The timing of the cochlear wave propagation : a comparative study of computational models

• It is believed that the phase of the cochlear wave propagation might play a crucial role in binaural perceptionand sound localization by generating cochlear disparities. Experimental data demonstrate that, while a tone is being played,an excitation pattern is formed extending from the base to the apex of the cochlea. The phase of the excitation patterndecays along the cochlear length until the slope of the phase curve (i.e. group delay) reaches its maximum at a locationwith the characteristic frequency (CF) that matches the frequency of the input tone. Thereafter, the phase stays almostconstant (group delay equals zero) until the apex. Computational models have been devised to simulate the cochlearresponses and thereby illuminate the underlying electromechanics of the human inner ear. These computational models canbe divided, according to their topology, into two groups: Parallel filterbanks that model the cochlea as several independentdecoupled filters versus cascade filterbanks (including transmission lines) which assume that the filters are coupled inseries. Due to their modeling principles, cascade filterbanks intrinsically include the longitudinal traveling wavepropagation whereas the parallel filterbank models lack this intrinsic feature since there is no longitudinal relation betweenthe filter stages in these models. The objective of this study is to verify if cascade filterbanks are actually more successfulin simulating the phase responses than parallel filterbanks. The excitation patterns generated by seven cochlear models(four parallel filterbanks, two cascade filterbanks and a transmission-line model) in response to 4 and 9 kHz tones wereestimated using an impulse, and the results were compared with corresponding experimental data recorded at comparablelengths in living mammalian cochleae. The accuracy of the model predictions was reported in mean absolute error (MAE)relative to the experimental data. The results show that cascade filterbank models are remarkably more successful withCARFAC and VERHULST models reproducing the experimental data most closely. However, DRNL model (a parallelfilterbank) also produces outcomes that are comparable in accuracy with those generated by cascade filterbank models.Further investigations showed that this specific parallel filterbank model externally incorporated correct phase delays inthe impulse responses of its filter stages. The results indicate that, if parallel filterbanks incorporate the phase delays intheir impulse responses according to the proposed method, they could successfully simulate the timing of the longitudinalwave propagation along the cochlea within the same accuracy range as cascade filterbank models do.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Medicinteknik -- Annan medicinteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Medical Engineering -- Other Medical Engineering (hsv//eng)

Nyckelord

auditory models; cochlea; cochlear amplifier; cochlear wave propagation

Physiology

fysiologi

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