Multi-talker Environments Research Articles

Effects of Acquired Aphasia on the Recognition of Speech Under Energetic and Informational Masking Conditions.

Persons with aphasia (PWA) often report difficulty understanding spoken language in noisy environments that require listeners to identify and selectively attend to target speech while ignoring competing background sounds or “maskers.” This study compared the performance of PWA and age-matched healthy controls (HC) on a masked speech identification task and examined the consequences of different types of masking on performance. Twelve PWA and 12 age-matched HC completed a speech identification task comprising three conditions designed to differentiate between the effects of energetic and informational masking on receptive speech processing. The target and masker speech materials were taken from a closed-set matrix-style corpus, and a forced-choice word identification task was used. Target and maskers were spatially separated from one another in order to simulate real-world listening environments and allow listeners to make use of binaural cues for source segregation. Individualized frequency-specific gain was applied to compensate for the effects of hearing loss. Although both groups showed similar susceptibility to the effects of energetic masking, PWA were more susceptible than age-matched HC to the effects of informational masking. Results indicate that this increased susceptibility cannot be attributed to age, hearing loss, or comprehension deficits and is therefore a consequence of acquired cognitive-linguistic impairments associated with aphasia. This finding suggests that aphasia may result in increased difficulty segregating target speech from masker speech, which in turn may have implications for the ability of PWA to comprehend target speech in multitalker environments, such as restaurants, family gatherings, and other everyday situations.

Two simultaneous talkers distract more than one in simulated multi-talker environments, regardless of overall sound levels typical of open-plan offices

The irrelevant speech effect (ISE) characterizes detriment to cognitive task performance in the presence of irrelevant speech. This paper examines whether the ISE varies due to the number of simultaneously active nearby talkers (for up to two talkers), or the overall sound level, within the context of a simulated open-plan office. Two experiments were conducted within a climate-controlled chamber that was set-up as a medium-sized open-plan office. The cognitive tasks performed by the participants included the digit recall task, and a writing task, within a room acoustic simulation of realistic multi-talker speech from spatially separated talkers. Within Experiment 1 (n = 60), an increase in the number of talkers from none (T0) to one (T1), and from one to two (T2) simultaneous talkers resulted in statistically significant decline in the digit recall task performances, with effect sizes of 24% (i.e., T1 vs. T0), and 12% (i.e., T2 vs. T1), respectively. The pauses between words during the writing task were similar for T0 and T1, but showed a statistically significant increase within T2 vs. T1, with an effect size of 12%. The findings of Experiment 1 are inconsistent with the maximally distracting status attributed to T1 in some studies, but is consistent with findings in other studies. Within Experiment 2 (n = 62), the cognitive performance in T2 remained largely invariant between 45 and 57 dB (A-weighted sound pressure levels), which represents a typical range of levels within open-plan offices. This finding is somewhat consistent with previous studies, where the ISE has been shown to be invariant over large changes to the overall level of more-or-less spatially-static single-talker speech. However, the current findings provide a more ecologically-valid representation of multi-talker level-invariance of the ISE. In general, these findings have relevance for characterizing auditory distraction within complex multi-talker environments; both in laboratory studies and actual open-plan offices.

Speech-in-noise research: From classrooms to Canadian Armed Forces operational environments

The importance of speech intelligibility in learning and occupational environments is evidenced by the abundance of research in room acoustics and auditory communication. In addition to environmental factors such as background noise and reverberation, individual factors including the presence of hearing loss, wearing of hearing aids and hearing protection devices (HPDs), and language proficiency must be considered. Previous work in these areas has provided a benchmark for the study of communication in complex, high noise environments. For Canadian Armed Forces (CAF) members, the high noise levels inside aircraft, armoured vehicles and sea vessels demand the use of HPDs and integrated radio communication systems. This presentation will summarize our research on speech understanding in noise and multi-talker environments using different communication headsets, simulated hearing loss and language proficiency. We will focus on our recent studies of communication between native (L1) and non-native (L2) English speakers, which is applicable to the CAF due to the relatively high percentage of L2 membership. L2 speakers obtained lower scores on speech-in-noise tests than L1 speakers for both radioed and face-to-face speech, despite having a high level of language proficiency. Preliminary results of an investigation of cognitive load for L2 listeners will also be presented.

