Auditory Speech Intelligibility Research Articles

Treatment of Age-Related Hearing Loss Alters Audiovisual Integration and Resting-State Functional Connectivity: A Randomized Controlled Pilot Trial.

Untreated age-related hearing loss increases audiovisual integration and impacts resting state functional brain connectivity. Further, there is a relation between crossmodal plasticity and audiovisual integration strength in cochlear implant patients. However, it is currently unclear whether amplification of the auditory input by hearing aids influences audiovisual integration and resting state functional brain connectivity. We conducted a randomized controlled pilot study to investigate how the McGurk illusion, a common measure for audiovisual integration, and resting state functional brain connectivity of the auditory cortex are altered by six-month hearing aid use. Thirty-two older participants with slight-to-moderate, symmetric, age-related hearing loss were allocated to a treatment or waiting control group and measured one week before and six months after hearing aid fitting with functional magnetic resonance imaging. Our results showed a statistical trend for an increased McGurk illusion after six months of hearing aid use. We further demonstrated that an increase in McGurk susceptibility is related to a decreased hearing aid benefit for auditory speech intelligibility in noise. No significant interaction between group and time point was obtained in the whole-brain resting state analysis. However, a region of interest (ROI)-to-ROI analysis indicated that hearing aid use of six months was associated with a decrease in resting state functional connectivity between the auditory cortex and the fusiform gyrus and that this decrease was related to an increase of perceived McGurk illusions. Our study, therefore, suggests that even short-term hearing aid use alters audiovisual integration and functional brain connectivity between auditory and visual cortices.

Single-channel vibrotactile feedback for voicing enhancement in trained and untrained perceivers

Auditory speech intelligibility can be enhanced by integrating information from other modalities, e.g., vision [Sumby & Pollack 1954, J. Acoust. Soc. Am. 26: 212] or direct manual touch [Gick et al. 2008. J. Acoust. Soc. Am. 123: EL72]. There are, nonetheless, many circumstances where shared visual attention may be hard to establish, or where in-person contact may be infeasible (e.g., in a noisy collaborative environment). To test the feasibility of using vibrotactile feedback to enhance intelligibility under noisy conditions, we use a portable voice-coil-based transducer that provides vibrotactile stimulation similar to laryngeal vibrations. Participants were asked to discriminate between minimal pairs in noise. These were distinguished in voicing and vowel height. Participants were asked to wear a vibrator on their fingers, or on their suprasternal notch. We contrasted vibrator placement with different vibration styles, such as a constant vibration on voicing, or vibrations driven by the amplitude envelope of the speech signal. In untrained perceivers we found that vibrotactile feedback increased accuracy regardless of placement. This effect, though significant, was not strong enough to be useful for everyday speech enhancement. These results, and those of a follow-up study with trained perceivers, will be reported. [Funding from NSERC.]

Acoustic features of auditory medical alarms-An experimental study of alarm volume.

Audible alarms are a ubiquitous feature of all high-paced, high-risk domains such as aviation and nuclear power where operators control complex systems. In such settings, a missed alarm can have disastrous consequences. It is conventional wisdom that for alarms to be heard, "louder is better," so that alarm levels in operational environments routinely exceed ambient noise levels. Through a robust experimental paradigm in an anechoic environment to study human response to audible alerting stimuli in a cognitively demanding setting, akin to high-tempo and high-risk domains, clinician participants responded to patient crises while concurrently completing an auditory speech intelligibility and visual vigilance distracting task as the level of alarms were varied as a signal-to-noise ratio above and below hospital background noise. There was little difference in performance on the primary task when the alarm sound was -11 dB below background noise as compared with +4 dB above background noise-a typical real-world situation. Concurrent presentation of the secondary auditory speech intelligibility task significantly degraded performance. Operator performance can be maintained with alarms that are softer than background noise. These findings have widespread implications for the design and implementation of alarms across all high-consequence settings.

Functional Connectivity between Face-Movement and Speech-Intelligibility Areas during Auditory-Only Speech Perception

It has been proposed that internal simulation of the talking face of visually-known speakers facilitates auditory speech recognition. One prediction of this view is that brain areas involved in auditory-only speech comprehension interact with visual face-movement sensitive areas, even under auditory-only listening conditions. Here, we test this hypothesis using connectivity analyses of functional magnetic resonance imaging (fMRI) data. Participants (17 normal participants, 17 developmental prosopagnosics) first learned six speakers via brief voice-face or voice-occupation training (<2 min/speaker). This was followed by an auditory-only speech recognition task and a control task (voice recognition) involving the learned speakers’ voices in the MRI scanner. As hypothesized, we found that, during speech recognition, familiarity with the speaker’s face increased the functional connectivity between the face-movement sensitive posterior superior temporal sulcus (STS) and an anterior STS region that supports auditory speech intelligibility. There was no difference between normal participants and prosopagnosics. This was expected because previous findings have shown that both groups use the face-movement sensitive STS to optimize auditory-only speech comprehension. Overall, the present findings indicate that learned visual information is integrated into the analysis of auditory-only speech and that this integration results from the interaction of task-relevant face-movement and auditory speech-sensitive areas.

Bimodal audio–visual training enhances auditory adaptation process

Effects of auditory training with bimodal audio-visual stimuli on monomodal aural speech intelligibility were examined in individuals with normal hearing using highly degraded noise-vocoded speech sound. Visual cue simultaneously presented with auditory stimuli during the training session significantly improved auditory speech intelligibility not only for words used in the training session, but also untrained words, when compared with the auditory training using only auditory stimuli. Visual information is generally considered to complement insufficient speech information conveyed by the auditory system during audio-visual speech perception. However, the present results showed another beneficial effect of audio-visual training that the visual cue enhances the auditory adaptation process to the degraded new speech sound, which is different from those given during bimodal training.

Critical bands in the perception of speech signals

Current auditory theory suggests a major role for the phenomenon of critical bands in hearing. The critical band is, essentially, a filtering process whereby sound is categorized according to its frequency content. While some empirical evidence suggests that the critical band may serve in the analysis of speech, this has never been directly demonstrated. In the present study, digital signal processing techniques have been developed for altering available recorded speech materials so that the frequency resolution available in the resultant stimuli may be controlled. Tapes have been produced wherein the frequency resolution is limited to narrower than, equal to, and wider than one critical band and these tapes have been used in intelligibility testing with normal listeners. The critical bandwidths of the subjects have been measured by an independent technique. By the use of the above recordings, it has been possible to test directly the hypothesis that the critical band is an essential element in auditory speech intelligibility. [Work supported in part by Naval Sea Systems Command.]