Perception of the Missing Fundamental

PERCEPTION OF THE MISSING FUNDAMENTAL

IN PATIENTS WITH LOW FREQUENCY HEARING LOSS

GARY PAUL HORVATH

B.Sc. (Hons.), The University of British Columbia, 1984

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

THE FACULTY OF GRADUATE STUDIES

(Department of Physiology)

We accept this thesis as conforming

to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA

October 1988

(c)Gary Paul Horvath, 1988 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 Physiology

The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3

Date October 17, 1988

DE-6G/81) ABSTRACT

The perception of the pitch of a harmonic complex tone missing its fundamental frequency was investigated in patients with unilateral sensorineural low-frequency hearing

loss. Using a two-alternative forced choice adaptive method and an adjustment technique, patients matched the pitch of a

complex tone consisting of the 3rd-7th or 3rd-10th harmonics, with a pure tone. Component frequencies were

chosen such that they would fall within the intact portion

of the patient's damaged ear, but whose fundamental

frequency would fall within the damaged frequency area.

Pitch matches were made monaurally and binaurally, with and

without low-pass filtered noise. Results indicated that the patients tended to match the pitch of the lacking

fundamentals to the complexes even though the frequency of

the residue pitch fell within the range of elevated pure

tone thresholds. It is concluded that information regarding the residue pitch is not mediated by cochlear nerve fibers

with characteristic frequencies corresponding to the

fundamental. Temporal cues carried by fibers with

characteristic frequencies corresponding to the partials within the complex stimulus are most likely involved in

pitch perception.

Ii TARLE OF CONTENTS

Abstract i i

List of Abbreviations v

List of Tables vi

List of Figures viii

Acknowledgements xi

Introduction 1

Methods : 17

A. Subjects 17

B. Stimuli 18

C. Procedure 19

Pure Tone Audiogram 19

Pitch Training 20

Pitch Matching of Complex Tones Using a Two-Alternative Forced Choice Adaptive Method 21

Pitch Matching of Complex Tones Using an Up-Down Adjustment Technique 28

D. Statistical Analysis 30

Results 31

Pure Tone Audiograms 31

Pitch Matching of Complex Tones Using a Two-Alternative Forced Choice Adaptive Method....38

iii TABLE OF CONTENTS (CONT.1

i) Pitch Matching Control 99

ii) Pitch Matching Control with Noise 99

iii) Pitch Matching Between Ears 100

iv) Pitch Matching Between Ears with Noise 101

Pitch Matching of Complex Tones Using an

Up-Down Adjustment Technique 102

i) Pitch Matching Control 102

ii) Pitch Matching Control with Noise 113

iii) Pitch Matching Between Ears 113

iv) Pitch Matching Between Ears with

No ise 114

Discuss ion 123

Bibliography 140

iv LIST OF ABBREVIATIONS approx. approximation bel. below betw. between dB decibel, freq. frequency fund. fundamental har. harmonic HL hearing level Hz hertz kHz kilohertz mm millimeter msec millisecond MHz megahertz oct. octave P.M. pitch matching sec sec SEM standard error of the mean seq. sequence SL sensation level SPL sound pressure level start. starting w. with

v T.TST DF' TABLES

Table 1: Stepsizes of the Comparison Pure Tone (£2) 26

Table 2: Decrease in Threshold with Increasing Frequency for Each Patient... 36

Table 3: Selection of Components for the Complex Test Sound Used in the Pitch Matching Experiments 37

Table 4: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient A.D. Using the Two-Alternative Forced Choice Adaptive Routine 87

Table 5: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient A.F. Using the Two-Alternative Forced Choice Adaptive Routine 89

Table 6: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient G.F. Using the Two-Alternative Forced Choice Adaptive Routine 91

Table 7: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient L.F. Using the Two-Alternative Forced Choice Adaptive Routine 93

Table 8: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient R.L. Using the Two-Alternative Forced Choice Adaptive Routine 95

Table 9: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient J.W. Using the Two-Alternative Forced Choice Adaptive Routine 97

vi LIST OF TABLES (CONT.)

Table 10: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient A.D. Using the Up-Down Adjustment Technique 103

Table 11: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient A.F. Using the Up-Down Adjustment Technique 105

Table 12: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient G.F. Using the Up-Down Adjustment Technique 107

Table 13: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient L.F. Using the Up-Down Adjustment Technique 109

Table 14: Pitch Values Assigned to the Pitch of the Complex Test Sound by Patient R.L. Using the Up-Down Adjustment Technique Ill

Table 15: Summary of the Number of Matches to either the Fundamental and its Octaves, or to the Odd Harmonics and the Octaves below these Partials 116

Table 16: Summary of the Number o£ Matches to either the Missing Fundamental, or to the Presented Partials 120

vii T.TBT OF FIGURES

Figure 1: Damaged and Intact Ear Audiograms of Patients A.D., A.F., and G.F 32

Figure 2: Damaged and Intact Ear Audiograms of Patients L.F., R.L., and J.W 34

Figure 3: Data from the Pitch Matching Control Procedure for Patient A.D. Using the Two-Alternative Forced Choice Adaptive Method 39

Figure 4: Data from the Pitch Matching Control with Noise Procedure for Patient A.D. Using the Two-Alternative Forced Choice Adaptive Method 41

Figure 5: Data from the Pitch Matching Between Ears Procedure for Patient A.D. Using the Two-Alternative Forced Choice Adaptive Method 43

Figure 6: Data from the Pitch Matching Between Ears with Noise Procedure for Patient A.D. Using the Two-Alternative Forced Choice Adaptive Method 45

Figure 7: Data from the Pitch Matching Control Procedure for Patient A.F. Using the Two-Alternative Forced Choice Adaptive Method 47

Figure 8: Data from the Pitch Matching Control with Noise Procedure for Patient A.F. Using the Two-Alternative Forced Choice Adaptive Method 49

Figure 9: Data from the Pitch Matching Between Ears Procedure for Patient A.F. Using the Two-Alternative Forced Choice Adaptive Method 51

Figure 10: Data from the Pitch Matching Between Ears with Noise Procedure for Patient A.F. Using the Two-Alternative Forced Choice Adaptive Method 53

viii LIST OF FIGURES (CONT.)

Figure 11: Data from the Pitch Matching Control Procedure for Patient G.F. Using the Two-Alternative Forced Choice Adaptive Method 55

Figure 12: Data from the Pitch Matching Control with Noise Procedure for Patient G.F. Using the Two-Alternative Forced Choice Adaptive Method 57

Figure 13: Data from the Pitch Matching Between Ears Procedure for Patient G.F. Using the Two-Alternative Forced Choice Adaptive Method 59

Figure 14: Data from the Pitch Matching Between Ears with Noise Procedure for Patient G.F. Using the Two-Alternative Forced Choice Adaptive Method 61

Figure 15: Data from the Pitch Matching Control Procedure for Patient L.F. Using the Two-Alternative Forced Choice Adaptive Method 63

Figure 16: Data from the Pitch Matching Control with Noise Procedure for Patient L.F. Using the Two-Alternative Forced Choice Adaptive Method 65

Figure 17: Data from the Pitch Matching Between Ears Procedure for Patient L.F. Using the Two-Alternative Forced Choice Adaptive Method 67

Figure 18: Data from the Pitch Matching Between Ears with Noise Procedure for Patient L.F. Using the Two-Alternative Forced Choice Adaptive Method 69

Figure 19: Data from the Pitch Matching Control Procedure for Patient R.L. Using the Two-Alternative Forced Choice Adaptive Method 71

lx LIST OF FIGURES (CONT.)

Figure 20: Data from the Pitch Matching Control with Noise Procedure for Patient R.L. Using the Two-Alternative Forced Choice Adaptive Method 73

Figure 21: Data from the Pitch Matching Between Ears Procedure for Patient R.L. Using the Two-Alternative Forced Choice Adaptive Method 75

Figure 22: Data from the Pitch Matching Between Ears with Noise Procedure for Patient R.L. Using the Two-Alternative Forced Choice Adaptive Method 77

Figure 23: Data from the Pitch Matching Control Procedure for Patient J.W. Using the Two-Alternative Forced Choice Adaptive Method ...79

Figure 24: Data from the Pitch Matching Control with Noise Procedure for Patient J.W. Using the Two-Alternative Forced Choice Adaptive Method 81

Figure 25: Data from the Pitch Matching Between Ears Procedure for Patient J.W. Using the Two-Alternative Forced Choice Adaptive Method 83

Figure 26: Data from the Pitch Matching Between Ears with Noise Procedure for Patient J.W. Using the Two-Alternative Forced Choice Adaptive Method 85

x ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to my supervisor, Dr. Dietrich Schwarz, for his encouragement and guidance throughout the duration of this project.

I would also like to thank Ward Tomlinson and

Joseph Li for their expert advice and help with instrumentation and computation.

xi INTRODUCTION

Historical Review

The pitch of complex sounds has long been a controversial subject. In 1843, G.S. Ohm formulated a rule by which the ear analyses complex musical tones, and this was later known as "Ohm's acoustical law". According to

Ohm, a complex of musical tones is being analysed as a sum of sinusoidal oscillations. The ear senses these simple tones, each of which corresponds to one simple sinusoid, whose pitch is determined by the corresponding period. The sensation of a musical tone is therefore compounded out of the sensations of several simple tones. The prime tone being generally louder than any of the upper partial tones, would alone determine the pitch of the complex

(Helmholtz,1954).

Ohm's law contradicted the hypothesis put forward by

Seebeck in 1841. Using an acoustic siren as a sound generator, Seebeck found that although the part-tone at the fundamental frequency corresponding to the pitch of a musical sound was subjectively strongest, the objective strength of that partial could be rather weak or absent. He concluded that the pitch of the musical sound is determined by the period of the signal's waveform and not by the

1 frequency of the lowest component (Seebeck,1841; de

Boer,1976) .

Ohm demonstrated mathematically that the musical sounds generated by Seebeck must have contained fundamental components of greater strength than reported by him

(Ohm, 1843 ). Showing once more that the objective strength of the fundamental could not correlate with the subjective strength, Seebeck (1843) counterargued that in a musical tone containing several simple tones, a portion of the intensity of the higher harmonics serve to strengthen the percept of the fundamental.

Ohm (1844) finally conceded that it was an "illusion of the ear" to apprehend the higher harmonics entirely or partly as a reinforcement for the complex tone whose pitch is determined by the fundamental. The notable German scientist Helmholtz (1954) supported Ohm and provided a physiological account for auditory analysis. He proposed that different frequencies will excite distinct resonating areas along the basilar membrane, and that information about an individual partial will be carried only by the nerve fibers innervating the corresponding area along the membrane. Thus pitch and other qualities of tones would be explained by the location of excited nerve fibers.

Later studies by von Bekesy (1960) on the spatial frequency analysis of sound in the cochlea, together with

2 the work of Helmholtz, led to the formulation of the "place

theory" of hearing. This theory postulates that the

frequency components of a complex sound are represented at

certain places in the cochlea where they elicit maximal

displacement of the basilar membrane. High frequency

stimuli maximally displace the basal portion of the

membrane, and low frequency stimuli the apical part. This

displacement causes a chain of events leading to the

stimulation of nerve fibers at a particular location. The

tone sensation arising from this stimulation will have a pitch corresponding to the characteristic frequency for that

locat ion.

The place theory can thus be thought of as consisting

of two mechanisms. The analysing mechanism spatially analyses a complex sound into its sinusoidal components on

the basilar membrane, whereas the transmitting mechanism will transmit information regarding the pitch of the complex along those neural fibers innervating the points of ~ maximal displacement of the membrane.

Seebeck's work had been largely forgotten until a major set-back for the "place" model arose from the work of

Schouten in the 1940's (Schouten,1940a,b,c). Using an optic siren to produce periodic signals of any desired waveform, Schouten (1940c) cancelled the fundamental tone of a complex stimulus whose fundamental frequency and pitch

3 corresponded to 200 Hs. He found that the sharp note o£ 200

Hz remained unchanged, still present in the perceived sound.

Moreover, after reintroducing the fundamental tone to the sound, it was heard separately as a pure tone having a pitch of 200 Hz but whose loudness was low compared to that of the second and third harmonic. The sound accordingly contained two components whose pitch was that of 200 Hz. One component having a pure tone quality was identical with the fundamental tone, whereas the other, having a sharp tone quality and great loudness, was of different origin.

By eliminating harmonics one by one, starting from the lowest, Schouten found that the sharp note, at first, did not change either in character or in loudness. There was, however, a gradual loss in both sharpness and loudness of the sharp note when the highest harmonics were removed first. From these results, he suggested that the sharp note is associated with the presence of high harmonics in the complex sound, and thereby confirmed Seebeck's original finding.

This additional subjective component whose existence could not be correlated with any single fequency of the sound, but which is, according to Schouten (1940c), a collective manifestation of unresolved higher harmonics was called a "residue".

Schouten (1940c) next determined which physical

4 property of these higher harmonics might determine the pitch of the residue: the distance between the harmonics or the periodicity of the total waveform of the harmonics were scrutinized. Comparing two waveforms having the same distance of 400 Hz between the harmonics but a different periodicity (200 Hz and 400 Hz), he found that the residue pitch in each of the waveforms had a frequency value equal to that of the periodicity, namely 200 and 400 Hz. Hence,

Schouten concluded that the ear assigns a pitch to a residue by virtue of the periodicity.

However, in one of Schouten's most crucial experiments

(Schouten,1940a), it was established that the situation was not as simple as was first assumed. By shifting a set of harmonics collectively over a small distance along the frequency scale, the pitch of the residue shifted in proportion to the change in the constituent frequencies.

Not only do these results imply that the pitch is not determined by the spacing of the harmonics since this remained constant, but they also imply that the envelope per iod ic ity is unrelated since this also remains unchanged following the shift of components (Schouten,1970).