Effects of hearing loss on maintaining and switching attention.

The ability to intentionally control attention based on task goals and stimulus properties is critical to communication in many environments. However, when a person has a damaged auditory system, such as with hearing loss, perceptual organization may also be impaired, making it more difficult to direct attention to different auditory objects in the environment. Here we examined the behavioral cost associated with maintaining and switching attention in people with hearing loss compared to the normal hearing population, and found a cost associated with attending to a target stream in a multi-talker environment that cannot solely be attributed to audibility issues.

Looking Behavior and Audiovisual Speech Understanding in Children With Normal Hearing and Children With Mild Bilateral or Unilateral Hearing Loss.

Visual information from talkers facilitates speech intelligibility for listeners when audibility is challenged by environmental noise and hearing loss. Less is known about how listeners actively process and attend to visual information from different talkers in complex multi-talker environments. This study tracked looking behavior in children with normal hearing (NH), mild bilateral hearing loss (MBHL), and unilateral hearing loss (UHL) in a complex multi-talker environment to examine the extent to which children look at talkers and whether looking patterns relate to performance on a speech-understanding task. It was hypothesized that performance would decrease as perceptual complexity increased and that children with hearing loss would perform more poorly than their peers with NH. Children with MBHL or UHL were expected to demonstrate greater attention to individual talkers during multi-talker exchanges, indicating that they were more likely to attempt to use visual information from talkers to assist in speech understanding in adverse acoustics. It also was of interest to examine whether MBHL, versus UHL, would differentially affect performance and looking behavior. Eighteen children with NH, eight children with MBHL, and 10 children with UHL participated (8-12 years). They followed audiovisual instructions for placing objects on a mat under three conditions: a single talker providing instructions via a video monitor, four possible talkers alternately providing instructions on separate monitors in front of the listener, and the same four talkers providing both target and nontarget information. Multi-talker background noise was presented at a 5 dB signal-to-noise ratio during testing. An eye tracker monitored looking behavior while children performed the experimental task. Behavioral task performance was higher for children with NH than for either group of children with hearing loss. There were no differences in performance between children with UHL and children with MBHL. Eye-tracker analysis revealed that children with NH looked more at the screens overall than did children with MBHL or UHL, though individual differences were greater in the groups with hearing loss. Listeners in all groups spent a small proportion of time looking at relevant screens as talkers spoke. Although looking was distributed across all screens, there was a bias toward the right side of the display. There was no relationship between overall looking behavior and performance on the task. The present study examined the processing of audiovisual speech in the context of a naturalistic task. Results demonstrated that children distributed their looking to a variety of sources during the task, but that children with NH were more likely to look at screens than were those with MBHL/UHL. However, all groups looked at the relevant talkers as they were speaking only a small proportion of the time. Despite variability in looking behavior, listeners were able to follow the audiovisual instructions and children with NH demonstrated better performance than children with MBHL/UHL. These results suggest that performance on some challenging multi-talker audiovisual tasks is not dependent on visual fixation to relevant talkers for children with NH or with MBHL/UHL.

Prior Knowledge Guides Speech Segregation in Human Auditory Cortex

Segregating concurrent sound streams is a computationally challenging task that requires integrating bottom-up acoustic cues (e.g. pitch) and top-down prior knowledge about sound streams. In a multi-talker environment, the brain can segregate different speakers in about 100 ms in auditory cortex. Here, we used magnetoencephalographic (MEG) recordings to investigate the temporal and spatial signature of how the brain utilizes prior knowledge to segregate 2 speech streams from the same speaker, which can hardly be separated based on bottom-up acoustic cues. In a primed condition, the participants know the target speech stream in advance while in an unprimed condition no such prior knowledge is available. Neural encoding of each speech stream is characterized by the MEG responses tracking the speech envelope. We demonstrate that an effect in bilateral superior temporal gyrus and superior temporal sulcus is much stronger in the primed condition than in the unprimed condition. Priming effects are observed at about 100 ms latency and last more than 600 ms. Interestingly, prior knowledge about the target stream facilitates speech segregation by mainly suppressing the neural tracking of the non-target speech stream. In sum, prior knowledge leads to reliable speech segregation in auditory cortex, even in the absence of reliable bottom-up speech segregation cue.

