Hearing-impaired Listeners Research Articles

The effect of stimulus intensity on neural envelope tracking

Objectives In recent years, there has been significant interest in recovering the temporal envelope of a speech signal from the neural response to investigate neural speech processing. The research focus is now broadening from neural speech processing in normal-hearing listeners towards hearing-impaired listeners. When testing hearing-impaired listeners, speech has to be amplified to resemble the effect of a hearing aid and compensate for peripheral hearing loss. Today it is not known with certainty how or if neural speech tracking is influenced by sound amplification. As these higher intensities could influence the outcome, we investigated the influence of stimulus intensity on neural speech tracking. Design We recorded the electroencephalogram (EEG) of 20 normal-hearing participants while they listened to a narrated story. The story was presented at intensities from 10 to 80 dB A. To investigate the brain responses, we analyzed neural tracking of the speech envelope by reconstructing the envelope from the EEG using a linear decoder and by correlating the reconstructed with the actual envelope. We investigated the delta (0.5–4 Hz) and the theta (4–8 Hz) band for each intensity. We also investigated the latencies and amplitudes of the responses in more detail using temporal response functions, which are the estimated linear response functions between the stimulus envelope and the EEG. Results Neural envelope tracking is dependent on stimulus intensity in both the TRF and envelope reconstruction analysis. However, provided that the decoder is applied to the same stimulus intensity as it was trained on, envelope reconstruction is robust to stimulus intensity. Besides, neural envelope tracking in the delta (but not theta) band seems to relate to speech intelligibility. Similar to the linear decoder analysis, TRF amplitudes and latencies are dependent on stimulus intensity: The amplitude of peak 1 (30-50 ms) increases, and the latency of peak 2 (140–160 ms) decreases with increasing stimulus intensity. Conclusion Although brain responses are influenced by stimulus intensity, neural envelope tracking is robust to stimulus intensity when using the same intensity to test and train the decoder. Therefore we can assume that intensity will not be a confounder when testing hearing-impaired participants with amplified speech using the linear decoder approach. In addition, neural envelope tracking in the delta band appears to be correlated with speech intelligibility, showing the potential of neural envelope tracking as an objective measure of speech intelligibility.

Sensitivity to haptic sound-localisation cues

Hearing aid and cochlear implant (CI) users often struggle to locate and segregate sounds. The dominant sound-localisation cues are time and intensity differences across the ears. A recent study showed that CI users locate sounds substantially better when these cues are provided through haptic stimulation on each wrist. However, the sensitivity of the wrists to these cues and the robustness of this sensitivity to aging is unknown. The current study showed that time difference sensitivity is much poorer across the wrists than across the ears and declines with age. In contrast, high sensitivity to across-wrist intensity differences was found that was robust to aging. This high sensitivity was observed across a range of stimulation intensities for both amplitude modulated and unmodulated sinusoids and matched across-ear intensity difference sensitivity for normal-hearing individuals. Furthermore, the usable dynamic range for haptic stimulation on the wrists was found to be around four times larger than for CIs. These findings suggest that high-precision haptic sound-localisation can be achieved, which could aid many hearing-impaired listeners. Furthermore, the finding that high-fidelity across-wrist intensity information can be transferred could be exploited in human–machine interfaces to enhance virtual reality and improve remote control of military, medical, or research robots.

Identification and Discrimination of Sound Textures in Hearing-Impaired and Older Listeners.

Sound textures are a broad class of sounds defined by their homogeneous temporal structure. It has been suggested that sound texture perception is mediated by time-averaged summary statistics measured from early stages of the auditory system. The ability of young normal-hearing (NH) listeners to identify synthetic sound textures increases as the statistics of the synthetic texture approach those of its real-world counterpart. In sound texture discrimination, young NH listeners utilize the fine temporal stimulus information for short-duration stimuli, whereas they switch to a time-averaged statistical representation as the stimulus’ duration increases. The present study investigated how younger and older listeners with a sensorineural hearing impairment perform in the corresponding texture identification and discrimination tasks in which the stimuli were amplified to compensate for the individual listeners’ loss of audibility. In both hearing impaired (HI) listeners and NH controls, sound texture identification performance increased as the number of statistics imposed during the synthesis stage increased, but hearing impairment was accompanied by a significant reduction in overall identification accuracy. Sound texture discrimination performance was measured across listener groups categorized by age and hearing loss. Sound texture discrimination performance was unaffected by hearing loss at all excerpt durations. The older listeners’ sound texture and exemplar discrimination performance decreased for signals of short excerpt duration, with older HI listeners performing better than older NH listeners. The results suggest that the time-averaged statistic representations of sound textures provide listeners with cues which are robust to the effects of age and sensorineural hearing loss.