Consequently, Schouten believes that the f ine t ime structure of the waveform must be taken into account, since it is this property that is altered following the pitch shift (Schouten et al.,1962). Pitch frequency would therefore be given by

5 the inverse o£ the time between the major positive peaks in the stimulus fine structure.

From the 'time' following Schouten's findings up until

the early 1970's7 there was a 'shift' in the relative weight afforded to place and timing mechanisms. It was during this

'period' that the emphasis was 'placed' on the timing of neural discharges, rather than the location of innervation of excited neurons. As early as the mid-sixties it was demonstrated that the majority of cochlear fibers have a restricted dynamic range between 20 and 50 dB (Kiang et al.,1965; Kiang,1968; Evans,1972). For levels above this range, the discharge rates in the fibers will be saturated for signals at the characteristic frequency of those fibers.

Psychophysical studies have, however, revealed that our perceptual dynamic range enables us to hear and analyse complex sounds over 100 dB or more (Riesz,1928;

Miller, 1947 ) . This presented a serious problem for place coding, since the frequency range over which cochlear fibers are saturated by loud tones can be very extensive

(Evans,1978b). Fibers with low background rates, high thresholds, and wide dynamic ranges, however, have been described (Liberman,1978; Liberman & Kiang,1978). It is thus conceivable that different fibers from the same basilar membrane location could explain pure tone pitch on the basis of the place theory, although there is, so far, no proof for

6 this possibility.

Several investigators suggest that cochlear fibers

transmit information in terms of the fine time structure of their discharge patterns (Goldstein & Srulovicz,1977;

Evans,1977,1978b). For frequency signals below 5 kHz, cochlear nerve firings have a tendency to occur at a

particular phase of the stimulating waveform, and the dynamic range over which this 'phase locking' occurs extends well beyond that of the mean discharge rate (Rose et al.,1971).

In the early 1970's, the emphasis on pitch perception moved from periodicity coding, to theories based upon pattern recognition models (Terhardt,1972,1974;

Goldstein,1973; Wightman,1973). These models involve a central neural processor which computes the pitch of complex

sounds in the following manner. Resolved frequency components of the complex sound, which have been analysed in

the periphery, provide the pitch cues. In most models this

information is conveyed by place mechanisms. Upon receiving

this information, the central neural processor matches these

frequency components to a harmonic series. The fundamental

frequency of those harmonics which best fits the resolved

components will then be selected by the central processor as

the pitch value (Evans,1978b).

The major difference between pattern recognition models

7 and Schouten's model for the residue pitch is that the

pattern recognition models require spectral resolution of

individual components in the stimulus, whereas Schouten's

temporal model requires interaction of components.

Furthermore, according to Schouten's model, the pitch of the

residue may still be heard when there are no resolved partials.

In 1972, Houtsma & Goldstein provided perhaps the most

convincing evidence demonstrating that the lacking

fundamental can be perceived when there is no possible

interaction of partials in the cochlea. Their experiment

involved presenting a subject with a musical message

consisting of two notes, each note comprised of two randomly

chosen successive upper harmonics, but with no energy at the

fundamental frequency itself. The subjects were asked to

identify the two-note melodies which were presented

monotically (two harmonics to one ear) and dichotically (one

harmonic to each ear). Subjects could recognize melodies

equally well with both methods of stimulus presentation.

This suggests that fundamentals of complex tone stimuli are

selected by a central mechanism which integrates and

processes the resolved stimulus harmonics from both

cochleae .

Schouten's temporal model explaining the residue pitch

by interacting partials is supported by the work of Ritsma

8 (1962,1963) who defined the existence region of the tonal residue. His subjects were required to indicate whether they could perceive a residue in response to complexes consisting of three consecutive harmonics. He found that the residue pitch could be heard even when the harmonic numbers of partials were around 20. Plomp (1964) had shown that for complex tones with more than two components, only the first five to eight harmonics are resolved.

Consequently, Ritsma showed that the residue can be perceived even when no individual partials of a complex tone are separately perceivable. Furthermore, he found that no tonal residue is perceived when component frequencies are higher than 5000 Hz. Since this value is also the limit of neural phase locking, temporal mechanisms cannot operate beyond it. Thus, our ability to perceive the tonal residue of a complex tone only occurs when partials are present in a frequency region which allows phase-locking of auditory fibers.

Rltsma's experiments were not entirely conclusive since he did not control for the possible influence of combination tones. Combination tones often have frequencies of the fundamental or low components, and the type 2fl-f2 may be individually perceivable even though the stimulus components are unresolved. To control for combination tones, Moore

(1973) conducted an experiment in which a multi-tone complex

9 with no resolvable partials was presented to subjects In the presence of a masking noise in the frequency region below the complex. Results indicated that the subjects heard a well-defined residue pitch, thus confirming Ritsma's conclusions.

Moore & Rosen (1979) have also provided more recent evidence supporting temporal coding of the residue pitch by testing subjects on their ability to recognize melodies from which rhythm information had been removed. The purpose of this test was to determine whether residue pitch produced by unresolvable high harmonics was of a musical value. To mask combination tones, low frequency noise was, again, present.

The subjects were able to identify simple tunes from the musical interval information. Thus, a sense of musical pitch was maintained with stimuli containing only harmonics too high to be individually analysed in the peripheral auditory system.

In the studies reviewed thus far, evidence was presented for pitch coding on the basis of either resolved partials (pattern recognition models) or interacting partials (temporal models) as if one hypothesis excluded the other. However both place and temporal cues may be used by the central nervous system. This possibility was first explored for coding of vowels (which are also harmonically structured sounds) by Young & Sachs (1979), and later was

10 extended to non-harmonic speech sounds, e.g., stop

consonants, by Miller & Sachs (1983). These authors

explored the representation of complex speech sounds in the

entire population of the cat's auditory nerve fibers. If

only the spike rates were used to express amplitudes for various frequencies at the characteristic locations along

the basilar membrane, it was not possible to reliably distinguish different sounds (e.g., the vowels |e| and |a|).

If the amplitudes were expressed, however, as the degree to which fibers synchronize with frequency components (by

phase-locking), characteristic patterns emerged for each

sound. The synchronization measure employed by Young and

collaborators was the "synchronization index" introduced by

Goldberg & Brown (1969). This index has its maximal value

close to a fiber's characteristic frequency, which is, of

course, localized on the basilar membrane. The measure for

complex sound coding was, therefore, called "average

localized synchronization rate" (ALSR), and was measured as

follows. First, obtained is the amplitude of response of a

stimulus component at that component frequency. Next, this

amplitude is averaged across fibers, but only those that are

tuned within plus or minus 0.25 octaves of the frequency of

the partial. This mean amplitude is then taken to represent

the ALSR of the stimulus component's population response.

Accordingly, the ALSR contains information, regarding both

11 time and place, about the neural response to a frequency:

Time because the average value of the amplitude measured is

synchronized rate, and place because the fibers included in

the averaging process are only those that are tuned near

that frequency (Sachs,1984).

Miller & Sachs (1983) have shown that some pitch

estimates can also be derived from ALSR measures with sufficient accuracy to permit tracking of small pitch

changes. Again using responses of large populations of cat

single auditory nerve fibers to consonant-vowel stimuli,

they also demonstrated little or no representation of pitch based solely upon the temporal structure of the stimulus

waveform, as measured by the envelope modulation of the post-stimulus time histograms (Miller & Sachs,1984). The

envelope modulations directly related to pitch period were shown only in those units with characteristic frequencies in

ranges where there are a number of pitch harmonics with approximately equal amplitude. Miller & Sachs (1984)

believe that this was a result of rectifier distortion contributed by pairs of response peaks. Units whose

responses were dominated by a single component showed no

such pitch-related fluctuations in their post stimulus time

histograms. However, the pitch-related harmonic structure

in the stimulus spectrum was preserved by the ALSR, a

representation of pitch based upon both the temporal

12 auditory-nerve responses and the cochlear place. This

finding has since been replicated in the guinea pig (Palmer

et al.,1986).

Experiments on the effect of noise on the synchronicity

of discharges revealed some very interesting facts. Kiang &

Moxon in 1974 recorded from single units in the auditory

nerve of the anesthetized cat, and showed that low-frequency masking noise scarcely affected the synchrony of low characteristic frequency units in respone to phonetic elements, even though the noise level was sufficient to saturate the discharge rate of most of these units. On the other hand, for high characteristic frequency units, a reduction in synchrony was found even at masking levels too low to saturate these fibers.

Similar findings have been reported by Rhode et al.

(1978) while recording from squirrel monkey auditory nerve

fibers. Narrow bands of noise centered around the characteristic frequency of low characteristic frequency

fibers resulted in flat rate curves above 40 dB SPL, whereas synchronization was maintained. Furthermore, they even

showed that a neuron which exhibited no response to pure

tones with intensities less than 50 dB SPL achieved a highly

significant degree of synchronization when a low intensity

noise was presented together with the tone at 40 dB SPL.

Rhode et al. suggest that this latter finding was the result

13 o£ the ability o£ the noise to increase the probability of the neuron's stimulus-induced potential to cross firing threshold under stimulus conditions that would normally not permit such crossings to occur. They draw an analogy to auditory neurons with low and high spontaneous.activity, the latter being more sensitive to tonal stimuli.

Delgutte (1980) also showed that although the relative rate response to a tone was decreased in the presence of noise in cat auditory fibers, the synchronization index remained approximately the same throughout the duration of a tone burst, both in the presence and absence of noise.

Furthermore, because noise did not affect the intervals between the spectral peaks of the response pattern to speech sounds, Delgutte concluded that the information about formant frequencies of vowels remained relatively stable in a noisy background. Similar findings have been obtained by

Abbas (1981) and Voigt et al. (1981).

In a further investigation, Sachs et al. (1983) found that addition of background noise to a steady-state vowel suppressed the synchronized responses to the formants in high characteristic frequency fibers, but only slightly reduced the synchrony to the formant frequencies at their peculiar low frequency place in the neural population.

More recently, Miller et al. (1987) obtained responses from anesthetized cat auditory nerve fibers to both a 1.0

14 kHz tone, and 1.0 kHz tone in background noise. Addition of the broadband noise resulted in maintainence of the synchrony only in those units with characteristic frequencies close to the 1.0 kHz stimulus, whereas phase- locking was lost in those auditory nerve fibers with characteristic frequencies far from the 1.0 kHz stimulus.

Similar findings have also been reported by Delgutte & Kiang

(1984) and by Miller (1986).

Rationale

The persistence of a high synchronization index in neural discharges of low frequency fibers during presentation of a low frequency masking noise makes it necessary to re-evaluate the significance of the findings by

Moore (1973) and Moore & Rosen (1979). To recall, these two studies examined the potential of stimuli containing only high, unresolved harmonics to evoke the percept of the residue pitch. Low frequency masking noise was used to eliminate any contribution of distortion products to the percept. But how effective was this masking noise in eliminating all the pitch cues relayed by the low characteristic frequency fibers? Information represented by discharges synchronized to the acoustic waveform would still be available to the central nervous system, information that might contain sufficient cues for the residue pitch.

15 Questions and speculations o£ this nature led to the design of the experiments presented here. Until now, no experiment testing the capability of a group of harmonics to evoke the lacking fundamental, without contribution from pitch cues provided by the frequency region of the missing fundamental, has been reported. These questions can be addressed in patients with a complete sensorineural hearing loss in the low frequency region (the presumed place representation of the fundamental), and a completely intact organ of Corti in a higher frequency band (the proper place for dominant higher components). Since such sharply limited damage is not known in cochlear pathology, it was attempted here to perform conclusive measurements in patients with more gradual partial low-frequency losses.

16 METHODS

A. Subjects

Subjects audiologically diagnosed with unilateral, low frequency sensorineural hearing loss of cochlear origin ranging in age from 33 to 66 were used. Hearing loss of this origin is frequently associated with degenerative changes in the auditory nerve (Schuknecht,1974). Only six such patients could be found in the audiology clinics' in

Vancouver. Three patients (A.D., A.F., and L.F.) had

Meniere's disease. This disease of unknown etiology is characterized by an abnormal accumulation of endolymph in the inner ear resulting in hearing loss, vertigo, and tinnitus (Schuknecht,1974). Retrocochlear involvement was excluded in patient G.F. as a result of normal auditory brainstem responses and normal acoustical reflexes.

Similarly, retrocochlear involvement was excluded in patient

R.L. as a result of a positive S.I.S.I. (Short increment

Sensitivity Index) test, and in patient J.W. as a result of intact acoustical reflexes and excellent speech discrimination. Pathological subjects were used in the study of a normal phenomenon since they could not hear low pure tones, and therefore perception of a low pitch of a complex tone by these patients would confirm the utilization of a central pitch process. The decrease in threshold with

17 increasing frequency in the patients' impaired ears ranged from 22.0 dB to 36.0 dB (refer to figures 1 and 2, and to table 2 in "results" for the audiograms and for the frequency ranges over which the thresholds decreased). All were paid for their services, and were instructed in frequency discrimination prior to testing. Two of the subjects (L.F. and R.L.) had previous musical training.

B. Stimuli

In order to measure perceived pitches, patients had to compare test tones to comparison tones. Test sounds consisted of harmonic series with component intensities set to the same SL levels. They were jointly varied during presentations from 20 to 30 dB SL in order to circumvent errors due to intensity cues. The series contained harmonic numbers three to ten maximally with the fundamental and second harmonic being absent. The choice of harmonics as well as the frequency value of the missing fundamental depended upon the individual hearing loss of each patient as described below.

The comparison tone was of a single sinusoid also presented at randomized intensities, again ranging from 20 to 30 dB SL. All tones were 500 ms long and had rise and fall times of 10 ms.

All stimuli were generated by a digital synthesizer

18 capable of producing up to 32 pure tone components at any frequency and amplitude. Frequencies and amplitudes of the components were controlled by a LSI 11-23+ computer system.

