Fig.2: Model predictions versus data for two masker levels.
Fig.1: Structure of the model to predict the masker-phase effect.
Context: The results from early psychoacoustic studies suggested that the human auditory system is insensitive to differences in the relative phases of spectral components of a multi-component sound. Recently, though, new results have proven evidence that the auditory system is sensitive to phase differences between components that interact within a single auditory filter. An exemplar of this sensitivity is the so-called masker-phase effect. Given a multi-component masker (say, a sum of sinusoids), the masker-phase effect refers to the variation in the amount of masking resulting from the modification of the phase relations between the components. The mechanisms underlying the masker-phase effect are not fully understood yet, but cochlear compression is believed to play a role.
To estimate the phase response of the cochlea, the masker-phase effect is usually measured using Schroeder-phase harmonic-complex maskers. A property of such maskers is that their phase curvature, defined as the second derivative of phase as function of frequency, can be controlled by one parameter. Then, assuming that the phase response of the cochlea adds to the phases of the individual components when such a Schroeder-phase masker is processed by the peripheral system, an estimate of the cochlea's phase response can be obtained provided a masker-phase effect is observed. Precisely, the phase curvature of the masker producing the smallest amount of masking is assumed to mirror the phase curvature of the cochlea. For more details on Schroeder-phase signals see Schroeder, 1970; IEEE Trans. Inf. Theory. vol.16 pp.85-89. For more details on the masker-phase effect and the estimation of the cochlea's phase response see, e.g., Lentz & Leek, 2001; J. Assoc. Res. Otolaryngol. vol.2 pp.408-422.
Method: To assess the particular role of compression in the estimate of the cochlear phase response, a first experiment was carried out that involved a Schroeder-phase harmonic-complex masker and a sinusoidal target. Masker and target were presented simultaneously. Masked thresholds were measured for various phase curvatures of the masker. To assess the potential effect of the efferent-induced reduction in compression (e.g. due to stimulation of the medial olivocochlear reflex, MOCR) on the masker-phase effect, conditions involving a "precursor" (i.e. a signal preceding the masker in time and designed to stimulate the MOCR) were also included. If compression actually plays a role, a smaller masker-phase effect, or even no effect at all, should be observed in presence than in absence of the precursor.
Because the phase response of the cochlea is likely to play a role in the perception of interaural time differences (ITD), that is the difference in time of arrival of a sound between the two ears, an alternative approach is taken here to estimate the cochlea's phase response. Precisely, in a second experiment, ITD thresholds (i.e. the shortest time difference for an ITD detection) were measured for various phase curvatures of a Schroeder-phase harmonic-complex masker. Assuming that ITD sensitivity depends on the envelope of the signal, and therefore on its phase curvature, the phase curvature producing the smallest ITD threshold is assumed to mirror the phase curvature of the cochlea.
Results: In the first experiment, a masker-phase effect was observed in both conditions (with; without precursor). Nonetheless, the presence of the precursor significantly decreased the masker-phase effect. This supports the idea that compression is important to observe a masker-phase effect. A modeling attempt was made using a model of the auditory periphery including three stages: an auditory filter, a nonlinearity to account for basilar membrane compression at mid to high levels, and a detection device. The model underestimated the masker-phase effects measured in both conditions. Adding a saturating function in the model, for instance to account for the compression of inner hair cells, allowed to account for the masker-phase effects in all conditions. The physiological interpretation of this result is currently under evaluation. The results of the second experiment are still under analysis but suggest that the ITD method is applicable to the measurement of the cochlea's phase response.
My contribution: Mostly involved in the modeling and interpretation of experimental data.
Potential applications: auditory models, hearing devices, sound localization and 3-D audio devices
Related contributions:
H. Tabuchi, B. Laback, T. Necciari, and P. Majdak. The role of compression in the simultaneous masker phase effect. The Journal of the Acoustical Society of America, 140(4):2680-2694, 2016.
H. Tabuchi, B. Laback, P. Majdak, T. Necciari, and K. Zenke. Modeling the Cochlear Phase Response Estimated in a Binaural Task. Presented at the 39th MidWinter Meeting of the ARO, San Diego, CA, USA, February 2016.
H. Tabuchi, B. Laback, P. Majdak, T. Necciari, and K. Zenke. Measuring the auditory phase response based on interaural time differences. Presented at the 169th Meeting of the ASA, Pittsburgh, PA, USA, May 2015.
H. Tabuchi, B. Laback, P. Majdak, and T. Necciari. The Role of Precursor in Tone Detection With Schroeder-Phase Complex Maskers. Presented at the 37th MidWinter Meeting of the ARO, San Diego, CA, USA, February 2014.
Estimating the cochlear phase response
Illustrations
Post-Doctoral Researcher in Audio Signal Processing & Psychoacoustics
Thibaud Necciari, PhD
Thibaud Necciari's personal Website, 2016-2018
orcid.org/0000-0003-2574-0948 | ResearcherID