Eugene Brandewie

Prior listening in rooms improves speech intelligibility.

Although results from previous studies have demonstrated that the acoustic effects of a single reflection are perceptually suppressed after repeated exposure to a particular configuration of source and reflection, the extent to which this dynamic echo suppression might generalize to speech understanding in room environments with multiple reflections and reverberation is largely unknown. Here speech intelligibility was measured using the coordinate response measure corpus both with and without prior listening exposure to a reverberant room environment, which was simulated using virtual auditory space techniques. Prior room listening exposure was manipulated by presenting either a two-sentence carrier phrase that preceded the target speech, or no carrier phrase within the room environment. Results from 14 listeners indicate that with prior room exposure, masked speech reception thresholds were on average 2.7 dB lower than thresholds without exposure, an improvement in intelligibility of over 18 percentage points on average. This effect, which is shown to be absent in anechoic space and greatly reduced under monaural listening conditions, demonstrates that prior binaural exposure to reverberant rooms can improve speech intelligibility, perhaps due to a process of perceptual adaptation to the acoustics of the listening room.

Time-forward speech intelligibility in time-reversed rooms

The effects of time-reversed room acoustics on word recognition abilities were examined using virtual auditory space techniques, which allowed for temporal manipulation of the room acoustics independent of the speech source signals. Two acoustical conditions were tested: one in which room acoustics were simulated in a realistic time-forward fashion and one in which the room acoustics were reversed in time, causing reverberation and acoustic reflections to precede the direct-path energy. Significant decreases in speech intelligibility--from 89% on average to less than 25%--were observed between the time-forward and time-reversed rooms. This result is not predictable using standard methods for estimating speech intelligibility based on the modulation transfer function of the room. It may instead be due to increased degradation of onset information in the speech signals when room acoustics are time-reversed.

Time course of a perceptual enhancement effect for noise-masked speech in reverberant environments

Speech intelligibility has been shown to improve with prior exposure to a reverberant room environment [Brandewie and Zahorik (2010). J. Acoust. Soc. Am. 128, 291-299] with a spatially separated noise masker. Here, this speech enhancement effect was examined in multiple room environments using carrier phrases of varying lengths in order to control the amount of exposure. Speech intelligibility enhancement of between 5% and 18% was observed with as little as 850 ms of exposure, although the effects time course varied considerably with reverberation and signal-to-noise ratio. In agreement with previous work, greater speech enhancement was found for reverberant environments compared to anechoic space.

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.

Speech intelligibility in rooms: Effect of prior listening exposure interacts with room acoustics

There is now converging evidence that a brief period of prior listening exposure to a reverberant room can influence speech understanding in that environment. Although the effect appears to depend critically on the amplitude modulation characteristic of the speech signal reaching the ear, the extent to which the effect may be influenced by room acoustics has not been thoroughly evaluated. This study seeks to fill this gap in knowledge by testing the effect of prior listening exposure or listening context on speech understanding in five different simulated sound fields, ranging from anechoic space to a room with broadband reverberation time (T60) of approximately 3 s. Although substantial individual variability in the effect was observed and quantified, the context effect was, on average, strongly room dependent. At threshold, the effect was minimal in anechoic space, increased to a maximum of 3 dB on average in moderate reverberation (T60 = 1 s), and returned to minimal levels again in high reverberation. This interaction suggests that the functional effects of prior listening exposure may be limited to sound fields with moderate reverberation (0.4 ≤ T60 ≤ 1 s).

Situational awareness assessment of hearing protection

Uncompromised situational awareness has become a critical component of hearing protection devices (HPDs). Situational awareness is a complex psychological phenomenon, which consists of several perceptual and cognitive factors. This study presents data from three experiments designed to analyze the performance of HPDs on measures of situational awareness and determine how multiple factors may impact in-the-field performance. Data are presented for four hearing protection devices on measures of sound localization, distance perception, spatial segregation, speech intelligibility, and dynamic scene analysis. Baseline (open-ear) data is also presented to contrast with the HPDs. Small differences in fine localization-discrimination and the number of large quadrant errors were observed, but these differences between devices were not observed in the more complex scene analysis task. A performance index was developed to determine overall performance of each HPD compared to open-ear performance. This index combined...

Sequential streaming under reverberation: Effects of the reverberant tail properties

A physical difference between two alternating stimuli can elicit perceptual segregation when the difference is sufficiently salient. One such cue involves differences in reverberation, potentially caused by differences in source distance. Here, we studied what aspects of difference in reverberation are most important in eliciting segregation using a rhythmic masking task. Two interleaved sequences of Gaussian noise bursts (target and interferer) were presented on each trial and listeners attempted to identify which of two rhythms was presented in the target sequence. The influence of the reverberation tail (or damped decay) was studied by parametrically changing its duration in the target sequence, while eliminating all binaural cues. The influence of spectral content of the tail was examined by simulating the spectral coloration produced by real rooms. Results suggest that damped tails can elicit perceptual segregation with tail durations less than 100 ms. In addition, the spectral content of the tail ca...

Improved speech understanding and amplitude modulation sensitivity in rooms: Wait a second!

Sound transmission between source and receiver can be profoundly affected by room acoustics, yet under many circumstances, these acoustical effects have relatively minor perceptual consequences. This may be explained, in part, by listener adaptation to the acoustics of the listening environment. Here, evidence that room adaptation improves speech understanding is summarized. The adaptation is rapid (around 1 s), and observable for a variety of speech materials. It also appears to depend critically on the amplitude modulation characteristic of the signal reaching the ear, and as a result, similar room adaptation effects have been observed for measurements of amplitude modulation sensitivity. A better understanding of room adaptation effects will hopefully contribute to improved methods for speech transmission in rooms for both normally hearing and hearing-impaired listeners. [Work supported by NIDCD.]

Speech intelligibility improves with listening exposure in reverberant rooms

Emerging evidence suggests that speech perception in a reverberant room can be altered by recent listening exposure to the room. This result is interesting and important because it suggests that perceptual aspects related to room acoustics are not constant as a function of listening time, and it may help to better understand why hearing-impaired listeners often report difficulty with speech understanding in reverberation. Virtual auditory space techniques have been a key component of the research on this effect, since they allow both realistic simulation of reverberant room listening environments, and a level of stimulus control that would be impossible for real-room listening. Here, recent work demonstrating objective improvements in speech intelligibility with room exposure is summarized, with particular focus on details of the effect including its time course and its sensitivity to different speech materials. [Work supported by the NIH/NIDCD.]