Spectrotemporal Modulation Sensitivity in Hearing-Impaired Listeners

Speech is characterized by temporal and spectral modulations. Hearing-impaired (HI) listeners may have reduced spectrotemporal modulation (STM) sensitivity, which could affect their speech understanding. This study examined effects of hearing loss and absolute frequency on STM sensitivity and their relationship to speech intelligibility, frequency selectivity and temporal fine-structure (TFS) sensitivity. Sensitivity to STM applied to four-octave or one-octave noise carriers were measured for normal-hearing and HI listeners as a function of spectral modulation, temporal modulation and absolute frequency. Across-frequency variation in STM sensitivity suggests that broadband measurements do not sufficiently characterize performance. Results were simulated with a cortical STM-sensitivity model. No correlation was found between the reduced frequency selectivity required in the model to explain the HI STM data and more direct notched-noise estimates. Correlations between low-frequency and broadband STM performance, speech intelligibility and frequency-modulation sensitivity suggest that speech and STM processing may depend on the ability to use TFS

Individual Differences Reveal Correlates of Hidden Hearing Deficits

Clinical audiometry has long focused on determining the detection thresholds for pure tones, which depend on intact cochlear mechanics and hair cell function. Yet many listeners with normal hearing thresholds complain of communication difficulties, and the causes for such problems are not well understood. Here, we explore whether normal-hearing listeners exhibit such suprathreshold deficits, affecting the fidelity with which subcortical areas encode the temporal structure of clearly audible sound. Using an array of measures, we evaluated a cohort of young adults with thresholds in the normal range to assess both cochlear mechanical function and temporal coding of suprathreshold sounds. Listeners differed widely in both electrophysiological and behavioral measures of temporal coding fidelity. These measures correlated significantly with each other. Conversely, these differences were unrelated to the modest variation in otoacoustic emissions, cochlear tuning, or the residual differences in hearing threshold present in our cohort. Electroencephalography revealed that listeners with poor subcortical encoding had poor cortical sensitivity to changes in interaural time differences, which are critical for localizing sound sources and analyzing complex scenes. These listeners also performed poorly when asked to direct selective attention to one of two competing speech streams, a task that mimics the challenges of many everyday listening environments. Together with previous animal and computational models, our results suggest that hidden hearing deficits, likely originating at the level of the cochlear nerve, are part of “normal hearing.

Individual Differences Reveal Correlates of Hidden Hearing Deficits

Clinical audiometry has long focused on determining the detection thresholds for pure tones, which depend on intact cochlear mechanics and hair cell function. Yet many listeners with normal hearing thresholds complain of communication difficulties, and the causes for such problems are not well understood. Here, we explore whether normal-hearing listeners exhibit such suprathreshold deficits, affecting the fidelity with which subcortical areas encode the temporal structure of clearly audible sound. Using an array of measures, we evaluated a cohort of young adults with thresholds in the normal range to assess both cochlear mechanical function and temporal coding of suprathreshold sounds. Listeners differed widely in both electrophysiological and behavioral measures of temporal coding fidelity. These measures correlated significantly with each other. Conversely, these differences were unrelated to the modest variation in otoacoustic emissions, cochlear tuning, or the residual differences in hearing threshold present in our cohort. Electroencephalography revealed that listeners with poor subcortical encoding had poor cortical sensitivity to changes in interaural time differences, which are critical for localizing sound sources and analyzing complex scenes. These listeners also performed poorly when asked to direct selective attention to one of two competing speech streams, a task that mimics the challenges of many everyday listening environments. Together with previous animal and computational models, our results suggest that hidden hearing deficits, likely originating at the level of the cochlear nerve, are part of “normal hearing.