C. Procedure

Pure Tone Audiogram

Prior to the experiments, pure tone audiograms were obtained for all patients. Sinusoidal frequencies of 125,

250, 500, 1000, 2000, 4000, and 8000 Hz were presented randomly via Sennheiser HD414X headphones, which had been calibrated with a Hewlett Packard HP3582A spectrum analyser in conjunction with a Bruel & Kjaer 4134 1/2-inch condenser microphone, and a 2619 microphone preamplifier using a 2804 microphone power supply. Sitting in a sound attenuating room, patients were presented with one of the pure tones at

30 dB above "hearing level" as determined from the most recent clinical audiograms obtained at audiology clinics in

Vancouver.

Subjects were instructed to push a button within 10 to

1500 msec after the onset of the tone. If the response was made within this time period, the intensity was reduced one step (initial stepsize: 8 dB), and another 500 msec tone of the same frequency was presented at this lower intensity level 3 sec following the response.

19 If no response was made within the 1490 msec response window at a particular intensity level, the tone was

repeated at the same intensity 3 sec later. After two consecutive tones without a response, the intensity

increased by one step, up to a limiting intensity level of

80 dB SPL, until an appropriate response was executed.

After three "crossovers" (an intensity increase/decrease or vice versa), the stepsize was reduced to one-half of its previous value (e.g., from 8 dB to 4 dB). When the stepsize equalled 0.5 dB, the sequence for a particular tone was terminated. Audiograms were then obtained by averaging the

intensity of the last three intensities for each tone.

Frequency sequences were randomized and the entire procedure automatized. Thresholds for intermediate frequencies were defined by linear interpolation and used to set SL levels of stimuli employed for pitch matching.

Pitch Training

Prior to the pitch matching experiments, each subject was asked to identify whether two sequentially presented

identical melodies were similar or different in pitch. Each melody consisted of five notes played on a Yamaha DX-7 programmable synthesizer and presented to the patient's

intact ear. Corresponding notes of the two melodies differed in either pitch or timbre (overtone structure).

20 When differing in pitch, melodies were transposed by a musical fourth or a fifth (e.g., the "G" above and below the

"C"). When differing in timbre, corresponding notes differed in the number of harmonic components present. Six choices were available; a pure tone, or a complex consisting of harmonics one to six, two to seven, three to eight, four to nine, or five to ten. Patients were trained until they could comfortably and correctly identify a similarity or difference in pitch between several paired melodies.

Pitch Matching of Complex Tones Using a

Two-Alternative Forced Choice Adaptive Method

Complex tones were presented to patients with low frequency hearing loss in order to investigate the relationship between cochlear damage and the ability to perceive the lacking fundamental. The test sound's components were chosen in accordance with the patients' audiograms such that harmonic components would fall within a frequency range with relatively normal thresholds, whereas the (lacking) fundamental would occupy a region with elevated thresholds. Harmonics chosen were the third to the tenth (i.e., eight components), except for two patients the eighth to the tenth harmonics were omitted since their frequencies would correspond to a second range with threshold elevations. The second harmonic was Intentionally

21 excluded from the complex in order to avoid octave

confusions (Deutsch,1974a,b,1975).

Duration of complex and pure tones was 500 msec

separated by a silent interval of 400 msec.

Both the complex test sound and the comparison pure

tone were presented via headphones using the following

procedures:

i) Pitch matching control.

Both sounds were presented to the patient's intact ear using

threshold data from that ear to set the component

intensities. This was necessary to permit comparison of pitch estimates by means of healthly and damaged ears in the

same subjects.

ii) Pitch matching control with low-pass filtered

noise.

As in i) but with low-pass filtered noise, sloping at 9G

dB/octave, added to the complex test sound in order to mask

only the region representing the fundamental, but not the

frequency area containing the presented partials. Corner

frequencies (3 dB attenuation) were logarithmically centered

between the fundamental and the third harmonic. Noise was

filtered by a Krohn-Hite 3343 Butterworth filter.

The masked threshold for a pure tone at the frequency

of the fundamental was determined for the intact ear. The

pure tone intensity was fixed at 30 dB SL (the maximum

22 intensity level for any one component presented in the experiments), and the intensity of the noise was increased until the patient could no longer perceive the tone. The resulting signal to noise ratio averaged -0.9 dB, and ranged

from -9.7 dB to +10.2 dB. This wide range was a result of the varying noise band width, which was adjusted to match the hearing loss in the damaged ear (Fletcher,1940;

Zwicker,1954; Patterson,1976).

iii) Pitch matching between ears.

The complex test sound was presented to the damaged ear only. This was alternated with the comparison tone presented only to the functional ear. Threshold data from the patient's intact ear were used to set the intensity of the pure tone, whereas the threshold data from the damaged ear served to set the component intensities of the complex sound. Since components of the complex fell within the

intact frequency range of the damaged ear, and the missing fundamental within the damaged frequency area, a contribution to the percept of the lacking fundamental by distortion products generated in the cochlea (Plomp,1965;

Greenwood,1971; Hall,1972a,b; Smoorenburg,1972) would be highly unlikely at the intensities employed.

iv) Pitch matching between ears with noise.

As in iii) but with added low-pass filtered noise presented together with the complex test sound as described in ii).

23 The low-pass filtered masking noise was used as an additional safeguard against possible contamination by distortion products.

Determination of the noise masked threshold was. as described in ii) with the exception of the pure tone and masking noise being presented to the damaged ear instead of the intact ear. The signal to noise ratio for the thresholds averaged +9.4 dB, and ranged from +3.4 dB to

+12.6 dB.

The 500 ms test tone was always followed by the 500 ms comparison tone. The subjects were required to push a yellow ("higher") button if the sinusoid (2nd tone) was higher, and a blue ("lower") button if it was lower in pitch than the complex tone (1st tone), both within 10 to 3500 msec after the onset of the comparison tone. A two- alternative forced choice adaptive method (Levitt,1971;

Jesteadt,1980) was used. In this procedure, the frequencies of stimuli in a given trial were dependent upon the subject's responses in previous trials. If a response was made within the 3490 msec response window, a 3 sec delay

followed between the response and the presentation of the first tone of the next trial. If no response was made in the response window, the identical two tones were repeated

in the next trial 3 sec following the termination of the response window.

2 4 Two randomly interleaved sequences ("A" and "B") of stimulus presentation were used for each subject. In sequence A, the frequency of the comparison tone (f2) was initially equal to 1.5 times the fundamental frequency (flo) of the test sound. If f2 was judged to have a higher pitch than the test sound, then the same f2 was presented in the following trial. If judged higher again, £2 decreased one stepsize (see table 1). If judged lower, f2 increased one step up. After three reversals (from up to down to up) the stepsize was reduced (e.g., from 1 to 2). Sequence A was terminated after the third reversal of the last step size.

The subjective pitch of the complex stimulus for sequence A was taken as the mean of the last four values of f2. If, however, two consecutive values were identical, only one of them was used. The following example illustrates f2 value selection for pitch calculation.

£2 values presentation number

--> 300 (n - 5)

337 (n - 4)

--> 337 (n - 3)

--> 300 (n - 2)

337 (n - 1)

--> 337 (n)

25 Tahl f. 1 Stftpsl gfts for th*. nompar 1 son pur* ton* ( f:2 )

When decreasing £2

Stepsize 1: f2 - (f2 / 1.5)

(maximal stepsize)

Stepsize 2: f2 - (f2 / 1.25)

Stepsize 3: £2 - (£2 / 1.125)

(minimal stepsize)

When increasing £2

Stepsize 1: (f2 x 1.5) - f2

(maximal stepsize)

Stepsize 2: (£2 x 1.25) - f2

Stepsize 3: (f2 x 1.125) - £2

(minimal stepsize)

* * *

£2 = last frequency value of comparison tone

26 The four values averaged to estimate the subjective pitch are those indicated by the arrows. The precision of this

pitch estimate depends, of course, on the final step size which is, in practice, well within the error range for most

normal subjects.

In sequence B, f2 initially was set one maximal step

below flo. In this sequence two consecutive lower responses were required to increase f2 by one stepsize, but only one

higher response was necessary to decrease f.2 (the reverse of sequence A). As in sequence A, the stepsize was reduced after three reversals (from down to up to down).

Termination of sequence B and calculation of the subjective

pitch of the complex stimulus were as described for sequence

Advantages of the two-alternative forced choice adaptive method (Jesteadt,1980) used in these experiments are:

1. The stimulus (f2) is automatically chosen at an appropriate degree of arduousness. As the subject improves his or her performance, the difficulty of the exercise

increases. Thus, the patient's task is formatted to his needs .

2. By using two randomly interleaved sequences (phases

A and B), the effects of directional bias is reduced.

3. Since subjects can not influence the choice of

27 stimuli, this procedure is relatively objective when compared with adjustment techniques.

Pitch Matching of Complex Tones Using an Up-Down

Adjustment Technique

Five of the six patients returned a week after participating in the aforementioned pitch matching experiments. Pitch training was again performed. Patients were then presented with the same complex test sound used in the previous pitch matching experiments followed by a pure tone of 100 or 1130 Hz. Complex tone fundamentals were always between these values. Patients were asked to adjust the frequency of the pure tone by turning a dial on a potentiometer connected to a voltage controlled oscillator

(Coulbourn S24-05), the source of the second pure tone.

The duration for each of the two tones was 500 ms with a silent interval of 200 ms. A 700 ms gap followed the end of the second tone before the first complex tone of the next group was started. Amplitude of the components of the complex was set at 30 dB SL by the LSI 11-23+ computer. The amplitude of the pure tone was also 30 dB SL, and adjusted by a Hewlett Packard 350D attenuator. Its frequency was monitored by a Hewlett Packard 5381A 80-MHz frequency counter.

Patients were allowed unlimited time to adjust the pure

28 tone to match the complex, as groups of the two tones were presented repeatedly to the patients. The patients were also encouraged to make broad sweeps at first, adjusting the

frequency above and below the pitch of the complex, and then gradually make finer adjustments to define the perceived pitch.

The patients were required to adjust the pure tone,

first from a start frequency (100 Hz) well below the complex tone fundamental and then, in a second run, from a higher start frequency (1130 Hz) far above the fundamental. These alternating start frequencies eliminated the influence of

frequency adjustment direction on the pitch matching.

The number of pitch matches each patient performed for each of the methods were as follows:

mean number of matches range

i) P.M. control : 7 4-10 ii) P.M. control

with noise : 6 4-10

iii) P.M. between

ears : 8 4-15

iv) P.M. between

ears with

noise : 7 4-15

29 D_. Statistical Analysis

Results from the two-alternative forced choice routine are shown as mean plus or minus SEM.

30 RESULTS

Pure Tone Audiograms

Pure tone audiograms of the six patients' damaged (D) and intact (I) ears are displayed in figures 1 and 2.

Thresholds are depicted in dB SPL and dB HL. The decrease

in threshold with increasing frequency ranged from 22.0 to

36.0 dB (see table 2 for the frequency ranges). From these audiograms the complex tone frequency components were chosen such that they would fall within the intact portion of the

patient's damaged ear, but whose lacking fundamental would

fall within the damaged frequency range. The criterion

given for an intact area was a threshold deficit at a particular frequency of no greater than 15 dB HL, while that

given for a damaged area was 18 dB HL or greater. These criteria were chosen following audiometric examination so as

to conform with the selection of presented components within

the intact frequency region, and the fundamental within the

damaged area. Selection of components for each patient is shown in table 3. As mentioned in "methods", for all but

two of the patients, eight components with harmonic numbers

three to ten were chosen. For patients L.F. and R.L., the

eighth to the tenth harmonic components were omitted since

their frequencies would have occupied a high frequency range

of threshold elevation.

31 Figure 1; Damaged ear (solid line) and intact ear

(dashed line) audiograms of patients

A.D./ A.F., and G.F.

Thresholds are displayed in dB HL.

Solid bars = range of intensities of the

presented stimulus components during the

two-alternative forced choice adaptive

method.

Dashed bar = range of intensity of the

comparison pure tone at the fundamental

frequency during the two-alternative

forced choice adaptive method.

Fl = fundamental frequency of the

presented complex tone.

32 -20-, -10- P- 10- 20-

m 4°-l "D 50 60- 70 80H Patient: A.D. F = 300 90 100 125 250 500 1K 2K 4K 8K -20-, -10- 0- 10- 20- =J 30-

§ 50- 60- 70- 80 90 Patient: A.F. F1 = 200 100-1 125 250 500 IK 2K 4K 8K -10 0 10- 20- -J 30- 40- Sl5 °- ; 60- 70- 80- Patient: G.F. F, = 200 90- 100 125 250 500 1K 2K 4K 8K

33 Figure 2: Damaged ear (solid line) and intact ear

(dashed line) audiograms of patients

L.F., R.L., and J.W.

Thresholds are displayed in dB HL.

Solid bars = range of intensities of the

presented stimulus components during the

two-alternative forced choice adaptive

method.

Dashed bar = range of intensity of the

comparison pure tone at the fundamental

frequency during the two-alternative

forced choice adaptive method.

Fl = fundamental frequency of the

presented complex tone.

34 -20-| -ioH

"O 50- 60- 70-

125 250 500 1K 2K 4K 8K

35 Table 2: Decrease in threshold with increasing frequency

for each patient.

patient decrease in threshold with frequency

increasing frequency (dB) range (Hz)

A.D. 26.0 250 1000

A.F. 26.0 250 2000

G.F. 32 . 0 125 500

L .F. 24.0 125 1000

R.L. 22.0 125 1000

J.W. 36.0 500 2000

36 Table 3: Selection of components for the complex test sound used in the pitch matching experiments. patient components harmonic fundamental frequency selected number of complex (Hz) (Hz)

A.D. 900 3 300 1200 4 1500 5 1800 6 2100 7 2400 8 2700 9 3000 10

A.F. 600 3 200 G.F. 800 4 1000 5 1200 6 1400 7 1600 8 1800 9 2000 10

L.F. 900 3 300 R.L. 1200 4 1500 5 1800 6 2100 7

J.W. 2100 3 700 2800 4 3500 5 4200 6 4900 7 5600 8 6300 9 7000 10

37 Pitch Matching of Complex Tones Using a Two-Alternative

Forced Choice Adaptive Method

Results of the pitch matching between the complex and

pure tones using the two-alternative forced choice adaptive

method are shown graphically in figures 3 to 26.

