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Extended-wear hearing aids (EWHAs) are small broadband analog amplification devices placed deeply enough in the ear canal to preserve most of the cues in the head-related transfer function. However, little is known about how EWHAs affect localization accuracy for normal hearing threshold (NHT) listeners. In this study, eight NHT participants were fitted with EWHAs and localized broadband sounds of different durations (250 ms and 4 s) and stimulus intensities (40, 50, 60, 70, and 80 dBA) in a spherical speaker array. When the EWHAs were in the active mode, localization accuracy was only slightly degraded relative to open-ear performance. However, when the EWHAs were turned off, localization performance was substantially degraded even at the highest stimulus intensities. An electro-acoustical evaluation of the EWHAs showed minimal effects of dynamic range compression on the signals and good preservation of the signal pattern for vertical polar sound localization. Between-study comparisons suggest that EWHA active mode localization accuracy is favorable compared to conventional active earplugs, and EWHA passive mode localization accuracy is comparable to conventional passive earplugs. These results suggest that the deep-insertion analog design of the EWHA is generally better at preserving localization accuracy of NHT listeners than conventional earplug devices.

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The extended-wear hearing aid (EWHA) is a hearing assistive device that combines a low-power analog amplification circuit with a soft biocompatible foam plug that allows it to remain in the ear canal for several months at a time without replacement. EWHAs fit snugly in the ear canal and are not vented and so produce insertion losses comparable to a passive earplug when inserted into the ear canal with the active circuitry turned off. However, EWHAs are not marketed as hearing protection devices, and other than a general warning to users that the device will have impaired auditory awareness when the device is inserted in the "off" mode, relatively little has been reported about the attenuation characteristics of EWHAs. In this study, commercially-available EWHAs were evaluated using the ANSI standard procedures for measuring hearing protector attenuation in impulse noise [ANSI (2010). S1242-2010, Methods for the Measurement of Insertion Loss of Hearing Protective Devices in Continuous or Impulsive Noise Using Microphone-In-Real-Ear or Acoustic Text Fixture Procedures (American National Standards Institute, New York)] and in continuous noise [ANSI (2006). S12.6, Methods for Measuring the Real-Ear Attenuation of Hearing Protectors (American National Standards Institute, New York)]. Attenuation values were also measured in double and triple protection conditions that combined EWHAs with traditional earplugs and earmuffs. The results show that properly-fit EWHAs can provide passive attenuation comparable to conventional passive earplugs, which may make it possible to use them to provide persistent protection from intermittent noise sources.

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Auditory detection can improve with practice. These improvements are often assumed to arise from selective attention processes, but longer-term plasticity as a result of training may also play a role. Here, listeners were trained to detect either an 861-Hz or 1058-Hz tone (counterbalanced across participants) presented in noise at SNRs varying from -10 to -24 dB. On the following day, they were tasked with detecting 861-Hz and 1058-Hz tones at an SNR of -21 dB. In between blocks of this active task, EEG was recorded during passive presentation of trained and untrained frequency tones in quiet. Detection accuracy and confidence ratings were higher for trials at listeners' trained, than untrained-frequency (i.e., learning occurred). During passive exposure to sounds, the P2 component of the auditory evoked potential (∼150 - 200 ms post tone onset) was larger in amplitude for the trained compared to the untrained frequency. An analysis of global field power similarly yielded a stronger response for trained tones in the P2 time window. These effects were obtained during passive exposure, suggesting that training induced improvements in detection are not solely related to changes in selective attention. Rather, there may be an important role for changes in the long-term neural representations of sounds.

