annotate man/man1/genbmm.1 @ 0:5242703e91d3 tip

Initial checkin for AIM92 aimR8.2 (last updated May 1997).

.TH GENBMM 1 "11 April 1994"
.LP
.SH NAME
.LP
genbmm \- generate basilar membrane motion
.LP
.SH SYNOPSIS
.LP
genbmm [ option=value | -option ] [ filename ]
.LP
.SH DESCRIPTION
.LP
The genbmm module of the AIM software simulates the spectral analysis
performed by the auditory system using a bank of auditory filters.
Specifically, genbmm converts an input wave into an array of filtered
waves, one for each channel of the filterbank. The surface of the
array of filtered waves is AIM's representation of basilar membrane
motion (BMM) as a function of time.  AIM provides two alternative
methods for generating the BMM, linear, gammatone filterbank
(Patterson et al, 1988; Slaney 1993, Cooke, 1993), or a nonlinear,
transmission-line filterbank (Giguere and Woodland, 1994). For
convenience, they are referred to as the 'functional' filterbank and
the 'physiological' filterbank, respectively.
.LP
.SH OPTIONS
.LP
There are three sets of options for genbmm; they are grouped by
function and identified by the suffixes _afb, _gtf and _tlf. The first
set controls the distribution of the filtered waves across frequency
(suffix _afb); the second specifies the shape of the gammatone filter
(suffix _gtf); and the third specifies the shape of the transmission
line filter (suffix _tlf). These three groups of options are the
subject of this manual entry, together with an option that specifies
the filter choice (gtf or tlf), and an option that specifies whether a
middle ear function should be used with the gtf filterbank.
.LP
.SS "The Outer/Middle Ear function: middle_ear "
.PP
In the auditory system the middle ear causes a progressive attenuation
of sound energy in the region below about 500 Hz and a progressive
attenuation in the region above about 4000 Hz.  There is also a
primary auditory canal resonance around 2700 Hz that provides a boost
in sound transmission. The resulting transfer function is a normal
aspect of auditory processing and preceeds spectral analysis. If the
functional filterbank is chosen (gtf), the outer/middle ear filter
acts directly on the input wave, and the stapes velocity wave it
generates is the input to the spectral filtering stage. If the
physiological filterbank is chosen (tlf), the outer/middle ear and
cochlear filter are performed simultaneously as in the auditory
system. The only parameter associated with this function is the
middle_ear switch which makes it possible to turn the outer/middle ear
filtering off when the functional filterbank is chosen.
.LP
.TP 13
middle_ear
Outer/middle ear switch
.RS
Switch. Default: on. 
.RE
.RS
.LP
It is also possible to specify a floating point number, in which 
case the middle ear output is multiplied by that value.
.RE
.LP
Note: The middle_ear option is ignored if option filter (see below) 
is set to tlf. This is because the outer/middle stage and the 
cochlear stage are bidirectionally coupled in the transmission 
line filter implementation, and cannot be separated. 
.RE
.LP
.SS "The Auditory FilterBank options: _afb "
.PP
The distribution of the filters across frequency and the total 
number of output filters in the bank are determined by four parameters: 
channels_afb, mincf_afb, maxcf_afb, and dencf_afb. 
.LP
.TP 13
channels_afb
The number of channels in the filterbank. 
.RS
Default unit: filters. Default value: 75 
.RE
.TP 13
mincf_afb
The minimum centre frequency 
.RS
Default unit: Hz. Default value: 100 Hz. 
.RE
.TP 13
maxcf_afb
The maximum centre frequency 
.RS
Default unit: Hz. Default value: 6000 Hz. 
.RE
.TP 13
dencf_afb
The density of the filters in the filterbank. 
.RS
Units: filters/critical band. Default: off 
.RE
.RS
.LP
dencf_afb provides an alternative method of specifying the number of channels 
in terms of the density of filters along the frequency scale. 
.RE
.LP
Note: channels_afb overrides dencf_afb whenever it has a non-zero 
value.  The values of dencf_afb and channels_afb may conflict at 
this point, in which case dencf_afb is ignored.
