Subjective Speech Intelligibility Drives Noise-Tolerance Domain Use During the Tracking of Noise-Tolerance Test.

OBJECTIVES: Recently, the Noise-Tolerance Domains Test (NTDT) was applied to study the noise-tolerance domains used by young normal-hearing (NH) listeners during noise acceptance decisions. In this study, we examined how subjective speech intelligibility may drive noise acceptance decisions by applying the NTDT on NH and hearing-impaired (HI) listeners at the signal to noise ratios (SNRs) around the Tracking of Noise-Tolerance (TNT) thresholds. DESIGN: A single-blind, within-subjects design with 22 NH and 17 HI older adults was followed. Listeners completed the TNT to determine the average noise acceptance threshold (TNTAve). Then, listeners completed the NTDT at the SNRs of 0, ±3 dB (re: TNTAve) to estimate the weighted noise-tolerance domain ratings (WNTDRs) for each domain criterion. Listeners also completed the Objective and Subjective Intelligibility Difference (OSID) Test to establish the individual intelligibility performance-intensity (P-I) functions of the TNT materials. All test measures were conducted at 75 and 82 dB SPL speech input levels. NH and HI listeners were tested in the unaided mode. The HI listeners were also tested using a study hearing aid. The WNTDRs were plotted against subjective speech intelligibilities extrapolated from individual P-I of the OSID at the SNRs corresponding to NTDT test conditions. Listeners were grouped according to their most heavily weighed domain and a regression analysis was performed against listener demographics as well as TNT and OSID performances to determine which variable(s) affected listener grouping. RESULTS: Three linear mixed effects (LMEs) models were used to examine whether WNTDRs changed with subjective speech intelligibility. All three LMEs found significant fixed effects of domain criteria, subjective intelligibility, and speech input level on WNTDRs. In general, heavier weights were assigned to speech interference and loudness domains at poorer intelligibility levels (<50%) with reversals to distraction and annoyance at higher intelligibility levels (>80%). The comparison between NH and HI-unaided showed that NH listeners assigned greater weights to loudness than the HI-unaided listeners. The comparison between NH and HI-aided groups showed similar weights between groups. The comparison between HI-unaided and HI-aided found that HI listeners assigned lower weights to speech interference and greater weights to loudness when tested in aided compared with unaided modes. In all comparisons, loudness was weighed heavier at the 82 dB SPL input level than at the 75 dB SPL input level with greater weights to annoyance in the NH versus HI-unaided comparison and lower weights to distraction in the HI-aided versus HI-unaided comparison. A generalized linear model determined that listener grouping was best accounted for by subjective speech intelligibility estimated at TNTAve. CONCLUSIONS: The domain criteria used by listeners were driven by their subjective speech intelligibility regardless of their hearing status (i.e., NH versus HI). In general, when subjective intelligibility was poor, the domains of speech interference and loudness were weighed the heaviest. As subjective intelligibility improved, the weightings on annoyance and distraction increased. Furthermore, a listener's criterion for >90% subjective speech understanding at the TNTAve may allow one to profile the listener.

Cortical sensory gating and reactions to dynamic speech-in-noise in older normal-hearing and hearing-impaired adults.

OBJECTIVE: To examine whether cortical sensory gating predicts how older adults with and without hearing loss perform the Tracking of Noise Tolerance (TNT) test. DESIGN: Single-blind mixed design. TNT performance was defined by average tolerated noise relative to speech levels (TNTAve) and by an average range of noise levels over a two-minute trial (excursion). Sensory gating of P1-N1-P2 components was measured using pairs of 1 kHz tone pips. STUDY SAMPLE: Twenty-three normal-hearing (NH) and 16 hearing-impaired (HI) older adults with a moderate-to-severe degree of sensorineural hearing loss. RESULTS: NH listeners tolerated significantly more noise than HI listeners, but the two groups did not differ in their excursion. Both NH and HI listeners exhibited significant gating of P1 amplitudes and N1P2 peak-to-peak amplitudes with no difference in gating magnitudes between listener groups. Sensory gating magnitudes of P1 and N1P2 did not predict TNTAve scores, but N1P2 gating negatively predicted excursion after accounting for listener age and hearing thresholds. CONCLUSIONS: Listeners' reactivity to a roving noise (excursion), but not their average noise tolerance (TNTAve), was predicted by sensory gating at N1P2 generators. These results suggest that temporal aspects of speech-in-noise processing may be affected by declines in the central inhibition of older adults.