Difficulty with understanding speech in background noise is predicted by broad binaural pitch fusion in bimodal cochlear implant users

Combined use of a cochlear implant (CI) and a contralateral hearing aid has been shown to improve CI users’ speech perception performance in multi-talker environments, presumably due to the use of acoustic temporal fine structure cues for separating one talker from several other talkers. However, there is large variability in this bimodal benefit. In this study, we show that differences in width of binaural pitch fusion, the fusion of dichotically presented tones that evoke different pitches across ears, explain a large part of this variability. Specifically, broad binaural pitch fusion could lead to fusion of multiple voices as one voice, and reduce the ability to use voice pitch differences to separate voices and understand speech in a multi-talker environment. Speech reception thresholds measured using male and female target talkers were compared with binaural pitch fusion results. Overall performance improved with different genders for target and maskers. A strong negative correlation was observed between voice gender benefit and breadth of binaural pitch fusion. These results suggest that sharp binaural pitch fusion is necessary for maximal speech perception in noise when acoustic hearing is available to transmit voice pitch cues. [Work supported by NIH-NIDCD Grant Nos. R01 DC01337 and F32 DC016193.]

The irrelevant speech effect in multi-talker environments: Applications to open-plan offices

Irrelevant speech from co-workers has consistently been listed as one of the major nuisances within open-plan work environments. To explore the psychoacoustic basis of the so-called irrelevant speech effect (ISE; which causes cognitive decline and increases acoustic distraction) within a multi-talker context, a series of laboratory-based experiments were run. These experiments used room acoustical simulations of various open-plan office environments within a climate-controlled chamber to test several factors relevant to the ISE. These factors included the number of simultaneously active talkers, their spatial arrangements, sound pressure levels and the semanticity of speech. The main findings thus far indicate that multi-talker speech lead to a stronger ISE than speech from a single talker, which further interacts with the overall sound level, semanticity, etc., to exhibit a more complicated effect than what has been proposed in previous studies. The effect of the number of active talkers alone suggests reconsiderations of some assumptions in the ISO 3382-3. More generally, the perception of speech “babble” seems to be affected by multiple factors in a realistic working environment. Some of our research is directly related to characterising speech babble and its function as a beneficial sound masker in multi-talker environments.Irrelevant speech from co-workers has consistently been listed as one of the major nuisances within open-plan work environments. To explore the psychoacoustic basis of the so-called irrelevant speech effect (ISE; which causes cognitive decline and increases acoustic distraction) within a multi-talker context, a series of laboratory-based experiments were run. These experiments used room acoustical simulations of various open-plan office environments within a climate-controlled chamber to test several factors relevant to the ISE. These factors included the number of simultaneously active talkers, their spatial arrangements, sound pressure levels and the semanticity of speech. The main findings thus far indicate that multi-talker speech lead to a stronger ISE than speech from a single talker, which further interacts with the overall sound level, semanticity, etc., to exhibit a more complicated effect than what has been proposed in previous studies. The effect of the number of active talkers alone suggests r...

Older adults show impaired modulation of attentional alpha oscillations: Evidence from dichotic listening.