.RE
.LP
WARNING: When using the transmission line filter (filter=tlf), the
channel density should be 3 or more filters/erb.  Using a lower
density may lead to excessive spatial discretization errors (see
Giguere and Woodland (1994) for a discussion).  To view a small number
of channels, use a reasonable density and reduce the number of
displayed channels using option downchannel.
.LP
.TP 14
audiogram_afb
The audiogram 
.RS
Units: none. Default: off. Status: obsolete.
.RE
.LP
Note: In the versions up to and including AIM R6.15, this parameter
was used as a means of approximating equal loudness contours, as well
as middle ear attenuation. It applies a spectral weighting function at
the output of the filterbank. With the addition of the outer/middle
ear transfer function, this parameter is obsolete, and so the default
value is off. Users who wish to use the audiogram parameter instead of
the new outer/middle filter as a loudness equilisation function can
still do so by setting audiogram_afb=on and middle_ear=off. As before,
audiogram_afb is applied as a power function and so as the value of
audiogram_afb decreases from 1 to 0, the degree of attenuation
decreases.  Values greater than unity are allowed but their
interpretation is unclear.
.RE
.LP
The ERB scale for the gammatone auditory filterbank
is specificed with three options: bwmin_afb, quality_afb, 
and mmerb_afb. 
.LP
.TP 13
bwmin_afb
The minimum bandwidth for an auditory filter. 
.RS
Default unit: Hz. Default value: 24.7 
.RE
.TP 13
quality_afb
The limiting quality factor for high frequency auditory filters. 
.RS
Units: scalar. Default: 9.265 
.RE
.TP 13
mmerb_afb
The length of one erb-rate unit along the basilar membrane.
.RS
Units: mm. Default: 0.89
.RE
.LP 13
A listing of the parameters for the filter in the bank can be directed
to the terminal at run time by setting info_afb=on.
.RE
.TP
info_afb
Print filterbank information to stderr.
Switch. Default: off.
.RE
.LP
The physiological data on human cochlear frequency-position 
function (Greenwood, 1990) and the psychoacoustic data on auditory 
filter bandwidth (Patterson and Moore, 1986) indicate that the 
spectral analysis performed in the cochlea is like a 'constant Q' 
system (quality_afb) that asymptotes to a minimum filter bandwidth 
(bwmin_afb) at low centre frequencies. That is,
.PD 0
.LP
.PD 4
.LP
	erb = bwmin_afb + centre-frequency/quality_afb.  
.PD 0
.LP
.PD 4
.LP
If we assume, as Greenwood suggests, that each filter bandwidth
corresponds to a constant distance (mmerb_afb) along the basilar
membrane, it is possible to scale frequency in terms of erb units (or
position along the basilar membrane) by integrating the inverse of the
erb function above.
.RE
.LP
Glasberg and Moore (1990) have reviewed the available human filter
shape data and concluded that the optimum values for bwmin_afb and
quality_afb are 24.7 and 9.265, respectively, together with mmerb_afb
of 0.89.  (As a rule of thumb for rapid estimation, erb = 25 + 10% of
cf ). The auditory scale used by Greenwood (1990) can be specified by
setting bwmin_afb=22.85, quality_afb=7.238 and mmerb_afb=1.0. A
reasonable approximation to the Bark scale (Zwicker, 1961) is obtained
by setting bwmin_afb=80, quality_afb=6.5 and mmerb_afb=0.89.
.RE
.LP
.SS "Auditory filter design: filter "
.PP
The choice of filterbank -- linear gammatone or nonlinear transmission
line -- is determined by option filter.
.LP
.TP 13
filter
The auditory filter design
.RS
Default: gtf. Choices: gtf, tlf, off.
.RE
.LP
When gtf is specified, the options below with suffix _gtf apply, and
when tlf is specified, the options below with suffix _tlf apply. When
off is specified, the input wave (or the stapes velocity) is passed on
directly to the next stage. This provides for non-auditory use of the
modules following the filterbank with their associated displays. For
example, the envelope of the input wave (or stapes velocity) can be
extracted using the rectification and integration modules that follow
genbmm. The entry point genasa has the most convenient default
settings for this purpose. The default value for the filter option is
gtf.
