Developmental changes in sound localization precision under conditions of the precedence effect.

The ability to give perceptual priority to an original sound source and ignore later-arriving echoes of that sound is termed the law of the first wave-front , or the precedence effect (PE). Little attention has been paid to the influence that echoes exert on localization accuracy for the leading sound. The present study investigated localization precision of children and adults in the presence of a simulated echo, using the minimal audible angle (MAA) task, which indicates the smallest change in the location of a sound that can be reliably discriminated. Three age groups were tested: 18-months, 5-years, and adults. Each age group was tested with one single-source (SS) stimulus, and two precedence effect (PE) stimuli: LEAD, in which the original sound shifted from midline and the echo remained at midline, and LAG, where the reverse occurred. Subjects were tested using an adaptive, 2-down/1-up, psychophysical algorithm. For all age groups, MAA thresholds were smallest for SS, larger for LEAD and largest for LAG. For all three stimulus conditions, the 18-month-olds\u27 thresholds were significantly larger than those of either 5-year-olds or adults. Five-year-olds\u27 MAA thresholds for SS sounds were very near to those of adults. However, their thresholds for the PE stimuli were significantly higher than those of adults\u27, and closer to those of 18-month-olds. When a lagging sound is inaudible as a separate auditory event, the auditory system presumably treats the leading and lagging sound as components of the same auditory percept, and uses both signals to compute the position of the sound source. The leading sound, which signals the onset of an auditory event, is assigned perceptual dominance thereby diminishing the nervous system\u27s interaural sensitivity for the later-arriving echo. This and related work has raised important questions concerning the neural mechanisms involved in spatial hearing in adults and children, especially those aspects which involve an active suppression of superfluous signals

Across-frequency combination of interaural time difference in bilateral cochlear implant listeners

The current study examined how cochlear implant (CI) listeners combine temporally interleaved envelope-ITD information across two sites of stimulation. When two cochlear sites jointly transmit ITD information, one possibility is that CI listeners can extract the most reliable ITD cues available. As a result, ITD sensitivity would be sustained or enhanced compared to single-site stimulation. Alternatively, mutual interference across multiple sites of ITD stimulation could worsen dual-site performance compared to listening to the better of two electrode pairs. Two experiments used direct stimulation to examine how CI users can integrate ITDs across two pairs of electrodes. Experiment 1 tested ITD discrimination for two stimulation sites using 100-Hz sinusoidally modulated 1000-pps-carrier pulse trains. Experiment 2 used the same stimuli ramped with 100 ms windows, as a control condition with minimized onset cues. For all stimuli, performance improved monotonically with increasing modulation depth. Results show that when CI listeners are stimulated with electrode pairs at two cochlear sites, sensitivity to ITDs was similar to that seen when only the electrode pair with better sensitivity was activated. None of the listeners showed a decrement in performance from the worse electrode pair. This could be achieved either by listening to the better electrode pair or by truly integrating the information across cochlear sites

The role of head-induced interaural time and level differences in the speech reception threshold for multiple interfering sound sources

Three experiments investigated the roles of interaural time differences ͑ITDs͒ and level differences ͑ILDs͒ in spatial unmasking in multi-source environments. In experiment 1, speech reception thresholds ͑SRTs͒ were measured in virtual-acoustic simulations of an anechoic environment with three interfering sound sources of either speech or noise. The target source lay directly ahead, while three interfering sources were ͑1͒ all at the target's location ͑0°,0°,0°͒, ͑2͒ at locations distributed across both hemifields ͑Ϫ30°,60°,90°͒, ͑3͒ at locations in the same hemifield ͑30°,60°,90°͒, or ͑4͒ co-located in one hemifield ͑90°,90°,90°͒. Sounds were convolved with head-related impulse responses ͑HRIRs͒ that were manipulated to remove individual binaural cues. Three conditions used HRIRs with ͑1͒ both ILDs and ITDs, ͑2͒ only ILDs, and ͑3͒ only ITDs. The ITD-only condition produced the same pattern of results across spatial configurations as the combined cues, but with smaller differences between spatial configurations. The ILD-only condition yielded similar SRTs for the ͑Ϫ30°,60°,90°͒ and ͑0°,0°,0°͒ configurations, as expected for best-ear listening. In experiment 2, pure-tone BMLDs were measured at third-octave frequencies against the ITD-only, speech-shaped noise interferers of experiment 1. These BMLDs were 4 -8 dB at low frequencies for all spatial configurations. In experiment 3, SRTs were measured for speech in diotic, speech-shaped noise. Noises were filtered to reduce the spectrum level at each frequency according to the BMLDs measured in experiment 2. SRTs were as low or lower than those of the corresponding ITD-only conditions from experiment 1. Thus, an explanation of speech understanding in complex listening environments based on the combination of best-ear listening and binaural unmasking ͑without involving sound-localization͒ cannot be excluded

The role of head-induced interaural time and level differences in the speech reception threshold for multiple interfering sound sources

