A New Approach to Model Pitch Perception Using Sparse Coding
Fig 6
(A) The AN population response for the missing-fundamental harmonic complex tone of Eq 6, with f0 = 225 Hz. The stimulus has an amplitude level of 30 dB SPL, and the AN population response is normalized to one, as usual. The x-axis shows post-stimulus time, and the y-axis denotes the (linear) mapping between locations along the cochlea and CFs. (B) The AN population response for the same spectral structure as in A (3–8 harmonics), but for a stimulus level of 90 dB SPL. For this relatively high stimulus level, the nonlinearity effects of the cochlea over the AN population response are apparent. (C–D) The solutions of the LS case (hLS) and the SC case (hSC) for the 30 dB (C) and 90 dB SPL (D) stimulus levels, respectively. (E–F) Probability functions of the LS (Sp,LS) and the SC (Sp,SC) cases, for the two amplitude levels, respectively. In the 30 dB SPL case (E), the same pitch is succesfully estimated for both the LS and the SC simulations (blue and red arrows indicate maximum peaks). However, for the 90 dB SPL case (F) only the SC solution proved to be robust and invariant to the stimulus level, as desired (red arrow indicates maximum peaks). In order to account for the cochlear nonlinearities due to the changing in the stimuli levels, all simulations of the AN fibers in this section were made using Carney's cochlea model (Zilany’s et al. [27–29]).