.RE
.LP
.SS "The GammaTone Filter options: _gtf "
.LP
.TP 13
order_gtf
The order of the gammatone filter 
.RS
Units: none. Default: 4 
.RE
.RS
.LP
The order of the filter, order_gtf, determines the number of filtering
stages and so it determines the slope of the skirts of the attenuation
function and their extent. The default value is 4 and the range of
useful values is from about 2 to 8.  The processing time increases
linearly with order above about order 2.
.RE
.LP
Note that the bandwidth calculation takes account of the fact that
changes in order_gtf affect bandwidth. Thus, as long as bwmin_afb is
fixed, changing the order will not affect the bandwidths of the
resulting filters.  Increasing the order of the filter increases the
delay of the onset of the impulse response but it has little effect on
the shape of the envelope of the impulse response for orders greater
than three. The human auditory system is not sensitive to small phase
changes between filter channels (Patterson, 1987) and so filter order
is not well constrained by human experimental data.  The default value
(4) is used because this value provides the best match between the
amplitude characteristics of the gammatone and roex filters for humans
(Patterson et al., 1988).
.LP
.TP 13
gain_gtf
Filter output amplification 
.RS
Units: scalar. Default: 4.
.RE
.RS
.LP
The ratio of input to output level across the auditory filter 
when the input is a sinusoid at the cf of the filter.
.RE
.TP 13
phase_gtf
The phase of the impulse response (obsolete)
.RS
Units: none. Default: 0. 
.RE
.LP
In the absence of phase compensation, the surface of basilar membrane
motion has a strong rightward skew in the low-frequency channels
because the filters get progressively narrower as centre frequency
decreases, and this narrowing is accompanied by a slower filter
response. There are occassionally non-auditory reasons for wanting to
align the channels across frequency in one way or another. The
software provides four alignment systems which are discussed at the
end of this entry just before the references under the title Phase
Alignment.
.RE
.LP
.SS "The Transmission Line Filter options: _tlf "
.LP
.TP 13
motion_tlf
The basilar membrane output motion variable
.RS
Default: vel. Choices: vel, disp.
.RE
.RS
.LP
If vel (velocity) is specified, the output of genbmm
is the basilar membrane velocity. If disp (displacement)
is specified, the output of genbmm is the basilar membrane
displacement. The default value is vel.
.RE
.TP 13
outdencf_tlf
The density of the filters outside the display
range. 
.RS
Units: filters/critical band. Default: 4.
.RE
.RS
.LP
In the transmission line filter implementation, it is necessary to
simulate the basilar membrane over its entire length.  The option
outdencf_tlf provides a means of specifying the number of additional
channels that must be computed at the basal and apical ends of the
cochlea, ie. outside the range specified by mincf_afb and maxcf_afb
(see above).  These additional channels are only computed for internal
use and are not passed to the next stage of processing.
.RE
.TP 13
qref_tlf
The local quality factor of each basilar membrane channel
.RS
Units: scalar. Default: 2. 
.RE
.RS
.LP
Note: With the transmission line filter, the bandwidth is not
determined by options bwmin_afb and quality_afb at high levels but
rather by option qref_tlf (see above).
.RE
.TP 13
feedback_tlf
The feedback gain of the outer hair cell circuit
.RS
Units: scalar. Default: 0.99
.RE
.RS
.LP
WARNING: A value for feedback_afb greater than or equal to 1.0 can
lead to unstable behaviour at low-levels (ie. oscillation).  However,
the model output will not grow unbound. The growth of the oscillations
will be limited by the saturating nonlinearity of the outer hair cell
circuit, and the model output will go into a kind of limit-cycle.
These model oscillations have not yet been studied in detail and are
likely to deviate substantially from real cochlear emissions.
.RE
.TP 13
dsat_tlf
The basilar membrane displacement at the half-saturation point 
of the outer hair cell circuit
.RS
Units: cm. Default: 5.75e-6
.RE
.TP 13
gain_tlf
Filter output amplification 
.RS
Units: scalar. Default: 4.
.RE
.RS
.LP
Note: There is an internal gain of 4.0 within the software of
the transmission line model itself. The total gain is therefore
4.0 times the value for gain_tlf.
