Subject: Auditory nerve correlates to rise time plus grouping in implants From: Stuart Rosen <stuart(at)PHONETICS.UCL.AC.UK> Date: Tue, 9 Mar 1993 11:28:09 GMT------------------------------------------------------------------------- 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