Left Lateralization of the Cortical Auditory-Evoked Potential Reflects Aided Processing and Speech-in-Noise Performance of Older Listeners With a Hearing Loss.

OBJECTIVES: We analyzed the lateralization of the cortical auditory-evoked potential recorded previously from aided hearing-impaired listeners as part of a study on noise-mitigating hearing aid technologies. Specifically, we asked whether the degree of leftward lateralization in the magnitudes and latencies of these components was reduced by noise and, conversely, enhanced/restored by hearing aid technology. We further explored if individual differences in lateralization could predict speech-in-noise abilities in listeners when tested in the aided mode. DESIGN: The study followed a double-blind within-subjects design. Nineteen older adults (8 females; mean age = 73.6 years, range = 56 to 86 years) with moderate to severe hearing loss participated. The cortical auditory-evoked potential was measured over 400 presentations of a synthetic /da/ stimulus which was delivered binaurally in a simulated aided mode using shielded ear-insert transducers. Sequences of the /da/ syllable were presented from the front at 75 dB SPL-C with continuous speech-shaped noise presented from the back at signal-to-noise ratios of 0, 5, and 10 dB. Four hearing aid conditions were tested: (1) omnidirectional microphone (OM) with noise reduction (NR) disabled, (2) OM with NR enabled, (3) directional microphone (DM) with NR disabled, and (4) DM with NR enabled. Lateralization of the P1 component and N1P2 complex was quantified across electrodes spanning the mid-coronal plane. Subsequently, listener speech-in-noise performance was assessed using the Repeat-Recall Test at the same signal-to-noise ratios and hearing aid conditions used to measure cortical activity. RESULTS: As expected, both the P1 component and the N1P2 complex were of greater magnitude in electrodes over the left compared to the right hemisphere. In addition, N1 and P2 peaks tended to occur earlier over the left hemisphere, although the effect was mediated by an interaction of signal-to-noise ratio and hearing aid technology. At a group level, degrees of lateralization for the P1 component and the N1P2 complex were enhanced in the DM relative to the OM mode. Moreover, linear mixed-effects models suggested that the degree of leftward lateralization in the N1P2 complex, but not the P1 component, accounted for a significant portion of variability in speech-in-noise performance that was not related to age, hearing loss, hearing aid processing, or signal-to-noise ratio. CONCLUSIONS: A robust leftward lateralization of cortical potentials was observed in older listeners when tested in the aided mode. Moreover, the degree of lateralization was enhanced by hearing aid technologies that improve the signal-to-noise ratio for speech. Accounting for the effects of signal-to-noise ratio, hearing aid technology, semantic context, and audiometric thresholds, individual differences in left-lateralized speech-evoked cortical activity were found to predict listeners' speech-in-noise abilities. Quantifying cortical auditory-evoked potential component lateralization may then be useful for profiling listeners' likelihood of communication success following clinical amplification.

Characteristics of the quick repeat-recall test (Q-RRT).

OBJECTIVE: To determine the reliability and validity of the Quick Repeat-Recall Test (Q-RRT). DESIGN: Within-subject repeated measures. Participants completed the Q-RRT at a speech level of 75 dB SPL in 2 noise configurations at signal-to-noise ratios of 5, 10, and 15 dB in a counterbalanced order, along with the full-RRT. The Q-RRT was repeated after 1-3 weeks to estimate within-session and between-session reliability. Participants also completed external validation measures relating speech-in-noise ability (Hearing-In-Noise Test, HINT), memory (Reading Span Test, RST; Forward Digit Span Test, DST-F), and noise acceptance (Tracking of Noise Tolerance, TNT). STUDY SAMPLE: Twenty-five normal-hearing listeners (mean age = 63.9 years). RESULTS: Group Repeat and Recall scores were similar between the full-RRT and the Q-RRT. However, Listening Effort and Tolerable Time ratings were significantly poorer for the full-RRT than the Q-RRT. The average repeat scores correlated with the HINT scores, while the recall scores correlated with the DST-F and RST scores. Tolerable Time ratings also correlated with the TNT scores. Within-session and between-session test-retest reliability using intraclass correlation coefficients were fair-to-excellent (0.41-0.91) depending on the outcome measures. CONCLUSIONS: The Q-RRT is a reliable and valid measure of speech-in-noise ability, working memory, listening effort, and noise acceptance.

