Monica L. Hawley

Speech intelligibility and localization in a multi-source environment

Natural environments typically contain sound sources other than the source of interest that may interfere with the ability of listeners to extract information about the primary source. Studies of speech intelligibility and localization by normal-hearing listeners in the presence of competing speech are reported on in this work. One, two or three competing sentences [IEEE Trans. Audio Electroacoust. 17(3), 225-246 (1969)] were presented from various locations in the horizontal plane in several spatial configurations relative to a target sentence. Target and competing sentences were spoken by the same male talker and at the same level. All experiments were conducted both in an actual sound field and in a virtual sound field. In the virtual sound field, both binaural and monaural conditions were tested. In the speech intelligibility experiment, there were significant improvements in performance when the target and competing sentences were spatially separated. Performance was similar in the actual sound-field and virtual sound-field binaural listening conditions for speech intelligibility. Although most of these improvements are evident monaurally when using the better ear, binaural listening was necessary for large improvements in some situations. In the localization experiment, target source identification was measured in a seven-alternative absolute identification paradigm with the same competing sentence configurations as for the speech study. Performance in the localization experiment was significantly better in the actual sound-field than in the virtual sound-field binaural listening conditions. Under binaural conditions, localization performance was very good, even in the presence of three competing sentences. Under monaural conditions, performance was much worse. For the localization experiment, there was no significant effect of the number or configuration of the competing sentences tested. For these experiments, the performance in the speech intelligibility experiment was not limited by localization ability.

The role of head-induced interaural time and level differences in the speech reception threshold for multiple interfering sound sources

Three experiments investigated the roles of interaural time differences (ITDs) and level differences (ILDs) in spatial unmasking in multi-source environments. In experiment 1, speech reception thresholds (SRTs) were measured in virtual-acoustic simulations of an anechoic environment with three interfering sound sources of either speech or noise. The target source lay directly ahead, while three interfering sources were (1) all at the targets location (0 degrees,0 degrees,0 degrees), (2) at locations distributed across both hemifields (-30 degrees,60 degrees,90 degrees), (3) at locations in the same hemifield (30 degrees,60 degrees,90 degrees), or (4) co-located in one hemifield (90 degrees,90 degrees,90 degrees). Sounds were convolved with head-related impulse responses (HRIRs) that were manipulated to remove individual binaural cues. Three conditions used HRIRs with (1) both ILDs and ITDs, (2) only ILDs, and (3) only ITDs. The ITD-only condition produced the same pattern of results across spatial configurations as the combined cues, but with smaller differences between spatial configurations. The ILD-only condition yielded similar SRTs for the (-30 degrees,60 degrees,90 degrees) and (0 degrees,0 degrees,0 degrees) configurations, as expected for best-ear listening. In experiment 2, pure-tone BMLDs were measured at third-octave frequencies against the ITD-only, speech-shaped noise interferers of experiment 1. These BMLDs were 4-8 dB at low frequencies for all spatial configurations. In experiment 3, SRTs were measured for speech in diotic, speech-shaped noise. Noises were filtered to reduce the spectrum level at each frequency according to the BMLDs measured in experiment 2. SRTs were as low or lower than those of the corresponding ITD-only conditions from experiment 1. Thus, an explanation of speech understanding in complex listening environments based on the combination of best-ear listening and binaural unmasking (without involving sound-localization) cannot be excluded.

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...

Comparison of adaptive procedures for obtaining psychophysical thresholds using computer simulation

In order to compare the efficacy and efficiency of various adaptive psychophysical procedures, a program that simulates these procedures has been developed and used to compare several adaptive methods for three experiments: binaural detection, interaural intensity discrimination, and interaural time discrimination. The simulation program takes as input a psychometric function, which specifies the probability of a correct response for any value of the adapting variable. A threshold is generated by choosing the next value of the variable according to the rules of the procedure being simulated, including the rules for stopping and calculating the threshold estimate. The software generates distributions of thresholds and statistical analyses are performed, such as bias and variance of the obtained distribution. The program has been applied to psychometric functions appropriate for normal‐hearing and hearing‐impaired listeners for each of the three experiments noted above, and has compared a number of adaptive...

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.

Benefit of binaural hearing in a multi‐source environment. II. Speech intelligibility.

A multi‐source listening environment was simulated under headphones by recording signals through KEMAR in a sound‐deadened room. Seven loudspeakers were each positioned in the frontal plane 5 ft from KEMAR at 30‐deg increments, ranging from +90 (right) to −90 (left). The recorded signals (IEEE Harvard sentences) were digitally mixed and played back under headphones in a sound‐proof booth using a Digital Audio Tape (DAT) player. Speech intelligibility was measured for a ‘‘target’’ sentence in the presence of various ‘‘jammers.’’ Three variables were manipulated. First, the number of ‘‘jammers’’ was either none, one, two, or three. Second, the relative location of the targets and jammers was varied, such that they were either in close proximity, widely separated, or some of each. Third, the jammer content comprised of either other sentences, speech‐shaped noise, babble or time‐reversed sentences. Normal‐hearing listeners were tested under binaural and monaural conditions. On each trial the location of the t...

Application of confidence intervals and joint confidence regions to the estimation of psychometric functions

A mathematical description of a psychometric function with two free parameters is fit to fixed‐increment data by a nonlinear gradient search technique that incorporates a weighted least squares algorithm. The statistical confidence in the parameter estimates is considered by comparing results from standard confidence interval analysis with those from joint confidence region analysis. Confidence intervals estimate the variability of each parameter alone, ignoring the interaction between the parameters, whereas the joint confidence region gives the confidence in the joint estimation of both parameters together. In our study, both analyses were applied to fixed‐increment data from a variety of tests (interaural time and intensity discrimination and N0Sπ binaural detection) and subjects for two‐interval forced choice experiments. Results show that the parameter estimates are affected primarily by the data collected near the midpoint which is not surprising since the parameters in the model are the slope and t...

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.

Effects of the spatial distribution of competing sounds on speech reception thresholds

The experiment tested whether listeners can suppress competing sound from several different locations simultaneously. Speech reception thresholds were measured adaptively in anechoic virtual auditory spaces with a target voice directly ahead and competing sounds in four spatial configurations. Three concurrent competing sounds were distributed on the horizontal plane among consecutively numbered positions at 30‐degree intervals, position 4 being directly ahead, 1 far left, and 7 far right. The competitor configurations were 444, 367, 567, and 777. Four types of competing sound were used: speech (same voice), reversed speech, speech‐shaped noise, and speech‐modulated, speech‐shaped noise. The patterns of results across spatial configurations were similar for each type of competitor, although binaural advantage (777 vs 444) was 2–3 dB greater for speech competitors than for noise. Speech gave thresholds 3 dB higher than reversed speech throughout, suggesting linguistic interference effects. Most notably, ho...

Binaural hearing by listeners with hearing impairments

The ability of listeners with hearing impairments to understand speech in the presence of competing speech sources is often compromised; however, the extent to which poor binaural hearing contributes to this compromise is not known. These studies are aimed at relating listeners’ abilities to utilize binaural information in speech‐based and non‐speech‐based tasks. In one set of measurements, speech intelligibility and localization of speech material were tested in the presence of one to three competing sources, placed at various spatial configurations. A second set of measurements tested the sensitivity to binaural information (i.e., MLD, ITD, and ILD discrimination). Listeners who obtained maximal binaural benefit in the speech intelligibility tasks generally showed good performance in all other tasks. Listeners who showed normal ITD/ILD discrimination could not always exploit that ability in more complicated tasks (MLD and speech‐based tasks). Data were compared with the prediction of a model [Zurek, in ...