.RE
.LP
Note: A linearized version of the transmission line filter with
roughly the same bandwidth as the gammatone filter can be obtained by
setting feedback_tlf=0 and qref_tlf to about 10.  The main difference
is that the low-frequency skirt of the transmission line filter is
less steep than that of the gammatone.
.LP
.SH FURTHER DESCRIPTION
.LP
.SS "The distribution of filter centres along the ERB scale. "
.LP
Given values for mincf_afb maxcf_afb and channels_afb (or 
dencf_afb), the program creates an array of centre frequencies 
in three steps:
.LP
1. It centres a filter at 1.0 kHz.
.RE
.LP
2. Then it centres filters below 1.0 kHz, one after another, 
until it encounters mincf_afb. (Thus, mincf_afb is actually the 
frequency below which no filters are centred). The step size, 
that is the distance between centre frequencies, is determined 
by dencf_afb. When dencf_afb is equal to one, the centre 
frequencies are 1 ERB apart. The ERB is the Equivalent 
Rectangular Bandwidth of the filter (about 14% larger than the 3 
dB bandwidth of the filter). The function relating the ERB to the 
centre frequency of the filter is taken from a `critical band' 
equation introduced by Greenwood (1961) and adapted to human 
auditory masking by Glasberg and Moore (1990).
.RE
.LP
3. Finally, the program centres filters one after another in 
the region above 1 kHz until it encounters maxcf_afb (which is, 
actually, the frequency above which no filters are centred). When 
dencf_afb is increased, say to two, the program allocates two 
filters per critical band and spaces them at half ERB steps.
.RE
.LP
Note: It is not the bandwidths of the filters that are 
controlled by dencf_afb but rather the density of filters along 
the frequency axis. Thus, doubling dencf_afb does not cause the 
bandwidth of the filters to be halved; rather it results in more 
overlap between adjacent filters. With regard to the images 
produced by genbmm, dencf_afb determines the density of lines on 
the surface rather than the shape of the features that appear on 
the surface.
.LP
.SH MOTIVATION
.LP
The motivation for adopting the gammatone filter shape is 
threefold:
.LP
1. It provides an excellent summary of physiological data 
concerning the impulse response of primary auditory neurons in 
small mammals such as cats (de Boer and de Jongh, 1978; Carney and 
Yin, 1989)
.RE
.LP
2. The amplitude characteristic of the gammatone filter is very 
similar to that of the Roex filter commonly used to represent the 
human auditory filter (Patterson, et al, 1982; Schofield, 1985; 
Patterson et al, 1988) .
.RE
.LP
3. There are recursive gammatone filters that make the calculation
particularly fast both on general purpose computers and special
purpose DSP chips (Holdsworth et al, 1988; Cooke, 1993; Slaney, 1993).
.RE
.LP
In summary, the gammatone filter is designed to provide a reasonable
trade-off between accuracy in simulating basilar membrane motion, and
computational load.
.RE
.LP
The motivation for adopting the transmission line filter is 
as follows:
.LP
1. The outer hair cell circuit of the transmission line filter is
level dependent and so this design produces level-dependent basilar
membrane tuning curves (Giguere and Woodland, 1994). There is now
ample evidence that the basilar membrane motion is indeed highly
nonlinear and a major source of level compression (eg. Johnstone et
al., 1986).
.LP
2. The internal structure of the transmission line filter model is
based on the physics of the auditory periphery and therefore provides
a more realistic cochlear simulation than parallel filterbanks. It
generates combination tones of the form 2f1-f2 as observed in the
auditory system and it has the potential to generate cochlear echoes.
.LP
3. The wave-digital-filter implementation of the transmission line
filterbank is only about twice as slow as the gammatone filterbank
for an equivalent number of channels.
.RE
.LP
.SH "Phase Alignment"
.LP
There is no question that the output of the cochlea has a phase lag
corresponding to the strong rightward skew. However, perceptual
evidence indicates that this phase lag has to be enormous (> 4ms) to
affect what we hear; indeed, reversing the phase lag with synthetic
stimuli does not change what we hear (Patterson, 1987).  Phase
information that appears in the basilar membrane motion but which we
do not hear, is removed in the third module by the strobe mechanism of
the temporal integration process. As a result, the stabilised auditory
images are always phase aligned even though the basilar membrane
motion and the neural activity patterns are not.