Alterations in auditory brain stem response distinguish occasional and constant tinnitus

BACKGROUND. The heterogeneity of tinnitus is thought to underlie the lack of objective diagnostic measures. METHODS. Longitudinal data from 20,349 participants of the Swedish Longitudinal Occupational Survey of Health (SLOSH) cohort from 2008 to 2018 were used to understand the dynamics of transition between occasional and constant tinnitus. The second part of the study included electrophysiological data from 405 participants of the Swedish Tinnitus Outreach Project (STOP) cohort. RESULTS. We determined that with increasing frequency of the occasional perception of self-reported tinnitus, the odds of reporting constant tinnitus after 2 years increases from 5.62 (95% CI, 4.83–6.55) for previous tinnitus (sometimes) to 29.74 (4.82–6.55) for previous tinnitus (often). When previous tinnitus was reported to be constant, the odds of reporting it as constant after 2 years rose to 603.02 (524.74–692.98), suggesting that once transitioned to constant tinnitus, the likelihood of tinnitus to persist was much greater. Auditory brain stem responses (ABRs) from subjects reporting nontinnitus (controls), occasional tinnitus, and constant tinnitus show that wave V latency increased in constant tinnitus when compared with occasional tinnitus or nontinnitus. The ABR from occasional tinnitus was indistinguishable from that of the nontinnitus controls. CONCLUSIONS. Our results support the hypothesis that the transition from occasional to constant tinnitus is accompanied by neuronal changes in the midbrain leading to a persisting tinnitus, which is then less likely to remit.publishedVersio

Relationship between headaches and tinnitus in a Swedish study

The heterogeneity of tinnitus is likely accounting for the lack of effective treatment approaches. Headaches have been related to tinnitus, yet little is known on how headaches impact tinnitus. We use cross-sectional data from the Swedish Tinnitus Outreach Project to i) evaluate the association between headaches and tinnitus (n = 1,984 cases and 1,661 controls) and ii) investigate the phenotypic characteristics of tinnitus subjects with tinnitus (n = 660) or without (n = 1,879) headaches. In a multivariable logistic regression model, headache was significantly associated with any tinnitus (odds ratio, OR = 2.61) and more so with tinnitus as a big problem (as measured by the tinnitus functional index, TFI ≥ 48; OR = 5.63) or severe tinnitus (using the tinnitus handicap inventory, THI ≥ 58; OR = 4.99). When focusing on subjects with tinnitus, the prevalence of headaches was 26% and reached 40% in subjects with severe tinnitus. A large number of socioeconomic, phenotypic and psychological characteristics differed between headache and non-headache subjects with any tinnitus. With increasing tinnitus severity, fewer differences were found, the major ones being vertigo, neck pain and other pain syndromes, as well as stress and anxiety. Our study suggests that headaches could contribute to tinnitus distress and potentially its severity.publishedVersio

Auditory brainstem response latency in noise as a marker of cochlear synaptopathy

Thesis: Ph. D., Harvard-MIT Program in Health Sciences and Technology, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 107-117).Communication in environments with multiple competing sound sources can be challenging, even for listeners with normal hearing thresholds (NHT). This difficulty in "normal" listeners is thought to arise from central sites of the auditory system with the assumption that sound encoding at the auditory nerve (AN) is robust. Despite this assumption, growing evidence from animal and human studies suggests that acoustic exposure, too modest to elevate hearing thresholds, can nonetheless cause "hidden hearing loss" that interferes with coding of supra-threshold sound. In animal studies, such noise exposure leads to cochlear synaptopathy (death of auditory nerve fibers or ANFs); however, there is no clinical test of synaptopathy in humans. In animals, synaptopathy reduces the amplitude of auditory brainstem response (ABR) wave-I. Unfortunately, ABR wave-I is difficult to measure in humans, limiting its clinical use. Here, using behavioral, otoacoustic, and electrophysiological measures in humans and mice in conjunction with computational models of sound processing by the auditory periphery and brainstem, we show that the effect of masking noise on the latency of the more robust ABR wave-V mirrors changes in ABR wave-I amplitude. In our human cohort, the effect of noise on wave-V latency predicts perceptual temporal sensitivity. Further, we show evidence that ABR wave-V latency in forward masking may be affected by ANF loss and is predictive of a listener's performance in a perceptual task related to speech intelligibility in noise. Our results suggest that measures of the effects of masking on ABR wave-V latency can be used to diagnose ANF survival in humans.by Golbarg Mehraei.Ph. D