The Rapid Decline in Interaural-Time-Difference Sensitivity for Pure Tones Can Be Explained by Peripheral Filtering.

PURPOSE: The interaural time difference (ITD) is a primary horizontal-plane sound localization cue computed in the auditory brainstem. ITDs are accessible in the temporal fine structure of pure tones with a frequency of no higher than about 1400 Hz. How listeners' ITD sensitivity transitions from very best sensitivity near 700 Hz to impossible to detect within 1 octave currently lacks a fully compelling physiological explanation. Here, it was hypothesized that the rapid decline in ITD sensitivity is dictated not by a central neural limitation but by initial peripheral sound encoding, specifically, the low-frequency (apical) portion of the cochlear excitation pattern produced by a pure tone. METHODS: ITD sensitivity was measured in 16 normal-hearing listeners as a joint function of frequency (900-1500 Hz) and level (10-50 dB sensation level). RESULTS: Performance decreased with increasing frequency and decreasing sound level. The slope of performance decline was 90 dB/octave, consistent with the low-frequency slope of the cochlear excitation pattern. CONCLUSION: Fine-structure ITD sensitivity near 1400 Hz may be conveyed primarily by "off-frequency" activation of neurons tuned to lower frequencies near 700 Hz. Physiologically, this could be realized by having neurons sensitive to fine-structure ITD up to only about 700 Hz. A more extreme model would have only a single narrow channel near 700 Hz that conveys fine-structure ITDs. Such a model is a major simplification and departure from the classic formulation of the binaural display, which consists of a matrix of neurons tuned to a wide range of relevant frequencies and ITDs.

The rapid decline in interaural-time-difference sensitivity for pure tones can be explained by peripheral filtering.

Purpose: The interaural time difference (ITD) is a primary horizontal-plane sound localization cue computed in the auditory brainstem. ITDs are accessible in the temporal fine structure of pure tones with a frequency of no higher than about 1400 Hz. Explaining how listeners' ITD sensitivity transitions from very best sensitivity near 700 Hz to impossible to detect within 1 octave currently lacks a fully compelling physiological explanation. Here, it was hypothesized that the rapid decline in ITD sensitivity is dictated not by a central neural limitation but by initial peripheral sound encoding, specifically, the low-frequency (apical) edge of the cochlear excitation pattern produced by a pure tone. Methods: ITD sensitivity was measured in 16 normal-hearing listeners as a joint function of frequency (900-1500 Hz) and level (10-50 dB sensation level). Results: Performance decreased with increasing frequency and decreasing sound level. The slope of performance decline was 90 dB/octave, consistent with the low-frequency slope of the cochlear excitation pattern. Conclusion: Fine-structure ITD sensitivity near 1400 Hz may be conveyed primarily by "off-frequency" activation of neurons tuned to lower frequencies near 700 Hz. Physiologically, this could be realized by having neurons sensitive to fine-structure ITD up to only about 700 Hz. A more extreme model would have only a single narrow channel near 700 Hz that conveys fine-structure ITDs. Such a model is a major simplification and departure from the classic formulation of the binaural display, which consists of a matrix of neurons tuned to a wide range of relevant frequencies and ITDs.

The effect of visual speech information on linguistic release from masking.

Listeners often experience challenges understanding a person (target) in the presence of competing talkers (maskers). This difficulty reduces with the availability of visual speech information (VSI; lip movements, degree of mouth opening) and during linguistic release from masking (LRM; masking decreases with dissimilar language maskers). We investigate whether and how LRM occurs with VSI. We presented English targets with either Dutch or English maskers in audio-only and audiovisual conditions to 62 American English participants. The signal-to-noise ratio (SNR) was easy at 0 audio-only and -8 dB audiovisual in Experiment 1 and hard at -8 and -16 dB in Experiment 2 to assess the effects of modality on LRM across the same and different SNRs. We found LRM in the audiovisual condition for all SNRs and in audio-only for -8 dB, demonstrating reliable LRM for audiovisual conditions. Results also revealed that LRM is modulated by modality with larger LRM in audio-only indicating that introducing VSI weakens LRM. Furthermore, participants showed higher performance for Dutch maskers compared to English maskers with and without VSI. This establishes that listeners use both VSI and dissimilar language maskers to overcome masking. Our study shows that LRM persists in the audiovisual modality and its strength depends on the modality.

Examination of Athlete Triad Symptoms Among Endurance-Trained Male Athletes: A Field Study.