The pitch values from the various procedures are shown

in tables 4 to 9. The values were calculated as described

in the methods. Also shown are frequency values

representing either the fundamental, its harmonic

components, or octaves below harmonics, which best

approximate the pitch values. The range of values used to

establish a match to either of these was calculated as

follows: The lower limit was taken as the precise value to which the obtained value was approximated divided by the

last stepsize (1.125). The upper limit was logarithmically the same distance away from the precise value as was the

lower limit. Since the precision to which the fundamental

is matched depends upon the final stepsize, a range of

frequencies, rather than one frequency at the fundamental, must be considered an exact match. This is presented below

each table. For example, figure 15 shows that patient L.F.

correctly made the right responses in matching to a 300 Hz

fundamental. However, because two of the four values used

in the calculation of the pitch were either one final

stepsize above or below the fundamental, the frequency range

38 Figure 3;

Pitch matching control for patient A.D. using a two-alternative forced choice adaptive method. Both the complex and pure tones were presented to the intact ear. The straight lines represent the harmonic components of the complex test sound (fl), i.e., harmonics 3-10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

The upper plot is sequence A, the lower plot is sequence B. Plots were dependent on the patient's response after each presentation. On the right, actual frequency values (Hz) of the pure tone for each presentation (first column) are depicted for sequence A (second column) and sequence B (third column).

39 Fund 300 Hz SEGA SEQB 161 3000 Hx 1 > 450 200 N 2) 450 300 6 3) 675 200 4> 675 133 5) 450 133 6) 675 199 7) 675 159 8) 450 159 e 9) 562 159 900 Hz 10) 562 127 11) 450 101 1.00 12) 562 89 13) 562 79 14) 450 79 15) 562 79 16) 562 89 0.E5 i i i i i i i i i i i i I II i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i 17) 450 89 18) 506 0 IT £7 T£ T6 T6 0 £ H 6 6 10 1£ 16 18 £0 eg £6 £8 30 3£ 3t 36 38 ^0 Vt 50 19) 506 0 PRESENTATION 20) 450 0 21) 506 0 22) 506 0 PhTIENTi A.D. FUNDAMENTAL•300 Hz 23) 450 0 Figure 4:

Pitch matching control with noise for patient A.D. using a two-alternative forced choice adaptive method.. Both the complex and pure tones were presented to the intact ear. The straight lines represent the harmonic components of the complex test sound (fl), i.e., harmonics 3 - 10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

41 Fund 300 Hz SEQA SEQB 1) 450 200 2) 450 300 3) 300 200 4) 300 133 5) 200 133 6) 300 199 161 3000 HJ 7) 300 159 N 8) 450 127 e 9) 450 127 10) 300 101 11) 375 101 12) 375 126 13) 300 126 14) 300 158 £' 15) 240 158 900 H2 16) 300 140 17) 300 124 1.00 18) 240 124 19) 300 139 20) 300 123 21) 240 0 22) 270 0 01 £5 I M I I I I I I M "1 I I I I I I U I I M "I I I | I I I I I I I I I I I I I I I I I I I I I II 23) 270 0 24) 240 0 0 £ T 6 8 10 1£ it 16 16 £0 ££ £T £6 £8 30 3£ 3T 36 38 70 Hfi 77 76 78 50 25) 240 0 PRESENTATION 26) 213 0 27) 239 0 28) 239 0 PATIENT 1 A.D. FUNDAMENTAL!300 Hz 29) 268 0 30) 268 0 31 ) 238 0 32) 238 0 33) 212 0 Figure 5:

Pitch matching beween ears for patient A.D. using a two-alternative forced choice adaptive method.

The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl), i.e., harmonics 3-10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

43 16- 330^ Ha Fund 300 Hz SEOA SEOB 1) 450 200 e 2) 675 300 3) 675 300 4) 450 450 T 5) 675 300 6) 675 200 7) 450 200 e 8) 562' 300 9) 562 300 l. 10) 450 239 11) 562 191 12) 562 191 13) 450 239 14) 562 191 15) 562 169 (3. £5 i i i i i i i i i i i i i i i i i i i I i i i in i i i I I i i i i i i i i i i i i i i i i i i i i 16) 450 169 £ f 6 8 10 i£ IT 16 16 £0 ££ £T £6 £6 30 3£ 3T 36 36 70 4£ 77 76 HQ 5& 17) 506 190 18) 506 190 PRESENTATION 19) 450 214 20) 506 214 21) 506 241 PATIENTi A.D. FUNDAMENTALi300 Hz 22) 569 214 23) 569 190 Figure 6:

Pitch matching beween ears with noise for patient

A.D. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

45 •3000 Fund 300 H; 16- Hs SEOA SEQB 1) 450 200 2) 450 200 3) 300 300 4) 450 200 5) 450 200 6) 675 200 7) 675 300 £' 8) 450 200 500 Hz 9) 562 200 10) 562 300 1,00' 1 1 ) 450 239 12) 450 191 13) 562 191 14) 562 239 15) 702 239 0.es i i i i i i i i i i i i i i i i i i i i i i i "i -i i i i i i i i -i i i i i i i i i i i i i i i i i i 16) 702 299 17) 562 239 0 £ T 6 8 10 i£ 17 16 16 £0 ££ £7 £6 £8 30 3£ 34 36 38 70 H£ Vt 76 76 50 18) 562 239 PRESENTATION , , 19) 632 299 20) 711 .265 21 ) 799 235 PATIENT 1 A.D. FUNDAMENTAL 1300 Hz 22) 799 0 23) 710 0 Figure 7:

Pitch matching control for patient A.F. using a two-alternative forced choice adaptive method.

Both the complex and pure tones were presented to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl), i.e., harmonics 3 - 10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

47 Fund : 200 Hz SEQA SEOB 1) 300 133 2) 300 199 16" £000 Hr 3) 200 199 4) 300 298 6" 5) 300 198 6) 200 198 7) 300 297 H 8) 300 198 9) 200 198 10) 250 297 £' 600 Hz 1 1 ) 312 237 12) 312 237 13) 1.00' 250 296 14) 312 236 15) 312 236 16) 250 295 17) 281 235 18) 316 235 0.E5 i i i i i i i i i i i i i i i i i i i i r- i i i i i i i i i i i i i i i i i r i i i i i r i i i i i 19) 316 294 20) 281 261 0 £ T 6 8 10 t£ IT 16 16 £0 ££ £7 £6 £8 30 3£ 3t 36 36 ^0 t£ Vt t6 H8 50 21 ) 316 261 PRESENTATION 22) 316 294 23) 0 261 24) 0 261 PhTIENH A.F. FUNDAMENTAL.!£00 Hz 25) 0 294 26) 0 261 27) 0 261 Figure 8:

Pitch matching control with noise for patient A.F. using a two-alternative forced choice adaptive method. Both the complex and pure tones were presented to the intact ear.

49 Fund 200 Hz SEQA SEOB 1) 300 133 2) 300 133 3) 200 199 16" £000 Hx 4) 300 199 5) 300 298 6) 200 198 8 7) 300 198 8) 300 297 9) 200 198 10) 250 198 11 ) 312 297

e 12) 312 237 600 Hz 13) 250 237 14) 312 296 1.001 15) 312 236 16) 250 236 17) 281 295 18) 281 235 19) 250 235 20) 281 0.85 i i i i i i i i i i i i i i i i i i" i i i i i i i I i I i I i i i i I I i I i i r i i i i i i i i i 294 21 ) 281 261 0 £ 4 6 8 10 IS IT 16 18 £0 £8 £4 £6 £8 90 3£ 34 36 38 40 4£ 44 46 48 50 22) 250 261 PRESENTATION 23) 281 294 24) 281 261 25) 0 261 26) 0 294 PATIENTi A.F. FUNDAMENTAL«£00 Hz 27) 0 261 28) 0 261 Figure 9:

Pitch matching between ears for patient A.F.

using a two-alternative forced choice adaptive method. The complex tone was presented to the

damaged ear, and the pure tone to the intact ear.

The straight lines represent the

harmonic components of the complex test sound (fl),

i.e., harmonics 3 - 10. The graphic plots represent

the frequency of the pure tone (f2) in relation to

the component frequencies on a logarithmic scale.

The upper plot is sequence A, the lower plot is

sequence B. Plots were dependent on the patient's

response after each presentation. On the right,

actual frequency values (Hz) of the pure tone for

each presentation (first column) are depicted for

sequence A (second column) and sequence B (third

column).

51 Fund 200 Hz SEQA SEOB 1 > 300 133 161 £000 H 2) 300 199 J 3) 200 199 \ 4) 300 298 6" 5) 300 198 6) 200 198 7) 300 297 V 8> 300 198 9) 200 198 10) £' 250 297 600 Hz 1 1) 250 237 12) 312 237 13) 312 296 1.001 14) 250 236 15) 312 236 16) 312 295 17) 250 235 18) 281 235 0i £51 i i i i i i i i i i i i i i i i i f i i i i' i i i i T i i i i i i i i i i i i i i i i i i i i i i i 19) 281 294 20) 250 261 0 £ H 6 8 10 1£ IT 16 18 £0 ££ £T £6 £8 3< 21 ) 281 261 PRESENTATION 22) 281 294 23) 250 261 24) 281 261 PATIENTi A.F. FUNDAMENTALi£00 Hz 25) 281 294 26) 0 261 27) 0 261 Figure 10:

Pitch matching between ears with noise for patient

A.F. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

53 Fund 200 Hz SEOA SEOB 1) 300 133 16 2:300 Hr 2) 300 199 \ 3) 200 199 4) 300 298 e 5) 300 198 6) 200 198 4 7) 300 297 8) 300 198 9) 200 198 e 10) 250 297 00 Hz 1 1 ) 312 237 12) 312 237 1.00 13) 250 296 14) 312 236 15) 312 236 16) 250 295 17) 281 235 0.£5 I I I I I I I I I I I I I I I I I I I I I I I I 1 I I I I I 1 I 1 I I I I I I I I I I I I I I I I I 18) 281 235 19) 250 294 0 2 4 6 6 10 1£ 14 16 18 £0 ££ £4 £6 £6 30 3£ 34 36 38 40 4£ 44 46 48 50 20) 281 261 PRESENTATION 21 ) 281 261 22) 250 232 23) 281 232 PATIENT'A.F, FUNDAMENTAL•£00 Hz 24) 281 261 25) 0 232 26) 0 232 ElguKe 11;

Pitch matching control for patient G.F. using a two-alternative forced choice adaptive method.

Both the complex and pure tones were presented to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl),

i.e., harmonics 3 - 10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

55 Fund 200 Hz SEOA SEOB 1 ) 300 133 2> 300 199 161 Hx 3) 200 199 4) 300 132 5) 300 132 6) 450 198 7) 450 132 8) 300 132 9) 300 198 10) 200 158 1 1 ) 250 158 ..^y>-t 600 Hz 12) 250 198 13) 200 158 14) 250 158 15) 312 198 50" 16) 312 158 17) 250 158 18) 281 198 £5 M ' i i i i 'i I i i i i i i i i i I i i i i i i i i i i i i i i i i i I i i i i i i i i i i i i i i 19) 316 176 20) 316 176 0 2 4 6 8 10 1£ IT 16 16 £0 ££ £4 £5 £8 30 3£ 34 36 38 40 H£ TT 46 48 50 21 ) 281 198 PRESENTATION 22) 316 198 23) 316 176 24) 0 176 PATIENTi G.F. FUNDAMENTALi£00 Hz 25) 0 198 26) 0 176 27) 0 176 Figure 12:

Pitch matching control with noise for patient G.F. using a two-alternative forced choice adaptive method. Both the complex and pure tones were presented to the intact ear.

