Auditory model responses to harmonic and inharmonic complex tones: Effects of the cochlear amplifier
Hopkins and Moore [J. Acoust. Soc. Am. 122, 1055-1068 (2007)] measured the ability of hearing-impaired (HI) listeners to discriminate harmonic (H) from inharmonic (I) – all harmonics shifted upwards by the same amount in Hz – complexes. The complexes were composed of many bandpass-filtered harmonics (shaped stimuli) or five equal-amplitude harmonics (non-shaped stimuli). HI listeners performed worse with the shaped stimuli than with the non-shaped stimuli. Since shaping of the complexes should minimize envelope and spectral cues, listeners should discriminate H from I stimuli mainly using temporal fine structure (TFS) cues even when the harmonics are not resolved. This ability seems to be worsened in HI listeners. This study employed an auditory model with a physical cochlear model to show how the cochlear amplifier affects responses to H and I stimuli. For the shaped stimuli, the TFS of the simulated neural signals for H and I stimuli differed, represented by low cross-correlation coefficients computed from the shuffled cross-polarity correlograms. However, for the passive auditory model (simulating HI), the inter-spike intervals smaller than half of the stimulus period were similar. This could explain the poor performance for HI listeners. For the non-shaped stimuli, differences in the inter-spike intervals were observed even for the passive model, which could contribute to the improved performance.
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