Background: Studies examining the physiological consequences associated with deficits in energy availability (EA) for male athletes are sparse. Purpose: To examine male athlete triad components; low energy availability (LEA) with or without an eating disorder risk (ED), reproductive hormone [testosterone (T)], and bone mineral density (BMD) in endurance-trained male athletes during different training periods. Methods: A cross-sectional design with 14 participants (age: 26.4 ± 4.2 years; weight: 70.6 ± 6.4 kg; height: 179.5 ± 4.3 cm; BMI: 21.9 ± 1.8 kg/m2) were recruited from the local community. Two separate training weeks [low (LV) and high (HV) training volumes] were used to collect the following: 7-day dietary and exercise logs, and blood concentration of T. Anthropometric measurements was taken prior to data collection. A one-time BMD measure (after the training weeks) and VO2max-HR regressions were utilized to calculate EEE. Results: Overall, EA presented as 27.6 ± 10.7 kcal/kgFFM·d-1 with 35% (n = 5) of participants demonstrating increased risk for ED. Examining male triad components, 64.3% presented with LEA (≤ 30 kcal/kgFFM·d-1) while participants presented with T (1780.6 ± 1672.6 ng/dl) and BMD (1.31 ±.09 g/cm2) within normal reference ranges. No differences were found across the 2 training weeks for EI, with slight differences for EA and EEE. Twenty-five participants (89.3%) under-ingested CHO across both weeks, with no differences between weeks. Conclusion: Majority of endurance-trained male athletes presented with one compromised component of the triad (LEA with or without ED risk); however, long-term negative effects on T and BMD were not demonstrated. Over 60% of the participants presented with an EA ≤ 30 kcal/kgFFM·d-1, along with almost 90% not meeting CHO needs. These results suggest male endurance-trained athletes may be at risk to negative health outcomes similar to mechanistic behaviors related to EA with or without ED in female athletes.

The effects of target-masker sex mismatch on linguistic release from masking.

Listeners often experience challenges understanding an interlocutor (target) in the presence of competing talkers (maskers). However, during linguistic release from masking (LRM), this difficulty decreases for native language targets (English) when paired with different language maskers (e.g., Dutch). There is considerable evidence that the linguistic similarity between target-masker pairs determines the size of LRM. This study investigated whether and how LRM is affected when the streams also differed in talker sex. Experiment 1 investigated intelligibility for English targets in sex-matched and mismatched conditions with Dutch or English maskers. While typical LRM effects were obtained when sex was matched, opposite effects were detected when sex was mismatched. In experiment 2, Mandarin maskers were used to increase linguistic dissimilarity and elicit stronger LRM effects. Despite the greater linguistic dissimilarity, the surprising reverse LRM effect in the sex-mismatch condition persisted. In experiment 3, the target stream was held constant and talker sex and language were manipulated in the masker. Here, expected LRM effects were obtained for both the sex-matched and sex-mismatched conditions. This indicated that the locus of the dissimilarities and not just relative properties affect LRM. Broadly, this study suggests that using naturally varying listening situations advances understanding of factors underlying LRM.

Listeners Experience Linguistic Masking Release in Noise-Vocoded Speech-in-Speech Recognition.

Purpose: The purpose of this study was to evaluate whether listeners with normal hearing perceiving noise-vocoded speech-in-speech demonstrate better intelligibility of target speech when the background speech was mismatched in language (linguistic release from masking [LRM]) and/or location (spatial release from masking [SRM]) relative to the target. We also assessed whether the spectral resolution of the noise-vocoded stimuli affected the presence of LRM and SRM under these conditions. Method: In Experiment 1, a mixed factorial design was used to simultaneously manipulate the masker language (within-subject, English vs. Dutch), the simulated masker location (within-subject, right, center, left), and the spectral resolution (between-subjects, 6 vs. 12 channels) of noise-vocoded target-masker combinations presented at +25 dB signal-to-noise ratio (SNR). In Experiment 2, the study was repeated using a spectral resolution of 12 channels at +15 dB SNR. Results: In both experiments, listeners' intelligibility of noise-vocoded targets was better when the background masker was Dutch, demonstrating reliable LRM in all conditions. The pattern of results in Experiment 1 was not reliably different across the 6- and 12-channel noise-vocoded speech. Finally, a reliable spatial benefit (SRM) was detected only in the more challenging SNR condition (Experiment 2). Conclusion: The current study is the first to report a clear LRM benefit in noise-vocoded speech-in-speech recognition. Our results indicate that this benefit is available even under spectrally degraded conditions and that it may augment the benefit due to spatial separation of target speech and competing backgrounds.

Spatially separating language masker from target results in spatial and linguistic masking release.

Several studies demonstrate that in complex auditory scenes, speech recognition is improved when the competing background and target speech differ linguistically. However, such studies typically utilize spatially co-located speech sources which may not fully capture typical listening conditions. Furthermore, co-located presentation may overestimate the observed benefit of linguistic dissimilarity. The current study examines the effect of spatial separation on linguistic release from masking. Results demonstrate that linguistic release from masking does extend to spatially separated sources. The overall magnitude of the observed effect, however, appears to be diminished relative to the co-located presentation conditions.