.RE
.LP
Prior to discovering the integration mechanism, we wanted to find 
a way of reducing the skew from the basilar membrane image, in 
order to provide a visual representation that was more like what 
we hear. The genbmm program provides the following options for 
phase aligning the responses of successive filters, determined 
by the value of the option phase_gtf:
.RE
.LP
Value Effect
.PP
.TP 7
-1
Envelope alignment. 
.RS
Shift the channels of output horizontally so that the points of 
maximum response to an impulse (ie the envelope maxima) will be aligned. 
.RE
.TP 7
-2
Envelope plus fine structure alignment. 
.RS
Perform envelope-peak alignment as in option -1 and then shift the 
fine structure phase in each channel so that a fine- structure peak 
coincides with the envelope peak. 
.RE
.TP 7
-4
Envelope plus peak alignment, `left justified'. 
.RS
Align the envelopes and fine structure of all of the impulse responses 
along the left edge of the image. 
.RE
.TP 6
0
No phase compensation. 
.TP 7
+n
Advance each channel by n cycles of the centre frequency of the channel. 
Approximate envelope alignment is achieved using phase_gtf = 3 
or 4.
.RE
.LP
We experimented with a number of phase compensation schemes 
(Patterson et al., 1989) and concluded that the best option was 
envelope plus peak alignment which corresponds to a value of 
phase_gtf = -4. Accordingly, we recommend the use of phase_gtf 
values of 0 (ie no phase compensation) or -4 (envelope plus peak 
alignment). The remaining options are occasionally useful and so 
they have been left in the software.
Note that for any phase compensation option other than 0 the time 
scale is strictly correct only for the lowest channel. For any 
other channel, the origin of the abscissa is offset to the right 
by an amount equal to the difference between `the envelope peak 
time of the lowest-frequency channel' and `the envelope peak time 
of the given channel'.
.RE
.LP
.SH REFERENCES
.LP
.RE
.TP 4
de Boer, E., and de Jongh, H.R. (1978). On cochlear encoding:
potentialities and limitations of the reverse-correlation
technique, J. Acoust. Soc. Am., 63, 115-135.
.RE
.LP
.TP 4
Carney, L.H. and Yin, C.T. (1988) 'Temporal coding of resonances
by low-frequency auditory nerve fibers: Single fibre responses
and a population model', J.Neurophysiology, 60, 1653-1677.
.RE
.LP
.TP 4
Cooke, M.P. (1993). Modelling Auditory Processing and
Organisation, Cambridge University Press.
.RE
.LP
.TP 4
Giguere, C. and Woodland, P.C. (1994). A computational model of
the auditory periphery for speech and hearing research. I. Ascending
path. J.Acoust. Soc. Am. 95: 331-342.
.RE
.LP
.TP 4
Glasberg, B.R. and B.C.J. Moore (1990). Derivation of auditory
filter shapes from notched-noise data. Hearing Research, 47,
103-138.
.RE
.LP
.TP 4
Greenwood, D.D. (1961)  'Critical bandwidth and the frequency
coordinates of the basilar membrane', J. Acoust. Soc. Am. 33,
1344-1356.
.RE
.LP
.TP 4
Greenwood, D.D. (1990). A cochlear frequency-position function
for several species - 29 years later. J. Acoust. Soc. Am., 87,
2592-2605.
.RE
.LP
.TP 4
Holdsworth, J., Nimmo-Smith, I., Patterson, R.D. and Rice, P.
(1988) Annex C of 'Spiral Vos Final Report, Part A: The
Auditory Filterbank,' APU report  2341.
.RE
.LP
.TP 4
Johnstone, B.M. et al. (1986). Hear Res. 22: 147-153.
.RE
.LP
.TP 4
Moore, B.C.J and Glasberg, B.R. (1983), "Suggested formulae for
calculating auditory filter bandwidths and excitiation patterns,"
J. Acoust. Soc. Am. 74, pp 750-753.
.RE
.LP
.TP 4
Patuzzi, R., and Robertson, D. (1988) "Tuning in the mammalian
cochlea," Physiological Reviews 68, 1009-1082.
