Cortical Entrainment to Speech Produced by Cochlear Implant Users and Normal-Hearing Talkers.

The perceived sound quality of speech produced by hard-of-hearing individuals greatly depends on the degree and configuration of their hearing loss. A cochlear implant (CI) may provide some compensation and auditory feedback to monitor/control speech production. However, to date, the speech produced by CI users is still different in quality from that produced by normal-hearing (NH) talkers. In this study, we attempted to address this difference by examining the cortical activity of NH listeners when listening to continuous speech produced by 8 CI talkers and 8 NH talkers. We utilized a discriminative model to decode and reconstruct the speech envelope from the single-trial electroencephalogram (EEG) recorded from scalp electrode in NH listeners when listening to continuous speech. The correlation coefficient between the reconstructed envelope and original speech envelope was computed as a metric to quantify the difference in response to the speech produced by CI and NH talkers. The same listeners were asked to rate the perceived sound quality of the speech as a behavioral sound quality assessment. Both behavioral perceived sound quality ratings and the cortical entrainment to speech envelope were higher for the speech set produced by NH talkers than for the speech set produced by CI talkers.

Cross-Frequency Coupling in Cortical Processing of Speech.

This study examines power-power cross-frequency coupling (CFC) between different frequency bands of cortical activity in normal-hearing (NH) listeners and its association to the processing temporal envelope (ENV) and temporal fine structure (TFS) of speech. CFC between alpha and theta bands and between gamma and theta bands was investigated when only ENV or TFS or the original speech itself were processed. Comparing the cortical activity in response to ENV and original speech, there was an increase in alpha-theta CFC and in gamma-theta CFC when listening to ENV alone. However, when comparing the response when to listening TFS alone, there was a reduction in gamma-theta CFC compared to the original speech and the alpha-theta CFC was comparable to the equivalent observed with original speech. The increase in CFC may suggest that there is more synchrony across different bands of cortical activity in processing ENV than TFS. These measures can serve as indicators when either ENV or TFS is perceived.

Cortical entrainment to speech produced by cochlear implant talkers and normal-hearing talkers.

Cochlear implants (CIs) are commonly used to restore the ability to hear in those with severe or profound hearing loss. CIs provide the necessary auditory feedback for them to monitor and control speech production. However, the speech produced by CI users may not be fully restored to achieve similar perceived sound quality to that produced by normal-hearing talkers and this difference is easily noticeable in their daily conversation. In this study, we attempt to address this difference as perceived by normal-hearing listeners, when listening to continuous speech produced by CI talkers and normal-hearing talkers. We used a regenerative model to decode and reconstruct the speech envelope from the single-trial electroencephalogram (EEG) recorded on the scalp of the normal-hearing listeners. Bootstrap Spearman correlation between the actual speech envelope and the envelope reconstructed from the EEG was computed as a metric to quantify the difference in response to the speech produced by the two talker groups. The same listeners were asked to rate the perceived sound quality of the speech produced by the two talker groups as a behavioral sound quality assessment. The results show that both the perceived sound quality ratings and the computed metric, which can be seen as the degree of cortical entrainment to the actual speech envelope across the normal-hearing listeners, were higher in value for speech produced by normal hearing talkers than that for CI talkers. The first purpose of the study was to determine how well the envelope of speech is represented neurophysiologically via its similarity to the envelope reconstructed from EEG. The second purpose was to show how well this representation of speech for both CI and normal hearing talker groups differentiates in term of perceived sound quality.

The effects of crowdedness and safety measures on restaurant patronage choices and perceptions in the COVID-19 pandemic.

This paper investigates the effects of crowdedness and in-restaurant safety measures on consumers' restaurant patronage choices (eat-in vs. order takeaway vs. not patronize) and their perceptions during the COVID-19 pandemic. In an online experiment with 593 US consumers and 591 Australian consumers, we assess the effects of three levels of crowdedness (low vs. medium vs. high crowdedness) and four types of in-restaurant safety measures (none vs. partition vs. increasing distances between tables vs. not using in-between tables) by showing participants an image of the restaurant setting. Results show that US consumers are more sensitive to crowdedness, whereas Australian consumers are more sensitive to different types of safety measures, which greatly influence their patronage choices. In general, safety measures featuring social distancing are preferred over partitions, and there is no preferential difference between the measure of increasing distances between tables and the measure of not using in-between tables.

