Binaural detection with narrowband and wideband reproducible noise maskers. IV. Models using interaural time, level, and envelope differences.
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ABSTRACT:
SUBMITTER: Mao J
PROVIDER: S-EPMC3985905 | biostudies-other | 2014 Feb
REPOSITORIES: biostudies-other
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Project description:Processing mechanisms used for detection of tones in noise can be revealed by using reproducible noise maskers and analyzing the pattern of results across masker waveforms. This study reports detection of a 500-Hz tone in broadband reproducible noise by rabbits using a set of masker waveforms for which human results are available. An appetitive-reinforcement, operant-conditioning procedure with bias control was used. Both fixed-level and roving-level noises were used to explore the utility of energy-related cues for detection. An energy-based detection model was able to partially explain the fixed-level results across reproducible noise waveforms for both rabbit and human. A multiple-channel energy model was able to explain fixed-level results, as well as the robust performance observed with roving-level noises. Further analysis using the energy model indicated a difference between species: human detection was influenced most by the noise spectrum surrounding the tone frequency, whereas rabbit detection was influenced most by the noise spectrum at frequencies above that of the tone. In addition, a temporal envelope-based model predicted detection by humans as well as the single-channel energy model did, but the envelope-based model failed to predict detection by rabbits. This result indicates that the contributions of energy and temporal cues to auditory processing differ across species. Overall, these findings suggest that caution must be used when evaluating neural encoding mechanisms in one species on the basis of behavioral results in another.
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Project description:Interaural time difference (ITD) arises whenever a sound outside of the median plane arrives at the two ears. There is evidence that ITD in the rapidly varying fine structure of a sound is most important for sound localization and for understanding speech in noise. Cochlear implants (CIs), neural prosthetic devices that restore hearing in the profoundly deaf, are increasingly implanted to both ears to provide implantees with the advantages of binaural hearing. CI listeners have been shown to be sensitive to fine structure ITD at low pulse rates, but their sensitivity declines at higher pulse rates that are required for speech coding. We hypothesize that this limitation in electric stimulation is at least partially due to binaural adaptation associated with periodic stimulation. Here, we show that introducing binaurally synchronized jitter in the stimulation timing causes large improvements in ITD sensitivity at higher pulse rates. Our experimental results demonstrate that a purely temporal trigger can cause recovery from binaural adaptation. Thus, binaurally jittered stimulation may improve several aspects of binaural hearing in bilateral recipients of neural auditory prostheses.
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