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Recent studies show that pre-stimulus band-specific power and phase in the electroencephalogram (EEG) can predict accuracy on tasks involving the detection of near-threshold stimuli. However, results in the auditory modality have been mixed, and few works have examined pre-stimulus features when more complex decisions are made (e.g. identifying supra-threshold sounds). Further, most auditory studies have used background sounds known to induce oscillatory EEG states, leaving it unclear whether phase predicts accuracy without such background sounds. To address this gap in knowledge, the present study examined pre-stimulus EEG as it relates to accuracy in a tone pattern identification task. On each trial, participants heard a triad of 40-ms sinusoidal tones (separated by 40-ms intervals), one of which was at a different frequency than the other two. Participants' task was to indicate the tone pattern (low-low-high, low-high-low, etc.). No background sounds were employed. Using a phase opposition measure based on inter-trial phase consistencies, pre-stimulus 7-10 Hz phase was found to differ between correct and incorrect trials ∼200 to 100 ms prior to tone-pattern onset. After sorting trials into bins based on phase, accuracy was found to be lowest at around π-+ relative to individuals' most accurate phase bin. No significant effects were found for pre-stimulus power. In the context of the literature, findings suggest an important relationship between the complexity of task demands and pre-stimulus activity within the auditory domain. Results also raise interesting questions about the role of induced oscillatory states or rhythmic processing modes in obtaining pre-stimulus effects of phase in auditory tasks.

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Recent research has focused on measuring neural correlates of metacognitive judgments in decision and post-decision processes during memory retrieval and categorization. However, many tasks (e.g., stimulus detection) may require monitoring of earlier sensory processing. Here, participants indicated which of two intervals contained an 80-ms pure tone embedded in white noise. One frequency (e.g., 1000 Hz) was presented on ∼80% of all trials (i.e., 'primary' trials). Another frequency (e.g., 2500 Hz) was presented on ∼20% of trials (i.e., 'probe' trials). The event-related potential (ERP) was used to investigate the processing stages related to confidence. Tone-locked N1, P2, and P3 amplitudes were larger for trials rated with high than low confidence. Interestingly, a P3-like late positivity for the tone-absent interval showed high amplitude for low confidence. No 'primary' vs. 'probe' differences were found. However, confidence rating differences between primary and probe trials were correlated with N1 and tone-present P3 amplitude differences. We suggest that metacognitive judgments can track both sensory- and decision-related processes (indexed by the N1 and P3, respectively). The particular processes on which confidence judgments are based likely depend upon the task an individual is faced with and the information at hand (e.g., presence or absence of a signal).

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Recent studies demonstrate that frontal midline theta power (4-8 Hz) enhancements in the electroencephalogram (EEG) relate to effortful listening. It has been proposed that these enhancements reflect working memory demands. Here, the need to retain auditory information in working memory was manipulated in a 2-interval 2-alternative forced-choice delayed pitch discrimination task ("Which interval contained the higher pitch?"). On each trial, two square wave stimuli differing in pitch at an individual's ∼70.7% correct threshold were separated by a 3-second ISI. In a 'Roving' condition, the lowest pitch stimulus was randomly selected on each trial (uniform distribution from 840 to 1160 Hz). In a 'Fixed' condition, the lowest pitch was always 979 Hz. Critically, the 'Fixed' condition allowed one to know the correct response immediately following the first stimulus (e.g., if the first stimulus is 979 Hz, the second must be higher). In contrast, the 'Roving' condition required retention of the first tone for comparison to the second. Frontal midline theta enhancements during the ISI were only observed for the 'Roving' condition. Alpha (8-13 Hz) enhancements were apparent during the ISI, but did not differ significantly between conditions. Since conditions were matched for accuracy at threshold, results suggest that frontal midline theta enhancements will not always accompany difficult listening. Mixed results in the literature regarding frontal midline theta enhancements may be related to differences between tasks in regards to working memory demands. Alpha enhancements may reflect task general effortful listening processes.

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Recent studies have related enhancements of theta- (∼4-8 Hz) and alpha-power (∼8-13 Hz) to listening effort based on parallels between enhancement and task difficulty. In contrast, nonauditory works demonstrate that, although increases in difficulty are initially accompanied by increases in effort, effort decreases when a task becomes so difficult as to exceed one's ability. Given the latter, we examined whether theta- and alpha-power enhancements thought to reflect effortful listening show a quadratic trend across levels of listening difficulty from impossible to easy. Listeners (n = 14) performed an auditory delayed match-to-sample task with frequency-modulated tonal sweeps under impossible, difficult (at ∼70.7% correct threshold), and easy (well above threshold) conditions. Frontal midline theta-power and posterior alpha-power enhancements were observed during the retention interval, with greatest enhancement in the difficult condition. Independent component-based analyses of data suggest that theta-power enhancements stemmed from medial frontal sources at or near the anterior cingulate cortex, whereas alpha-power effects stemmed from occipital cortices. Results support the notion that theta- and alpha-power enhancements reflect effortful cognitive processes during listening, related to auditory working memory and the inhibition of task-irrelevant cortical processing regions, respectively. Theta- and alpha-power dynamics can be used to characterize the cognitive processes that make up effortful listening, including qualitatively different types of listening effort.