57 Fund 200 Hz SEQA SEOB 1) 300 133 2) 300 199 3) 200 199 4) 300 298 16- £000 HE 5) 300 298 6) 200 198 7) 300 198 8) 300- 297 9) 375 198 10) 375 198 11) 300 297 12) 300 237 e 13) 375 237 14) 375 296 15) 300 236 1.00 16) 375 236 / 17) 375 295 18) 300 295 19) 337 235 20) 337 235 0.£5 I I I I I I I I I I I I I I I I I I I I I I I I •» I I 1 I I I I I I I I I I I I 1 I I I I I I I I I 21) 300 294 22) 337 261 0 10 IT 77 50 e t 6 e ie 16 ie es ee et £6 ee 30 ae at 36 38 40 te 46 te 23) 337 261 24) 300 232 25) 337 232 PRESENTATION , 26) 337 261 27) 0 261 28) 0 294 PATIENT 1 G.F. FUNDAMENTAL 1£00 Hz 29) 0 261 30) 0 261 Figure 13:

Pitch matching between ears for patient G.F. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

The straight lines represent the harmonic components of the complex test sound (£1), i.e., harmonics 3 - 10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

59 Fund 200 Hz SEOA SEOD 1) 300 133 2) 450 199 16i Hs 3) 450 132 4) 300 132 5) 450 198 6) 450 198 7) 300 132 e> 375 132 9) 375 198 10) 300 158 1.1 ) 375 158 12) 375 198 13) 300 158 14) 375 158 15) 375 198 16) 300 158 17) 337 158 18) 379 198 0.£51 i i i i i i i i i i i i i i i i i i i i i i ri • i i i i i i i i i i i i i i i i i i i i i i i i i i 19) 379 198 20) 337 176 0 £ 7 6 6 10 1£ 14 16 16 £0 ££ £4 £6 £8 30 3£ 3V36 36 40 T£ Vt 46 48 50 21 ) 379 176 22) 379 198 PRESENTATION 23) 0 176 24) 0 176 25) 0 198 i G F i 26) 0 176 PATIENT - - FUNDAMENTAL £00 Hz 27) 0 176 Figure 14:

Pitch matching between ears with noise for patient

G.F. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl), i.e., harmonics 3 - 10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

61 Fund 200 Hz SEQA SEOB 1) 300 133 2) 300 199 3) 200 199 4) 300 298 16" sowa Hx 5) 300 198 6) 200 198 300 297 e 7) 8) 300 297 9) 200 198 10) 250 198 11) 250 297 12) 312 237 237 e1 600 Hz 13) 312 14) 250 296 15) 312 236 1.00 16) 312 236 17) 250 295 18) 281 235 19) 281 235 20) 250 294 0.£5 i i i i i i i i i i i i i i i i i n i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i 21 > 281' 294 22) 281 261 0 £ T 6 6 10 1£ 1T 16 16 £0 ££ £7 £6 £6 30 3£ 34 36 36 70 7£ 77 46 H8 50 23) 316 261 PRESENTATION 24) 316 294 25) 0 261 26) 0 261 PATIENTi G.F. FUNDAMENTALi£00 Hz 27) 0 294 28) 0 261 29) 0 261 Figure 15:

Pitch matching control for patient L.F. using a two-alternative forced choice adaptive method.

Both the complex and1pure tones were presented to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl),

i.e., harmonics 3-7. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

63 Fund 300 Hz 8EQA SEOB 1 ) 450 200 i&1 aiacf Hi 2) 450 300 3> 300 200 4) 450 200 6" 5) 450 300 6) 300 200 7) 450 200 8) 450 300 9) 300 239 10) 375 239 4-4. M M 900 Hz 11) 375 299 12) 300 239 1.001 13) 375 239 14) 375 299 15) 300 239 16) 375 239 17) 375 299 18) 300 265 0, £5 I i i i i i i i "i i i i i i i i i i l i l I I i i I l l I I I i i 'i T i i i i i I II i i I i i I i i 19) 337 265 0 £ T 6 6 10 1£ 14 16 18 £0 ££ £7 £6 £9 90 3£ 37 36 59 70 4£ 77 46 78 50 20) 337 298 PRESENTATION 21) 300 264 22) 337 264 23) 337 297 PATIENT 1 L.F. FUNDAMENTAL 1300 Hz 24) 300 264 25) 337 264 26) 337 0 Figure 16:

Pitch matching control with noise for patient L.F. using a two-alternative forced choice adaptive method. Both the complex and pure tones were presented to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl), i.e., harmonics 3-7. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

65 Fund 300 Hz SEQA SEOB 1&1 S100 HE 1) 450 200 2) 450 300 6- 3) 300 200 4) 450 200 5) 450 300 6) 300 200 7) 450 200 8) 450 300 e1 S00. Hz 9) 300 239 10) 375 239 .00 11) 375 299 1 12) 300 239 13) 375 239 0.50 14) 375 299 15) 300 239 16) 375 239 01 £5 I i i' i i i i i i i ri i i i i i i i i i i i i i i I i I i i i i i i i i i i r i v i i i i i i i i i 1717)) 375 299 18) 300 265 0 2 7 6 8 10 1£ 14 16 16 £0 ££ £t £6 £8 3 19) 337 265 PRESENTATION 20) 337 298 21 ) 379 264 22) 379 264 PATIENTi L.F. FUNDAMENTAL•300 Hz 23) 337 297 24) 379 . 264 25) 379 264 Figure 17:

Pitch matching between ears for patient L.F. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

The straight lines represent the harmonic components of the complex test sound (£1), i.e., harmonics 3-7. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

67 Fund 300 Hz SEOA SEOB 1 > 450 200 16" £100 Hi 2) 450 300 3) 300 200 4) 450 200 5) 450 300 6) 300 200 7) 450 200 8) 450 300 9) 300 239 £' 10) 375 239 800 Hz 11) 375 299 12) 300 239 00" 13) 375 239 14) 375 299 15) 300 239 501 16) 375 239 17) 375 • 299 18) 300 265 £5 I I l I I i I i I i i I I I l i I I I i l I" M l I l I I i l i I i I i I i i i I i i i I i i i I i i 19) 337 265 0 £ 4 6 6 10 1£ IT 16 16 £0 ££ £T £6 £8 30 3£ 3T 36 38 70 T£ TT T6 T8 50 20) 337 298 21) 300 264 PRESENTATION 22) 337 264 23) 337 297 24) 300 264 PATIENTi L.F. FUNDAMENTALi300 Hz 25) 337 264 26) 337 0 Figure 18:

Pitch matching between ears with noise for patient

L.F. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl),

i.e., harmonics 3 - 7. The graphic plots represent the frequency of the pure tone (£2) in relation to the component frequencies on a logarithmic scale.

69 Fund 300 Hz SEOA SEOB 1) 450 200 16" £100 Hx 2) 450 300 3) 300 200 450 200 e 4) 5) 450 300 6) 300 200 7) 450 200 8) 450 300 9) 300 239 e 300 Hz 10) 375 239 1 1) 375 299 12) 300 239 1.00 13) 375 239 14) 375 299 15) 300 239 16) 375 239 17) 375 299 01 £5 i i i i i i i i 'M i i i i i i i i i" i i i i i "i i i i i i i i i i i i i i i i i i i i i i i i i nr 18) 300 265 0 £ t 6 8 10 1£ It 16 18 £0 ££ £t £6 £8 30 3£ 3t 36 36 t0 t£ tt t6 t85 0 19) 337 265 20) 337 235 PRESENTATION 21 ) 300 235 22) 337 264 23) 337 234 PATIENTi L.F. FUNDAMENTALi300 Hz 24) 300 234 25) 337 0 26) 337 0 Figure 19:

Pitch matching control for patient R.L. using a two-alternative forced choice adaptive method.

Both the complex and pure tones were presented to the intact ear.

71 Fund 300 Hz 16 8100 Hx SEOA SEOB 1 > 450 200 2) 675 300 61 3) 675 300 h 4) 450 450 A 5) 4 675 300 R 6) 675 300 M 7) 450 450 0 £1 8) 562 300 N 900 Hz 9) 562 300 I 10) 702 450 1.00 11 ) 702 359 12) 562 287 13) 702 287 14) 702 359 15) 562 287 16) 632 287 0.£5 i I I I i I I I I I I I I I I I I I I I I I 1 I I I'l I I I I I i I I I I I I I I I l l I I I I I l 17) 711 359 0 2 4 6 8 10 1£ 14 16 18 £0 ££ £4 £6 £6 30 3£ 34 36 38 40 4£ 44 46 48 50 18) 711 319 19) 632 319 PRESENTATION 20) 711 283 21 > 711 283 22) 0 318 23) 0 282 K-L- 1 PATIENTi FUNDAMENTAL 300 Hz 24) 0 282 Figure 20:

Pitch matching control with noise for patient R.L. using a two-alternative forced choice adaptive method. Both the complex and pure tones were presented to the intact ear.

73 Fund 300 Hz SEOA SEOB 1) 450 200 2) 450 200 16- slaw HJ 3) 300 300 4) 450 300 5) 450 450 6) 300 300 7) 450 300 8) 450 450 9) 300 300 10) 375 300 11) 375 450 12) 300 359 13) 375 359 1.00" 14) 468 449 15) 468 359 16) 374 359 17) 420 449 18) 420 359 19) 472 359 01 £5 1 i i l i i i 'i i i ii i i i i i i i i i i i i i i I l l I i I l i i l i i I l i l l i i i I I I I i 20) 472 449

0 £ 7 6 6 10 te IT 16 18 £0 ££ £4 £6 £6 3i 21 ) 420 399 22) 472 399 23) 472 449 PRESENTATION 24) 0 399 25) 0 399 26) 0 449 PATIENTi R.L. FUNDAMENTALi300 Hz 27) 0 399 28) 0 399 Figure 21:

Pitch matching between ears for patient R.L. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the Intact ear.

75 Fund 300 Hz SEOA SEQP 1) 450 200 2) 450 300 16- £100 Hz 3) 300 300 4) 300 450 5) 450 300 • 6- : 6) 450 300 7) 300 450 8) 450 300 9) 450 300 10) 300 450 1 1 ) 375 359 900 Hz 12) 468 359 13) 468 449 1.001 14) 374 359 15) 467 359 16) 467 449 17) 374 359 18) 420 359 0.£5 I i i i i i i i i i i i i i i i i i i i i i i i i i i i l i i i i i i i i i i r i r i i i ri i i i i 19) 472 449 20) 472 399 0 £ t 6 6 10 1£ It 16 19 £0 £E £t £6 £9 30 3£ 3t 36 39 t0 t£ tt t6 t9 50 21) 420 399 PRESENTATION 22) 472 449 23) 472 399 24) 0 399 PATIENTi R.L. FUNDAMENTALi300 Hz 25) 0 449 26) 0 399 27) 0 399 Figure 22:

Pitch matching between ears with noise for patient

R.L. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

77 Fund 300 Hz 161 B100 Ha SEQA SEOB 1 > 450 200 2) 450 300

6' 3) 300 300 4) 450 450 5) 450 300 6) 300 300 7) 450 450 8) 450 300 £1 900 Hz 9) 300 300 10) 375 450 11) 468 359 i .00- 12) 468 359 13) 374 449 14) 467 359 15) 467 359 16) 374 449 0.£5 I i i i i i i i i i i i i i i i i i r i i i i i i i i i i i i i i i i i i i i i i i i i i i i'» i i i 17) 420 359 18) 420 359 0 £ 4 6 6 10 1£ IT 16 16 £0 ££ £4 £6 £8 3J 19) 420 449 PRESENTATION 20) 373 399 21 ) 419 354 22) 419 314 PATIENTi R.L. FUNDAMENTALi300 Hz 23) 372 314 24) 418 0 25) 418 0 Figure 23:

Pitch matching control for patient J.w. using a two-alternative forced choice adaptive method.

Both the complex and pure tones were presented to the intact ear.

79 16- 7000 Hx Fund: 700 Hz SEOA SEOB N 1) 1050 467 8" 2) 1575 700 3) 1575 466 4) 1050 466 4 5) 1575 310 6) 1575 310 £' /A/A/-^A^v^s^* 7) 1050 465 t\m Hz 8) 1312 371 9) 1640 296 i. m 10) 1640 296 1 1) 1312 370 12) 1640 370 13) 1640 463 14) 1312 370 15) 1476 370 01£5 I i i i i i i i i i i i i i i i i i i i i i II " i i i I I i I i l i M i i i i i i i i i i i i i i i 16) 1476 328 0 £ 4 6 8 10 IS 14 15 18 £0 ££ £4 £6 £8 30.38 34 36 38 40 4£ 44 46 46 50 17) 1312 291 PRESENTATION 18) 1476 291 19) 1476 327 20) 1312 327 21 ) 1476 PATIENTi j.w. FUNDAMENTAL•700 Hz 290 22) 1476 290 Figure 24:

Pitch matching control with noise for patient J.W. using a two-alternative forced choice adaptive method. Both the complex and pure tones were presented to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl),

i.e., harmonics 3 - 10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

81 Fund 700 Hz 7000 Hr SEOA SEOB X 1) 1050 467 2) 1050 700 3> 1050 700 4) 700 1050 5) 1050 700 6) 1050 700 7) 700 1050 8) 1050 700 £100 Hz 9) 1050 700 10) 700 1050 11) 875 839 12) 1093 671 13) 1093 671 14) 874 839 15) 1092 671 i i i i i i 11 i i i i t i i i i i i i i i i i i i i i i i i i 'i i t i 'i i i i i i i i i i i i i i" 16) 1092 671 17) 874 839 0 8 4 6 6 10 1£ 14 16 18 £0 ££ £4 £6 £8 30 3£ 34 36 38 40 4£ 44 46 48 50 18) 983 745 PRESENTATION 19) 983 745 20) 874 838 21 ) 983 744 PATIENT" J.W. FUNDAMENTALi700 Hz 22) 1 105 744 23) 1 105 837 Figure 25:

Pitch matching between ears for patient J.W.

using a two-alternative forced choice adaptive method. The complex tone was presented to the

damaged ear, and. the pure tone to the intact ear.

The straight lines represent the

harmonic components of the complex test sound (fl),

i.e., harmonics 3 - 10. The graphic plots represent

the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

The upper plot is sequence A, the lower plot is sequence B. Plots were dependent on the patient's

response after each presentation. On the right, actual frequency values (Hz) of the pure tone for

each presentation (first column) are depicted for

sequence A (second column) and sequence B (third

column).

83 Fund 700 Hi SEOA SEQB 16" 7000 Ha 1) 1050 467 2) 1050 700 \ 3) 1575 700 6' 4) 1575 1050 5) 1050 700 6) 1575 700

T" 7) 1575 1050 8) 1050 700 9) 1312 700 E" £100 Hz 10) 1312 1050 11) 1050 839 12) 1312 839 1.00" 13) 1312 671 14) 1050 671 fli.Efli" 15) 1312 839 16) 1312 83*9 17) 1050 1049 0.S5- i i i i i i i i i i i i i i i i i i'i i i i n i i"i i i i i i i i i i i i i i i i i i i i i i i i 18) 1181 839 19) 1328 839 0 £ T 6 6 10 IE It 16 16 £0 £E £t £6 £6 30 3E 3t 36 36 t0 t£ tt t6 t6 50 20) 1328 1049 21 ) 1 180 932 PRESENTATION 22) 1 180 828 23) 1049 828 24) 1049 931 PATIENTi J.w. FUNDAMENTALi700 Hz 25) 1 180 827 26) 1 180 0 Figure 26:

Pitch matching between ears with noise for patient

J.W. using a two-alternative forced choice adaptive method. The complex tone was presented to the damaged ear, and the pure tone to the intact ear.

