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 activitypattern (NAP) and summarises the NAP as a sequence of excitationpatterns (EPNs). The operation takes place in three stages: spectralanalysis, neural encoding, and temporal integration (Patterson etal. 1995) . In the spectral analysis stage, the input wave isconverted into an array of filtered waves, one for each channel of theauditory filterbank. The surface of the array of filtered waves isAIM’s representation of basilar membrane motion (BMM) as a function oftime (see genbmm). In the neural encoding stage, compression,adaptation and, optionally, suppression, are used to convert each wavefrom the filterbank into a simulation of the aggregate neural responseto that wave. The array of responses is AIM’s simulation of themulti-channel neural activity pattern (NAP) in the auditory nerve atabout the level of the cochlear nucleus (see gennap). Finally, the NAPis converted into a sequence of excitation patterns (EPNs) bycalculating the envelope of the NAP and extracting spectral slicesfrom the envelope every ’frstep_epn’ ms (Patterson, 1994a). Theenvelope is calculated continuously, by lowpass filtering theindividual channels of the NAP as they flow from the cochleasimulation.

The excitation pattern produced by genepn is intended to simulate thespectral representation of a sound as it occurs in the peripheralauditory system after neural transduction at about the level of thecochlea nucleus. As a result, the frequency resolution of theanalysis varies with the center frequency of the channel, and thedistribution of channels across frequency is chosen to match that inthe 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 eachchannel as a function of the centre frequency of the auditory filterthat defines the channel. In AIM, the suffix ’epn’ is used todistinguish this spectral representation from the other spectralrepresentations provided by the software (’asa’ auditory spectralanalysis, ’sgm’ auditory spectrogram, and ’cgm’ cochleogram).

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

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

NOTE: The cochlea simulations impose compression of one form oranother on the NAP and the notes on compression in the man pages forgennap apply to genepn as well.

stages_idt	Number of stages of lowpass filteringDefault unit: scalar. Default value: 2
tup_idt	The time constant for each filter stageDefault unit: ms. Default value: 8 ms. The Equivalent Rectandular Duration (ERD) of a two stage lowpassfilter is about 1.6 times the time constant of each stage, or12.8 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 tofacilitate a different mode of thinking about time-series data.
frstep_epn	The time between successive spectral framesDefault unit: ms. Default value: 10 ms. With a frstep_epn of 10 ms, genepn will producespectral 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 modulararchitecture and a software platform," J. Acoust. Soc. Am. 98-3, (inpress).

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 feeis hereby granted for research purposes, provided that this copyrightnotice appears in all copies and in all supporting documentation, and thatthe software is not redistributed for any fee (except for a nominalshipping charge). Anyone wanting to incorporate all or part of thissoftware in a commercial product must obtain a license from the MedicalResearch Council.

The MRC makes no representations about the suitability of thissoftware for any purpose. It is provided "as is" without express orimplied warranty.

THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDINGALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALLTHE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGESOR 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 THISSOFTWARE.

The AIM software was developed for Unix workstations by JohnHoldsworth and Mike Allerhand of the MRC APU, under the direction ofRoy Patterson. The physiological version of AIM was developed byChristian Giguere. The options handler is by Paul Manson. The revisedSAI module is by Jay Datta. Michael Akeroyd extended the postscriptfacilites and developed the xreview routine for auditory imagecartoons.

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