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gencgm


Manual Reference Pages  - GENCGM (1)

NAME

gencgm - generate a cochleogram

CONTENTS

Synopsis
Description
I. Display Defaults
Ii. Leaky Integration
References
Files
See Also
Bugs
Copyright
Acknowledgements

SYNOPSIS

gencgm [ option=value | -option ] [ filename ]

DESCRIPTION

Gencgm converts the input wave into a simulated neural activity pattern (NAP) and summarises the NAP as a sequence of excitation patterns (EPNs) (Patterson et al. 1992a, 1993a). The operation takes place in three stages: spectral analysis, neural encoding, and temporal integration (Patterson et al. 1995). In the spectral analysis stage, the input wave is converted into an array of filtered waves, one for each channel of a gammatone auditory filterbank. The surface of the array of filtered waves is AIM’s representation of basilar membrane motion (BMM) as a function of time. In the neural encoding stage, compression, adaptation and suppression, are used to convert each wave from the filterbank into a simulation of the aggregate neural response to that wave. The array of responses is AIM’s simulation of the neural activity pattern (NAP) in the auditory nerve at about the level of the cochlear nucleus. Finally, the NAP is converted into a sequence of excitation patterns (EPNs) by calculating the envelope of the NAP and extracting spectral slices from the envelope every ’frstep_epn’ ms (Patterson et al. 1994). The envelope is calculated continuously, by lowpass filtering the individual channels of the NAP as they flow from the cochlea simulation.

When the sequence of excitation patterns is presented in spectrographic format, it is referred to as a ’cochleogram’ (CGM). The spectrographic format has time on the abscissa (x-axis), filter centre-frequency on the ordinate (y-axis), and activity level as the degree of black in the display. In AIM, the suffix ’cgm’ is used to distinguish this spectral representation from the other spectral representations provided by the software (’asa’ auditory spectral analysis, ’sgm’ auditory spectrogram, and ’epn’ excitation pattern).

The neural activity pattern produced by genepn is the same as that produced by gennap. The primary differences are in the defaults for the Displays and the fact that the Leaky Integration is used to construct spectral slices from the NAP rather than simulating loss of phase locking. As a result, this manual entry is restricted to describing the options that differ from those in gennap.

I. DISPLAY DEFAULTS

The default values for three of the display options are reset to produce a spectrographic format rather than a landscape. Specifically, display=greyscale, bottom=0 and top=2500. The number of channels is set to 128 for compatibility with the auditory spectrum modules, genasa and genepn. When using AIM as a preprocessor for speech recognition the number of channels would typically be reduced to between 24 and 32. Use option ’downsample’ if it is necessary to reduce the output to less than 24 channels across the speech range.

NOTE: The cochlea simulations impose compression of one form or another on the NAP and the notes on compression in the man pages for gennap apply to gencgm as well.

    Transduction

transduction Neural transduction switch (at, meddis, off) Switch. Default: at.

II. LEAKY INTEGRATION

stages_idt Number of stages of lowpass filtering Default unit: scalar. Default value: 2
tup_idt The time constant for each filter stage Default unit: ms. Default value: 8 ms.

The Equivalent Rectandular Duration (ERD) of a two stage lowpass filter is about 1.6 times the time constant of each stage, or 12.8 ms in the current case.

downsample The time between successive spectral frames. Default unit: ms. Default value: 10 ms.

Downsample is simply another name for frstep_epn, provided to facilitate a different mode of thinking about time-series data.

frstep_epn The time between successive spectral frames Default unit: ms. Default value: 10 ms.

With a frstep_epn of 10 ms, gencgm will produce spectral frames at a rate of 100 per second.

REFERENCES

Patterson, R.D., Holdsworth, J. and Allerhand M. (1992a).
  "Auditory Models as preprocessors for speech recognition," In: The Auditory Processing of Speech: From the auditory periphery to words, M.E.H. Schouten (ed), Mouton de Gruyter, Berlin, 67-83.

Patterson, R.D., Allerhand, M.H. and Holdsworth, J. (1993a) "Auditory representations of speech sounds," In Visual representations of speech signals, Eds. Martin Cooke, Steve Beet, and Malcolm Crawford, John Wiley & Sons, Chichester. 307-314.

Patterson, R.D., Anderson, T., and Allerhand, M. (1994). "The auditory image model as a preprocessor for spoken language," in Proc. Third ICSLP, Yokohama, Japan, 1395-1398.

Patterson, R.D., Allerhand, M., and Giguere, C., (1995). "Time-domain modelling of peripheral auditory processing: A modular architecture and a software platform," J. Acoust. Soc. Am. 98-3, (in press).

FILES

The options file for gencgm.

SEE ALSO

gensgm, genasa, genepn, gennap, genbmm

BUGS

None currently known.

COPYRIGHT

Copyright (c) Applied Psychology Unit, Medical Research Council, 1995

Permission to use, copy, modify, and distribute this software without fee is hereby granted for research purposes, provided that this copyright notice appears in all copies and in all supporting documentation, and that the software is not redistributed for any fee (except for a nominal shipping charge). Anyone wanting to incorporate all or part of this software in a commercial product must obtain a license from the Medical Research Council.

The MRC makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

ACKNOWLEDGEMENTS

The AIM software was developed for Unix workstations by John Holdsworth and Mike Allerhand of the MRC APU, under the direction of Roy Patterson. The physiological version of AIM was developed by Christian Giguere. The options handler is by Paul Manson. The revised SAI module is by Jay Datta. Michael Akeroyd extended the postscript facilites and developed the xreview routine for auditory image cartoons.

The project was supported by the MRC and grants from the U.K. Defense Research Agency, Farnborough (Research Contract 2239); the EEC Esprit BR Porgramme, Project ACTS (3207); and the U.K. Hearing Research Trust.


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