Measuring the Influence of Noise Reduction on Listening Effort in Hearing-Impaired Listeners Using Response Times to an Arithmetic Task in Noise.

Single microphone noise reduction (NR) in hearing aids can provide a subjective benefit even when there is no objective improvement in speech intelligibility. A possible explanation lies in a reduction of listening effort. Previously, we showed that response times (a proxy for listening effort) to an auditory-only dual-task were reduced by NR in normal-hearing (NH) listeners. In this study, we investigate if the results from NH listeners extend to the hearing-impaired (HI), the target group for hearing aids. In addition, we assess the relevance of the outcome measure for studying and understanding listening effort. Twelve HI subjects were asked to sum two digits of a digit triplet in noise. We measured response times to this task, as well as subjective listening effort and speech intelligibility. Stimuli were presented at three signal-to-noise ratios (SNR; –5, 0, +5 dB) and in quiet. Stimuli were processed with ideal or nonideal NR, or unprocessed. The effect of NR on response times in HI listeners was significant only in conditions where speech intelligibility was also affected (–5 dB SNR). This is in contrast to the previous results with NH listeners. There was a significant effect of SNR on response times for HI listeners. The response time measure was reasonably correlated (R142 = 0.54) to subjective listening effort and showed a sufficient test–retest reliability. This study thus presents an objective, valid, and reliable measure for evaluating an aspect of listening effort of HI listeners.

No Evidence That Music Training Benefits Speech Perception in Hearing-Impaired Listeners: A Systematic Review.

As musicians have been shown to have a range of superior auditory skills to non-musicians (e.g., pitch discrimination ability), it has been hypothesized by many researchers that music training can have a beneficial effect on speech perception in populations with hearing impairment. This hypothesis relies on an assumption that the benefits seen in musicians are due to their training and not due to innate skills that may support successful musicianship. This systematic review examined the evidence from 13 longitudinal training studies that tested the hypothesis that music training has a causal effect on speech perception ability in hearing-impaired listeners. The papers were evaluated for quality of research design and appropriate analysis techniques. Only 4 of the 13 papers used a research design that allowed a causal relation between music training and outcome benefits to be validly tested, and none of those 4 papers with a better quality study design demonstrated a benefit of music training for speech perception. In spite of the lack of valid evidence in support of the hypothesis, 10 of the 13 papers made claims of benefits of music training, showing a propensity for confirmation bias in this area of research. It is recommended that future studies that aim to evaluate the association of speech perception ability and music training use a study design that differentiates the effects of training from those of innate perceptual and cognitive skills in the participants.

Quantization-Aware Binaural MWF Based Noise Reduction Incorporating External Wireless Devices

For hearing-impaired listeners, both ambient noise suppression and binaural cues preservation of directional sources are required, such that a complete spatial awareness of the acoustic scene can be obtained. It was shown that the binaural multichannel Wiener filter (MWF) with partial noise preservation can achieve joint noise reduction and binaural cues preservation and incorporating an external microphone signal improves the performance of binaural MWFs. Motivated by this, we propose a binaural MWF incorporating external wireless devices in this paper. First, we theoretically analyze the performance of the MWF in terms of output signal-to-noise ratio (SNR) and binaural cues preservation errors. As in practice the external devices are power driven with a limited amount of battery resource and the power consumption heavily depends on the transmission rate, given an expected noise reduction performance we then optimize the bit-rate for a single external microphone. Further, we consider to minimize the total power consumption over multiple external devices under a constraint on the output SNR, which turns out to be a rate distribution problem. The proposed rate-distributed binaural MWF is evaluated using a hearing-aid setup with various dynamics. It is shown that the proposed method can obtain a desired SNR at a much lower bit-rate, and an expected trade-off between SNR gain and binaural cues preservation accuracy can be obtained by optimizing the bit-rates. Increasing the bit-rates improves both instrumental speech quality and speech intelligibility.

Comparison of Behavioral and Physiological Measures of the Status of the Cochlear Nonlinearity.