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An important application of cognitive architectures is to provide human performance models that capture psychological mechanisms in a form that can be "programmed" to predict task performance of human-machine system designs. Although many aspects of human performance have been successfully modeled in this approach, accounting for multitalker speech task performance is a novel problem. This article presents a model for performance in a two-talker task that incorporates concepts from psychoacoustics, in particular, masking effects and stream formation.

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This study examined event-related potential (ERP) correlates of auditory spatial benefits gained from rendering sounds with individualized head-related transfer functions (HRTFs). Noise bursts with identical virtual elevations (0°-90°) were presented back-to-back in 5-10 burst "runs" in a roving oddball paradigm. Detection of a run's start (i.e., elevation change detection) was enhanced when bursts were rendered with an individualized compared to a non-individualized HRTF. ERPs showed increased P3 amplitudes to first bursts of a run in the individualized HRTF condition. Condition differences in P3 amplitudes and behavior were positively correlated. Data suggests that part of the individualization benefit reflects post-sensory processes.

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Speech recognition was measured as a function of the target-to-masker ratio (TMR) with syntactically similar speech maskers. In the first experiment, listeners were instructed to report keywords from the target sentence. Data averaged across listeners showed a plateau in performance below 0 dB TMR when masker and target sentences were from the same talker. In this experiment, some listeners tended to report the target words at all TMRs in accordance with the instructions, while others reported keywords from the louder of the sentences, contrary to the instructions. In the second experiment, stimuli were the same as in the first experiment, but listeners were also instructed to avoid reporting the masker keywords, and a payoff matrix penalizing masker keywords and rewarding target keywords was used. In this experiment, listeners reduced the number of reported masker keywords, and increased the number of reported target keywords overall, and the average data showed a local minimum at 0 dB TMR with same-talker maskers. The best overall performance with a same-talker masker was obtained with a level difference of 9 dB, where listeners achieved near perfect performance when the target was louder, and at least 80% correct performance when the target was the quieter of the two sentences.

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Single-sided deafness prevents access to the binaural cues that help normal-hearing listeners extract target speech from competing voices. Little is known about how listeners with one normal-hearing ear might benefit from access to severely degraded audio signals that preserve only envelope information in the second ear. This study investigated whether vocoded masker-envelope information presented to one ear could improve performance for normal-hearing listeners in a multi-talker speech-identification task presented to the other ear. Target speech and speech or non-speech maskers were presented unprocessed to the left ear. The right ear received no signal, or either an unprocessed or eight-channel noise-vocoded copy of the maskers. Presenting the vocoded maskers contralaterally yielded significant masking release from same-gender speech maskers, albeit less than in the unprocessed case, but not from opposite-gender speech, stationary-noise, or modulated-noise maskers. Unmasking also occurred with as few as two vocoder channels and when an attenuated copy of the target signal was added to the maskers before vocoding. These data show that delivering masker-envelope information contralaterally generates masking release in situations where target-masker similarity impedes monaural speech-identification performance. By delivering speech-envelope information to a deaf ear, cochlear implants for single-sided deafness have the potential to produce a similar effect.

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When competing speech sounds are spatially separated, listeners can make use of the ear with the better target-to-masker ratio. Recent studies showed that listeners with normal hearing are able to efficiently make use of this "better-ear," even when it alternates between left and right ears at different times in different frequency bands, which may contribute to the ability to listen in spatialized speech mixtures. In the present study, better-ear glimpsing in listeners with bilateral sensorineural hearing impairment, who perform poorly in spatialized speech mixtures, was investigated. The results suggest that this deficit is not related to better-ear glimpsing.