Auditory attention is critical for selectively listening to speech from a single talker in a multitalker environment (e.g., Cherry, 1953). Listening in such situations is notoriously more difficult and more poorly encoded to long-term memory in older than in young adults (Tun, O'Kane, & Wingfield, 2002). Recent work by Payne, Rogers, Wingfield, and Sekuler (2017) in young adults demonstrated a neural correlate of auditory attention in the directed dichotic listening task (DDLT), where listeners attend to one ear while ignoring the other. Measured using electroencephalography, differences in alpha band power (8-14 Hz) between left and right hemisphere parietal regions mark the direction to which auditory attention is focused. Little prior research has been conducted on alpha power modulations in older adults, particularly with regard to auditory attention directed toward speech stimuli. In the current study, an older adult sample was administered the DDLT and delayed recognition procedures used by Payne et al. (2017). Compared to young adults, older adults showed reduced selective attention in the DDLT, evidenced by a higher rate of intrusions from the unattended ear. Moreover, older adults did not exhibit attention-related alpha modulation evidenced by young adults, nor did their event-related potentials (ERPs) to recognition probes differentiate between attended or unattended probes. Older adults' delayed recognition did not reveal a pattern of suppression of unattended items evidenced by young adults. These results serve as evidence for an age-related decline in selective auditory attention, potentially mediated by age-related decline in the ability to modulate alpha oscillations. (PsycINFO Database Record

Voice Discrimination by Adults with Cochlear Implants: the Benefits of Early Implantation for Vocal-Tract Length Perception.

Cochlear implant (CI) users find it extremely difficult to discriminate between talkers, which may partially explain why they struggle to understand speech in a multi-talker environment. Recent studies, based on findings with postlingually deafened CI users, suggest that these difficulties may stem from their limited use of vocal-tract length (VTL) cues due to the degraded spectral resolution transmitted by the CI device. The aim of the present study was to assess the ability of adult CI users who had no prior acoustic experience, i.e., prelingually deafened adults, to discriminate between resynthesized "talkers" based on either fundamental frequency (F0) cues, VTL cues, or both. Performance was compared to individuals with normal hearing (NH), listening either to degraded stimuli, using a noise-excited channel vocoder, or non-degraded stimuli. Results show that (a) age of implantation was associated with VTL but not F0 cues in discriminating between talkers, with improved discrimination for those subjects who were implanted at earlier age; (b) there was a positive relationship for the CI users between VTL discrimination and speech recognition score in quiet and in noise, but not with frequency discrimination or cognitive abilities; (c) early-implanted CI users showed similar voice discrimination ability as the NH adults who listened to vocoded stimuli. These data support the notion that voice discrimination is limited by the speech processing of the CI device. However, they also suggest that early implantation may facilitate sensory-driven tonotopicity and/or improve higher-order auditory functions, enabling better perception of VTL spectral cues for voice discrimination.

Improving Speech Intelligibility by Hearing Aid Eye-Gaze Steering: Conditions With Head Fixated in a Multitalker Environment

The behavior of a person during a conversation typically involves both auditory and visual attention. Visual attention implies that the person directs his or her eye gaze toward the sound target of interest, and hence, detection of the gaze may provide a steering signal for future hearing aids. The steering could utilize a beamformer or the selection of a specific audio stream from a set of remote microphones. Previous studies have shown that eye gaze can be measured through electrooculography (EOG). To explore the precision and real-time feasibility of the methodology, seven hearing-impaired persons were tested, seated with their head fixed in front of three targets positioned at −30°, 0°, and +30° azimuth. Each target presented speech from the Danish DAT material, which was available for direct input to the hearing aid using head-related transfer functions. Speech intelligibility was measured in three conditions: a reference condition without any steering, a condition where eye gaze was estimated from EOG measures to select the desired audio stream, and an ideal condition with steering based on an eye-tracking camera. The “EOG-steering” improved the sentence correct score compared with the “no-steering” condition, although the performance was still significantly lower than the ideal condition with the eye-tracking camera. In conclusion, eye-gaze steering increases speech intelligibility, although real-time EOG-steering still requires improvements of the signal processing before it is feasible for implementation in a hearing aid.

