Auditory nerve correlates to rise time plus grouping in implants

[Stuart Rosen <stuart@xxxxxxxxxxxxxxxxxxx>]

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To Al Bregman:

Dear Al,

Sorry I haven't replied sooner, but there are at least two studies
relevant to your question regarding the way in which changes in
rise time are reflected in auditory nerve activity:

Delgutte, B. (1980) Representation of speech-like sounds in the
     discharge patterns of auditory-nerve fibers. Journal of the
     Acoustical Society of America 68:843-857.

This paper describes an experiment in which it is shown that faster
rise times (in noise bursts meant to represent the frication portions of
cha's and sha's) lead to bigger onsets in auditory nerve firing patterns
(i.e., a bigger peak at stimulus onset in PST histograms). Note, though,
that the result probably has little import for the phonetic contrast
in question because the rise times used are inappropriate for speech
(a P&P paper - 1988? - by K. Kluender and some one else casts doubt on
the importance of rise time per se on this contrast anyway - as does
some new data we have obtained)

Delgutte, B. (1982).  Some correlates of phonetic distinctions
     at the level of the auditory nerve, in The Representation
     of Speech in the Peripheral Auditory System, edited by R.
     Carlson and B. Granstrom (Elsevier Biomedical Press,
     Amsterdam).

This paper describes a way to account for a particular trading of cues
in speech perception through a completely auditory mechanism. In essence,
it is based on the same idea as in the previous paper. Only model results
are shown. A nice idea, although, again, there are a number of reasons
to believe that it will not account for phenomenon in real speech.

As far as grouping in multi-channel cochlear implants, I myself have little
experience, but I have heard Mike Dorman talk anecdotally (about
Inner-aid (sp?) patients) that
the most basal channels (high frequencies) can split off perceptually.
Best to contact him. It is also worth noting that the more apical channels
(low frequencies) will already be comodulated at the fundamental
frequency insofar as there is energy from voiced speech sounds spreading
across more than one channel. Unlike the situation in normal hearing,
even the most apical channel is quite wide, allowing the interaction of
a number of harmonics.

Yours - Stuart Rosen