Performance of older normal-hearing listeners on the tracking of noise tolerance (TNT) test.

OBJECTIVE: To gather preliminary reference data on older normal-hearing (NH) adults for the refined Tracking of Noise Tolerance (TNT) test. DESIGN: Within-subject repeated measures. Participants were tested on the TNT in the sound-field and under headphones. In the sound-field, speech stimuli were presented at 75 dB SPL and 82 dB SPL from 0° with a speech-shaped noise presented either from 0° or 180° at a level controlled by the participants. The order of signal level, mode of presentation, noise azimuth, and TNT passages were counterbalanced across listeners. Testing was repeated for one condition after 1-3 weeks to estimate within-session and between-session reliability. STUDY SAMPLE: Twenty-five NH listeners (51-82 yrs of age). RESULTS: Mean TNT scores (TNTAve) were about 4 dB at a speech input of 75 dB SPL and 3 dB at 82 dB SPL. The TNTAve was similar between the headphone and sound-field presentations in the co-located noise. TNTAve scores measured with noise-back were about 1 dB better than those measured from the front. The 95% confidence intervals of absolute test-retest differences were about 1.2 dB within-session and 2.0 dB between sessions. CONCLUSIONS: The refined TNT may be a reliable tool to measure noise acceptance and subjective speech intelligibility.

Measuring the effect of adaptive directionality and split processing on noise acceptance at multiple input levels.

OBJECTIVE: This study used the multi-level Tracking of Noise Tolerance (TNT) test to compare Augmented Focus (AF) or split processing over non-AF processing with adaptive directionality (non-AF-dirm) and with an omnidirectional microphone (non-AF-omni). DESIGN: This was a single-blind, within-subject repeated measures design. STUDY SAMPLE: Nineteen listeners with a mild-to-moderate hearing loss. The listeners' task was to determine their tolerable noise level (TNL) in the sound-field at four fixed speech levels (i.e. 62, 68, 75, and 85 dB SPL) in the unaided condition and the different aided conditions. The speech passages were presented from 0° while a continuous speech-shaped noise was presented from 180°. Each condition was tested twice, each in a different counterbalanced order. RESULTS: AF improved TNL by an average of 2.9 dB over non-AF-dirm. Adaptive directionality improved the aided TNL by 4.7 dB over the non-AF-omni condition. The unaided TNL was similar to the aided non-AF-omni TNL. Whereas a stable TNL was reached in 20-30 s for non-AF-dirm, it took AF < 15 s to reach a stable TNL at all input levels. CONCLUSIONS: This study shows that AF allowed 2.9 dB of signal-to-noise ratio (SNR) improvement over that of non-AF-dirm and 7.6 dB over the aided non-AF-omni condition.

Performance of normal-hearing listeners on the Repeat-Recall test in different noise configurations.

OBJECTIVE: This study measured the performance of normal-hearing listeners on the Repeat-Recall Test (RRT) in two noise types (2-talker babble [2TBN] and continuous speech-shaped noise [SSN]) by two noise azimuths (0° and 180°) configurations at signal-to-noise ratios (SNRs) of 0, 5, 10, and 15 dB and quiet. DESIGN: Within-subject repeated measures. STUDY SAMPLE: Twenty-one listeners with normal hearing who also passed cognitive screening were tested in the sound-field with the speech stimulus presented from 0° at 75 dB SPL in 4 noise configurations. The order of SNRs, noise configurations, and RRT topic conditions was counterbalanced across listeners. RESULTS: Analysis revealed that repeat scores were significantly better for 2TBN, for noise at 180°, and for high context (HC) sentences. Recall performance was significantly better for SSN and HC sentences. Listening effort ratings were higher for SSN and for noise front condition at SNR ≤ 10 dB. The 2TBN noise was tolerated longer than SSN. Performance on all measures improved with SNRs. CONCLUSIONS: These data showed performance differences among noise configurations and provided a preliminary basis for comparison with hearing-impaired listeners' performance on the RRT.

Effects of Directional Microphone and Noise Reduction on Subcortical and Cortical Auditory-Evoked Potentials in Older Listeners With Hearing Loss.

