Bleeck, S., Ingham, N., Carlyon, R.P. and Winter, I.M.
Challenges to inter-spike interval models of pitch: the responses of cochlear nucleus neurons to band-pass filtered pulse trains
At 29th Annual MidWinter Research Meeting: Association for Research in Otolaryngology.
05 - 09 Feb 2006.
Full text not available from this repository.
Carlyon et al. (J Acoust Soc Am 112: 621-33, 2002) found
that a pulse train with alternating inter-pulse intervals
between 4 and 6 ms (“4-6 stimulus”) is perceived as
having a periodicity of 5.7ms. Using a model that relies on
neuronal first order intervals (FOIs) for pitch perception,
they showed that the recovery of the auditory nerve from
adaptation is not sufficient to explain this effect and
suggested that a weighting function that favours longer
FOI intervals was needed to account for the perceived
pitch. Here we investigate whether there are neurons, or
populations of neurons, at the next stage of processing,
the cochlear nucleus (CN), that give greater representation
to longer intervals. We measured the responses of single
neurons in the ventral CN of anesthetised guinea pigs to
isochronous and anisochronous pulse trains. Pulse trains
were band-pass filtered between 3900 Hz and 5300 Hz.
Isochronous pulse trains had interpulse intervals of 3, 4, 5,
6 and 7 ms. Anisochronous pulse trains had alternating
interpulse intervals between 4 and 6 ms. The results are
based on the responses of 58 units, classified by the
shape of their post stimulus time histograms as Primary
with notch (PN, 9), transient chopper (CT, 22), sustained
chopper (CS, 10) and onsets (ON, 17). PN and CT units
showed a recovery behaviour that is quantitatively similar
to the auditory nerve. ON and CS units showed a faster
recovery between 4 and 6 ms, but not enough to account
for the size of the psychophysical effect. The average of
FOI distributions for single units generally has too many
long intervals to account for the observed pitch of the 4-6
stimulus. When sequentially interleaving the spikes from
all units the average FOI distribution contains more shorter
intervals, but, by interleaving spikes from just 2 to 4 units the average FOI becomes small enough to explain the observed pitch of the 4-6 stimulus. The location of units that may participate in such an analysis remains obscure.
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