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Manual Reference Pages  - GENEPN (1)

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NAME

genepn - generate excitation pattern

CONTENTS

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

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

Genepn converts the input wave into a simulated neural activity pattern (NAP) and summarises the NAP as a sequence of excitation patterns (EPNs). 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 the auditory filterbank. The surface of the array of filtered waves is AIM’s representation of basilar membrane motion (BMM) as a function of time (see genbmm). In the neural encoding stage, compression, adaptation and, optionally, 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 multi-channel neural activity pattern (NAP) in the auditory nerve at about the level of the cochlear nucleus (see gennap). 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, 1994a). The envelope is calculated continuously, by lowpass filtering the individual channels of the NAP as they flow from the cochlea simulation.

The excitation pattern produced by genepn is intended to simulate the spectral representation of a sound as it occurs in the peripheral auditory system after neural transduction at about the level of the cochlea nucleus. As a result, the frequency resolution of the analysis varies with the center frequency of the channel, and the distribution of channels across frequency is chosen to match that in the auditory system (Patterson and Moore, 1986; Glasberg and Moore, 1990). For details, see the manual entry for genbmm and Patterson (1994a) The excitaion pattern is a plot of the activity in each channel as a function of the centre frequency of the auditory filter that defines the channel. In AIM, the suffix ’epn’ is used to distinguish this spectral representation from the other spectral representations provided by the software (’asa’ auditory spectral analysis, ’sgm’ auditory spectrogram, and ’cgm’ cochleogram).

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.

The default values for three of the display options are reset to produce a spectral format rather than a landscape. Specifically, display=excitation, bottom=0 and top=2500. The number of channels is increased to 128 to ensure reasonable frequency resolution in the excitation pattern display.

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 genepn as well.

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, genepn will produce spectral frames at a rate of 100 per second.

	Glasberg, B. R. and B. C. J. Moore (1990). "Derivation of auditory filter shapes from notched-noise data," Hearing Research, 47, 103-138.

	Patterson, R.D. (1994a). "The sound of a sinusoid: Spectral models," J. Acoust. Soc. Am. 96, 1409-1418.

	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

.genepnrc	The options file for genepn.

genasa, gennap, genbmm, gensgm, gencgm

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.

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.