Michael J. Hewitt

Bio: Michael J. Hewitt is an academic researcher from Loughborough University. The author has contributed to research in topics: Cochlear nucleus & Inferior colliculus. The author has an hindex of 11, co-authored 15 publications receiving 1502 citations.

Virtual pitch and phase sensitivity of a computer model of the auditory periphery. I: Pitch identification

Abstract: Licklider made his original suggestion in an attempt to explain the human ability to perceive the pitch of a complex tone even though that tone contained no spectral component corresponding to that pitch. He rejected the prevailing theory (Fletcher, 1924) that distortion products of nonlinear cochlear responses could wholly explain the phenomenon. He pointed to the fact that the waveform envelope of unresolved harmonic components could be used to extract pitch information if an autocorrelation analysis could be performed. He thought that this might be achieved by a delay line mechanism at a low level in the auditory nervous system. His theory depended on the idea that the harmonic com

Modeling the identification of concurrent vowels with different fundamental frequencies.

Abstract: Human listeners are better able to identify two simultaneous vowels if the fundamental frequencies of the vowels are different. A computational model is presented which, for the first time, is able to simulate this phenomenon at least qualitatively. The first stage of the model is based upon a bank of bandpass filters and inner hair‐cell simulators that simulate approximately the most relevant characteristics of the human auditory periphery. The output of each filter/hair‐cell channel is then autocorrelated to extract pitch and timbre information. The pooled autocorrelation function (ACF) based on all channels is used to derive a pitch estimate for one of the component vowels from a signal composed of two vowels. Individual channel ACFs showing a pitch peak at this value are combined and used to identify the first vowel using a template matching procedure. The ACFs in the remaining channels are then combined and used to identify the second vowel. Model recognition performance shows a rapid improvement in ...

Implementation details of a computation model of the inner hair‐cell auditory‐nerve synapse

Abstract: A simple and computationally efficient model of auditory-neural transduction at the inner hair cell has recently been described, (Meddis, 1986a nd 1988). This paper briefly presents a short computer program to implement the model, an exploration of the effects of modifying the parameters of the model, anew set of parameters for simulating an auditory nerve fiber showing amedium rate of spontaneous activity with extended ynamic range, and some methods of quickly estimating some of the characteristics. It is intended as advice for researchers who wish to implement he model as part of a speech recognition device or as input to another model of more centrally located neurophysiological functions.

A computer model of amplitude‐modulation sensitivity of single units in the inferior colliculus

Abstract: A computer model is presented of a neural circuit that replicates amplitude-modulation (AM) sensitivity of cells in the central nucleus of the inferior colliculus (ICC). The ICC cell is modeled as a point neuron whose input consists of spike trains from a number of simulated ventral cochlear nucleus (VCN) chopper cells. Input to the VCN chopper cells is provided by simulated spike trains from a model of the auditory periphery [Hewitt et al., J. Acoust. Soc. Am. 91, 2096-2109 (1992)]. The performance of the model at the output of the auditory nerve, the cochlear nucleus and ICC simulations in response to amplitude-modulated stimuli is described. The results are presented in terms of both temporal and rate modulation transfer functions (MTFs) and compared with data from physiological studies in the literature. Qualitative matches were obtained to the following main empirical findings: (a) Auditory nerve temporal-MTFs are low pass, (b) VCN chopper temporal-MTFs are low pass at low signal levels and bandpass at moderate and high signal levels, (c) ICC unit temporal-MTFs are low pass at low signal levels and broadly tuned bandpass at moderate and high signal levels, and (d) ICC unit rate-MTFs are sharply tuned bandpass at low and moderate signal levels and flat at high levels. VCN and ICC units preferentially sensitive to different rates of modulation are presented. The model supports the hypothesis that cells in the ICC decode temporal information into a rate code [Langner and Schreiner, J. Neurophysiol. 60, 1799-1822 (1988)], and provides a candidate wiring diagram of how this may be achieved.

Virtual pitch and phase sensitivity of a computer model of the auditory periphery. II: Phase sensitivity

Abstract: In a companion article [Meddis and Hewitt, J. Acoust. Soc. Am. 89, 2866–2882 (1991)] it was shown that a computational model of the auditory periphery followed by a system of autocorrelation analyses was able to account for a wide range of human virtual pitch perception phenomena. In this article it is shown that the same model, with no substantial modification, can predict a number of results concerning human sensitivity to phase relationships among harmonic components of tone complexes. The model is successfully evaluated using (a) amplitude-modulated and quasifrequency-modulated stimuli, (b) harmonic complexes with alternating phase change and monotonic phase change across harmonic components, and (c) mistuned harmonics. The model is contrasted with phase-insensitive theories of low-level auditory processing and offered as further evidence in favor of the value of analysing time intervals among spikes in the auditory nerve when explaining psychophysical phenomena.