Deep recurrent neural networks based binaural speech segregation for the selection of closest target of interest

An auditory attention model that consists of binaural source segregation and also full localization of a target speech signal in a multi-talker environment is presented. The joint acoustic features, such as monaural, binaural and direct to reverberant ratio (DRR) that are successfully incorporated into deep recurrent neural network (DRNN) based joint discriminative model for the speech source segregation process. The monaural and binaural features are extracted from binaural speech mixtures of two speakers by using mean Hilbert envelope coefficients (MHEC) and interaural time, and level differences, respectively. The performance of deep recurrent network based speech segregation is validated in terms of signal to interference, signal to distortion and signal to artifacts and compared with existing architectures, including deep neural network (DNN). The proposed system is observed and found to be more suitable than monaural speech segregation especially when the desired target and interfering sources are located at different positions. The study also proposes full localization of segregated speech source that created the possibility to select the desired speaker of interest from an input acoustic speech mixture in a reverberant environment. The developed system has the capability to handle binaural segregation problem in multi-source and reverberation conditions. The auditory attention model provides accurate information about speech sources even when the desired targets are located at 2 m and above with higher reverberation time.

Comparison of scoring methods for spatial release from masking for speech based on analysis of psychometric function slope

The ability to benefit from the spatial separation of talkers in a multi-talker environment is critical to speech communication. A headphone-based test of spatial release from masking for speech (SR2) has been shown to be sensitive to differences between young, healthy listeners and listeners with various auditory deficits. Existing studies relied on a simplistic method to score SR2, comparing the number of correct responses in conditions of collocated and spatially-separated background talkers. Psychometric functions were fit to trial data compiled across multiple studies in order to evaluate if an alternative scoring method could improve diagnostic power. We hypothesized that differences in informational masking between collocated and spatially separated conditions would result in a difference in condition-specific slope estimates, thus leading to a relationship between scoring method and diagnostic power. Results showed a small but significant difference in slope between conditions, consistent with expectations, but the difference between scoring methods was not clinically significant. This information will be used to guide the development of a portable, rapid implementation of SR2 for clinical and research applications. [Funding provided by NIH R01 DC015051.]

Continued search for better prediction of aided speech understanding in multi-talker environments

To better understand issues of hearing-aid benefit during natural listening, this study examined the added demand placed by the goal of understanding speech over the more typically studied goal of simply recognizing speech sounds. The study compared hearing-aid benefit in two conditions, and examined factors that might account for the observed benefits. In the phonetic condition, listeners needed only identify the correct sound to make a correct response. In the semantic condition, listeners had to understand what they had heard to respond correctly, because the answer did not include any keywords from the spoken speech. Hearing aids provided significant benefit for listeners in the phonetic condition. In the semantic condition on the other hand, there were large inter-individual differences, with many listeners not experiencing any benefit of aiding. Neither a set of cognitive and linguistic tests, nor age, could explain this variability. Furthermore, analysis of psychometric functions showed that enhancement of the target speech fidelity through improvement of signal-to-noise ratio had a larger impact on listeners' performance in the phonetic condition than in the semantic condition. These results demonstrate the importance of incorporating naturalistic elements in the simulation of multi-talker listening for assessing the benefits of intervention in communication success.

The Effect of Interaural Mismatches on Contralateral Unmasking With Single-Sided Vocoders.

