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Title:
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Processing of Speech Variability: Vowel reduction in Japanese
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Author:
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Naomi Ogasawara
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Email:
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click here to access email
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Degree Awarded:
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University of Arizona
, Department of Linguistics
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Degree Date:
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2007
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Linguistic Subfield(s):
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Phonetics
Phonology
Psycholinguistics
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Director(s):
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Natasha Warner
Andrew B. Wedel
Timothy Vance
Merrill Garrett
Adam Ussishkin
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Abstract:
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This dissertation investigates the processing of speech variability,
allophonic and indexical variation in Japanese. A series of speech
perception experiments were conducted with reduced and fully voiced vowels
in Japanese as a test case. Reduced vowels should be difficult for
listeners to hear because they are acoustically less salient than fully
voiced vowels, due to the lack of relevant physiological properties. On the
other hand, reduced vowels between voiceless consonants represent more
common phonological patterns than fully voiced vowels. Furthermore,
previous studies found that Japanese listeners were capable of hearing
completely deleted vowels. Listeners intuitively maintain CV syllables in
perception, hearing a vowel after each consonant in order to avoid
obstruent clusters (a violation of Japanese phonotactics).
It was found that listeners made good use of acoustic, phonological, and
phonotactic knowledge of their native language for processing allophonic
variants. In word recognition, listeners performed better when reduced
vowels were in the environment where vowel reduction was expected. The
phonological appropriateness of an allophone was judged in relation to
adjacent consonants on both sides, and the facilitatory effect of
appropriateness of reduced vowels surpassed the inhibitory effect of their
acoustic weakness. However, in terms of sound detection, listeners found
reduced and fully voiced vowels equally easy to hear in an environment
where vowel reduction was expected. Although reduced vowels were
phonologically appropriate between voiceless consonants, the phonological
appropriateness merely balanced out acoustic weakness; it was not strong
enough to surpass it. In addition, the phonological appropriateness of an
allophone was judged based only on the preceding consonant, which suggests
that listeners processed sounds linearly. Furthermore, the study found that
phonological appropriateness of the allophone was affected by dialectal
differences and speech rates. Listeners’ preference for a certain allophone
was influenced by the phonology of a listeners’ native dialect and
expectation was skewed by fast speech rates.
This study suggests that current speech perception models need modification
to account for the processing of speech variability taking
language-specific phonological knowledge into consideration. The study
demonstrated that it is important to investigate at which stage
phonological inference takes place during processing.
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