YIN, a fundamental frequency estimator for speech and music

Abstract: An algorithm is presented for the estimation of the fundamental frequency (F0) of speech or musical sounds. It is based on the well-known autocorrelation method with a number of modifications that combine to prevent errors. The algorithm has several desirable features. Error rates are about three times lower than the best competing methods, as evaluated over a database of speech recorded together with a laryngograph signal. There is no upper limit on the frequency search range, so the algorithm is suited for high-pitched voices and music. The algorithm is relatively simple and may be implemented efficiently and with low latency, and it involves few parameters that must be tuned. It is based on a signal model (periodic signal) that may be extended in several ways to handle various forms of aperiodicity that occur in particular applications. Finally, interesting parallels may be drawn with models of auditory processing.

Neural processing of amplitude-modulated sounds.

Abstract: Joris, P. X., C. E. Schreiner, and A. Rees. Neural Processing of Amplitude-Modulated Sounds. Physiol Rev 84: 541–577, 2004; 10.1152/physrev.00029.2003.—Amplitude modulation (AM) is a temporal featu...

The Organization of the Cochlear Receptor

Abstract: The yield of alkenols and cycloalkenols is substantially improved by carrying out the reaction of olefins with formaldehyde in the presence of selected catalysts. In accordance with one embodiment, alk-3-en-1-ols are produced in good yields from isobutylene and formaldehyde in the presence of organic carboxylic acid salts of Group IB metals.

Multiresolution spectrotemporal analysis of complex sounds

Abstract: A computational model of auditory analysis is described that is inspired by psychoacoustical and neurophysiological findings in early and central stages of the auditory system The model provides a unified multiresolution representation of the spectral and temporal features likely critical in the perception of sound Simplified, more specifically tailored versions of this model have already been validated by successful application in the assessment of speech intelligibility [Elhilali et al, Speech Commun 41(2-3), 331-348 (2003); Chi et al, J Acoust Soc Am 106, 2719-2732 (1999)] and in explaining the perception of monaural phase sensitivity [R Carlyon and S Shamma, J Acoust Soc Am 114, 333-348 (2003)] Here we provide a more complete mathematical formulation of the model, illustrating how complex signals are transformed through various stages of the model, and relating it to comparable existing models of auditory processing Furthermore, we outline several reconstruction algorithms to resynthesize the sound from the model output so as to evaluate the fidelity of the representation and contribution of different features and cues to the sound percept

Modeling auditory processing of amplitude modulation I. Detection and masking with narrow-band carriers

Abstract: This paper presents a quantitative model for describing data from modulation-detection and modulation-masking experiments, which extends the model of the ‘‘effective’’ signal processing of the auditory system described in Dau et al. @J. Acoust. Soc. Am. 99, 3615‐3622 ~1996!#. The new element in the present model is a modulation filterbank, which exhibits two domains with different scaling. In the range 0‐10 Hz, the modulation filters have a constant bandwidth of 5 Hz. Between 10 Hz and 1000 Hz a logarithmic scaling with a constant Q value of 2 was assumed. To preclude spectral effects in temporal processing, measurements and corresponding simulations were performed with stochastic narrow-band noise carriers at a high center frequency ~5 kHz!. For conditions in which the modulation rate ( f mod) was smaller than half the bandwidth of the carrier (D f ), the model accounts for the low-pass characteristic in the threshold functions @e.g., Viemeister, J. Acoust. Soc. Am. 66, 1364‐1380 ~1979!#. In conditions with f mod.D f /2, the model can account for the high-pass characteristic in the threshold function. In a further experiment, a classical masking paradigm for investigating frequency selectivity was adopted and translated to the modulation-frequency domain. Masked thresholds for sinusoidal test modulation in the presence of a competing modulation masker were measured and simulated as a function of the test modulation rate. In all cases, the model describes the experimental data to within a few dB. It is proposed that the typical low-pass characteristic of the temporal modulation transfer function observed with wide-band noise carriers is not due to ‘‘sluggishness’’ in the auditory system, but can instead be understood in terms of the interaction between modulation filters and the inherent fluctuations in the carrier. © 1997 Acoustical Society of America.@S0001-4966~97!05611-7#