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Attempts to identify physiological correlates of listening effort have mainly focused on peripheral measures (e.g. pupillometry) and auditory-evoked/event-related potentials. Although nonauditory studies have suggested that sustained time-frequency electroencephalographic (EEG) features in the θ-band (4-7 Hz) are correlated with domain-general mental effort, little work has characterized such features during effortful listening. Here, high-density EEG data was collected while listeners performed a sentence-recognition task in noise, the signal-to-noise ratio (SNR) of which varied across blocks. Frontal midline θ (Fmθ), largely driven by sources localized in or near the medial frontal cortex, showed greater power with decreasing SNR and was positively correlated with self-reports of effort. Increased Fmθ was present before speech onset and during speech presentation. Fmθ power also differed across SNRs when including only trials in which all words were recognized, suggesting that the effects were unrelated to performance differences. Results suggest that frontal cortical networks play a larger role in listening as acoustic signals are increasingly masked. Further, sustained time-frequency EEG features may usefully supplement previously used peripheral and event-related potential measures in psychophysiological investigations of effortful listening.

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In listening tasks where a target speech signal is spatially separated from a masking voice, listeners can often gain a substantial advantage in performance by attending to the ear with the better signal-to-noise ratio (SNR). However, this better-ear strategy becomes much more complicated when a target talker located in front of the listener is masked by interfering talkers positioned at symmetric locations to the left and right of the target. When this happens, there are no long-term SNR advantages at either ear and the only binaural SNR advantages available are the result of complicated better-ear glimpses that vary as a function of frequency and rapidly switch back and forth between the two ears according to the natural fluctuations in the relative levels of the two masking voices. In this study, a signal processing technique was used to take the better-ear glimpses that would ordinarily be randomly distributed across the two ears in a binaural speech signal and move them all into the same ear. This resulted in a monaural signal that contained all the information available to an ideal listener using an optimal binaural glimpsing strategy. Speech intelligibility was measured with these optimized monaural stimuli and compared to performance with unprocessed binaural speech stimuli. Performance was similar in these two conditions, suggesting that listeners with normal hearing are able to efficiently extract information from better-ear glimpses that fluctuate rapidly across frequency and across the two ears.

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Adaptive signal-to-noise ratio (SNR) tracking is often used to measure speech reception in noise. Because SNR varies with performance using this method, data interpretation can be confounded when measuring an SNR-dependent effect such as the fluctuating-masker benefit (FMB) (the intelligibility improvement afforded by brief dips in the masker level). One way to overcome this confound, and allow FMB comparisons across listener groups with different stationary-noise performance, is to adjust the response set size to equalize performance across groups at a fixed SNR. However, this technique is only valid under the assumption that changes in set size have the same effect on percentage-correct performance for different masker types. This assumption was tested by measuring nonsense-syllable identification for normal-hearing listeners as a function of SNR, set size and masker (stationary noise, 4- and 32-Hz modulated noise and an interfering talker). Set-size adjustment had the same impact on performance scores for all maskers, confirming the independence of FMB (at matched SNRs) and set size. These results, along with those of a second experiment evaluating an adaptive set-size algorithm to adjust performance levels, establish set size as an efficient and effective tool to adjust baseline performance when comparing effects of masker fluctuations between listener groups.

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In many multitalker listening tasks, the degradation in performance that occurs when the number of interfering talkers increases from one to two is much larger than would be predicted from the corresponding decrease in the signal-to-noise ratio (SNR). In this experiment, a variety of contextually-relevant speech maskers, contextually-irrelevant speech maskers and non-speech maskers were used to examine the impact that the characteristics of the interfering sound sources have on the magnitude of this "multimasker penalty." The results show that a significant multimasker penalty only occurred in cases where two specific conditions were met: 1) the stimulus contained at least one contextually-relevant masker that could be confused with the target; and 2) the signal-to-noise ratio of the target relative to the combined masker stimulus was less than 0 dB. Remarkably, in cases where one masker was contextually relevant, the specific characteristics of the second masker had virtually no impact on the size of the multimasker penalty. Indeed, when the results were corrected for random guessing, there was essentially no difference in performance between conditions with three contextually-relevant talkers and those with two contextually-relevant talkers and one irrelevant talker. The results of a second experiment suggest that the listeners are generally able to hear keywords spoken by all three talkers even in situations where the multimasker penalty occurs, implying that the primary cause of the penalty is a degradation in the listener's ability to use prosodic cues and voice characteristics to link together words spoken at different points in the target phrase.