OBJECTIVES: Understanding how signal processing influences neural activity in the brain with hearing loss is relevant to the design and evaluation of features intended to alleviate speech-in-noise deficits faced by many hearing aid wearers. Here, we examine whether hearing aid processing schemes that are designed to improve speech-in-noise intelligibility (i.e., directional microphone and noise reduction) also improve electrophysiological indices of speech processing in older listeners with hearing loss. DESIGN: The study followed a double-blind within-subjects design. A sample of 19 older adults (8 females; mean age = 73.6 years, range = 56-86 years; 17 experienced hearing aid users) with a moderate to severe sensorineural hearing impairment participated in the experiment. Auditory-evoked potentials associated with processing in cortex (P1-N1-P2) and subcortex (frequency-following response) were measured over the course of two 2-hour visits. Listeners were presented with sequences of the consonant-vowel syllable /da/ in continuous speech-shaped noise at signal to noise ratios (SNRs) of 0, +5, and +10 dB. Speech and noise stimuli were pre-recorded using a Knowles Electronics Manikin for Acoustic Research (KEMAR) head and torso simulator outfitted with hearing aids programmed for each listener's loss. The study aid programs were set according to 4 conditions: (1) omnidirectional microphone, (2) omnidirectional microphone with noise reduction, (3) directional microphone, and (4) directional microphone with noise reduction. For each hearing aid condition, speech was presented from a loudspeaker located at 1 m directly in front of KEMAR (i.e., 0° in the azimuth) at 75 dB SPL and noise was presented from a matching loudspeaker located at 1 m directly behind KEMAR (i.e., 180° in the azimuth). Recorded stimulus sequences were normalized for speech level across conditions and presented to listeners over electromagnetically shielded ER-2 ear-insert transducers. Presentation levels were calibrated to match the output of listeners' study aids. RESULTS: Cortical components from listeners with hearing loss were enhanced with improving SNR and with use of a directional microphone and noise reduction. On the other hand, subcortical components did not show sensitivity to SNR or microphone mode but did show enhanced encoding of temporal fine structure of speech for conditions where noise reduction was enabled. CONCLUSIONS: These results suggest that auditory-evoked potentials may be useful in evaluating the benefit of different noise-mitigating hearing aid features.

Cortical indices of sound localization mature monotonically in early infancy.

In human neonates, orienting behavior in response to an off-midline sound source disappears around the first postnatal month, only to re-emerge at ~4 months. To date, it is unclear whether sound localization processes continue to operate between postnatal months 1 and 3. Here, we used an event-related potential, reflecting change detection in the auditory cortices, to measure the cortical responses elicited by large (± 90° relative to midline), infrequent changes in sound source location in 2-, 5-, 8- and 13-month-old infants. Both fast-negative mismatch negativity (MMN) Näätänen et al. (2007) and slow-positive mismatch response (MMR) Trainor et al. (2003) were elicited from all age groups. However, both components were smaller and the fast-negative component occurred later in the 2-month-old group than in older age groups. Additionally, the slow-positive component tended to diminish in amplitude with increasing age, whereas the fast-negative component grew larger and tended to occur earlier with increasing age. These results suggest that the cortical representation of sound location matures similarly to representations of pitch and duration. A subsequent investigation of 2-month-old infants confirmed that the observed MMR and MMN were elicited by changes in sound source location, and were not merely attributable to changes in loudness cues. The presence of both MMR and MMN in the 2-month-old group indicates that the cortex is able to detect changes in sound location despite the behavioral insensitivity observed around 1-3 months of age.

Alpha-Band Dynamics of Hearing Aid Wearers Performing the Repeat-Recall Test (RRT).