While an audiogram is a useful method of characterizing hearing loss, it has been suggested that including a complementary, suprathreshold measure, for example, a measure of the status of the cochlear active mechanism, could lead to improved diagnostics and improved hearing-aid fitting in individual listeners. While several behavioral and physiological methods have been proposed to measure the cochlear-nonlinearity characteristics, evidence of a good correspondence between them is lacking, at least in the case of hearing-impaired listeners. If this lack of correspondence is due to, for example, limited reliability of one of such measures, it might be a reason for limited evidence of the benefit of measuring peripheral compression. The aim of this study was to investigate the relation between measures of the peripheral-nonlinearity status estimated using two psychoacoustical methods (based on the notched-noise and temporal-masking curve methods) and otoacoustic emissions, on a large sample of hearing-impaired listeners. While the relation between the estimates from the notched-noise and the otoacoustic emissions experiments was found to be stronger than predicted by the audiogram alone, the relations between the two measures and the temporal-masking based measure did not show the same pattern, that is, the variance shared by any of the two measures with the temporal-masking curve-based measure was also shared with the audiogram.

Supervised binaural source separation using auditory attention detection in realistic scenarios

Speech separation in crowded environments is challenging for hearing-impaired listeners. Unfortunately, hearing aids cannot segregate the main speaker from other interferences without knowing to which speaker the listener attends. In this paper, a new robust binaural speech separation system based on a supervised deep neural network (DNN) is introduced to separate attended speaker in different simulated room conditions (i.e., noisy and reverberant room with different azimuthal locations of the target speaker). For each speaker in the mixture of sound sources, a set of DNNs yields estimated ratio masks where one of them is selected by the auditory attention detection (AAD) procedure to separate the attended speech. The detection of the attended speaker among others is achieved by a Bi-directional long short-term memory (Bi-LSTM) network using phase-locking values (PLVs) extracted from the electroencephalography (EEG) signals. Two experiments are conducted to assess the performance of the proposed AAD-based binaural separation system vs. a state-of-the-art monaural segregation system from the literature, used as a baseline. The results of evaluating the AAD processing unit show high detection accuracy as compared with the detection method used in the baseline system. Also, systematic evaluations of the proposed binaural separation system against the baselines confirm its superiority in terms of various objective intelligibility and quality measures. The new AAD-based binaural separation system is advantageous in several aspects. The AAD method determines the direction of attention from single-trial EEG signals without access to audio signals from the speakers. The model presented in this research can be considered as an important processing tool in the structure of neuro-steered hearing aid devices employed in cocktail party scenarios.

Noninvasive Measures of Distorted Tonotopic Speech Coding Following Noise-Induced Hearing Loss.

Animal models of noise-induced hearing loss (NIHL) show a dramatic mismatch between cochlear characteristic frequency (CF, based on place of innervation) and the dominant response frequency in single auditory-nerve-fiber responses to broadband sounds (i.e., distorted tonotopy, DT). This noise trauma effect is associated with decreased frequency-tuning-curve (FTC) tip-to-tail ratio, which results from decreased tip sensitivity and enhanced tail sensitivity. Notably, DT is more severe for noise trauma than for metabolic (e.g., age-related) losses of comparable degree, suggesting that individual differences in DT may contribute to speech intelligibility differences in patients with similar audiograms. Although DT has implications for many neural-coding theories for real-world sounds, it has primarily been explored in single-neuron studies that are not viable with humans. Thus, there are no noninvasive measures to detect DT. Here, frequency following responses (FFRs) to a conversational speech sentence were recorded in anesthetized male chinchillas with either normal hearing or NIHL. Tonotopic sources of FFR envelope and temporal fine structure (TFS) were evaluated in normal-hearing chinchillas. Results suggest that FFR envelope primarily reflects activity from high-frequency neurons, whereas FFR-TFS receives broad tonotopic contributions. Representation of low- and high-frequency speech power in FFRs was also assessed. FFRs in hearing-impaired animals were dominated by low-frequency stimulus power, consistent with oversensitivity of high-frequency neurons to low-frequency power. These results suggest that DT can be diagnosed noninvasively. A normalized DT metric computed from speech FFRs provides a potential diagnostic tool to test for DT in humans. A sensitive noninvasive DT metric could be used to evaluate perceptual consequences of DT and to optimize hearing-aid amplification strategies to improve tonotopic coding for hearing-impaired listeners.

The Effect of Background Noise on Immediate Free Recall of Words in Younger and Older Listeners with Hearing Loss.