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Although many psychoacoustic studies have been conducted to examine the detection of masked target sounds, the vast majority of these studies have been conducted in carefully controlled laboratory listening environments, and their results may not apply to the detection of real-world sounds in the presence of naturalistic ambient sound fields. Those studies that have examined the detection of realistic naturally-occurring sounds have been conducted in uncontrolled listening environments (i.e., outdoor listening tests) where the experimenters were unable to precisely control, or even measure, the specific characteristics of the target and masker at the time of the detection judgment. This study represents an attempt to bridge the gap between unrealistic laboratory listening studies and uncontrolled outdoor listening studies through the use of pseudorandomly-presented real world recordings of target and masking sounds. Subjects were asked to detect helicopter signals in the context of an ongoing ambient recording in a two interval detection task. The results show that the signal-to-noise ratio required to detect an aircraft sound varies across different types of ambient environments (i.e., rural, suburban, or urban).

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The goals of this study were to measure sensitivity to the direct-to-reverberant energy ratio (D/R) across a wide range of D/R values and to gain insight into which cues are used in the discrimination process. The main finding is that changes in D/R are discriminated primarily based on spectral cues. Temporal cues may be used but only when spectral cues are diminished or not available, while sensitivity to interaural cross-correlation is too low to be useful in any of the conditions tested. These findings are based on an acoustic analysis of these variables and the results of two psychophysical experiments. The first experiment employs wideband noise with two values for onset and offset times to determine the D/R just-noticeable difference at -10, 0, 10, and 20 dB D/R. This yielded substantially higher sensitivity to D/R at 0 and 10 dB D/R (2-3 dB) than has been reported previously, while sensitivity is much lower at -10 and 20 dB D/R. The second experiment consists of three parts where specific cues to D/R are reduced or removed, which enabled the specified rank ordering of the cues. The acoustic analysis and psychophysical experiments also provide an explanation for the "auditory horizon effect."

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When listeners hear a target signal in the presence of competing sounds, they are quite good at extracting information at instances when the local signal-to-noise ratio of the target is most favorable. Previous research suggests that listeners can easily understand a periodically interrupted target when it is interleaved with noise. It is not clear if this ability extends to the case where an interrupted target is alternated with a speech masker rather than noise. This study examined speech intelligibility in the presence of noise or speech maskers, which were either continuous or interrupted at one of six rates between 4 and 128 Hz. Results indicated that with noise maskers, listeners performed significantly better with interrupted, rather than continuous maskers. With speech maskers, however, performance was better in continuous, rather than interrupted masker conditions. Presumably the listeners used continuity as a cue to distinguish the continuous masker from the interrupted target. Intelligibility in the interrupted masker condition was improved by introducing a pitch difference between the target and speech masker. These results highlight the role that target-masker differences in continuity and pitch play in the segregation of competing speech signals.

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When listening to natural speech, listeners are fairly adept at using cues such as pitch, vocal tract length, prosody, and level differences to extract a target speech signal from an interfering speech masker. However, little is known about the cues that listeners might use to segregate synthetic speech signals that retain the intelligibility characteristics of speech but lack many of the features that listeners normally use to segregate competing talkers. In this experiment, intelligibility was measured in a diotic listening task that required the segregation of two simultaneously presented synthetic sentences. Three types of synthetic signals were created: (1) sine-wave speech (SWS); (2) modulated noise-band speech (MNB); and (3) modulated sine-band speech (MSB). The listeners performed worse for all three types of synthetic signals than they did with natural speech signals, particularly at low signal-to-noise ratio (SNR) values. Of the three synthetic signals, the results indicate that SWS signals preserve more of the voice characteristics used for speech segregation than MNB and MSB signals. These findings have implications for cochlear implant users, who rely on signals very similar to MNB speech and thus are likely to have difficulty understanding speech in cocktail-party listening environments.

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