«Pitch perception prior to cortical maturation Bonnie K. Lau A dissertation submitted in partial fulfillment of the requirements for the degree of ...»
Pitch perception prior to cortical maturation
Bonnie K. Lau
submitted in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy
University of Washington
Lynne A. Werner, Chair
Andrew J. Oxenham
David L. Horn
Authorized to Offer Degree:
Speech and Hearing Science
© Copyright 2014
Bonnie K. Lau
University of Washington
Pitch perception prior to cortical maturation Bonnie K. Lau
Chair of the Supervisory Committee:
Professor Lynne A. Werner Speech and Hearing Sciences Pitch perception plays an important role in many complex auditory tasks including speech perception, music perception, and sound source segregation. Because of the protracted and extensive development of the human auditory cortex, pitch perception might be expected to mature, at least over the first few months of life. This dissertation investigates complex pitch perception in 3-month-olds, 7-month-olds and adults – time points when the organization of the auditory pathway is distinctly different. Using an observer-based psychophysical procedure, a series of four studies were conducted to determine whether infants (1) discriminate the pitch of harmonic complex tones, (2) discriminate the pitch of unresolved harmonics, (3) discriminate the pitch of missing fundamental melodies, and (4) have comparable sensitivity to pitch and spectral changes as adult listeners. The stimuli used in these studies were harmonic complex tones, with energy missing at the fundamental frequency. Infants at both three and seven months of age discriminated the pitch of missing fundamental complexes composed of resolved and unresolved harmonics as well as missing fundamental melodies, demonstrating perception of complex pitch by three months of age. More surprisingly, infants in both age groups had lower pitch and spectral discrimination thresholds than adult listeners. Furthermore, no differences in performance on any of the tasks presented were observed between infants at three and seven months of age.
These results suggest that subcortical processing is not only sufficient to support pitch perception prior to cortical maturation, but provides adult-like sensitivity to pitch by three months.
TABLE OF CONTENTS1 PITCH PERCEPTION: AN INTRODUCTION
6 CONCLUDING REMARKS 103
LIST OF FIGURESFigure 1-1: Pure tone pitch
Figure 1-2: Complex pitch
Figure 1-3: Spectral pitch
Figure 2-1: Harmonic structures of stimuli in Experiment I and II.
Figure 2-2: Mean trials to criterion, Experiment I, no noise
Figure 2-3: Mean trials to criterion, Experiment II, with noise
Figure 2-4: Mean trials to criterion comparision, noise and no noise.
Figure 2-5: Harmonic structures of stimuli in Experiment III
Figure 2-6: Mean trials to criterion, Experiment III
Figure 2-7: Mean trials to criterion comparision, Experiment II & III
Figure 3-1: Schematic diagram of unresolved stimuli.
Figure 3-2: Harmonic structures of unresolved stimuli
Figure 3-3: Participant success..
Figure 3-4: Mean trials to criterion, HIGH and LOW conditions.
Figure 4-1: Schematic diagram of the melody
Figure 4-2: Participant success.
Figure 4-3: Mean trials to criterion, MF melody discrimination
Figure 5-1: Schematic diagram of the pitch discrimination stimuli
Figure 5-2: Percent pitch change and background F0
Figure 5-3: Mean trials to criterion, resolved and unresolved.
Figure 5-4: Pitch thresholds
Figure 5-5: Group sensitivity (d').
Figure 5-6: Schematic diagram of the spectral discrimination stimuli..
Figure 5-7: Percent timbre change and background CF.
Figure 5-8: Mean trials to criterion, spectral discrimination
Figure 5-9: Timbre thresholds.
I would like to thank the members of my dissertation committee, my general examination committee and especially my doctoral advisor, Lynne Werner, for their time, wisdom, and willing academic guidance; the past and present members of the Infant Hearing Lab, the University of Washington Department of Speech and Hearing Sciences and the funding sources of my work; my many mentors, teachers, and professors at all the institutions throughout my academic life; my friends, family, and my classmates for their help, humour, support, and encouragement; and most of all, my mother, father, and boyfriend for their love and belief in all that I do.
1 Pitch perception: An IntroductionWith the careful pluck of a string, a harpist captivates her audience using the enchanting sound of a musical note. Whether it is for the enjoyment of music, to understand the words spoken around them, or perhaps to hear out the voice of the barista holding their espresso in a noisy coffee shop, humans rely on pitch to navigate their acoustic environment every day. In speech, pitch contributes to vowel identity (Fujisaki and Kawashima, 1968), is a cue for word segmentation (Kemler Nelson et al., 1989), conveys emotion (Ohala, 1983; Trainor et al., 2000), and can even change word meaning in tonal languages. In music, pitch is an essential building block, with musical scales composed of notes with different pitch relationships and melodic contours composed of patterns of pitch changes. Pitch also plays a role in the formation of auditory objects and the segregation of simultaneous sound sources. If pitch is critical to so many auditory tasks, can humans perceive pitch once hearing begins? What parts of the auditory system are required to perceive pitch? What do infants perceive when the string of a harp is plucked?
