Cochlear impulse responses resolved into sets of gammatones: the case for beating of closely spaced local resonances

Andrew Bell*, Hero P. Wit

*Corresponding author for this work

    Research output: Contribution to journalArticleAcademicpeer-review

    2 Citations (Scopus)
    180 Downloads (Pure)

    Abstract

    Gammatones have had a long history in auditory studies, and recent theoretical work suggests they may play an important role in cochlear mechanics as well. Following this lead, the present paper takes five examples of basilar membrane impulse responses and uses a curve-fitting algorithm to decompose them into a number of discrete gammatones. The limits of this 'sum of gammatones' (SOG) method to accurately represent the impulse response waveforms were tested and it was found that at least two and up to six gammatones could be isolated from each example. Their frequencies were stable and largely independent of stimulus parameters. The gammatones typically formed a regular series in which the frequency ratio between successive members was about 1.1. Adding together the first few gammatones in a set produced beating-like waveforms which mimicked waxing and waning, and the instantaneous frequencies of the waveforms were also well reproduced, providing an explanation for frequency glides. Consideration was also given to the impulse response of a pair of elastically coupled masses-the basis of two-degree-of-freedom models comprised of coupled basilar and tectorial membranes-and the resulting waveform was similar to a pair of beating gammatones, perhaps explaining why the SOG method seems to work well in describing cochlear impulse responses. A major limitation of the SOG method is that it cannot distinguish a waveform resulting from an actual physical resonance from one derived from overfitting, but taken together the method points to the presence of a series of closely spaced local resonances in the cochlea.

    Original languageEnglish
    Article number6016
    Number of pages36
    JournalPeerJ
    Volume6
    DOIs
    Publication statusPublished - 27-Nov-2018

    Keywords

    • Impulse response
    • Coupled oscillators
    • Gammatones
    • Beating
    • Instantaneous frequency
    • Basilar membrane
    • Tectorial membrane
    • BASILAR-MEMBRANE RESPONSES
    • MECHANICAL WAVE-FORM
    • TECTORIAL MEMBRANE
    • AUDITORY-NERVE
    • INTERFERENCE PATTERNS
    • FREQUENCY GLIDES
    • CLICK RESPONSES
    • TIME-DOMAIN
    • MODEL
    • FILTER

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