This study measured electroencephalographic activity in the alpha band, often associated with task difficulty, to physiologically validate self-reported effort ratings from older hearing-impaired listeners performing the Repeat-Recall Test (RRT)-an integrative multipart assessment of speech-in-noise performance, context use, and auditory working memory. Following a single-blind within-subjects design, 16 older listeners (mean age = 71 years, SD = 13, 9 female) with a moderate-to-severe degree of bilateral sensorineural hearing loss performed the RRT while wearing hearing aids at four fixed signal-to-noise ratios (SNRs) of -5, 0, 5, and 10 dB. Performance and subjective ratings of listening effort were assessed for complementary versions of the RRT materials with high/low availability of semantic context. Listeners were also tested with a version of the RRT that omitted the memory (i.e., recall) component. As expected, results showed alpha power to decrease significantly with increasing SNR from 0 through 10 dB. When tested with high context sentences, alpha was significantly higher in conditions where listeners had to recall the sentence materials compared to conditions where the recall requirement was omitted. When tested with low context sentences, alpha power was relatively high irrespective of the memory component. Within-subjects, alpha power was related to listening effort ratings collected across the different RRT conditions. Overall, these results suggest that the multipart demands of the RRT modulate both neural and behavioral measures of listening effort in directions consistent with the expected/designed difficulty of the RRT conditions.

Using Alpha-Band Power to Evaluate Hearing Aid Directionality Based on Multistream Architecture.

PURPOSE: The aim of the study was to evaluate whether behavioral speech-in-noise (SiN) benefits of hearing aid directivity based on multistream architecture (MSA) might result in reduced electroencephalographic activity in the alpha-band, as is often associated with task difficulty. METHOD: A single-blind within-subject design was used in this study. Thirteen older adults (Mage = 73.5 years, range: 62-82 years, six women) with sensorineural hearing loss participated in the study. Participants wearing study hearing aids first performed an adaptive sentence-level SiN test in an MSA-enabled condition (i.e., MSA-ON) to determine the signal-to-noise ratios (SNRs) corresponding to speech reception thresholds for 50% correct performance (i.e., SRT-50s). Participants were then tested at their individualized SNRs with target sentences alternating on each trial between two loudspeakers positioned in the front at 0° and -30° azimuth, such as to simulate turn-taking between two talkers seated across from the listener. Electroencephalographic activity was recorded as participants performed this SiN test in two hearing aid conditions: MSA-OFF and MSA-ON. RESULTS: Neural oscillations in the alpha-band were significantly reduced over centroparietal electrode sites when listeners performed SiN testing in MSA-ON versus MSA-OFF conditions. Alpha-band power was also observed to increase significantly over the course of 60 test trials, possibly indicative of listener fatigue. Reductions in alpha-band power were not significantly related to likewise improvements in SiN performance. CONCLUSIONS: Hearing aid directivity based on the MSA algorithm resulted in significantly lower neural activity associated with listening task difficulty in a simulated multitalker situation. Although these results align with the behavioral SiN improvements associated with MSA, magnitudes of change in alpha-band power did not correlate with the degree of behavioral benefit at the level of individual listeners. Measuring neural oscillations in the alpha-band might be useful for evaluating and gaining greater insight into the impact of hearing aid processing on listening effort in challenging acoustic environments.

Impact of Hearing Aid Processing Delay on Stop Consonant Voicing Perception in Open Fittings.

PURPOSE: Hearing aid (HA) processing delay results in asynchronous overlap of the input sound and the delayed amplified sound at the eardrum in open-ear fittings. This may distort the temporal cues used for stop-consonant voicing distinctions. The current study evaluated the impact of HA processing delay on voiced-voiceless categorization of syllable initial consonants /d/ and /t/ for a range of voice onset times (VOTs). METHOD: Nineteen older listeners (Mage = 73 years) with mild-moderate sensorineural hearing loss participated. All listeners performed the voiced-voiceless categorization task in double-blind within-subjects design. Thirteen stimulus tokens along the /di:/ - /ti:/ continuum were created by varying VOTs. Stimuli were then processed using an HA simulator, which simulated the overall sound pressure levels measured at the eardrum in open-ear fittings with four processing delay times (0, 0.5, 5, and 8 ms). Individualized stimuli were generated for each listener based on their audiogram and presented via calibrated ear inserts at the most comfortable listening level. Performance across all VOT intervals was fitted with psychometric functions, which were then used to estimate the voiced-voiceless crossover point and the slope parameter for each simulated delay condition. RESULTS: The crossover point along the voiced-voiceless continuum shifted systematically with increased processing delay toward voiced /di:/ over unvoiced /ti:/ percepts. The shift in the crossover point between the 0-ms reference condition and the 8-ms processing delay condition corresponded to 5.8 ms of change in VOT. The 8-ms processing delay condition resulted in significantly shallower categorization slopes compared to the 0- and 0.5-ms delay conditions. CONCLUSIONS: Temporal distortions created by HA processing delay in open-ear fittings impacted voicing perception of syllable initial stop-consonant stimuli near the voiced-voiceless crossover point. Short HA processing delay should be considered for open-ear fittings to preserve the natural VOT cues used for voicing detection.

