Effect of the basilar membrane nonlinearities on rate-place representation of vowel in the cochlear nucleus : A modeling approach

Effects of the basilar membrane (BM) nonlinearities on fine representation of vowel formants of chopper units in the anteroventral cochlear nucleus (AVCN) are investigated using an auditory model. A functional model of ventral cochlear nucleus (VCN) units is proposed and is evaluated by comparing responses of the model with the physiological data. Rate-place representation of the models to the vowel /ε/ is recorded for a wide range of characteristic frequencies (CFs) at both low and high sound levels. Evaluation shows that the model is able to simulate shape of post-stimulus time histogram to short-tone bursts, discharge regularity and phase locking properties of accrual chopper units. Simulation using vowel /ε/ as stimulus shows that inhibitory inputs from the AN model have effectively suppressed firing rate of the model of VCN units having CF between the first and the second formant of the vowel /ε/ at high sound revel only. This results from change of frequency selectivity of the nonlinear BM model related sound level. This rate-place representation is similar to that of actual chopper units in the AVCN. The simulated results suggest that BM-nonlinearities-related sound level play an important role for fine representation of vowel formants of the chopper units in the AVCN. This modeling approach can effectively be applied for a clear representation of speech in the auditory pathway