While infants begin responding to sound during the third trimester of gestation (Birnholz and Benacerraf, 1983; Starr et al., 1977), the human auditory system develops over an extended period of time. At three months of age, the auditory cortex is markedly immature with activation of only the most superficial layer by the reticular articulating system pathway (Eggermont and Moore, 2012). Infantsʼ responses to sound at this age are likely supported by brainstem processing (Moore, 2002). By seven months however, infants have access to mature thalamocortical connections despite significant immaturities in the auditory cortex that persist (Eggermont and Moore, 2012). The
primary question this dissertation addresses is whether subcortical processing is sufficient to support early pitch perception prior to cortical maturation. Each of the four following chapters is intended to be an independent article that investigates infantsʼ ability to perceive complex pitch under different stimulus manipulations.
The participants in each study were 3-month-olds, 7-month-olds, and adults, ages when the organization of the auditory pathway is distinctly different. The same observer-based psychophysical procedure (Werner, 1995) is used throughout all four studies but the stimuli and test phases differ according to the questions proposed.
Chapters two, three, and four, examine whether infants demonstrate the ability to perceive the pitch of resolved harmonics, unresolved harmonics, as well as missing fundamental melodies. Chapter five investigates infant sensitivity to pitch and spectral changes in the presence of variation in the other attribute (i.e., discrimination of pitch in the presence of spectral variation and vice versa). The remainder of this chapter will define pitch and the peripheral codes for periodicity as considered in the following chapters.
1.1 Definition of pitch The American National Standards Institute defines pitch as “that auditory attribute of sound according to which sounds can be ordered on a scale from low to high”, (ANSI, 1994). Many researchers have used the ability of a sound to produce a recognizable melody to determine whether or not that sound evokes a pitch (e.g., Burns and Viemeister, 1981). Chapter four employs the same rationale to investigate whether infants are indeed discriminating complex tones on the basis of perceived pitch. Another important point to note is that pitch is defined perceptually rather than by a physical property of the sound.
Sound is typically described according to three physical properties: frequency, intensity, and time/phase. In the simplest case of a pure tone with a single frequency, frequency is the physical correlate of pitch. A description of this relationship for more complex pitch-evoking stimuli however, is not as straightforward. The primary physical property correlated to a pitch percept is periodicity, repetition over time. A signal x(t) is periodic if there exists a number τ ≠ 0 such that x(t) = x(t-τ) for all time t. Sounds that fit well with this description tend to have a salient pitch that depends on the period τ. As stimuli differs from this description, becoming inharmonic, the salience of its pitch decreases. Despite the large number of stimulus conditions that evoke a percept of pitch, they fall into three main categories.
1.2.1. Pure tone pitch The sound produced when you strike a tuning fork approximates a sinusoid or pure tone. The pitch of a pure tone corresponds to the period of the waveform in the time
(Fig. 1-1B). Pure tones are rarely encountered in a natural listening environment but are a class of stimuli that are often used in studies of pitch perception.
1.2.2. Complex pitch or Periodicity pitch Harmonic complex sounds such as a musical note or a vowel in speech contain multiple frequency components that are all integer multiples of the fundamental frequency (F0). Its pitch is a unitary percept that corresponds to a pure tone at the F0. In the time domain, this would be the period (Fig. 1-2A) and in the spectral domain, the F0
A classic phenomenon in pitch perception is that the pitch of a harmonic complex is the same regardless of whether energy at the fundamental is present. Missing fundamental complexes are used throughout the studies as a method of controlling for responses to pitch as opposed to frequency or other spectral changes.
been described to be helical, with pitch chroma distributed circularly and pitch height Figure 4.
distributed linearly. Pitch chroma is the dimension that accounts for the similarity between notes separated by an octave while pitch height is the dimension that they differ on. The focus of this dissertation is on the perception of pitch height. The term pitch and complex pitch are used interchangeably and will refer to periodicity pitch unless otherwise specified.
evoke a pitch related to the F0 and a pitch related to the flocus. Both spectral and periodicity pitch are represented in the time domain as well as the spectral domain (Fig.
1-3). The pitch categorization task presented to listeners in the first four studies control for responses to spectral pitch by requiring participants to ignore random spectral variation and respond only to changes in fundamental frequency.
1.3 Peripheral codes for periodicity The studies in chapters three and five examine the two peripheral codes for pitch that coincide with the waveform and spectrum of a sound, both of which have been shown to contribute to pitch perception. The spectrum is represented in a rate-place code, which forms the basis of place models of pitch perception (Goldstein, 1973;
Terhardt 1974; Wightman, 1973). When a sound enters the ear, the basilar membrane performs a spectral analysis; high-frequency components excite the basilar membrane towards the base and low-frequency components towards the apex. The place of excitation on the basilar membrane provides a code for frequency and the firing rate of
auditory nerve fibers at each place provides a code for intensity. Representation of the time waveform, referred to as the temporal code, is the basis of temporal models of pitch perception (Licklider,1951). The temporal code is based on phase locking, the tendency for auditory nerve fibers to fire at the same time during each cycle of vibration of the time waveform. Synchronous firing to the time waveform provides a code for the fine structure of low-frequency components and modulation in firing rate provides a code for envelope fluctuations at all frequencies. There is evidence suggesting that temporal information matched to the correct tonotopic place is important for the generation of a pitch percept (Oxenham et al., 2004).
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