Three experiments investigated the roles of interaural time differences ͑ITDs͒ and level differences ͑ILDs͒ in spatial unmasking in multi-source environments. In experiment 1, speech reception thresholds ͑SRTs͒ were measured in virtual-acoustic simulations of an anechoic environment with three interfering sound sources of either speech or noise. The target source lay directly ahead, while three interfering sources were ͑1͒ all at the target's location ͑0°,0°,0°͒, ͑2͒ at locations distributed across both hemifields ͑Ϫ30°,60°,90°͒, ͑3͒ at locations in the same hemifield ͑30°,60°,90°͒, or ͑4͒ co-located in one hemifield ͑90°,90°,90°͒. Sounds were convolved with head-related impulse responses ͑HRIRs͒ that were manipulated to remove individual binaural cues. Three conditions used HRIRs with ͑1͒ both ILDs and ITDs, ͑2͒ only ILDs, and ͑3͒ only ITDs. The ITD-only condition produced the same pattern of results across spatial configurations as the combined cues, but with smaller differences between spatial configurations. The ILD-only condition yielded similar SRTs for the ͑Ϫ30°,60°,90°͒ and ͑0°,0°,0°͒ configurations, as expected for best-ear listening. In experiment 2, pure-tone BMLDs were measured at third-octave frequencies against the ITD-only, speech-shaped noise interferers of experiment 1. These BMLDs were 4 -8 dB at low frequencies for all spatial configurations. In experiment 3, SRTs were measured for speech in diotic, speech-shaped noise. Noises were filtered to reduce the spectrum level at each frequency according to the BMLDs measured in experiment 2. SRTs were as low or lower than those of the corresponding ITD-only conditions from experiment 1. Thus, an explanation of speech understanding in complex listening environments based on the combination of best-ear listening and binaural unmasking ͑without involving sound-localization͒ cannot be excluded

The benefit of binaural hearing in a cocktail party: Effect of location and type of interferer

The “cocktail party problem” was studied using virtual stimuli whose spatial locations were generated using anechoic head-related impulse responses from the AUDIS database [Blauert et al., J. Acoust. Soc. Am. 103, 3082 (1998)]. Speech reception thresholds (SRTs) were measured for Harvard IEEE sentences presented from the front in the presence of one, two, or three interfering sources. Four types of interferer were used: (1) other sentences spoken by the same talker, (2) time-reversed sentences of the same talker, (3) speech-spectrum shaped noise, and (4) speech-spectrum shaped noise, modulated by the temporal envelope of the sentences. Each interferer was matched to the spectrum of the target talker. Interferers were placed in several spatial configurations, either coincident with or separated from the target. Binaural advantage was derived by subtracting SRTs from listening with the “better monaural ear” from those for binaural listening. For a single interferer, there was a binaural advantage of 2–4 dB for all interferer types. For two or three interferers, the advantage was 2–4 dB for noise and speech-modulated noise, and 6–7 dB for speech and time-reversed speech. These data suggest that the benefit of binaural hearing for speech intelligibility is especially pronounced when there are multiple voiced interferers at different locations from the target, regardless of spatial configuration; measurements with fewer or with other types of interferers can underestimate this benefit

Conducting clinical trials in persons with Down syndrome : summary from the NIH INCLUDE Down syndrome clinical trials readiness working group

The recent National Institute of Health (NIH) INCLUDE (INvestigation of Co-occurring conditions across the Lifespan to Understand Down syndromE) initiative has bolstered capacity for the current increase in clinical trials involving individuals with Down syndrome (DS). This new NIH funding mechanism offers new opportunities to expand and develop novel approaches in engaging and effectively enrolling a broader representation of clinical trials participants addressing current medical issues faced by individuals with DS. To address this opportunity, the NIH assembled leading clinicians, scientists, and representatives of advocacy groups to review existing methods and to identify those areas where new approaches are needed to engage and prepare DS populations for participation in clinical trial research. This paper summarizes the results of the Clinical Trial Readiness Working Group that was part of the INCLUDE Project Workshop: Planning a Virtual Down Syndrome Cohort Across the Lifespan Workshop held virtually September 23 and 24, 2019

Signal Transmission in the Auditory System

Contains table of contents for Section 3 and reports on four research projects.National Institutes of Health Grant R01 DC00194National Institutes of Health Grant P01 DC00119National Science Foundation Grant IBN 96-04642W.M. Keck Foundation Career Development ProfessorshipNational Institutes of Health Grant R01 DC00238Thomas and Gerd Perkins Award ProfessorshipAlfred P Sloan Foundation Instrumentation GrantJohn F. and Virginia B. Taplin Award in Health Sciences and TechnologyNational Institutes of Health/National Institute of Deafness and Other Communication DisordersNational Institutes of Health/National Institute of Deafness and Other Communication Disorders Grant PO1 DC0011

Signal Transmission in the Auditory System

Contains table of contents for Section 3, an introduction and reports on six research projects.National Institutes of Health Grant RO1-DC-00194-11National Institutes of Health Grant PO1-DC00119 Sub-Project 1National Institutes of Health Grant F32-DC00073-3National Institutes of Health Contract P01-DC00119National Institutes of Health Grant R01 DC00238National Institutes of Health Grant P01-DC00119National Institutes of Health Grant T32-DC00038National Institutes of Health Contract P01-DC00361National Institutes of Health Grant R01-DC00235National Institutes of Health Contract NO1-DC2240

Signal Transmission in the Auditory System

Contains table of contents for Section 3, an introduction and reports on seven research projects.National Institutes of Health Grant P01-DC-00119National Institutes of Health Grant R01-DC-00194National Institutes of Health Grant R01 DC00238National Institutes of Health Grant R01-DC02258National Institutes of Health Grant T32-DC00038National Institutes of Health Grant P01-DC00361National Institutes of Health Grant 2RO1 DC00235National Institutes of Health Contract N01-DC2240