rapid near threshold, but growth becomes normal at suprathreshold levels. Therefore, to evaluate whether RT-I functions are a reliable measure of loudness growth in rats, we obtained auditory RTs across a range of stimulus intensities, durations, and bandwidths, in both quiet and in the presence of background/masking noise. We found that reaction time patterns across stimulus parameters were repeatable over several months in rats and generally consistent with human loudness perceptual data. Our results provide important building blocks for future animal model studies of loudness perception and loudness perceptual disorders.