The straight lines represent the harmonic components of the complex test sound (fl), i.e., harmonics 3 - 10. The graphic plots represent the frequency of the pure tone (f2) in relation to the component frequencies on a logarithmic scale.

85 Fund 700 Hz SEOA SEOB 1 > 1050 467 a) 1050 700 16 7000 Hs 3) 1050 700 \_ 4) 1050 466 5) 700 466 e 6) 1050 699 7) 1050 466 t 8) 700 466 9) 1050 699 10) 1050 699 e £100 Hz 1 1 ) 700 559 12) 875 559 13) 875 699 1. 14) 700 699 15) 875 874 16) 1093 699 17) 1093 699 18) 874 559 0,£5 I I I l l I l i l i l l I l l i l I I i I l l i I i I l' I I I l l i I I I I I l I I l I I I I i l l I 19) 983 559 20) 983 699 IT ££ £T 3T T£ TT T8 0 £ t 6 6 10 1£ 16 18 £0 £6 £8 30 3£ 36 38 t0 t6 50 21 ) 1105 699 PRESENTrtTION 22) 1 105 874 23) 982 776 24) 982 689 PrlTIENTi j.w. FUNDAMENTAL!700 Hz 25) 1 104 689 26) 1 104 775 27) 0 688 28) 0 688 Table 4,:

Pitch values assigned to the pitch of the complex test sound by patient A.D. for sequences A and B for each procedural method using the two-alternative forced choice adaptive routine. Below each sequence is the

frequency value representing either the fundamental

of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

Dashed line represents no match.

87 Patient;; A.D.

Pitch Matching Procedure

P.M. control P.M. control P.M. betw. P.M. betv. with noise ears ears w. noise

Seq. A pitch 478 +/- 32 239 +/- 23 508+/-49 713 +/- 68 value (Hz)

Freq. 450 750 approx, (oct. bel. (oct. bel. (Hz) 3rd har.) 5th har.)

Seq. B pitch 90 + /- 9 132 +/- 9 215+/-21 260 +/- 30 value (Hz)

Fr eq. approx (Hz) range of frequency values to which an exact matching to the fundamental occurs: 281 - 319 Hz

88 Table 5:

Pitch values assigned to the pitch of the complex test sound by patient A.F. for sequences A and B for each procedural method using the two-alternative forced choice adaptive routine. Below each sequence is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values .

Dashed line represents no match.

89 Patient: A.F.

Pitch Matching Procedure

P.M. control P.M. control P.M. betv. P.M. betw. with noise ears ears w. noise Seq. A pitch 299 +/- 20 266 +/- 18 266+/-18 266 +/- 18 value (Hz)

Freq. 300 approx. (oct. bel. (Hz) 3rd har.)

Seq. B pitch 278 +/- 19 278 +/- 19 278+/-19 247 +/- 17 value (Hz)

Freq. 300 300 300 approx (oct. bel. (oct. bel. (oct. bel (Hz) 3rd har.) 3rd har.) 3rd har) range of frequency values to which an exact matching to the fundamental occurs: 183 - 212 Hz

90 Table 6:

Pitch values assigned to the pitch of the complex test sound by patient G.F. for sequences A and B for each procedural method using the two-alternative forced choice adaptive routine. Below each sequence is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

Dashed line represents no match.

91 Patient: G.F.

Pitch Matching Procedure

P.M. control P.M. control P.M. betw. P.M. betw with noise ears ears w. noise Seq. A pitch 299 +/- 20 319 +/- 21 358+/-24 282 +/- 27 value (Hz)

Freq. 300 300 400 300 approx (oct. bel. (oct. bel. (2nd har . ) (oct. bel. (Hz) 3rd har.) 3rd har . ) 3rd har.)

Seq. B pitch 187 +/- 13 262 +/- 25 187+/-13 278 +/- 19 value (Hz)

Freq. 200 200 300 approx (fund.) (fund . ) (oct. bel. (Hz) 3rd har.) range of frequency values to which an exact matching to the fundamental occurs: 183 - 212 Hz

92 Table 7:

Pitch values assigned to the pitch of the complex test

sound by patient L.F. for sequences A and B for each procedural method using the two-alternative forced

choice adaptive routine. Below each sequence is the

frequency value representing either the fundamental

of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

Dashed line represents no match.

93 paUent; L.F.

Pitch Matching Procedure

P.M. control P.M. control P.M. betw. P.M. betw, with noise ears ears w. noise Seq. A pitch 319 +/- 21 358 +/- 24 319+/-21 319 +/- 21 value (Hz)

Freq. 300 300 300 approx. (fund. ) (fund.) (fund.) (Hz)

Seq. B pitch 281 +/- 19 281 +/- 19 281+/-19 250 +/- 17 value (Hz)

Freq. 300 300 300 approx (fund.) (fund.) (fund.) (Hz) range of frequency values to which an exact matching to the fundamental occurs: 281 - 319 Hz

94 Table 8:

Pitch values assigned.to the pitch of the complex test sound by patient R.L. for sequences A and B for each procedural method using the two-alternative forced choice adaptive routine. Below each sequence is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

Dashed line represents no match.

95 Patient; R.L.

Pitch Matching Procedure

P.M. control P.M. control P.M. betw. P.M. betw. with noise ears ears w. noise

Seq. A pitch 672 + /- 46 446 +/- 30 446+/-30 396 +/- 27 value (Hz)

Freq. 600 450 450 approx (2nd har . ) (oct. bel. (oct. bel (Hz) 3rd har . ) 3rd har)

Seq. B pitch 301 +/- 21 424 +/- 29 424+/-29 379 +/- 58 value (Hz)

Freq. 300 450 450 approx (fund. ) (oct. be 1. (oct. bel (Hz) 3rd har.) 3rd har) range of frequency values to which an exact matching to the fundamental occurs: 281 - 319 Hz

96 Table 9;

Pitch values assigned to the pitch of the complex test sound by patient J.W. for sequences A and B for each procedural method using the two-alternative forced choice adaptive routine. Below each sequence is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

Dashed line represents no match.

97 Patient: J.W.

Pitch Matching Procedure

P.M. control P.M. control P.M. betw. P.M. betw with noise ears ears w. noise Seq. A pitch 1394 +/- 95 986 +/- 94 1184 +/- 1044 +/- 70 value 114 (Hz)

Freq. 1400 1050 1050 approx, (2nd har.) (oct. bel. (oct. bel. (Hz) 3rd har.) 3rd har.)

Seq. B 309 +/- 21 791 +/- 54 880+/-60 732 +/- 50 pitch value (Hz)

Freq. 700 approx (fund.) (Hz) range of frequency values to which an exact matching to the fundamental occurs: 657 - 742 Hz

98 o£ an exact match is 281-319 Hs.

i) Pitch matching control

Figures 11, 15, and 19 and tables 6, 7, and 8 show that patients G.F., L.F., and R.L. matched the complex test sound to its fundamental frequency when both the complex test sound and the comparison pure tone were presented to the intact ear (pitch matching control). Both G.F. and R.L. matched to the fundamental when sequence B was used (i.e., the pure tone's starting frequency presented lower than the fundamental of the complex), while patient L.F. matched to the fundamental regardless of which sequence was

Implemented.

Patients A.D. (figure 3; table 4), A.F. (figure 7; table 5), and G.F. (figure 11; table 6) matched to the octave below the third harmonic, while R.L. and J.W.

(figures 19 and 23; tables 8 and 9) matched to the (not presented) second harmonic (the octave above the fundamental) during the pitch matching control procedure.

A.F. displayed octave confusion during pitch matching regardless of the sequence.

UJ Pitch matching control with noise

With the addition of the low-pass filtered noise to the complex test sound while still maintaining both complex and

99 pure tones to the intact ear, patients A.D. (figure 4; table

4) and A.F. (figure 8; table 5) failed again to match the complex to the fundamental as they did without the noise.

Patients R.L. and J.W. (figures 20 and 24; tables 8 and

9), who matched either to the fundamental or to the octave above the fundamental during pitch matching control, failed to do so in the presence of noise and instead matched either to the octave below the third harmonic or had no match at all. Furthermore, patient G.F. (figure 12; table 6), who matched either to the fundamental or to the octave below the third harmonic during pitch matching control, failed to match to the fundamental in the presence of noise. Patient

L.F., however, still matched to the fundamental even in the presence of noise, but now only in sequence B (figure 16; table 7).

Ill) Pitch matching between ears

When the complex test sound was presented to the damaged ear and the comparison pure tone to the intact ear

(i.e., pitch matching between ears) both G.F. and L.F. matched the complex with its fundamental, as they did when both sounds were presented to their intact ears (figure 13 and 17; tables 6 and 7). In addition, patient G.F., who had matched to the octave below the third harmonic during pitch matching control for sequence A, now matched to the octave

100 above the fundamental during pitch matching between ears for

the same sequence. Patients R.L. and J.W., however, failed to match to the fundamental or to the second harmonic as

they did when both sounds were presented to their intact ear, and instead matched to the octave below the third harmonic (figure 21; table 8) or had no match at all (figure

25; table 9).

Patients A.D. and A.F. (figures 5,9; tables 4,5) continued to have difficulty matching to the fundamental since no match to any component occurred except in one case when there was a match to the octave below the third harmonic.

IvJ Pitch matching between ears with noise

Addition of low-pass filtered noise to the complex test sound during pitch matching between ears resulted in

preservation of the ability of patient L.F. to pitch match to the lacking fundamental (figure 18; table 7), but only during sequence A. One patient (J.W.) who had not previously matched to the fundamental did so during this

procedure in sequence B (figure 26; table 9). Octave confusion to the octave below the third harmonic was also displayed, however, for this patient.

Patient G.F. was unable to match to the fundamental with the addition of noise to the complex in spite of his

101 apparent ability to do so without noise. Instead he matched

to the octave below the third harmonic during both sequences

(figure 14; table 6). No reasonable match was made during this procedure for patients A.D., A.F., and R.L. (figures

6,10,22: tables 4,5,8) except once when a match was made by patient A.D. to the octave below the fifth harmonic.

Pitch Matching of Complex Tones Using an Up-Down Adjustment

Technique

Results of the pitch matching between the complex and

pure tones using the up-down adjustment technique are shown

in tables 10 to 14.

JJ Pitch matching control

Tables 10 to 14 show that all the patients except A.F. matched the complex test sound to its fundamental frequency at least once when both the complex test sound and the

comparison pure tone were presented to the intact ear (pitch matching control). For patients L.F. and R.L. .(tables 13 and 14, respectively) this occurred regardless of whether the starting frequency of the pure tone (f2) was above or

below the fundamental frequency of the complex (fl).

However, the matching to the fundamental occurred twice for

A.D., only when the starting frequency of f2 was above the

fundamental frequency, and once for G.F., only when the

102 Table 10:

Pitch values assigned to the pitch of. the complex test sound by patient A.D. for each procedural method using the up-down adjustment technique. Listed are the values obtained when the patient started the match with the pure tone frequency above or below that of the fundamental of the complex.

In parentheses is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

A dashed line represents no match.

103 Patient; A.D.

Pitch Matchina Procedure

P.M. control P.M. control P .M. betw. P.M. betw. with noise ears ears w. noi

Pitch 274 332 329 291 value ( 300 - (300 - (300 - (300 - with fund.) fund.) fund.) fund.) start. f req. 297 894 549 312 above ( 300 - (900 - (600 - ( 300 - fund. fund.) 3rd har.) 2nd har. ) fund.) (Hz)

Pitch 583 159 474 167 value ( 600 - (150 - (450 - (150 - with 2nd har. ) oct. bel. oct. bel. oct. bel. start. fund.) 3rd har. ) fund.) freq. below 589 810 679 501 fund. (600 - (900 - (750 - ( 450 - (Hz) 2nd har . ) 3rd har.) oct. bel. oct. bel. 5th har.) 3rd har . )

104 Table 11:

Pitch values assigned to the pitch of the complex test sound by patient A.F. for each procedural method using the up-down adjustment technique. Listed are the values obtained when the patient started the match with the pure tone frequency above or below that of the fundamental of the complex.

In parentheses is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonic, which best approximate the pitch values.

A dashed line represents no match.

105 Pitch Matching Procedure

M. control P.M. control P.M. betw. P.M. betw. with noise ears ears w. noise

588 437 408 200 (600 - (400 - (400 - (200 - 3rd har.) 2nd har.) 2nd har.) fund.)

737 446 412 581 (- - -) (400 - (400 - (600 - 2nd har.) 2nd har.) 3rd har.)

811 ( 800 - 4th har . )

411 318 140 223 (400 - (300 - (- - -) (200 - 2nd har.) oct. bei. fund.) 3rd har.)

435 411 183 248 (400 - (400 - (200 - (- - -) 2nd har.) 2nd har.) fund.)

470 (500 - oct. bei. 5th har.)

602 ( 600 - 3rd har.)

106 Table 12:

Pitch values assigned to the pitch of the complex test sound by patient G.F. for each procedural method using the up-down adjustment technique. Listed are the values obtained when the patient started the match with the pure tone frequency above or below that of the fundamental of the complex.

In parentheses is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

A dashed line represents no match.

107 Pitch Matching Procedure

M. control P.M. control P.M. betw. P.M. betw. with noise ears ears w. noise

496 813 132 135

( ) (500 - (800 - ( ) oct. bel. 4th har.) 5th har.)

589 830 134 204 ( 600 - ( 800 - ( ) ( 200 - 3rd har.) 4th har.) fund.)

