Nirmal Kumar Srinivasan

Prior listening exposure to a reverberant room improves open-set intelligibility of high-variability sentences.

Previous studies have demonstrated that speech understanding in reverberant rooms improves when listeners are given prior exposure to the room. Results from these room-adaptation studies are limited, however, because they were conducted with materials that are not representative of the high acoustic variability observed in speech signals during everyday communication. Here, room adaptation effects were measured using an open-set speech corpus with high lexical and indexical variability and virtual auditory space techniques to simulate binaural listening in rooms. Room adaptation effects of comparable magnitude to previous studies were observed, suggesting general importance for facilitating speech intelligibility in reverberation.

Enhancement of speech intelligibility in reverberant rooms: Role of amplitude envelope and temporal fine structure

The temporal envelope and fine structure of speech make distinct contributions to the perception of speech in normal-hearing listeners, and are differentially affected by room reverberation. Previous work has demonstrated enhanced speech intelligibility in reverberant rooms when prior exposure to the room was provided. Here, the relative contributions of envelope and fine structure cues to this intelligibility enhancement were tested using an open-set speech corpus and virtual auditory space techniques to independently manipulate the speech cues within a simulated room. Intelligibility enhancement was observed only when the envelope was reverberant, indicating that the enhancement is envelope-based.

Amplitude modulation detection by human listeners in reverberant sound fields: Carrier bandwidth effects and binaural versus monaural comparison

Previous work [Zahorik et al., POMA, 12, 050005 (2011)] has reported that for a broadband noise carrier signal in a simulated reverberant sound field, human sensitivity to amplitude modulation (AM) is higher than would be predicted based on the broadband acoustical modulation transfer function (MTF) of the listening environment. Interpretation of this result was complicated by the fact that acoustical MTFs of rooms are often quite different for different carrier frequency regions, and listeners may have selectively responded to advantageous carrier frequency regions where the effective acoustic modulation loss due to the room was less than indicated by a broadband acoustic MTF analysis. Here, AM sensitivity testing and acoustic MTF analyses were expanded to include narrowband noise carriers (1-octave and 1/3-octave bands centered at 4 kHz), as well as monaural and binaural listening conditions. Narrowband results were found to be consistent with broadband results: In a reverberant sound field, human AM sensitivity is higher than indicated by the acoustical MTFs. The effect was greatest for modulation frequencies above 32 Hz and was present whether the stimulation was monaural or binaural. These results are suggestive of mechanisms that functionally enhance modulation in reverberant listening.

Amplitude modulation detection by human listeners in sound fields

The temporal modulation transfer function (TMTF) approach allows techniques from linear systems analysis to be used to predict how the auditory system will respond to arbitrary patterns of amplitude modulation (AM). Although this approach forms the basis for a standard method of predicting speech intelligibility based on estimates of the acoustical modulation transfer function (MTF) between source and receiver, human sensitivity to AM as characterized by the TMTF has not been extensively studied under realistic listening conditions, such as in reverberant sound fields. Here, TMTFs (octave bands from 2 - 512 Hz) were obtained in 3 listening conditions simulated using virtual auditory space techniques: diotic, anechoic sound field, reverberant room sound field. TMTFs were then related to acoustical MTFs estimated using two different methods in each of the listening conditions. Both diotic and anechoic data were found to be in good agreement with classic results, but AM thresholds in the reverberant room were lower than predictions based on acoustical MTFs. This result suggests that simple linear systems techniques may not be appropriate for predicting TMTFs from acoustical MTFs in reverberant sound fields, and may be suggestive of mechanisms that functionally enhance modulation during reverberant listening.

Voice gender release from masking in cochlear implant users is correlated with binaural pitch fusion

Spatial and voice gender separation of target from masking speech leads to substantial release from masking in normal-hearing listeners. However, binaural pitch fusion is often broad in cochlear implant (CI) listeners, such that dichotic stimuli with pitches differing by up to 3-4 octaves are fused (Reiss et al., 2014). We hypothesized that broad binaural fusion could reduce a listener’s ability to separate competing speech streams with different voice pitches, and thus reduce the voice gender as well as spatial benefit for speech perception in noise. Speech reception thresholds were measured in both bilateral and bimodal CI users, using male and female target talkers at two spatial configurations (co-location and 60-degrees of target-masker separation). Binaural pitch fusion was also measured. Different-gender maskers improved target detection performance in bimodal CI users, and performance was better with female than male targets in bilateral CI users. No spatial benefit was seen in either CI group. As hypothesized, voice gender masking release was strongly correlated with binaural fusion range in bimodal CI users. These results suggest that sharp binaural fusion is necessary for maximal speech perception in noise in bimodal CI users, but does not benefit bilateral CI users. [Work supported by NIH-NIDCD grant R01 DC01337.]Spatial and voice gender separation of target from masking speech leads to substantial release from masking in normal-hearing listeners. However, binaural pitch fusion is often broad in cochlear implant (CI) listeners, such that dichotic stimuli with pitches differing by up to 3-4 octaves are fused (Reiss et al., 2014). We hypothesized that broad binaural fusion could reduce a listener’s ability to separate competing speech streams with different voice pitches, and thus reduce the voice gender as well as spatial benefit for speech perception in noise. Speech reception thresholds were measured in both bilateral and bimodal CI users, using male and female target talkers at two spatial configurations (co-location and 60-degrees of target-masker separation). Binaural pitch fusion was also measured. Different-gender maskers improved target detection performance in bimodal CI users, and performance was better with female than male targets in bilateral CI users. No spatial benefit was seen in either CI group. As...