Measuring objective and subjective intelligibility using speech materials from the Tracking of Noise Tolerance (TNT) test.

BACKGROUND: The results of tests measuring objective speech intelligibility are similar to those measuring subjective speech intelligibility using speech materials with minimal context. It is unclear if such is the case with contextual materials. PURPOSE: To compare objective and subjective intelligibility difference (OSID) between normal-hearing (NH) and hearing-impaired (HI) listeners in the unaided and aided modes using speech materials adapted from the Tracking of Noise Tolerance (TNT) test. RESEARCH DESIGN: Single-blind within-subjects design. STUDY SAMPLE: Twenty-four NH and 17 HI older adults. DATA COLLECTION AND ANALYSIS: Listeners completed the objective and subjective intelligibility measures at 75 dB SPL and 82 dB SPL speech input levels. Five signal-to-noise ratios (SNR) were tested to generate the objective and subjective speech intelligibility performance-intensity (P-I) functions. Both NH and HI listeners were tested in the unaided mode. The HI listeners were also tested using their own hearing aids (HAs). Objective and subjective speech-reception thresholds at a 50% criterion (SRT50s) were estimated from each individual P-I function. The difference between the objective SRT50 and subjective SRT50 was used to estimate OSID. RESULTS: Objective and subjective SRT50s were significantly better in NH than in HI listeners (χ2(1) = 26.29, p < 0.001) at each speech input level in the unaided mode. However, there was a significant interaction between listener group and intelligibility type (χ2(1) = 9.43, p = 0.002) where SRT50s were lower for subjective than objective P-I functions only in the HI group. The SRT50s of HI listeners were also affected by hearing mode, where both objective and subjective intelligibility was improved when HI listeners were tested while wearing their own HAs. In general, objective and subjective SRT50s showed moderate-to-strong correlations across most combinations of listener groups and test conditions (r = 0.59-0.86, p < 0.01) except for HI listeners tested with their own HAs (r = 0.39, p = 0.128). CONCLUSIONS: Similar objective and subjective intelligibility was observed in NH listeners but better subjective intelligibility than objective intelligibility was noted in HI listeners when tested in the unaided and aided modes.

Use of Emotional and Neutral Speech in Evaluating Compression Speeds.

BACKGROUND: Emotional speech differs from neutral speech in its envelope characteristics. Use of emotional speech materials may be more sensitive for evaluating signal processing algorithms that affect the temporal envelope. PURPOSE: Subjective listener preference was compared between variable speed compression (VSC) and fast acting compression (FAC) amplitude compression algorithms using neutral and emotional speech. RESEARCH DESIGN: The study used a single-blinded, repeated measures design. STUDY SAMPLE: Twenty hearing-impaired (HI) listeners with a bilaterally symmetrical, mild- to-moderately severe sensorineural hearing loss and 21 listeners with normal hearing (NH) participated. INTERVENTION: Speech was processed using FAC and VSC algorithms. DATA COLLECTION AND ANALYSIS: A paired-comparison paradigm assessed subjective preference for FAC versus VSC using emotional and neutral speech materials. The significance of subjective preference for compression algorithm (FAC or VSC) was evaluated using a linear mixed effects model at each combination of stimulus type (emotional or neutral speech) and hearing group (NH or HI). RESULTS: HI listeners showed a preference for VSC over FAC when listening to emotional speech. The same listeners showed a nonsignificant, preference for VSC over FAC when listening to neutral speech. NH listeners showed preference for VSC over FAC for both neutral and emotional speech materials. CONCLUSION: These results suggest that the subjective sound quality of emotional speech is more susceptible than neutral speech to changes in the signal introduced by FAC. Clinicians should consider including emotional speech materials when evaluating listener preference for different compression speeds in the clinic.

An Integrative Evaluation of the Efficacy of a Directional Microphone and Noise-Reduction Algorithm under Realistic Signal-to-Noise Ratios.