Auditory working memory is a crucial factor for complex cognitive tasks such as speech-in-noise understanding because speech communication in noise engages multiple auditory and cognitive capacities to encode, store, and retrieve information. An immediate free recall task of words has been used frequently as a measure of auditory working memory capacity. The present study investigated performance on the immediate free recall of words in quiet and noisy conditions for hearing-impaired listeners. Fifty hearing-impaired listeners (30 younger and 20 older) participated in this study. Lists of 10 phonetically and lexically balanced words were presented with a fixed presentation rate in quiet and noise conditions. Target words were presented at an individually determined most comfortable level (MCL). Participants were required to recall as many of the words in an arbitrary order immediately after the end of the list. Serial position curves were determined from the accuracy of free recall as a function of the word position in the sequence. Three-way analyses of variance with repeated measures were conducted on the percent-correct word recall scores, with two independent within-group factors (serial position and listening condition) and a between-group factor (younger, older). A traditional serial position curve was found in hearing-impaired listeners, yet the serial position effects depended on the listening condition. In quiet, the listeners with hearing loss were likely to recall more words from the initial and final positions compared with the middle-position words. In multi-talker babble noise, more difficulties were observed when recalling the words in the initial position compared with the words in the final position. Without a noise, a traditional U-shaped serial position curve consisting of primacy and recency effects was observed from hearing-impaired listeners, in accord with previous findings from normal-hearing listeners. The adverse impact of background noise was more pronounced in the primacy effect than in the recency effect.

A binaural model implementing an internal noise to predict the effect of hearing impairment on speech intelligibility in non-stationary noises.

A binaural model predicting speech intelligibility in envelope-modulated noise for normal-hearing (NH) and hearing-impaired listeners is proposed. The study shows the importance of considering an internal noise with two components relying on the individual audiogram and the level of the external stimuli. The model was optimized and verified using speech reception thresholds previously measured in three experiments involving NH and hearing-impaired listeners and sharing common methods. The anechoic target, in front of the listener, was presented simultaneously through headphones with two anechoic noise-vocoded speech maskers (VSs) either co-located with the target or spatially separated using an infinite broadband interaural level difference without crosstalk between ears. In experiment 1, two stationary noise maskers were also tested. In experiment 2, the VSs were presented at different sensation levels to vary audibility. In experiment 3, the effects of realistic interaural time and level differences were also tested. The model was applied to two datasets involving NH listeners to verify its backward compatibility. It was optimized to predict the data, leading to a correlation and mean absolute error between data and predictions above 0.93 and below 1.1 dB, respectively. The different internal noise approaches proposed in the literature to describe hearing impairment are discussed.

Senescent Decline in Verbal-Emotion Identification by Older Hearing-Impaired Listeners - Do Hearing Aids Help?

PurposeTo assess the ability of older-adult hearing-impaired (OHI) listeners to identify verbal expressions of emotions, and to evaluate whether hearing-aid (HA) use improves identification performance in those listeners.MethodsTwenty-nine OHI listeners, who were experienced bilateral-HA users, participated in the study. They listened to a 20-sentence-long speech passage rendered with six different emotional expressions (“happiness”, “pleasant surprise”, “sadness”, “anger”, “fear”, and “neutral”). The task was to identify the emotion portrayed in each version of the passage. Listeners completed the task twice in random order, once unaided, and once wearing their own bilateral HAs. Seventeen young-adult normal-hearing (YNH) listeners were also tested unaided as controls.ResultsMost YNH listeners (89.2%) correctly identified emotions compared to just over half of the OHI listeners (58.7%). Within the OHI group, verbal emotion identification was significantly correlated with age, but not with audibility-related factors. The number of OHI listeners who were able to correctly identify the different emotions did not significantly change when HAs were worn (54.8%).ConclusionIn line with previous investigations using shorter speech stimuli, there were clear age differences in the recognition of verbal emotions, with OHI listeners showing a significant reduction in unaided verbal-emotion identification performance that progressively declined with age across older adulthood. Rehabilitation through HAs did not provide compensation for the impaired ability to perceive emotions carried by speech sounds.

Binaural Pitch Fusion: Binaural Pitch Averaging in Cochlear Implant Users With Broad Binaural Fusion.

