Ecological validity of masking release with speech-like stimuli

Comodulated masking noise and binaural cues can facilitate detecting a target sound from noise. These cues can induce a decrease in detection thresholds, quantified as comodulation masking release (CMR) and binaural masking level difference (BMLD), respectively. However, their relevance to speech perception is unclear as most studies have used artificial stimuli different from speech. Here, we investigated their ecological validity using sounds with speech-like spectro-temporal dynamics. We evaluated the ecological validity of such grouping effect with stimuli reflecting formant changes in speech. We set three masker bands at formant frequencies F1, F2, and F3 based on CV combination: /gu/, /fu/, and /pu/. We found that the CMR was little (< 3 dB) while BMLD was comparable to previous findings (~ 9 dB). In conclusion, we suggest that other features may play a role in facilitating frequency grouping by comodulation such as the spectral proximity and the number of masker bands.

Neural correlates of masked and unmasked tones: psychoacoustics and late auditory evoked potentials (LAEPs)

Hearing thresholds can be used to quantify one's hearing ability. In various masking conditions, hearing thresholds can vary depending on the auditory cues. With comodulated masking noise and interaural phase disparity (IPD), target detection can be facilitated, lowering detection thresholds. This perceptual phenomenon is quantified as masking release: comodulation masking release (CMR) and binaural masking level difference (BMLD). As these measures only reflect the low limit of hearing, the relevance of masking release at supra-threshold levels is still unclear. Here, we used both psychoacoustic and electro-physiological measures to investigate the effect of masking release at supra-threshold levels. We investigated whether the difference in the amount of masking release will affect listening at supra-threshold levels. We used intensity just-noticeable difference (JND) to quantify an increase in the salience of the tone. As a physiological correlate of JND, we investigated late auditory evoked potentials (LAEPs) with electroencephalography (EEG). The results showed that the intensity JNDs were equal at the same intensity of the tone regardless of masking release conditions. For LAEP measures, the slope of the P2 amplitudes with a function of the level was inversely correlated with the intensity JND. In addition, the P2 amplitudes were higher in dichotic conditions compared to diotic conditions. Estimated the salience of the target tone from both experiments suggested that the salience of masked tone at supra-threshold levels may only be beneficial with BMLD.

The effect of the preceding masking noise on monaural and binaural release from masking

When a target tone is preceded by a noise, the threshold for target detection can be increased or decreased depending on the type of a preceding masker. The effect of preceding masker to the following sound can be interpreted as either the result of adaptation at the periphery or at the system level. To disentangle these, we investigated the time constant of adaptation by varying the length of the preceding masker. For inducing various masking conditions, we designed stimuli that can induce masking release. Comodulated masking noise and binaural cues can facilitate detecting a target sound from noise. These cues induce a decrease in detection thresholds, quantified as comodulation masking release (CMR) and binaural masking level difference (BMLD), respectively. We hypothesized that if the adaptation results from the top-down processing, both CMR and BMLD will be affected with increased length of the preceding masker. We measured CMR and BMLD when the length of preceding maskers varied from 0 (no preceding masker) to 500 ms. Results showed that CMR was more affected with longer preceding masker from 100 ms to 500 ms while the preceding masker did not affect BMLD. In this study, we suggest that the adaptation to preceding masking sound may arise from low level (e.g. cochlear nucleus, CN) rather than the temporal integration by the higher-level processing.

Engaging stories eradicate age effects in dip-listening

Fluctuating background masking sounds facilitate speech intelligibility by providing speech ‘glimpses’ (masking release). Older adults benefit less from glimpses, but masking release is typically investigated using isolated sentences. Recent work indicates that naturalistic speech (spoken stories) may qualitatively alter speech-in-noise listening. Moreover, neural sensitivity to different amplitude envelopes profiles (ramped vs. damped) changes with age, but whether this impacts speech listening is unknown. In three experiments, we investigate how masking release in younger and older adults differs for masked disconnected sentences and stories, and how intelligibility varies with masker temporal profile. Intelligibility was generally greater for damped compared to ramped maskers for both age groups and speech types. Masking release was reduced in older relative to younger adults for disconnected sentences (Experiment 1), and stories with a randomized sentence order (Experiment 3). When listening to stories with a coherent narrative, older adults demonstrated equal (Experiment 3) or greater (Experiment 2) masking release compared to younger adults. Reduced masking release previously observed in older adults does not appear to generalize to sounds with an engaging, connected narrative: this reinforces the idea that the listening materials qualitatively change listening behavior and that standard intelligibility paradigms may underestimate speech-listening abilities in older adults.

Tone detection thresholds in interaurally delayed noise of different bandwidths

Differences between the interaural phase of a noise and a target tone improve detection thresholds. The maximum masking release is obtained for detecting an antiphasic tone (Sπ) in diotic noise (N0). It has been shown in several studies that this benefit gradually declines as an interaural time delay (ITD) is applied to the noise. This decline has been attributed to the reduced interaural coherence of the noise. Here, we report detection thresholds for a 500 Hz tone in masking noise with ITDs up to 8 ms and bandwidths from 25 to 1000 Hz. Reducing the noise bandwidth from 100 to 50 and 25 Hz increased the masking release for 8-ms ITD, as expected for increasing temporal coherence with decreasing bandwidth. For bandwidths of 100–1000 Hz no significant difference in masking release was observed. Detection thresholds with these wider-band noises had an ITD dependence that is fully described by the temporal coherence imposed by the typical monaurally determined auditory-filter bandwidth. A binaural model based on interaural phase-difference fluctuations accounts for the data without using delay lines.

Comodulation masking release effect in children with and without dyslexia

<p class="abstract"><strong>Background:</strong> Speech recognition in a modulating noise background can be facilitated by a process attributable to comodulation masking release (CMR). CMR is usually assumed to depend on comparisons of the outputs of different auditory filters. There was an immense importance to study to find the CMR effect in children with and without dyslexia.</p><p class="abstract"><strong>Methods:</strong> The study was to find the CMR effect in children with and without dyslexia. The current research was carried out through five steps i.e. auditory attention task stimuli preparation, auditory performance test, CMR stimuli preparation, CMR task and statistical analysis. Through these processes for measuring the CMR was done for the children with and without dyslexia. All the data were tabulated and statistically computed for the analysis of the data. SPSS software version 16 was used for the statistical analysis of the data. </p><p class="abstract"><strong>Results:</strong> Independent t-test was used for the statistical analysis while the comparison between groups. Paired t- test was used for the statistical analysis while the comparison within the group at 95% confidence interval. These results indicated that the amount effect of CMR is greater in children with dyslexia. There was not a significant difference of CMR between the children with and without dyslexia to the effect of CMR was not significantly different between the ears in children without dyslexia and with dyslexia.</p><p class="abstract"><strong>Conclusions:</strong> The present study indicates that children with dyslexia have selective inability to use the temporal and spectral cues necessary for signal extraction in CMR.</p>