BACKGROUND: Many studies on the efficacy of directional microphones (DIRMs) and noise-reduction (NR) algorithms were not conducted under realistic signal-to-noise ratio (SNR) conditions. A Repeat-Recall Test (RRT) was developed previously to partially address this issue. PURPOSE: This study evaluated whether the RRT could provide a more comprehensive understanding of the efficacy of a DIRM and NR algorithm under realistic SNRs. Possible interaction with listener working memory capacity (WMC) was assessed. RESEARCH DESIGN: This study uses a double-blind, within-subject repeated measures design. STUDY SAMPLE: Nineteen listeners with a moderate degree of hearing loss participated. DATA COLLECTION AND ANALYSIS: The RRT was administered with participants wearing the study hearing aids (HAs) under two microphones (omnidirectional versus directional) by two NR (on versus off) conditions. Speech was presented from 0° at 75 dB SPL and a continuous noise from 180° at SNRs of 0, 5, 10, and 15 dB. The order of SNR and HA conditions was counterbalanced across listeners. Each test condition was completed twice in two 2-hour sessions separated by one month. RESULTS: The recall scores of listeners were used to group listeners into good and poor WMC groups. Analysis using linear mixed-effects models revealed significant effects of context, SNR, and microphone for all four measures (repeat, recall, listening effort, and tolerable time). NR was only significant on the listening effort scale in the DIRM mode at an SNR of 5 dB. Listeners with good WMC performed better on all measures of the RRT and benefitted more from context. Although DIRM benefitted listeners with good and poor WMC, the benefits differed by context and SNR. CONCLUSIONS: The RRT confirmed the efficacy of DIRM and NR on several outcome measures under realistic SNRs. It also highlighted interactions between WMC and sentence context on feature efficacy.

Using the Repeat-Recall Test to Examine Factors Affecting Context Use.

BACKGROUND: The effect of context on speech processing has been studied using different speech materials and response criteria. The Repeat-Recall Test (RRT) evaluates listener performance using high context (HC) and low context (LC) sentences; this may offer another platform for studying context use (CU). OBJECTIVE: This article aims to evaluate if the RRT may be used to study how different signal-to-noise ratios (SNRs), hearing aid technologies (directional microphone and noise reduction), and listener working memory capacities (WMCs) interact to affect CU on the different measures of the RRT. DESIGN: Double-blind, within-subject repeated measures design. STUDY SAMPLE: Nineteen listeners with a mild-to-moderately severe hearing loss. DATA COLLECTION: The RRT was administered with participants wearing the study hearing aids under two microphone (omnidirectional vs. directional) by two noise reduction (on vs. off) conditions. Speech was presented from 0 degree at 75 dB sound pressure level and a continuous speech-shaped noise from 180 degrees at SNRs of 0, 5, 10, and 15 dB. The order of SNR and hearing aid conditions was counterbalanced across listeners. Each test condition was completed twice in two 2-hour sessions separated by 1 month. RESULTS: CU was calculated as the difference between HC and LC sentence scores for each outcome measure (i.e., repeat, recall, listening effort, and tolerable time). For all outcome measures, repeated measures analyses of variance revealed that CU was significantly affected by the SNR of the test conditions. For repeat, recall, and listening effort measures, these effects were qualified by significant two-way interactions between SNR and microphone mode. In addition, the WMC group significantly affected CU during recall and rating of listening effort, the latter of which was qualified by an interaction between the WMC group and SNR. Listener WMC affected CU on estimates of tolerable time as qualified by significant two-way interactions between SNR and microphone mode. CONCLUSION: The study supports use of the RRT as a tool for measuring how listeners use sentence context to aid in speech processing. The degree to which context influenced scores on each outcome measure of the RRT was found to depend on complex interactions between the SNR of the listening environment, hearing aid features, and the WMC of the listeners.

Tracking of Noise Tolerance to Predict Hearing Aid Satisfaction in Loud Noisy Environments.

