BiPhase: Binaural Hearing and the Cochlear Phase Response
While it is often assumed that our auditory system is phase-deaf, there is a body of literature showing that listeners are very sensitive to phase differences between spectral components of a sound. Particularly, for spectral components falling into the same perceptual filter, the so-called auditory filter, a change in relative phase across components causes a change in the temporal pattern at the output of the filter. The phase response of the auditory filter is thus important for any auditory tasks that rely on within-channel temporal envelope information, most notably temporal pitch or interaural time differences.
Within-channel phase sensitivity has been used to derive a psychophysical measure of the phase response of auditory filters (Kohlrausch and Sanders, 1995). The basic idea of the widely used masking paradigm is that a harmonic complex whose phase curvature roughly mirrors the phase response of the auditory filter spectrally centered on the complex causes a maximally modulated (peaked) internal representation and, thus, elicits minimal masking of a pure tone target at the same center frequency. Therefore, systematic variation of the phase curvature of the harmonic complex (the masker) allows to estimate the auditory filter’s phase response: the masker phase curvature causing minimal masking reflects the mirrored phase response of the auditory filter.
Besides the obvious importance of detecting the target in the temporal dips of the masker, particularly of the target is short compared to the modulation period of the masker (Kohlrausch and Sanders, 1995), there are several indications that fast compression in the cochlea is important to obtain the masker-phase effect (e.g., Carlyon and Datta, 1997; Oxenham and Dau, 2004). One indication is that listeners with sensorineural hearing impairment (HI), characterized by reduced or absent cochlear compression due to loss of outer hair cells, show only a very weak masker-phase effect, making it difficult to estimate the cochlear phase response.
In the BiPhase project we propose a new paradigm for measuring the cochlear phase response that does not rely on cochlear compression and thus should be applicable in HI listeners. It relies on the idea that the amount of modulation (peakedness) in the internal representation of a harmonic complex, as given by its phase curvature, determines the listener’s sensitivity to envelope interaural time difference (ITD) imposed on the stimulus. Assuming that listener’s sensitivity to envelope ITD does not rely on compression, systematic variation of the stimulus phase curvature should allow to estimate the cochlear phase response both in normal-hearing (NH) and HI listeners. The main goals of BiPhase are the following:
- Aim 1: Assessment of the importance of cochlear compression for the masker-phase effect at different masker levels. Masking experiments are performed with NH listeners using Schroeder-phase harmonic complexes with and without a precursor stimulus, intended to reduce cochlear compression by activation of the efferent system controlling outer-hair cell activity. In addition, a quantitative model approach is used to estimate the contribution of compression from outer hair cell activity and other factors to the masker-phase effect. The results are described in Tabuchi, Laback, Necciari, and Majdak (2016). A follow-up study on the dependency of the masker-phase effect on masker and target duration, the target’s position within the masker, the masker level, and the masker bandwidth and conclusions on the role of compression of underlying mechanisms in simultaneous and forward masking is underway.
- Aim 2: Development and evaluation of an envelope ITD-based paradigm to estimate the cochlear phase response. The experimental results on NH listeners, complemented with a modeling approach and predictions, are described in Tabuchi and Laback (2017). This paper also provides model predictions for HI listeners.
Besides the consistency of the overall pattern of ITD thresholds across phase curvatures with data on the masking paradigm and predictions of the envelope ITD model, an unexpected peak in the ITD thresholds was found for a negative phase curvature which was not predicted by the ITD model and is not found in masking data. Furthermore, the pattern of results for individual listeners appeared to reveal more variability than the masking paradigm. Data were also collected with an alternative method, relying on the extent of laterality of a target with supra-threshold ITD, as measured with an interaural-level-difference-based pointing stimulus. These data showed no nonmonotonic behavior at negative phase curvatures. Rather, they showed good correspondence with the ITD model prediction and more consistent results across individuals compared to the ITD threshold-based method (Zenke, Laback, and Tabuchi, 2016).
- Aim 3: Development of a ITD-based method to account for potentially non-uniform curvatures of the phase response in HI listeners. Using two independent iterative approaches, NH listeners adjusted the phase of individual harmonics of an ITD-carrying complex so that it elicited maximum extent of laterality. Although the pattern of adjusted phases very roughly resembled the expected pattern, there was a large amount of uncertainty (Zenke, 2014), preventing the method from further use. Modified versions of the method will be considered in a future study.
This project is funded by the Austrian Science Fund (FWF, Project # P24183-N24, awarded to Bernhard Laback). It run from 2013 to 2017
- Tabuchi, H. and Laback, B. (2017): Psychophysical and modeling approaches towards determining the cochlear phase response based on interaural time differences, The Journal of the Acoustical Society of America 141, 4314–4331.
- Tabuchi, H., Laback, B., Necciari, T., and Majdak, P (2016). The role of compression in the simultaneous masker phase effect, The Journal of the Acoustical Society of America 140, 2680-2694.
- Tabuchi, H., Laback, B., Majdak, P., and Necciari, T. (2014). The role of precursor in tone detection with Schroeder-phase complex maskers. Poster presented at 37th Association for Research in Otolaryngology (ARO) Meeting, San Diego, California.
- Tabuchi, H., Laback, B., Majdak, P., and Necciari, T. (2014). The perceptual consequences of a precursor on tone detection with Schroeder-phase harmonic maskers. Invited talk at Alps Adria Acoustics Association, Graz, Austria.
- Tabuchi, H., Laback, B., Majdak, P., Necciari, T., and Zenke,K. (2015). Measuring the auditory phase response based on interaural time differences. Talk at 169th Meeting of the Acoustical Society of America, Pittsburgh, Pennsylvania.
- Zenke, K., Laback, B., and Tabuchi, H. (2016). Towards an Efficient Method to Derive the Phase Response in Hearing-Impaired Listeners. Talk at 37th Association for Research in Otolaryngology (ARO) Meeting, San Diego, California.
- Tabuchi, H., Laback, B., Majdak, P., Necciari, T., and Zenke, K. (2016). Modeling the cochlear phase response estimated in a binaural task. Talk at 39th Association for Research in Otolaryngology (ARO) Meeting, San Diego, California.
- Laback, B., and Tabuchi, H. (2017). Psychophysical and modeling approaches towards determining the cochlear phase response based on interaural time differences. Invited Talk at AABBA Meeting, Vienna, Austria.
- Laback, B., and Tabuchi, H. (2017). Psychophysical and Modeling Approaches towards determining the Cochlear Phase Response based on Interaural Time Differences. Invited Talk at 3rd Workshop “Cognitive neuroscience of auditory and cross-modal perception, Kosice, Slovakia.
- Carlyon, R. P., and Datta, A. J. (1997). "Excitation produced by Schroeder-phase complexes: evidence for fast-acting compression in the auditory system," J Acoust Soc Am 101, 3636-3647.
- Kohlrausch, A., and Sander, A. (1995). "Phase effects in masking related to dispersion in the inner ear. II. Masking period patterns of short targets," J Acoust Soc Am 97, 1817-1829.
- Oxenham, A. J., and Dau, T. (2004). "Masker phase effects in normal-hearing and hearing-impaired listeners: evidence for peripheral compression at low signal frequencies," J Acoust Soc Am 116, 2248-2257.