A potential neurophysiological correlate of electric-acoustic pitch matching in adult cochlear implant users: Pilot data.

The overall goal of this study was to identify an objective physiological correlate of electric-acoustic pitch matching in unilaterally implanted cochlear implant (CI) participants with residual hearing in the non-implanted ear. Electrical and acoustic stimuli were presented in a continuously alternating fashion across ears. The acoustic stimulus and the electrical stimulus were either matched or mismatched in pitch. Auditory evoked potentials were obtained from nine CI users. Results indicated that N1 latency was stimulus-dependent, decreasing when the acoustic frequency of the tone presented to the non-implanted ear was increased. More importantly, there was an additional decrease in N1 latency in the pitch-matched condition. These results indicate the potential utility of N1 latency as an index of pitch matching in CI users.

Stimulus presentation strategies for eliciting the acoustic change complex: increasing efficiency.

OBJECTIVE: The purpose of this study was to compare four strategies for stimulus presentation in terms of their efficiency when generating a speech-evoked cortical acoustic change complex (ACC) in adults and children. DESIGN: Ten normally hearing adults (aged 22 to 31 yrs) and nine normally hearing children (aged 6 to 9 yrs) served as participants. The ACC was elicited using a 75-dB SPL synthetic vowel containing 1000 Hz changes of second formant frequency, creating a change of perceived vowel between /u/ and /i/. The ACC was recorded from Cz using four stimulus formats:ACC magnitude was expressed as the standard deviation of the voltage waveform within a window believed to span the ACC. Noise magnitude was estimated from the variances at each sampling point in the same window. Efficiency was expressed in terms of the ACC to noise magnitude ratio divided by testing time. RESULTS: ACC magnitude was not significantly different for the two directions of second formant change. Reducing interonset interval from 2 to 1 sec increased efficiency by a factor close to two. Combining data from the two directions of change increased efficiency further, by a factor approximating the square root of 2. CONCLUSION: Continuous alternating stimulus presentation is more efficient than interrupted stimulus presentation in eliciting the ACC. The benefits of eliminating silent periods and doubling the number of acoustic changes presented in a given time period are not seriously offset by a reduction in root mean square response amplitude, at least in young adults and in children as young as 6 yrs.

Speech evoked potentials: from the laboratory to the clinic.

Speech-evoked auditory event-related potentials (ERPs) provide insight into the neural mechanisms underlying speech processing. For this reason, ERPs are of great value to hearing scientists and audiologists. This article will provide an overview of ERPs frequently used to examine the processing of speech and other sound stimuli. These ERPs include the P1-N1-P2 complex, acoustic change complex, mismatch negativity, and P3 responses. In addition, we focus on the application of these speech-evoked potentials for the assessment of (1) the effects of hearing loss on the neural encoding of speech allowing for behavioral detection and discrimination; (2) improvements in the neural processing of speech with amplification (hearing aids, cochlear implants); and (3) the impact of auditory training on the neural processing of speech. Studies in these three areas are reviewed and implications for audiologists are discussed.

Can the acoustic change complex be recorded in an individual with a cochlear implant? Separating neural responses from cochlear implant artifact.

The purpose of this case study was to determine whether the P1-N1-P2 acoustic change complex (ACC) could be recorded in an individual with a cochlear implant. In a cochlear implant recipient, stimulus-related artifact from the implant can overlap the evoked potential of interest, making it difficult to determine whether the recorded response is neural or a simple reflection of the artifact. This is an even greater technical challenge for the ACC because stimuli having relatively long durations are used. The subject was a 24-year-old with a diagnosis of auditory neuropathy/auditory dys-synchrony and used a MED-EL Tempo+ cochlear implant in her left ear. The ACC was recorded to synthetic vowels containing a change of F2 at midpoint ranging from 0 (no change) to 1200 Hz (perceived as /ui/). The stimuli were presented randomly at 75 dB SPL via a loudspeaker. In one condition the subject ignored the stimuli and watched a captioned video. In the other, the subject pressed one button on a response pad if she perceived an acoustic change at stimulus midpoint and another if she did not. Cortical auditory evoked potentials were recorded from 32 scalp electrodes. Results indicated that the ACC was present and could be teased apart from the cochlear implant stimulus artifact. ACC thresholds showed good agreement with behavioral discrimination performance, and therefore, results are positive for the potential clinical application of the ACC technique to individuals with cochlear implants.