795 881 1110 641 ( 800 - (800 - (1000 - (600 - 4th har.) 4th har.) 5th har. ) 3rd har. )

192 797 191 137 (200 - (800 - (200 - (- - -) fund.) 4th har.) fund.)

639 814 574 685 (600 - (800 - (600 - (- - -) 3rd har.) 4th har.) 3rd har.)

812 878 901 908 (800 - (800 - (--•-) (- - -) 4th har.) 4th har.)

108 Table 13:

Pitch values assigned to the pitch of the complex

test sound by patient L.F. for each procedural method

using the up-down adjustment technique. Listed are

the values obtained when the patient started the match with the pure tone frequency above or below that of

the fundamental of the complex.

In parentheses is the frequency value representing

either the fundamental of the complex, its harmonic

components, or octaves below harmonics, which best

approximate the pitch values.

A dashed line represents no match.

109 Patient: L.F.

Pitch Matching ProceciuKe

P.M. control P.M. control P.M. betw, P.M. betw. with noise ears ears w. noise

Pitch 296 302 286 204 value ( 300 - ( 300 - (300 - ( ) with fund.) fund.) fund.) start. freq. 301 306 287 210 above ( 300 - ( 300 - ( 300 - ) fund. fund.) fund.) fund.) (Hz) 691 290 354 (750 - ( 300 - oct. bei. fund.) 5th har.)

897 291 364 (900 - ( 300 - ( ) 3rd har.) fund.)

366 375 373 3 89 397 389 ) ( )

Pitch 188 298 286 210 value ( ) (300 - ( 300 - ( ) with fund.) fund.) start. freq. 291 301 290 212 be low (300 - (300 - ( 300 - ( ) fund. fund. ) fund.) fund.) (Hz) 297 290 339 ( 300 - (300 - ( ) fund.) fund.)

239 372 349 378 376 380 376 387 394 401 ( ) ( )

110 Table 14?

Pitch values assigned to the pitch of the complex test sound by patient R.L. for each procedural method using the up-down adjustment technique. Listed are

the values obtained when the patient started the match with the pure tone frequency above or below that of the fundamental of the complex.

In parentheses is the frequency value representing either the fundamental of the complex, its harmonic components, or octaves below harmonics, which best approximate the pitch values.

A dashed line represents no match.

Ill Patient: R.L.

Pitch Matching Procedure

P.M. control P.M. control P.M. betw. P.M. betw. with noise ears ears w. noise

Pitch 309 310 301 313 value (300 - (300 - ( 300 - ( 300 - with fund.) fund. ) fund.) fund. ) start. freq. 582 588 311 313 above (600 - (600 - ( 300 - ( 300 - fund. 2nd har. ) 2nd har . ) fund.) fund. ) (Hz) 591 591 565 318 (600 - (600 - (600 - (300 - 2nd har. ) 2nd har.) 2nd har. ) fund. )

595 599 580 (600 - (600 - 586 2nd har. ) 2nd har.) (600 - 2nd har . )

596 601 847 (600 - ( 600 - (900 - 2nd har. ) 2nd har.) 3rd har. )

Pitch 308 579 300 313 value ( 300 - ( 600 - ( 300 - ( 300 - with fund.) 2nd har . ) fund.) fund. ) start. freq. 580 580 307 315 below (600 - (600 - ( 300 - ( 300 - fund. 2nd har . ) 2nd har . ) fund.) fund. ) (Hz) 580 581 586 316 (600 - (600 - (600 - (300 - 2nd har. ) 2nd har . ) 2nd har . ) fund. )

584 590 600 594 (600 - (600 - 2nd har.) 2nd har.)

112 starting frequency of £2 was below the fundamental frequency of the complex. In spite of not matching to the fundamental, patient A.F. did match on two occasions to the octave above the fundamental.

ii) Pitch matching control with noise

With the addition of low-pass filtered noise to the complex test sound, both presented to the intact ear, patients A.D., L.F., and R.L. (tables 10, 13, and 14, respectively) were still able to match to the fundamental, although for patient R.L. this now occurred only when f2 was initially presented above the fundamental of fl. Patient

G.F. did not match even once to the fundamental (table 12).

However, on every trial he did match two octaves above the fundamental. Similarly, patient A.F. who was still unable to match to the fundamental (table 11), matched three times to the octave above the fundamental.

JJJJ Pitch matching between ears

When the complex test sound was presented to the damaged ear and the comparison pure tone presented to the intact ear (i.e., pitch matching between ears) all patients were able to match at least once to the fundamental of the complex (tables 10 to 14). Thus, patient A.F. who was unable to match to the fundamental during the pitch matching

113 control procedure did so during the pitch matching between

ears procedure when the pure tone frequency was initially

presented below that of the fundamental of the complex

(table 11). The other patients matched to the fundamental

at least once during both the pitch matching control and the

pitch matching between ears procedures (tables 10, 12, 13,

and 14).

iv) Pitch matching between ears with noise

Addition of low-pass filtered noise to the complex test

sound during the pitch matching between ears procedure

resulted in at least one match to the fundamental of the

complex for all patients except L.F. who reported difficulty

defining any pitch (see tables 10 to 14). Patient A.D., who matched once to the fundamental during pitch matching

between ears, matched twice to the fundamental when noise

was presented along with the complex tone (table 10). Also,

patient A.F., who matched to the fundamental during pitch

matching between ears only when the pure tone frequency was

initially below that of the fundamental, matched to the

fundamental when the pure tone was initially presented above

or below that of the fundamenatal after addition of noise

(table 11). Better performances in the presence of noise

were observed also in patient R.L. who matched to the

fundamental six out of six times regardless of the initial

114 frequency setting of the pure tone (see table 14). Patient

G.F., who matched once to the fundamental during pitch matching between ears when the pure tone frequency was initially set below that of the fundamental, matched to the fundamental after adding noise, but only when the pure tone frequency was initially set above the fundamental (see table

12) .

Table 15 summarizes the number of matches the patients made to either the fundamental and the octaves above and below the fundamental, or to the presented partials and their related octaves. The first group represents matches made in the "synthetic" mode of hearing as described by

Terhardt (1972,1974,1978) since the fundamental was not physically presented in the complex stimulus. The latter group represents matches made in the "analytic" mode of hearing also described by Terhardt, and represents matches based upon individual partials. Note that a match to the fourth harmonic of the fundamental (i.e., the second octave above the fundamental) was counted in both groups since it not only represents octave confusion to the fundamental, but also was a physically presented partial in the complex stimulus. The total number of trials was 48 for the two- alternative forced choice adaptive method, and 135 for the up-down adjustment technique.

115 Table 15:

Summary of the number of matches the patients made to either the fundamental and the octaves above and below the fundamental, or to the presented partials and their related octaves.

Matches to the fourth harmonic (second octave above the fundamental) were tabulated in both groups. n refers to the number of total patients.

N.B.: Matching to octaves related to the fundamental were considered as evidence in support of the ability to perceive the missing fundamental, and are therefore grouped together (see "discussion" for explanation).

116 Pitch Matching Technique

Two-Alternative Forced Choice Adaptive Method n = 6

matches to the matches to the fundamental or presented its related partials or octaves their related octaves

P.M. Procedure

P.M. control 6 4

P.M. control 1 .5 with noise

P.M. between 4 3 ears

P.M. between 2 4 ears with noise

Up-Down Adjustment Technique n =5

matches to the matches to the fundamental or presented its related partials or octaves their related octaves

P.M. control 23 11

P.M. control 24 9 with noise

P.M. between 21 5 ears

P.M. between 12 3 ears with noise

117 The table shows the following:

1) Using the two-alternative forced choice adaptive

method, more matches were made to the fundamental or its related octaves as compared to matches to the presented

partials or their related octaves, except in the presence of noise.

2) Using the two-alternative forced choice adaptive method, two more matches to the fundamental or its related ocataves were made during pitch matching control as compared

to pitch matching between ears, but one more match was made during the latter procedure as compared to the former when noise was present.

3) The total number of matches during the two- alternative forced choice adaptive method was 29, thereby giving an overall match rate of 60% (29/48).

4) Using the up-down adjustment technique, two to four times as many matches were made to the fundamental or its related octaves as compared to matches to the presented partials or their related octaves, regardless of the pitch matching procedure.

5) Using the up-down adjustment technique, pitch matching control with noise and pitch matching between ears had little effect on the total number of matches to the

fundamental or its related octaves as compared to pitch matching control.

118 6) The total number of matches during the up-down adjustment technique was 108, thereby giving an overall match rate of 80% (108/135).

The results can also be summarized slightly differently

by looking only at matches to the missing fundamental or to the presented partials (i.e., harmonics 3 to 7, or 3 to 10).

Table 16 shows the following:

1) Using the two-alternative forced choice adaptive method, the synthetic mode of hearing was clearly dominant since a total of 10 matches were made to the fundamental,

but none to the presented partials.

2) Using the two-alternative forced choice adaptive

method, one more match to the fundamental occurred during pitch matching control as compared to pitch matching between

ears, but one more match was made during the latter procedure as compared to the former when noise was present.

3) Using the two-alternative forced choice adaptive method, fewer matches were made to the fundamental during

procedures with noise than without noise.

4) The total number of matches during the two-

alternative forced choice adaptive method was 10, thereby giving an overall match rate of 21% (10/48).

5) Using the up-down adjustment technique, the number

of matches to the fundamental and to the presented partials

was approximately the same during pitch matching control

119 TABLE 16:

Summary of the number of matches the patients made to either the missing fundamental, or to the presented partials. n refers to the number of total patients.

120 P 1 tr.h Match 1 ng Tsnhn 1 qiift

Two-Alternative Forced Choice Adaptive Method n = 6

matches to the matches to the fundamental presented part ials

P.Mi F-CQC$d.u,ce.

P.M. control 4 0

P.M. control 1 0 with noise

P.M. between ears

P.M. between ears with noise

Up-Down Adjustment Technique n =5

matches to the matches to the fundamental presented part ials

P.M. control 9 8

P.M. control 6 8 with noise

P.M. between 14 3 ears

P.M. between 11 2 ears with noise

121 with or without noise, but matching to the fundamental was clearly dominant during pitch matching between ears regardless of noise.

6) The total number of matches during the up-down adjustment technique was 61, thereby giving an overall match rate of 45% (61/135).

122 DISCUSSION

Previous studies investigating the perception of the lacking fundamental have used low frequency masking noise to eliminate distortion products which could contribute to the percept (Moore,1973; Moore & Rosen, 1979). However, low characteristic frequency fibers maintain synchrony of neural discharges to signal waveforms even in the presence of noise

(Kiang & Moxon,1974; Rhode et al.,1978; Sachs et al.,1983).

Therefore, by using patients with unilateral low frequency hearing loss, pitch of the missing fundamental, and thus, pitch perception in general, was addressed in the absence of the contribution provided by low characteristic frequency f ibers .

The results clearly indicate that the patients with low frequency hearing loss were able to match a complex tone to the lacking fundamental or its related octaves even though the fundamental fell within a damaged area along the basilar membrane innervated by nerve fibers with corresponding characteristic frequency. Using the up-down adjustment technique, the patients made four times as many matches to the missing fundamental and its related octaves as compared to the presented partials and their related octaves during pitch matching between ears with or without noise (see table

123 15) . When considering only matches to the fundamental or the presented partials (i.e., disregarding octave confusion), then this ratio increases to five (see table

16) . Neither the low-pass filtered noise nor the fact that the complex tone was presented to the patient's damaged ear seemed to have affected their ability to perceive the

lacking fundamental. Performance was even improved during these procedures since only a two fold difference in the number of matches to the fundamental or its octaves as compared to the presented partials or their octaves occurred during the control procedures (table 15). Furthermore, when considering only matches to the fundamental or the presented partials, this ratio was one-to-one during the control procedures (table 16). Looking at the absolute number of matches to the fundamental using the up-down adjustment technique (table 16) also shows how matching to the residue was of greater ease during pitch matching between ears with and without noise (14 and 11 matches, respectively) as compared to pitch matching control with and without noise (9 and 6 matches, respectively). This ability to perceive the missing fundamental or its related octaves demonstrates that the patients were able to perceive pitch using a "synthetic" mode of hearing as described by Terhardt (1972,1974,1978), that is to hear the complex stimulus as an entity rather than analytically breaking it down into its individual

124 components.

The overall error rate during the up-down adjustment

technique was 20% (i.e., match rate of 80%) when considering matches to the fundamental or its related octaves, and to

the presented partials or their related octaves. When considering only matches to the fundamental and the

presented partials, the error rate was 55% (i.e., match rate of 45%). These error rates do, however, indicate a good performance level in view of the following simple calculations. Since a precision factor of 1.125 above and below a target frequency was used to establish a match, the

frequency range from 100 to 1130 Hz used in the up-down adjustment technique can thus be subdivided into approximately 10 contiguous precision bans, and the

probability of correct identification of the target

frequency would be 1/10 or 10%. This would translate into an error rate of 90%. Clearly the observed error rates were considerably better, in spite of the difficulties of the

tasks.

One difficulty was the requirement to match a pure tone

to a complex tone. Due to the different timbres of these two stimuli, it can be very difficult to compare pitches when the tones are presented in isolation (rather than in the context of a melody). Nonetheless, the use of a

comparison pure tone rather than a complex tone was

125 desirable in these experiments in order to investigate

whether the ability to hear pure tones at the fundamental

was necessary to perceive the missing fundamental.

Furthermore, octave confusion made it difficult for

patients to match precisely to the fundamental. This was

expected since the complex tone is dominated by the octave

when compared with other musical intervals. It is generally

easier to identify a musical interval than absolute

fundamental frequency between two tones. The "octave

illusion" (Duetsch,1974a,b,1975) is a phenomenon whereby two

presented notes an octave apart alternating between ears is

perceived in each ear as either one of the two notes.

