Musical interval perception with pulsatile electrical stimulation of profoundly deaf ears

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 ofGraduat