Effects of low-pass noise masking on auditory event-related potentials to speech.

OBJECTIVE: This study investigated the effects of decreased audibility in low-frequency spectral regions, produced by low-pass noise masking, on cortical event-related potentials (ERPs) to the speech sounds /ba/ and /da/. DESIGN: The speech sounds were presented to normal-hearing adults (N = 10) at 65- and 80-dB peak-to-peak equivalent SPL while they were engaged in an active condition (pressing a button to deviant sounds) and a passive condition (ignoring the stimuli and reading a book). Broadband masking noise was simultaneously presented at an intensity sufficient to mask the response to the 65-dB speech sounds and subsequently low-pass filtered. The conditions were quiet (no masking), low-pass noise cutoff frequencies of 250, 500, 1000, 2000, and 4000 Hz, and broadband noise. RESULTS: As the cutoff frequency of the low-pass noise masker was raised, ERP latencies increased and amplitudes decreased. The low-pass noise affected N1 differently than the other ERP or behavioral measures, particularly for responses to 80-dB speech stimuli. N1 showed a smaller decrease in amplitude and a smaller increase in latency compared with the other measures. Further, the cutoff frequency where changes first occurred was different for N1. For 80-dB stimuli, N1 amplitudes showed significant changes when the low-pass noise masker cutoff was raised to 4000 Hz. In contrast, d', MMN, N2, and P3 amplitudes did not change significantly until the low-pass noise masker was raised to 2000 Hz. N1 latencies showed significant changes when the low-pass noise masker was raised to 1000 Hz, whereas RT, MMN, N2, and P3 latencies did not change significantly until the low-pass noise masker was raised to 2000 Hz. No significant differences in response amplitudes were seen across the hemispheres (electrode sites C3M versus C4M) in quiet, or in masking noise. CONCLUSIONS: These results indicate that decreased audibility, resulting from the masking, affects N1 in a differential manner compared with MMN, N2, P3, and behavioral measures. N1 indexes the presence of audible stimulus energy, being present when speech sounds are audible, whether or not they are discriminable. MMN indexes stimulus discrimination at a pre-attentive level. It was present only when behavioral measures indicated the ability to differentiate the speech sounds. N2 and P3 also were present only when the speech sounds were behaviorally discriminated. N2 and P3 index stimulus discrimination at a conscious level. These cortical ERP in low-pass noise studies provide insight into the changes in brain processes and behavioral performance that occur when audibility is reduced, such as with low frequency hearing loss.

Maturation of mismatch negativity: a scalp current density analysis.

OBJECTIVE: Auditory evoked potentials provide the opportunity to better understand the central processing of auditory stimuli, which is the basis of speech and language perception. The purpose of this study was to examine maturational changes in the topography of one of these auditory evoked potentials, the mismatch negativity (MMN), using scalp current density (SCD) analysis. DESIGN: Subjects were children ages 4 to 11 yr (N = 53), and adults (N = 12). Stimuli were 85 dB peSPL 1000 Hz standard tones and 1200 Hz deviant tones (deviant probability = 0.15). Auditory evoked potentials were recorded using surface electrodes placed at 32 locations on the head while subjects ignored the stimuli by watching a silent video. RESULTS: Significant maturational changes in topography of MMN were seen over frontal and left lateral sites. CONCLUSIONS: Differences in MMN for the children compared to adults indicate that the MMN generators or their orientation, and thus the neural processes underlying discrimination of simple tones, are not yet mature by 11 yr of age.