Cochlear-implant (CI) users with single-sided deafness (SSD)-that is, one normal-hearing (NH) ear and one CI ear-can obtain some unmasking benefits when a mixture of target and masking voices is presented to the NH ear and a copy of just the masking voices is presented to the CI ear. NH listeners show similar benefits in a simulation of SSD-CI listening, whereby a mixture of target and masking voices is presented to one ear and a vocoded copy of the masking voices is presented to the opposite ear. However, the magnitude of the benefit for SSD-CI listeners is highly variable across individuals and is on average less than for NH listeners presented with vocoded stimuli. One possible explanation for the limited benefit observed for some SSD-CI users is that temporal and spectral discrepancies between the acoustic and electric ears might interfere with contralateral unmasking. The present study presented vocoder simulations to NH participants to examine the effects of interaural temporal and spectral mismatches on contralateral unmasking. Speech-reception performance was measured in a competing-talker paradigm for NH listeners presented with vocoder simulations of SSD-CI listening. In the monaural condition, listeners identified target speech masked by two same-gender interferers, presented to the left ear. In the bilateral condition, the same stimuli were presented to the left ear, but the right ear was presented with a noise-vocoded copy of the interfering voices. This paradigm tested whether listeners could integrate the interfering voices across the ears to better hear the monaural target. Three common distortions inherent in CI processing were introduced to the vocoder processing: spectral shifts, temporal delays, and reduced frequency selectivity. In experiment 1, contralateral unmasking (i.e., the benefit from adding the vocoded maskers to the second ear) was impaired by spectral mismatches of four equivalent rectangular bandwidths or greater. This is equivalent to roughly a 3.6-mm mismatch between the cochlear places stimulated in the electric and acoustic ears, which is on the low end of the average expected mismatch for SSD-CI listeners. In experiment 2, performance was negatively affected by a temporal mismatch of 24 ms or greater, but not for mismatches in the 0 to 12 ms range expected for SSD-CI listeners. Experiment 3 showed an interaction between spectral shift and spectral resolution, with less effect of interaural spectral mismatches when the number of vocoder channels was reduced. Experiment 4 applied interaural spectral and temporal mismatches in combination. Performance was best when both frequency and timing were aligned, but in cases where a mismatch was present in one dimension (either frequency or latency), the addition of mismatch in the second dimension did not further disrupt performance. These results emphasize the need for interaural alignment-in timing and especially in frequency-to maximize contralateral unmasking for NH listeners presented with vocoder simulations of SSD-CI listening. Improved processing strategies that reduce mismatch between the electric and acoustic ears of SSD-CI listeners might improve their ability to obtain binaural benefits in multitalker environments.

Electro-oculography based horizontal gaze tracking: A perspective for attention-driven hearing aids

Users of hearing aids with standard directional microphones can have difficulties in complex listening situations such as multi-talker environments because they must turn their heads to follow conversations that move rapidly from one talker to the next. The use of gaze-pointed hearing aid directionality has been suggested as a way to potentially alleviate this problem [Kidd et al. (2013); J. Acoust. Soc. Am. 2013; 133(3): EL202-7.] However, to arrive at a practical and usable device, there is the need for unobstructive and mobile technology for gaze tracking. Here, we propose and evaluate an algorithm for estimating eye-gaze angle based solely on the single channel electro-oculogram (EOG), which can be obtained directly from the ear canal using conductive hearing aid molds. In contrast to conventional techniques, we use an algorithm which calculates the absolute eye angle by statistical analysis of the saccades. This results in robust long term performance where predicted eye angles significantly correlate with actual eye angles. This opens up the possibility of an attention driven beam-former for hearing aids without the need for eye-tracking goggles. [This work was supported by the Medical Research Council [grant number U135097131], Chief Scientist Office (Scotland) and Oticon Foundation.]

Interaural level difference-based model of speech localization in multi-talker environment

Horizontal localization is based on extraction of the interaural time and level differences (ITD, ILD). Even in complex scenes with multiple talkers and reverberation, the auditory system is remarkably good at estimating the individual talker locations. Several previous models proposed mechanisms that stressed the importance of ITD in the localization process. Here, we examine whether azimuth estimation in complex scenarios can be based solely on ILD. We implemented a model (based on Faller and Merimaa, 2004) in which azimuth estimation was based on ILDs of signal parts with high interaural correlation and with spectral profile matching that of the target. Comparison with experimental data (Kopco et al., 2010) showed that highly correlated parts of the signal, if available, provide reliable ILD estimates sufficient for precise target localization. However, for lateral target positions, at which the target dominates one ear but not the other, interaural correlation was too low to guide ILD extraction. In such cases, a new model based on finding maximum ILD provided good estimates even if maskers dominated in the worse ear. The combined model predictions matched the experimental data with target locations between -50° and 50° and for 4 maskers in reverberation. [Work supported by APVV-0452-12, H2020-MSCA-RISE-2015 #691229.]Horizontal localization is based on extraction of the interaural time and level differences (ITD, ILD). Even in complex scenes with multiple talkers and reverberation, the auditory system is remarkably good at estimating the individual talker locations. Several previous models proposed mechanisms that stressed the importance of ITD in the localization process. Here, we examine whether azimuth estimation in complex scenarios can be based solely on ILD. We implemented a model (based on Faller and Merimaa, 2004) in which azimuth estimation was based on ILDs of signal parts with high interaural correlation and with spectral profile matching that of the target. Comparison with experimental data (Kopco et al., 2010) showed that highly correlated parts of the signal, if available, provide reliable ILD estimates sufficient for precise target localization. However, for lateral target positions, at which the target dominates one ear but not the other, interaural correlation was too low to guide ILD extraction. In s...

