Graeme Clark Collection

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Author: Busby, Peter × Author: COHEN, LAWRENCE × End date: 1999 × Start date: 1990 × Type: Journal Article × Subject: cochlear implant ×

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    Cochlear implant place psychophysics: 1. Pitch estimation with deeply inserted electrodes
    Cohen, Lawrence T. ; Busby, Peter A. ; Whitford, Lesley A. ; Clark, Graeme M. ( 1996)
    Numerical estimation of pitch was performed by 8 adult subjects implanted with cochlear prostheses manufactured by Cochlear Limited. The electrode arrays had been inserted into the scala tympani to between one and one and a half turns of the cochlea. Using bipolar stimulation, the pitch estimates for each subject showed an overall reduction with insertion depth of the stimulated electrode. However, for several subjects, after decreasing regularly for the more basal electrodes, pitch estimates showed an abrupt decrease, followed in some cases by a region of low pitch. Two of the subjects, implanted with a modified electrode array, the '20 + 2' which allowed monopolar in addition to bipolar stimulation, exhibited an abrupt decrease in pitch estimate with bipolar but not with monopolar stimulation. In these two subjects, for stimulating electrodes inserted more deeply than about three quarters of a turn, bipolar stimuli produced lower pitch sensations, and presumably more apical neural excitation patterns, than monopolar stimuli.
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    Cochlear implant place psychophysics: 2. Comparison of forward masking and pitch estimation data
    Cohen, Lawrence T. ; Busby, Peter A. ; Clark, Graeme M. ( 1996)
    Results for forward masking and numerical estimation of pitch were compared in a group of 6 adult subjects implanted with cochlear prostheses manufactured by Cochlear Limited. Data were collected for bipolar +1 stimulation in all subjects, and for stimulation in one other mode, either common ground or monopolar, for all subjects but one. The pitch data show various irregularities and in each case can be seen to be broadly consistent with the corresponding forward masking data. It is shown that a 'centre of gravity' of the forward masking distribution varies with masker electrode in a manner that is qualitatively very similar to the variation of pitch estimate. It is suggested that, while pitch estimation results are consistent with those from forward masking, the latter contain more detailed information that may be useful in understanding intersubject variations in speech comprehension.