| Summary: | This research examines, in a musical context, the
measurement of pitches heard by Nucleus cochlear implant
recipients upon systematic variation of electrical pulse
rates, delivered to single intracochlear electrodes at a
comfortable listening level. Stimuli were configured by a
computer in tandem with the Boys Town National Institute
Interface for psychophysical research with the Nucleus
cochlear implant. Seventeen subjects participated in a 30-
item tune recognition test (Experiment I). Many subjects
identified a substantial number of items.
Three subjects underwent a more detailed investigation to
determine whether pitches resulting from pulse rate variation
were sufficiently salient for musical interval perception.
The results of a closed—set melody recognition test
(Experiment II) suggested that recognition was possible on the
basis of melody, i.e., even in the complete absence of
rhythmical information, and that recognition was possible over
a range of pulse rates. However, these results did not
determine whether performance was based on ordinal properties
of the pitches, or whether successive pitches defined
identifiable musical intervals.
Intonation quality judgements (Experiment III) of
intervals ranging in size from a minor 3rd to a 5th provided
evidence that the frequency ratios which characterize
acoustical musical intervals also apply to electrical pulse
rate pitch. Further evidence of musical ratio recognition was
obtained using the method of adjustment (Experiments IV and
V). At least 2 out of 3 subjects were able, by means of the
adjustment of a variable pulse rate, to reconstruct selected
musical intervals abstracted from melodies well—known to the
subjects. Two subjects, furthermore, were able to transpose
these melodic patterns to higher and lower pulse rates, in a
manner similar to that demonstrated by normal—hearing subjects
when listening to musical intervals.
These results suggest that temporally mediated pitches
are capable of conveying ratio pitch information, in the sense
that equal ratios of pulse rates appear to produce equal
musical pitch intervals. These findings lend support to
temporal theories of musical pitch and interval perception. === Medicine, Faculty of === Graduate
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