Perception of a note an octave above or below a presented

note could therefore be attributed to "perception" of that

presented note. Thus, matching to octaves related to the

fundamental can be considered as evidence in support of our

ability to perceive the missing fundamenatal.

The results from the two-alternative forced choice

adaptive method did not illustrate to the same extent, in absolute number of matches, the ability to perceive the

missing fundamental as compared to the up-down adjustment

technique, regardless of the procedure. Also, overall match

rates were about 20% lower during the forced choice adaptive

method as compared to the adjustment technique. However,

because the patients were not restricted to pitch match

126 within a frequency range as In the up-down adjustment- technique, the entire auditory frequency range (20 Hz to 16 kHz) was available. Using the same precision factor as in the up-down technique, this range can be subdivided into approximately 30 contiguous precision bands,1 and the probability of correct identification of the target frequency would be 1/30 or 3%. This would translate into an error rate of 97% for the two-alternative forced choice adaptive method, as opposed to 90% for the up-down adjustment technique. In spite of the difficulty of the task, there were still more matches to the fundamental and its octaves as compared to matches to individual components and their octaves during pitch matching control and pitch matching between ears (see table 15), thereby strengthening the aforementioned conclusions. Furthermore, when considering only matches to the fundamental or to presented partials (see table 16), the synthetic mode of hearing was clearly dominant in all procedures as there were no matches at all to the presented partials, but at least one match to the fundamental in all procedures. The addition of noise made it more difficult to perceive the lacking fundamental using this technique (tables 15 and 16), but the fact that matches were made to the fundamental, regardless of the number, demonstrates that perception of the missing fundamental did indeed occur.

127 It is interesting to note that the best performers with

regard to matching to the fundamental or its related octaves

were those patients with musical training (L.F. and R.L.),

suggesting that the ease to which we are able to perceive

the lacking fundamental is directly related to our musical

experience.

The question that arises from these studies is the

following: How are those patients able to perceive the

pitch of the missing fundamental when no pitch cues are

transmitted via the low characteristic frequency fibers;

those fibers whose place of innervation along the basilar

membrane corresponds to the place of maximal displacement when stimulated by sound waves with frequency corresponding

to that of the fundamental?

One possible explanation is that since the patients

used in this study did not have absolute low frequency loss,

it might have been possible that enough information was

conducted along those low characteristic frequency fibers to

the central nervous system enabling them to perceive the

pitch of the missing fundamental. Even though a combination

tone generated from the components of the complex, whose

frequency corresponded to the fundamental, probably would

not have been of sufficient intensity to stimulate those low

frequency fibers innervating the damaged region of the

cochlea, the possibility should not be ruled out that a

128 sufficient- number of fibers innervating partially damaged areas with hearing thresholds low enough to be stimulated could conduct the necessary pitch cues.

However, if information pertaining to the pitch of the missing fundamental was carried in the low characteristic frequency fibers, how was it possible for the patients to perform as well as, or even better, when the complex test sound was presented to the damaged ear as compared to the intact ear?

Many studies have been done on the effects of hearing impairment upon frequency discrimination. Zurek & Formby

(1981) attempted to determine how the ability to detect a change in the frequency of a pure tone is affected in subjects with sensorineural hearing loss. They showed that the ability of hearing-impaired listeners to detect a pure tone frequency change was more disrupted for low frequency tones than for high frequency tone's, given the same degree of hearing loss at the test frequency. This finding can be explained by the asymmetrical spread of excitation in the cochlea. A low frequency tone has a maximum excitation pattern at the apex of the basilar membrane, but extends broadly to a lesser extent through the middle and basal cochlear regions. Therefore, a given amount of damage in the apical region of the cochlea may result in a smaller threshold shift because of the excitation in the more basal

129 areas. Thus, Zurek & Formby propose that at low frequencies a given threshold shift may indicate more damage than at higher frequencies. Therefore relatively large changes in frequency discrimination at low frequencies would be associated with small changes in hearing threshold.

Goldstein & Srulovicz (1977) and Srulovicz & Goldstein

(1983) have shown that mathematical modeling of auditory- nerve fiber interspike intervals can predict the frequency discrimination of pure tones. Their model implies that impaired phase-locking ability in damaged cochleas would result in a deterioration of frequency discrimination. They imply that frequency discrimination is based primarily on temporal aspects of single-fiber activity.

The results of Zurek & Formby suggest that the patients with low frequency hearing loss, investigated ln this study, have suffered a far more extensive loss of hair cells and/or neurons along a greater extent of the basilar membrane than their audiograms would imply. This would result in a considerable deterioration of phase-locking for fibers with low (and also higher) characteristic frequencies. Perhaps the deterioration of the temporal code is more severe in these cases than that of the spatial code. Since the data do not suggest that the perception of the lacking fundamental via the damaged ears was inferior when compared with the intact ears, it seems highly unlikely that the

130 fundamental frequency could have been mediated by either a

spatial or a temporal code in the low characteristic

frequency fibers.

Other investigators have found that the hearing

impaired have a deficit in their frequency resolution

(Hoekstra,1979; Glasberg & Moore,1986; Moore &

Glasberg,1986a,b; Tyler & Tye-Murray,1986). This refers to

the ability to detect, a sound of one frequency as distinct

in the presence of another with a different frequency.

Impaired resolution has been found to result in a

deterioration in the ability to extract pitch information

(Evans,1978a), and to lead to poor speech perception

(Scharf,1978; Florentine et al.,1980). In addition, hearing-impaired listeners perform poorly in temporal

resolution tasks as, for example, in gap detection (Irwin et al.,1981; Fitzgibbons & Wightman,1982; Irwin & McAuley,1987;

Glasberg et al.,1987; Moore & Glasberg,1988). Impaired temporal processing may contribute to poof speech perception

in patients with hearing loss (Tyler et al.,1982; Dreschler

& Plomp, 1985). Also, improved hearing in patients with

cochlear implants has been shown to depend on their temporal

(gap detection) acuity (Hochmair-Desoyer et al.,1984).

Other evidence suggests there is a reduction in the

synchrony of the discharge from Vlllth-nerve fibers that

innervate the region of hearing loss (Wakefield &

131 Nelson,1985), and that this reduction is responsible for the

impaired frequency resolution (Woolf et al.,1981).

Furthermore, studies involving loudness summation have suggested that the critical band is affected in cochlear

impairment (Scharf & Hellman,1966; Martin,1974;

Bonding,1979). Critical bands are compared to an internal acoustic filter system which splits the acoustical intensity

into contiguous frequency bands.

Collectively then, it appears that the patients in the present experiment should have experienced greater difficulty in pitch matching to the missing fundamental in the diseased ear than in the intact ear if the frequency

signals corresponding to the pitch were originating in cochlear nerve fibers with characteristic frequencies

corresponding to the fundamental. As this was not the case

in the present study, the above assumption regarding the

conduction of pitch cues along the low characteristic

frequency fibers remains doubtful.

Another possible Interpretation of the present results

is that the spread of excitation towards the base, generated

by the cubic difference tone, could be responsible for pitch

cues carried in the first higher frequency fibers

innervating a normal hearing threshold area. Whether these

higher frequency fibers are capable of conveying information

regarding the missing fundamental is debatable.

132 in 1950, Davis et al. shoved that subjects with unilateral noise-induced hearing loss, when matching pure tones between ears, showed large upward displacements of pitch by as much as three-quarters of an octave. Similar findings have also been demonstrated in patients with unilateral Meniere's disease (Jones & Pracy,1971). The explanation of this upward shift in pitch was attributed to characteristics of the sensory units of the auditory nerve.

Because sensitivity of nerve fibers falls off rapidly as the frequency is increased from its characteristic frequency, and slowly as the frequency is decreased, a given frequency would then excite more easily sensory units that are tuned to higher frequencies much more so than those tuned to lower frequencies.

These studies, involving unilateral hearing loss and the upward displacement of pure tone pitch, again indicate that the missing fundamental pitch heard by patients in the present study was not due to peripheral excitation by the fundamental frequency. The first higher frequency fibers available basal to the damaged region innervated by the low frequency fibers should have been excited, and an upward shift in pitch should have occurred. This was not evident in the present study.

The most probable explanation regarding the ability of the patients in the present study to perceive the missing

133 fundamental does not depend on the generation of combination tones, but involves the conduction of pitch cues along those neural fibers whose characteristic frequencies correspond to the actual presented component stimuli contained within the complex.

The concept of a dominant frequency region for pitch information was introduced by Ritsma (1967a,b,1970) and

Bilsen & Ritsma (1967). It was found that for fundamental frequencies in the range 100 to 400 Hz, the frequency band containing the third, fourth, and fifth harmonics dominated the pitch percept. Thus the dominance region is the spectral region of three to five times the frequency of the perceived pitch.

All complexes presented in the present study contained the third, fourth, and fifth harmonics, and in addition, the fundamental frequencies chosen were within the 100 to 400 Hz range with the exception of 700 Hz which was used for patient J.W. This patient did pitch match once to the lacking fundamental. Therefore, for all but one patient, harmonic components and the frequency range of the missing fundamental that were used in this study fit the criteria necessasry for optimal extraction of the lacking fundamental.

Other work by Miller & Sachs (1984) showed that responses of auditory nerve fibers to a voiced stimulus were

134 dominated by harmonics of the fundamental frequency. It was found that the pitch-related harmonic structure within the spectrum was preserved in the ALSR in that the voice pitch was represented by peaks in the temporal responses at harmonic places in the nerve fibers.

These findings support the possibility that the auditory fibers responding to the component stimuli of a complex sound could have signaled in their response pattern periodicities the necesssary information to perceive the missing fundamental in patients with ear damage to the low characteristic frequency regions.

More supporting evidence comes from several investigators interested in brainstem responses to auditory stimuli who evaluated the relationship between the frequency-following response (FFR) recorded from humans and the low pitch of complex tones (Smith et al.,1978; Greenberg

& Marsh,1979,1980; Greenberg et al.,1987). It has been suggested that the neural events which generate the FFR result from a collection of the individual activity of a group of phase-locking neurons within the brain stem

auditory nuclei (Smith et al.,1975; Sohmer et al.71977;

Gardi et al.71979). Bojanowski et al. (in press) have, in fact, recorded corresponding microphonic potentials in the medial superior olive. Smith et al. (1978) and Greenberg et al. (1987) found that the FFR to harmonic signals with an

135 absent fundamental frequency was similar to that generated by pure tones equal to the lacking fundamental of the complex stimuli. The likelihood that the FFR to the missing fundamental was a product of nonlinear distortion in the periphery was ruled out since the FFRs to the pure tone and the complex tone of equivalent fundamental frequency differed in response latency and amplitude. Furthermore, although the amplitude of the FFR to the pure tone was greatly reduced by low-frequency band-passed noise centered at the frequency of the lacking fundmental, the amplitude of the FFR to the complex tone was relatively unaffected by the noise .

With regard to the existence of the dominant region of the residue, Greenberg & Marsh (1979) and Greenberg et al.

(1987) found that the magnitude of the FFR to the fundamental was greatest when generated by the third to the fifth harmonics. The amount of energy in this frequency band dissipated with increasing harmonic number and was virtually absent for harmonics eight and nine. Because the first and second harmonics by themselves did not generate a large FFR, this further suggests that distortion products generated at the tonotopic location corresponding to the residue were not responsible for the responses.

Frequency regions that generated the largest FFR were between 500 and 1000 Hz which are consistent with the

136 frequencies suggested by Ritsma (1967b) generating the strongest pitch. Since this is also the frequency region where the most precise phase-locking occurs (Johnson,1980),

Greenberg et al. (1987) suggest that the magnitude of the

FFR reflects the precision of synchronized activity to the stimulus frequencies.

It is interesting to note that the FFRs of the largest magnitude are generated by complexes whose fundamental falls between 100 and 500 Hz, and are virtually non-existent beyond fundamentals of 1 kHz (Greenberg,1980). The fundamentals chosen in the present experiments were 200,

300, and 700 Hz. Patient J.W., whose presented complex had a fundamental frequency of 700 Hz, was only able to match once to the lacking fundamental. A 700 Hz fundamental falls within a non-optimal frequency area for FFR generation. In addition, the lowest frequency component within that complex was 2100 Hz; outside the optimal 500 to 1000 Hz range found by Greenberg et al. As suggested by the FFR studies, if the synchronized activity is reflected in the FFR, then patient

J.W.'s difficulty in perceiving the residue pitch may have resulted from a lack of synchronization within the neural f ibers .

It has recently become possible to apply the underlying neural mechanisms of theoretical pitch perception models by directly stimulating the auditory nerve in a controlled and

137 localized manner. Deaf subjects have been implanted with intracochlear electrode devices in an attempt to bypass their destroyed hair cells. With multiple electrodes implanted at various locations along the cochlea, investigators have found that patients can make pitch judgments corresponding to the cochlear place stimulated

(House,1976; Eddington et al.,1978a,b; Townshend et al.,1987), and discriminate pairs of simple speech sounds

(Eddington,1980).

However, even with just a single electrode on the surface of the cochlea, patients are able to detect changes in the frequency of electrical stimulation (Merzenich et al.,1973; House,1976; Douek et al.,1977; Fourcin et al.,1978; Townshend et al.,1987), can perform pitch scaling exercises over a several hundred hertz frequency range

(Merzenich et al.,1973), and can accurately judge melodic intervals (Eddington et al., 1978b; Rosen et al., 1978 ). With only a single electrode used, the place of stimulation remains the same for all stimulating frequencies, hence these abilities are dependent on temporal information (Moore

& Rosen,1979). The findings from the present study support the importance of such information for the perception of pitch.

In summary, perception of the missing fundamental found in patients with low frequency hearing loss is most likely

138 the result. of temporal pitch cues in the form o£ synchronized neuronal activity conducted along the auditory

nerve fibers whose characteristic frequencies correspond to

the third, fourth, and fifth harmonic components of the

complex stimulus.

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