Reverberation enhances onset dominance in sound localization

Head movement and its relation to hearing

Head position at any point in time plays a fundamental role in shaping the auditory information that reaches a listener, information that continuously changes as the head moves and reorients to different listening situations. The connection between hearing science and the kinesthetics of head movement has gained interest due to technological advances that have increased the feasibility of providing behavioral and biological feedback to assistive listening devices that can interpret movement patterns that reflect listening intent. Increasing evidence also shows that the negative impact of hearing deficits on mobility, gait, and balance may be mitigated by prosthetic hearing device intervention. Better understanding of the relationships between head movement, full body kinetics, and hearing health, should lead to improved signal processing strategies across a range of assistive and augmented hearing devices. The purpose of this review is to introduce the wider hearing community to the kinesiology of head movement and to place it in the context of hearing and communication with the goal of expanding the field of ecologically-specific listener behavior.

Binaural detection thresholds and audio quality of speech and music signals in complex acoustic environments

Every-day acoustical environments are often complex, typically comprising one attended target sound in the presence of interfering sounds (e.g., disturbing conversations) and reverberation. Here we assessed binaural detection thresholds and (supra-threshold) binaural audio quality ratings of four distortions types: spectral ripples, non-linear saturation, intensity and spatial modifications applied to speech, guitar, and noise targets in such complex acoustic environments (CAEs). The target and (up to) two masker sounds were either co-located as if contained in a common audio stream, or were spatially separated as if originating from different sound sources. The amount of reverberation was systematically varied. Masker and reverberation had a significant effect on the distortion-detection thresholds of speech signals. Quality ratings were affected by reverberation, whereas the effect of maskers depended on the distortion. The results suggest that detection thresholds and quality ratings for distorted speech in anechoic conditions are also valid for rooms with mild reverberation, but not for moderate reverberation. Furthermore, for spectral ripples, a significant relationship between the listeners' individual detection thresholds and quality ratings was found. The current results provide baseline data for detection thresholds and audio quality ratings of different distortions of a target sound in CAEs, supporting the future development of binaural auditory models.

Remote-Microphone Benefit in Noise and Reverberation for Children Who are Hard of Hearing

BACKGROUND

 Remote-microphone (RM) systems are designed to reduce the impact of poor acoustics on speech understanding. However, there is limited research examining the effects of adding reverberation to noise on speech understanding when using hearing aids (HAs) and RM systems. Given the significant challenges posed by environments with poor acoustics for children who are hard of hearing, we evaluated the ability of a novel RM system to address the effects of noise and reverberation.

PURPOSE

 We assessed the effect of a recently developed RM system on aided speech perception of children who were hard of hearing in noise and reverberation and how their performance compared to peers who are not hard of hearing (i.e., who have hearing thresholds no greater than 15 dB HL). The effect of aided speech audibility on sentence recognition when using an RM system also was assessed.

STUDY SAMPLE

 Twenty-two children with mild to severe hearing loss and 17 children who were not hard of hearing (i.e., with hearing thresholds no greater than 15 dB HL) (7-18 years) participated.

DATA COLLECTION AND ANALYSIS

 An adaptive procedure was used to determine the signal-to-noise ratio for 50 and 95% correct sentence recognition in noise and noise plus reverberation (RT 300 ms). Linear mixed models were used to examine the effect of listening conditions on speech recognition with RMs for both groups of children and the effects of aided audibility on performance across all listening conditions for children who were hard of hearing.

RESULTS

 Children who were hard of hearing had poorer speech recognition for HAs alone than for HAs plus RM. Regardless of hearing status, children had poorer speech recognition in noise plus reverberation than in noise alone. Children who were hard of hearing had poorer speech recognition than peers with thresholds no greater than 15 dB HL when using HAs alone but comparable or better speech recognition with HAs plus RM. Children with better-aided audibility with the HAs showed better speech recognition with the HAs alone and with HAs plus RM.

CONCLUSION

 Providing HAs that maximize speech audibility and coupling them with RM systems has the potential to improve communication access and outcomes for children who are hard of hearing in environments with noise and reverberation.