Individuals who use hearing aids (HAs) or cochlear implants (CIs) can experience broad binaural pitch fusion, such that sounds differing in pitch by as much as 3 to 4 octaves are perceptually integrated across ears. Previously, it was shown in HA users that the fused pitch is a weighted average of the two monaural pitches, ranging from equal weighting to dominance by the lower pitch. The goal of this study was to systematically measure the fused pitches in adult CI users, and determine whether CI users experience similar pitch averaging effects as observed in HA users. Twelve adult CI users (Cochlear Ltd, Sydney, Australia) participated in this study: six bimodal CI users, who wear a CI with a contralateral HA, and six bilateral CI users. Stimuli to HA ears were acoustic pure tones, and stimuli to CI ears were biphasic pulse trains delivered to individual electrodes. Fusion ranges, the ranges of frequencies/electrodes in the comparison ear that were fused with a single electrode (electrode 22, 18, 12, or 6) in the reference ear, were measured using simultaneous, dichotic presentation of reference and comparison stimuli in opposite ears, and varying the comparison stimulus. Once the fusion ranges were measured, the fused binaural pitch of a reference-pair stimulus combination was measured by finding a pitch match to monaural comparison stimuli presented to the paired stimulus ear. Fusion pitch weighting in CI users varied depending on the pitch difference of the reference-pair stimulus combination, with equal pitch averaging occurring for stimuli closer in pitch and lower pitch dominance occurring for stimuli farther apart in pitch. The averaging region was typically 0.5 to 2.3 octaves around the reference for bimodal CI users and 0.4 to 1.5 octaves for bilateral CI users. In some cases, a bias in the averaging region was observed toward the ear with greater stimulus variability. Fusion pitch weighting effects in CI users were similar to those observed previously in HA users. However, CI users showed greater inter-subject variability in both pitch averaging ranges and bias effects. These findings suggest that binaural pitch averaging could be a common underlying mechanism in hearing-impaired listeners.

Uni- and bilateral spectral loudness summation and binaural loudness summation with loudness matching and categorical loudness scaling

Objective Current hearing aid prescription rules assume that spectral loudness summation decreases with hearing impairment and that binaural loudness summation is independent of hearing loss and signal bandwidth. Previous studies have shown that these assumptions might be incorrect. Spectral loudness summation was measured and compared for loudness scaling and loudness matching. Design In this study, the effect of bandwidth on binaural summation was investigated by comparing loudness perception of low-pass filtered, high-pass filtered, and broadband pink noise at 35 Categorical Units for both unilateral and bilateral presentation. Study sample Sixteen hearing-impaired listeners. Results The results show that loudness differences between the three signals are different for bilateral presentation than for unilateral presentation. In specific, binaural loudness summation is larger for the low-pass filtered pink noise than for the high-pass filtered pink noise. Finally, individual variability in loudness perception near loudness discomfort level was found to be very large. Conclusions Loudness matching is offered as a fast and reliable method to measure individual loudness perception. As discomfort with loud sounds is one of the major problems encountered by hearing aid users, measurement of individual loudness perception could improve hearing aid fitting substantially.

Temporal Auditory Coding Features for Causal Speech Enhancement

Perceptually motivated audio signal processing and feature extraction have played a key role in the determination of high-level semantic processes and the development of emerging systems and applications, such as mobile phone telecommunication and hearing aids. In the era of deep learning, speech enhancement methods based on neural networks have seen great success, mainly operating on the log-power spectra. Although these approaches surpass the need for exhaustive feature extraction and selection, it is still unclear whether they target the important sound characteristics related to speech perception. In this study, we propose a novel set of auditory-motivated features for single-channel speech enhancement by fusing temporal envelope and temporal fine structure information in the context of vocoder-like processing. A causal gated recurrent unit (GRU) neural network is employed to recover the low-frequency amplitude modulations of speech. Experimental results indicate that the exploited system achieves considerable gains for normal-hearing and hearing-impaired listeners, in terms of objective intelligibility and quality metrics. The proposed auditory-motivated feature set achieved better objective intelligibility results compared to the conventional log-magnitude spectrogram features, while mixed results were observed for simulated listeners with hearing loss. Finally, we demonstrate that the proposed analysis/synthesis framework provides satisfactory reconstruction accuracy of speech signals.

Impact of phase distortion and phase-insensitive speech enhancement on speech quality perceived by hearing-impaired listeners

Phase is important for speech since it contributes to the quality and intelligibility during speech perception. Many speech enhancement algorithms lack the ability to predict phase for speech reconstruction and apply the noisy phase instead. In this study, we investigated the influence of phase distortion on the speech-quality ratings of both normal-hearing (NH) and hearing-impaired (HI) listeners by applying different degrees of random phase on speech. In one set of conditions, the speech was embedded in babble noise at 4 different signal-to-noise ratios (SNRs) from -5 to 10 dB, while in another set of conditions, the SNR was fixed at 10 dB and the speech and noise mixture was presented in simulated rooms with reverberation times ranged from 100 to 1000 ms. The speech level was kept at 65 dB SPL for NH listeners; while amplification was applied to ensure the audibility for HI listeners. Ideal ratio mask (IRM) was used for speech enhancement. Speech-quality ratings were collected following the MUSHRA procedure and compared to two objective evaluation metrics (i.e., PESQ and HASQI). Results suggest that phase distortion has negative impact on speech quality for both NH and HI listeners and this effect becomes dominant when speech enhancement was applied.

