MUSICAL INTERVAL PERCEPTION WITH PULSATILE ELECTRICAL STIMULATION OF PROFOUNDLY DEAF EARS by SIPKE PIJL B.Ed., The University of British Columbia, 1975 M.A., Western Washington University, 1977 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Neuroscience Program) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February 1994 ® Sipke Pijl, 1994 __________________________ In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of URO(t.Lc The University of British Columbia Vancouver, Canada Date 1 i99L. DE-6 (2/88) ABSTRACT 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. ii TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iii LIST OF TABLES V LIST OF FIGURES vi LIST OF ABBREVIATIONS viii DEFINITION OF TERMS ix ACKNOWLEDGEMENTS Xiii DEDICATION xiv INTRODUCTION 1 METHODS: General 13 Experimental Setup 18 Preliminary Psychophysical Measurements 22 Experimental Subjects 25 Results 28 Discussion 32 EXPERIMENT I: Open-Set Tune Identification 38 Methods 39 Results 42 Discussion 48 iii EXPERIMENT II: Closed-Set Melody Identification 55 Methods 56 Results 60 Discussion 64 EXPERIMENT III: Intonation Quality Judgements 69 Methods 70 Results 76 Discussion 90 EXPERIMENT IV: Musical Interval Reconstruction 100 Methods 101 Results 106 Discussion 111 EXPERIMENT V: Musical Interval Transposition 122 Methods 122 Results 128 Discussion 143 GENERAL DISCUSSION 152 REFERENCES 171 APPENDICES 1. Open-Set Tunes: Experiment I 184 2. Pulse Rates for 7-Note Melodies: Experiment II 187 iv LIST OF TABLES Table Page 1. Subject Data 23 2. Intonation Quality Judgements: points of subjective equality (PSE) and standard deviations 78 3. Method of Adjustment: interval reconstruction data 107 4. Method of Adjustment: interval transposition data for Subject 7 130 5. Method of Adjustment: interval transposition data for Subject 10 - ascending intervals 134 6. Method of Adjustment: interval transposition data for Subject 11 - descending intervals 137 v LIST OF FIGURES Figure Page 1. Equipment set-up 21 2. Current amplitudes at comfortable loudness: effect of pulse width 29 3. Current amplitudes at comfortable loudness for 4 subjects 29 4. Current amplitudes at comfortable loudness: Subject 10 versus Subject 11 30 5. Current amplitudes at comfortable loudness: replicability of measurements 30 6. Open-set tune identification: percent correct scores 44 7. Open-set tune identification: Number of positive identifications of each tune 45 8. Tune identification performance versus speech perception scores 47 9. Closed-set melody identification: percent correct scores 61 10. Schematic representation of intonation quality judgements 72 11. Intonation Quality Judgements: interval of a 5th 79 12. Intonation Quality Judgements: minor 3rd 80 13. Intonation Quality Judgements: interval of a 4th 81 14. Intonation Quality Judgements: major 6th 82 15. Point of subjective equality and standard deviations for intervals from a minor 3rd to a major 6th 83 vi Figure Page 16. Intonation Quality Judgements: effect of electrodes on interval of a 5th 87 17. Intonation Quality Judgements: effect of pulse rate of starting note on interval of a 5th 89 18. Interval reconstruction: mean interval size and standard deviations 109 19. Interval reconstruction: percentage of adjustments 0-2 semitones from target 112 20. Interval transposition: mean interval size and standard deviations — intervals of a 5th and minor 3rd. Subject 7 131 21. Interval transposition: mean interval size and standard deviations - interval of a 4th. Subject 7 132 22. Interval transposition: mean interval size and standard deviations — ascending intervals. Subject 10 135 23. Interval transposition: mean interval size and standard deviations — descending intervals. Subject 10 138 24. Interval transposition: differences in interval size related to adjustment of upper or lower note 140 25. Interval transposition: percentage of adjustments 2 semitones or less from target 144 vii LIST OF ABBREVIATIONS ANOVA Analysis of Variance ANSI American National Standards Institute BTNI Boys Town National Institute E electrode Hz Hertz kHz kiloHertz MHz MegaHertz msec milliseconds pps pulses per second PSE points of subjective equality S Subject SD standard deviation sec microseconds microamps viii DEFINITION OF TERMS (Items arranged in logical sequence) Musical pitch: That aspect of pitch (related to chroma, not pitch height) that is capable of conveying musical interval information. The musical scale specifies exactly the frequency ratios that are to be used to establish musical intervals. These ratios are thus on the stimulus side of the “equation”, and not on the phenomenal side of pitch. Musical intervals characterized by tones in equal frequency ratios are judged to be subjectively equivalent by musicians, but not necessarily or generally by others, except as listeners acquire experience with music. For any listener, subjectively equal musical intervals do not necessarily represent equal nonmusical pitch (pitch height) differences. The latter differences depend on the relative position of the intervals on the frequency scale. Musical scale: The full set of discrete musical intervals which are permitted. In the music of Western culture, these steps are defined by frequency ratios, and are derived from the octave as the basic interval. The unit of the Western musical scale is the semitone, which for the equal temperament scale, is obtained by dividing the octave into 12 equal frequency intervals. Pairs of tones separated by a given number of semitones (and a given frequency ratio) are given the same name, such as minor 3rd, major 6th, and so forth, regardless of where they occur in the musical scale. The ratios used for all the calculations in the experiments reported in this paper are based on the equal temperament scale. Musical intervals: Tones in one of a set of standard frequency ratios which ideally characterize the frequency relationships between musical notes. Intervals characterized by identical frequency ratios are generally (at least for musicians) perceived as being musically equivalent. In the music of Western European culture, interval size is measured in semitoies. One semitone equals one—twelfth of an octave (21/12), or a frequency ratio of approximately 1:1.059. The intervals commonly referred to in the experiments detailed in this paper, together with the accompanying frequency ratio and number of semitones, are described briefly as follows: ix Name of Interval Ratio qm -i tric semitone 21/12 or 1:1.059 1 major second 22/12 or 1:1.122 2 minor third 23/12 or 1:1.189 3 major third 24/12 or 1:1.257 4 fourth 25/12 or 1:1.335 5 tritone 26/12 or 1:1.414 6 fifth 27/12 or 1:1.498 7 major sixth 29/12 or 1:1.681 9 octave 1:2 12 Melody: For this paper, melody is defined as an ordered series of musical intervals, in the absence