Effects of hearing impairment on sensitivity to dynamic spectral change

The loss of peripheral auditory sensitivity, precise temporal processing, and frequency selectivity associated with hearing loss suggests that the results obtained for pure tone glide stimuli will not necessarily correspond to results obtained with more complex dynamic stimuli for listeners with hearing impairment. Normally hearing (NH) and hearing-impaired (HI) listeners identified changes in frequency as rising or falling both for tone glides and for spectrotemporal ripples. Tones glided linearly up or down in frequency with an extent of 1, 0.66, or 0.33 octaves centered around 500 or 1500 Hz. Ripple stimuli, presented in octave bands centered around 500 or 1500 Hz or in a broadband condition extending from 20–20,000 Hz, had a spectral density of 2 cycles/octave and temporal modulation gliding up or down at rates of 1, 4, or 16 Hz. Sensitivity to dynamic changes was assessed as percent correct direction identification and bias was characterized as the ratio of correctly-identified rising versus falling ...

Combined effects of amplitude compression and reverberation on speech modulations

It is well documented that reverberation in listening environments is common, and that reverberation reduces speech intelligibility for hearing impaired listeners. it has been proposed that multichannel wide-dynamic range compression (mWDRC) in hearing aids can overcome this difficulty. However, the combined effect of reverberation and mWDRC on speech intelligibility has not been examined quantitatively. In this study, 16 nonsense syllables (/aCa/ format) recorded in a double-walled sound booth were distorted using virtual acoustic methods to simulate eight reverberant listening environments. Each signal was then run through a hearing-aid simulation which applied four-channel WDRC similar to that which might be applied in a wearable aid. Compression release time was varied between 12 and 1500 ms. Consonant confusion matrices were predicted analytically by comparing the similarity in the modulation spectra for clean speech and compressed reverberant speech. Results of this acoustical analysis suggest that ...

Phonemic restoration effect reversed in a reverberant room

Classic demonstrations of the phonemic restoration effect show increased intelligibility of interrupted speech when the interruptions are caused by a plausible masking sound rather than by silent periods. Previous studies of this effect have been conducted exclusively under anechoic or nearly anechoic listening conditions. This study demonstrates that the effect is reversed when sounds are presented in a realistically simulated reverberant room (broadband T(60) = 1.1 s): intelligibility is greater for silent interruptions than for interruptions by unmodulated noise. Additional results suggest that the reversal is primarily due to filling silent intervals with reverberant energy from the speech signal.

The effect of semantic context on speech intelligibility in reverberant rooms.

Although it is well known that semantic context affects speech intelligibility and that different reverberant rooms affect speech intelligibility differentially, these effects have seldom been studied together. Revised SPIN sentences in a background of Gaussian noise in simulated rooms with reverberation time (T60) of 1 and 0.25 s were used. The carrier phrase and the target word of the speech stimuli were manipulated to be either in the same room or in different rooms. As expected, intelligibility of predictable sentences was higher compared to unpredictable sentences-the context effect. The context effect was higher in the low-reverberant room as compared to the high-reverberant room. When the carrier phrase and target words were in different rooms, the context effect was higher when the carrier phrase was in the low-reverberant room and target word in the high-reverberant room. For predictable sentences, changing the target word from high-reverberation to low reverberation with a high reverberant carrier increased intelligibility. However, with a low-reverberant carrier and different rooms for the target word, there was no change in intelligibility. Overall, it could be concluded that there is an interaction between semantic context and room acoustics for speech intelligibility.

Development and validation of Portable Automated Rapid Testing (PART) measures for auditory research

The current state of consumer-grade electronics means that researchers, clinicians, students, and members of the general public across the globe can create high-quality auditory stimuli using tablet computers, built-in sound hardware, and calibrated consumer-grade headphones. Our laboratories have created a free application that supports this work: PART (Portable Automated Rapid Testing). PART has implemented a range of psychoacoustical tasks including: spatial release from speech-on-speech masking, binaural sensitivity, gap discrimination, temporal modulation, spectral modulation, and spectrotemporal modulation (STM). Here, data from the spatial release and STM tasks are presented. Data were collected across the globe on tablet computers using applications available for free download, built-in sound hardware, and calibrated consumer-grade headphones. Spatial release results were as good or better than those obtained with standard laboratory methods. Spectrotemporal modulation thresholds were obtained rapidly and, for younger normal hearing listeners, were also as good or better than those in the literature. For older hearing impaired listeners, rapid testing resulted in similar thresholds to those reported in the literature. Listeners at five different testing sites produced very similar STM thresholds, despite a variety of testing conditions and calibration routines. Download Spatial Release, PART, and Listen: An Auditory Training Experience for free at https://bgc.ucr.edu/games/.