BACKGROUND: A method that tracked tolerable noise level (TNL) over time while maintaining subjective speech intelligibility was reported previously. Although this method was reliable and efficacious as a research tool, its clinical efficacy and predictive ability of real-life hearing aid satisfaction were not measured. PURPOSE: The study evaluated an adaptive method to estimate TNL using slope and variance of tracked noise level as criteria in a clinical setting. The relationship between TNL and subjective hearing aid satisfaction in noisy environments was also investigated. RESEARCH DESIGN: A single-blinded, repeated-measures design. STUDY SAMPLE: Seventeen experienced hearing aid wearers with bilateral mild-to-moderately-severe sensorineural hearing loss. DATA COLLECTION AND ANALYSIS: Participants listened to 82-dB SPL continuous speech and tracked the background noise level that they could "put up with" while subjectively understanding >90% of the speech material. Two trials with each babble noise and continuous speech-shaped noise were measured in a single session. All four trials were completed aided using the participants' own hearing aids. The stimuli were presented in the sound field with speech from 0° and noise from the 180° azimuth. The instantaneous tolerable noise level was measured using a custom program and scored in two ways; the averaged TNL (aTNL) over the 2-min trial and the estimated TNL (eTNL) as soon as the listeners reached a stable noise estimate. Correlation between TNL and proportion of satisfied noisy environments was examined using the MarkeTrak questionnaire. RESULTS: All listeners completed the tracking of noise tolerance procedure within 2 min with good reliability. Sixty-five percent of the listeners yielded a stable noise estimate after 59.9 sec of actual test time. The eTNL for all trials was 78.6 dB SPL (standard deviation [SD] = 4.4 dB). The aTNL for all trials was 78.0 dB SPL (SD = 3.3 dB) after 120 sec. The aTNL was 79.2 dB SPL (SD = 5.4 dB) for babble noise and 77.0 dB SPL (SD = 5.9 dB) for speech-shaped noise. High within-session test-retest reliability was evident. The 95% confidence interval was 1.5 dB for babble noise and 2.8 dB for continuous speech-shaped noise. No significant correlation was measured between overall hearing aid satisfaction and the aTNL (ρ = 0.20 for both noises); however, a significant relationship between aTNL and proportion of satisfied noisy situations was evident (ρ = 0.48 for babble noise and ρ = 0.55 for speech-shaped noise). CONCLUSION: The eTNL scoring method yielded similar results as the aTNL method although requiring only half the time for 65% of the listeners. This time efficiency, along with its reliability and the potential relationship between TNL and hearing aid satisfaction in noisy listening situations suggests that this procedure may be a good clinical tool to evaluate whether specific features on a hearing aid would improve noise tolerance and predict wearer satisfaction with the selected hearing aid in real-life loud noisy situations. A larger sample of hearing aid wearers is needed to further validate these potential uses.

Simultaneously-evoked auditory potentials (SEAP): A new method for concurrent measurement of cortical and subcortical auditory-evoked activity.

Recent electrophysiological work has evinced a capacity for plasticity in subcortical auditory nuclei in human listeners. Similar plastic effects have been measured in cortically-generated auditory potentials but it is unclear how the two interact. Here we present Simultaneously-Evoked Auditory Potentials (SEAP), a method designed to concurrently elicit electrophysiological brain potentials from inferior colliculus, thalamus, and primary and secondary auditory cortices. Twenty-six normal-hearing adult subjects (mean 19.26 years, 9 male) were exposed to 2400 monaural (right-ear) presentations of a specially-designed stimulus which consisted of a pure-tone carrier (500 or 600 Hz) that had been amplitude-modulated at the sum of 37 and 81 Hz (depth 100%). Presentation followed an oddball paradigm wherein the pure-tone carrier was set to 500 Hz for 85% of presentations and pseudo-randomly changed to 600 Hz for the remaining 15% of presentations. Single-channel electroencephalographic data were recorded from each subject using a vertical montage referenced to the right earlobe. We show that SEAP elicits a 500 Hz frequency-following response (FFR; generated in inferior colliculus), 80 (subcortical) and 40 (primary auditory cortex) Hz auditory steady-state responses (ASSRs), mismatch negativity (MMN) and P3a (when there is an occasional change in carrier frequency; secondary auditory cortex) in addition to the obligatory N1-P2 complex (secondary auditory cortex). Analyses showed that subcortical and cortical processes are linked as (i) the latency of the FFR predicts the phase delay of the 40 Hz steady-state response, (ii) the phase delays of the 40 and 80 Hz steady-state responses are correlated, and (iii) the fidelity of the FFR predicts the latency of the N1 component. The SEAP method offers a new approach for measuring the dynamic encoding of acoustic features at multiple levels of the auditory pathway. As such, SEAP is a promising tool with which to study how relationships between subcortical and cortical processes change through early development and auditory learning as well as by hearing loss and aging.