Spectral weighting functions for lateralization and localization of complex sound

Perceptual weighting of sound localization cues across spectral components was measured over headphones [experiment (expt.) 1] and in the free field (expt. 2) and quantified in the form of spectral weighting functions (SWFs). Stimuli consisted of five complex sounds (conditions), each containing seven frequency components. Participants judged the spatial position of the stimuli with spatial cues varying across frequency components. In separate experiments, free-field stimuli were presented anechoically (expt. 2), in the presence of simulated reverberation (expt. 3), or with stimuli varying in level either corrected for equal loudness (expt. 4.1) or sloped by ±6 dB per component (expt. 4.2). Overall results revealed greatest weight in the vicinity of 800 Hz, for both localization and interaural time difference (ITD)-based lateralization, although specific features of the SWFs did vary across stimulus conditions. The shape of the SWF follows the pattern of ITD sensitivity across frequency and is consistent with previous descriptions of an ITD "dominance region" peaking around 600-800 Hz. The close similarity of free field and ITD-based SWFs is further consistent with the hypothesized dominant role of low-frequency ITD in localization of broadband sounds. Other conditions revealed relatively modest effects of reverberation and component level.

Spectro-temporal weighting of interaural time differences in speech

Numerous studies have demonstrated that the perceptual weighting of interaural time differences (ITDs) is non-uniform in time and frequency, leading to reports of spectral and temporal "dominance" regions. It is unclear however, how these dominance regions apply to spectro-temporally complex stimuli such as speech. The authors report spectro-temporal weighting functions for ITDs in a pair of naturally spoken speech tokens ("two" and "eight"). Each speech token was composed of two phonemes, and was partitioned into eight frequency regions over two time bins (one time bin for each phoneme). To derive lateralization weights, ITDs for each time-frequency bin were drawn independently from a normal distribution with a mean of 0 and a standard deviation of 200 μs, and listeners were asked to indicate whether the speech token was presented from the left or right. ITD thresholds were also obtained for each of the 16 time-frequency bins in isolation. The results suggest that spectral dominance regions apply to speech, and that ITDs carried by phonemes in the first position of the syllable contribute more strongly to lateralization judgments than ITDs carried by phonemes in the second position. The results also show that lateralization judgments are partially accounted for by ITD sensitivity across time-frequency bins.

The impact of peripheral mechanisms on the precedence effect

When two similar sounds are presented from different locations, with one (the lead) preceding the other (the lag) by a small delay, listeners typically report hearing one sound near the location of the lead sound source-this is called the precedence effect (PE). Several questions about the underlying mechanisms that produce the PE are asked. (1) How might listeners' relative weighting of cues at onset versus ongoing stimulus portions affect perceived lateral position of long-duration lead/lag noise stimuli? (2) What are the factors that influence this weighting? (3) Are the mechanisms invoked to explain the PE for transient stimuli applicable to long-duration stimuli? To answer these questions, lead/lag noise stimuli are presented with a range of durations, onset slopes, and lag-to-lead level ratios over headphones. Monaural, peripheral mechanisms, and binaural cue extraction are modeled to estimate the cues available for determination of perceived laterality. Results showed that all three stimulus manipulations affect the relative weighting of onset and ongoing cues and that mechanisms invoked to explain the PE for transient stimuli are also applicable to the PE, in terms of both onset and ongoing segments of long-duration, lead/lag stimuli.

Localization of broadband sounds carrying interaural time differences: Effects of frequency, reference location, and interaural coherence

The auditory processes involved in the localization of sounds in rooms are still poorly understood. The present study investigated the auditory system's across-frequency processing of interaural time differences (ITDs) and the impact of the interaural coherence (IC) of the stimuli in ITD discrimination and localization. First, ITD discrimination thresholds were measured as a function of signal frequency, reference ITD, and IC using critical-band wide noises. The resulting data were fitted with a set of analytical functions and ITD weights were derived using concepts from signal detection theory. Inspired by the weighted-image model [Stern, Zeiberg, and Trahiotis. (1988). J. Acoust. Soc. Am. 84, 156-165], the derived ITD weights were then integrated in a simplified localization model using an optimal combination of ITD information across frequency. To verify this model, a series of localization experiments were conducted using broadband noise in which ITD and IC were varied across frequency. The model predictions were in good agreement with the experimental data, supporting the assumption that the auditory system performs a weighted integration of ITD information across frequency to localize a sound source. The results could be valuable for the design of new paradigms to measure localization in more complex acoustic conditions and may provide constraints for future localization models.