Benefits of wearing hearing aids in a natural complex auditory environment

A simulation of multi-talker environments (Hafter et al., Basic Aspects of Hearing. 2013) asks subjects to process a continuous flow of information from spoken stories. Subjects respond manually to visually-presented questions that appear soon after occurrence of the relevant information in one of the stories. In the present study, hearing-impaired listeners either do or do not receive gain through their hearing aids, and special interest is in responses to questions based on phonetic cues vs. those which require semantic analysis of the acoustic signal. Our aim is to determine the benefit of receiving hearing-aid amplification, comparing the benefit observed for phonetically based questions to that observed with semantically-based questions, and in terms of individual linguistic and cognitive abilities as measured by frequently used tests for the purpose. Results showed a strong benefit of aided listening among subjects when the need is only to recognize speech but, large individual difference in aided benefits when the listener was required to understand the meaning of the speech, with auditory, linguistic and cognitive capabilities all being factors that determine successful understanding. The incorporation of naturalistic elements in the simulation of multi-talker listening is important for unearthing the large individual variability in communication success.

Development and evaluation of a mixed gender, multi-talker matrix sentence test in Australian English

Objective: To develop, in Australian English, the first mixed-gender, multi-talker matrix sentence test. Design: Speech material consisted of a 50-word base matrix whose elements can be combined to form sentences of identical syntax but unpredictable content. Ten voices (five female and five male) were recorded for editing and preliminary level equalization. Elements were presented as single-talker sentences-in-noise during two perceptual tests: an optimization phase that provided the basis for further level correction, and an evaluation phase that perceptually validated those changes. Study sample: Ten listeners participated in the optimization phase; these and an additional 32 naïve listeners completed the evaluation test. All were fluent in English and all but one had lived in Australia for >2 years. Results: Optimization reduced the standard deviation (SD) and speech reception threshold (SRT) range across all speech material (grand mean SRT = −10.6 dB signal-to-noise ratio, median = −10.8, SD =1.4, range =13.7, slope =19.3%/dB), yielding data consistent with cross-validated matrix tests in other languages. Intelligibility differences between experienced and naïve listeners were minimal. Conclusions: The Australian matrix corpus provides a robust set of test materials suitable for both clinical assessment and research into the dynamics of active listening in multi-talker environments.

Localization-based audiovisual speech-recognition benefit with degraded spatial cues

Degraded sound-localization accuracy is usually associated with reduced spatial awareness, but can also lead to reduced speech intelligibility in cases where audiovisual speech cues are available from a talker in an unknown location. Previous work showed that sound-localization cues improved speech perception for bilateral cochlear implantees by helping them face the talker of interest in a multitalker environment. This study evaluated the degree of localization accuracy required to obtain an audiovisual benefit. Normal-hearing adults used auditory localization cues to orient their gaze toward a video of a target talker. The target-talker location varied randomly among four azimuths spanning 180°. Auditory-localization cues were parametrically degraded with a real-time hearing-loss simulator without affecting auditory speech-recognition performance. Results revealed a maximum audiovisual benefit for speech recognition in noise of 5 dB, diminishing to zero with increasing localization degradation. Head tra...