+1 Recommend
0 collections
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      A method to enhance the use of interaural time differences for cochlear implants in reverberant environments

      The Journal of the Acoustical Society of America

      Read this article at

          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.


          The ability of normal-hearing (NH) listeners to exploit interaural time difference (ITD) cues conveyed in the modulated envelopes of high-frequency sounds is poor compared to ITD cues transmitted in the temporal fine structure at low frequencies. Sensitivity to envelope ITDs is further degraded when envelopes become less steep, when modulation depth is reduced, and when envelopes become less similar between the ears, common factors when listening in reverberant environments. The vulnerability of envelope ITDs is particularly problematic for cochlear implant (CI) users, as they rely on information conveyed by slowly varying amplitude envelopes. Here, an approach to improve access to envelope ITDs for CIs is described in which, rather than attempting to reduce reverberation, the perceptual saliency of cues relating to the source is increased by selectively sharpening peaks in the amplitude envelope judged to contain reliable ITDs. Performance of the algorithm with room reverberation was assessed through simulating listening with bilateral CIs in headphone experiments with NH listeners. Relative to simulated standard CI processing, stimuli processed with the algorithm generated lower ITD discrimination thresholds and increased extents of laterality. Depending on parameterization, intelligibility was unchanged or somewhat reduced. The algorithm has the potential to improve spatial listening with CIs.

          Related collections

          Most cited references41

          • Record: found
          • Abstract: not found
          • Article: not found

          On the Minimum Audible Angle

            • Record: found
            • Abstract: found
            • Article: not found

            Speech perception, localization, and lateralization with bilateral cochlear implants.

            Five bilateral cochlear implant users were tested for their localization abilities and speech understanding in noise, for both monaural and binaural listening conditions. They also participated in lateralization tasks to assess the impact of variations in interaural time delays (ITDs) and interaural level differences (ILDs) for electrical pulse trains under direct computer control. The localization task used pink noise bursts presented from an eight-loudspeaker array spanning an arc of approximately 108 degrees in front of the listeners at ear level (0-degree elevation). Subjects showed large benefits from bilateral device use compared to either side alone. Typical root-mean-square (rms) averaged errors across all eight loudspeakers in the array were about 10 degrees for bilateral device use and ranged from 20 degrees to 60 degrees using either ear alone. Speech reception thresholds (SRTs) were measured for sentences presented from directly in front of the listeners (0 degrees) in spectrally matching speech-weighted noise at either 0 degrees, +90 degrees or -90 degrees for four subjects out of five tested who could perform the task. For noise to either side, bilateral device use showed a substantial benefit over unilateral device use when noise was ipsilateral to the unilateral device. This was primarily because of monaural head-shadow effects, which resulted in robust SRT improvements (P<0.001) of about 4 to 5 dB when ipsilateral and contralateral noise positions were compared. The additional benefit of using both ears compared to the shadowed ear (i.e., binaural unmasking) was only 1 or 2 dB and less robust (P = 0.04). Results from the lateralization studies showed consistently good sensitivity to ILDs; better than the smallest level adjustment available in the implants (0.17 dB) for some subjects. Sensitivity to ITDs was moderate on the other hand, typically of the order of 100 micros. ITD sensitivity deteriorated rapidly when stimulation rates for unmodulated pulse-trains increased above a few hundred Hz but at 800 pps showed sensitivity comparable to 50-pps pulse-trains when a 50-Hz modulation was applied. In our opinion, these results clearly demonstrate important benefits are available from bilateral implantation, both for localizing sounds (in quiet) and for listening in noise when signal and noise sources are spatially separated. The data do indicate, however, that effects of interaural timing cues are weaker than those from interaural level cues and according to our psychophysical findings rely on the availability of low-rate information below a few hundred Hz.
              • Record: found
              • Abstract: found
              • Article: not found

              Enhancing sensitivity to interaural delays at high frequencies by using "transposed stimuli".

              It is well-known that thresholds for ongoing interaural temporal disparities (ITDs) at high frequencies are larger than threshold ITDs obtained at low frequencies. These differences could reflect true differences in the binaural mechanisms that mediate performance. Alternatively, as suggested by Colburn and Esquissaud [J. Acoust. Soc. Am. Suppl. 1 59, S23 (1976)], they could reflect differences in the peripheral processing of the stimuli. In order to investigate this issue, threshold ITDs were measured using three types of stimuli: (1) low-frequency pure tones; (2) 100% sinusoidally amplitude-modulated (SAM) high-frequency tones, and (3) special, "transposed" high-frequency stimuli whose envelopes were designed to provide the high-frequency channels with information similar to that available in low-frequency channels. The data and their interpretation can be characterized by two general statements. First, threshold ITDs obtained with the transposed stimuli were generally smaller than those obtained with SAM tones and, at modulation frequencies of 128 and 64 Hz, were equal to or smaller than threshold ITDs obtained with their low-frequency pure-tone counterparts. Second, quantitative analyses revealed that the data could be well accounted for via a model based on normalized interaural correlations computed subsequent to known stages of peripheral auditory processing augmented by low-pass filtering of the envelopes within the high-frequency channels of each ear. The data and the results of the quantitative analyses appear to be consistent with the general ideas comprising Colburn and Esquissaud's hypothesis.

                Author and article information

                J Acoust Soc Am
                J. Acoust. Soc. Am.
                The Journal of the Acoustical Society of America
                24 November 2017
                August 2016
                30 November 2017
                : 140
                : 2
                : 1116
                Medical Research Council Institute of Hearing Research, Nottingham, United Kingdom
                Author notes

                Present address: The Australian Hearing Hub, Sydney, Australia.


                Present address: Audio Information Processing, Technische Universität, München, Germany.


                All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).



                Comment on this article