.RE
.LP
.TP 4
Patterson, R.D. (1976). Auditory filter shapes derived with
noise stimuli. J. Acoust. Soc. Am., 59, 640-654.
.RE
.LP
.TP 4
Patterson, R.D. (1987). A pulse ribbon model of monaural phase
perception. J. Acoust. Soc. Am., 82, 1560-1586.
.RE
.LP
.TP 4
Patterson, R.D., Nimmo-Smith, I., Weber, D.L., and Milroy, R.
(1982).  The deterioration of hearing with age:  Frequency
selectivity, the critical ratio, the audiogram, and speech
threshold.  J. Acoust. Soc. Am., 72, 1788-1803.
.RE
.LP
.TP 4
Patterson, R.D., Allerhand, M.H. and Holdsworth, J. (1992)
'Auditory representations of speech sounds', In Visual
representations of speech signals, Eds. Martin Cooke and Steve
Beet, John Wiley & Sons. 307-314.
.RE
.LP
.TP 4
Patterson, R. D., Holdsworth, J., Nimmo-Smith, I., and Rice, P.
(1988). SVOS Final Report: The Auditory Filterbank. APU report 2341.
.RE
.LP
.TP 4
Patterson, R.D. and B.C.J. Moore (1986). Auditory filters and
excitation patterns as representations of frequency
resolution. In: Frequency Selectivity in Hearing (B. C. J.
Moore, ed.), pp. 123-177. Academic Press, London.
.RE
.LP
.TP 4
Schofield, D. (1985) 'Visualisations of speech based on a model
of the peripheral auditory system', NPL Report DITC 62/85.
.RE
.LP
.TP 4
Slaney, M. (1993) An efficient implementation of the Patterson-
Holdsworth auditory filter bank. Apple Computer Technical
Report #35.
.RE
.LP
.TP 4
Zwicker, E. (1961) Subdivision of the audible frequency range into
critical bands (frequenzgruppen).  J. Acoust. Soc. Am.  33, 248.
.LP
.SH EXAMPLES
.LP
The following command generates basilar membrane motion using the
gammatone filter design (the default) for an input filename cegc:
.RE
.LP
example% genbmm cegc
.RE
.LP
The following command generates basilar membrane motion using the
gammatone filter design (the default) for a filterbank with cf from
200 Hz to 5000 Hz at a density of 4 filters/critical band for the same
input filename:
.RE
.LP
example% genbmm channels=0 mincf=200 maxcf=5000 dencf=4. cegc
.RE
.LP
The following command generates basilar membrane motion using the
gammatone filter design (the default) and the audiogram function
instead of the outer/middle ear filter:
.RE
.LP
example% genbmm middle_ear=off audiogram=on cegc
.RE
.LP
The following command generates the basilar membrane motion using the
transmission line filter design instead of the default gammatone
filter:
.RE
.LP
example% genbmm filter=tlf cegc
.RE
.LP
The following command generates the basilar membrane motion using the
transmission line filter design and the auditory scale of Greenwood
(1990):
.RE
.LP
example% genbmm filter=tlf bwmin=22.85 quality=7.238 mmerb=1.0 cegc
.RE
.LP
The following command generates the basilar membrane motion using the
transmission line filter design, but with the nonlinear outer hair
cell feedback mechanism turned off:
.RE
.LP
example% genbmm filter=tlf feedback=off cegc
.LP
.SH FILES
.LP
.TP 13
 .genbmmrc 
The options file for genbmm.
.LP
.SH SEE ALSO
.LP
genasa, gensgm
.LP
.SH BUGS
.LP
There is a bug in the hiddenline plotting of genbmm. It shows up when
the surface has deep valleys and there is a large phase delay. The
negative peaks show through on surfaces where they should be hidden.
.SH COPYRIGHT
.LP
Copyright (c) Applied Psychology Unit, Medical Research Council, 1995
.LP
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.
.LP
The MRC makes no representations about the suitability of this 
software for any purpose.  It is provided "as is" without express or 
implied warranty.
.LP
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.
.LP
.SH ACKNOWLEDGEMENTS
.LP
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.
.LP
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.