Cross-frequency weights for loudness, pitch, and duration and their relation to speech recognition in normal-hearing and hearing-impaired listeners

Cross-frequency weights for loudness, pitch, and duration and their relation to speech recognition in normal-hearing and hearing-impaired listeners

Acoustic characteristics of conversational and clear speech produced in quiet and in noise by older adults with hearing loss

When communication occurs in noise or with hearing-impaired listeners, talkers often modify their speech. Speech produced in noise, or “Lombard speech,” and speech produced by talkers instructed to speak as though their communication partner has a hearing loss, or “clear speech,” usually feature a reduced speaking rate and a higher and more variable voice pitch than quiet and/or conversational-style speech. Both styles are also generally more intelligible than quiet/conversational speech. Although clear speech in particular is meant to accommodate the needs of listeners with hearing loss, most of the talkers in previous studies have been young adults with normal hearing. We hypothesize that talkers with hearing loss, having experience as listeners with hearing loss, would better know what listeners with hearing loss need than talkers with normal hearing, and that the magnitude of the acoustic differences would change accordingly. In the present study, talkers aged 65–85 years with bilateral mild-to-moderately severe sloping sensorineural hearing loss were recorded reading sentences in quiet and in the presence of white noise under instructions to speak conversationally and then clearly. Acoustic differences between the styles for these talkers will be compared to those observed previously in young normal-hearing adults using the same recording protocol.

Evaluating tests of binaural hearing for hearing impaired listeners using a portable device

Individuals with sensorineural hearing loss may have similar monaural thresholds (i.e., pure tone audiogram) but perform quite differently on tests of speech-in-noise. Additional testing using complex, binaural signals may be able to differentiate individuals with similar pure-tone hearing. Here, individuals with mild-to-moderate hearing losses were evaluated using tests of spectral, temporal, and spectrotemporal modulation, diotic and dichotic frequency modulation, gap detection, 2 kHz tone-in-noise, and spatial release from masking. Binaural psychoacoustic measurements were evaluated on an iPad using the Portable Automated Rapid Test (PART) app. Normal hearing listeners were evaluated as controls. Normal hearing results were similar to normative data previously collected by Lelo de Larrea-Mancera and colleagues (2020) and hearing-impaired results were elevated for most binaural measurements evaluated compared to normal hearing controls. Binaural psychoacoustic data were successfully measured for individuals with mild-to-moderate amounts of hearing loss using a portable system. Results show that evaluating complex stimuli on clinical populations using a portable device is feasible. Additionally, if accomplished on a larger scale the current test battery may likely add useful information on how hearing-impaired listeners process complex binaural stimuli and could compliment current clinical diagnostic test battery and, potentially, guide hearing aid fittings.

Effects of hearing aid processing on speech intelligibility in virtual restaurant settings

Hearing-impaired listeners struggle to understand speech in complex environments like restaurants. Environmental factors (signal-to-noise ratio and reverberation time) and hearing aid processing (digital noise reduction and wide dynamic range compression [WDRC]) have been shown to affect speech intelligibility in these contexts. We examine the independent and synergistic effects of these environmental factors and processing strategies on speech intelligibility. Virtual space techniques were used to build a virtual restaurant. The target talker was located directly in front of the listener and competing talkers were located to the listener’s right in various positions around the restaurant. Signal-to-noise ratio was varied randomly, centered on 0 dB with a standard deviation of 2 dB. Reverberation time was either 0.8 or 1.8 s. Hearing aid processing was simulated using custom software. WDRC was either fast or slow with the following attack/release times: 5/50 ms and 100/2000 ms. Digital noise reduction was either on or off. Customized gain and frequency shaping were applied to the signals. Listeners heard low-context sentences through insert earphones and repeated the target sentence. Responses were scored based on the number of correctly repeated keywords. Preliminary results show that the effect of WDRC depended on reverberation time. [Work supported by NIH.]