Concepts from ideal observer theory will be used to study auditory category learning and speech perception. Ideal observers provide a benchmark for assessing human performance on perceptual tasks and may serve as an appropriate starting point for developing models of actual performance. In the first set of experiments, listeners will learn to categorize novel non-speech stimuli. Prior probabilities of the categories and degree of category overlap will be varied to assess listeners'sensitivity to the distributional properties of the stimuli. The second set of experiments will test whether selective adaptation and contrast effects in speech and non- speech perception can be modeled as changes in the listeners'prior probability and stimulus likelihood distributions. The third set of experiments will extend recent pilot work in our laboratory aimed at developing ideal classifiers for naturally produced speech sounds. The results of this pilot work suggest that listeners adopt a strategy of optimizing categorization performance with respect to the natural distributional properties of phonemes in their language. This hypothesis will be comprehensively tested in these experiments. The fourth set of experiments will examine how observers weight and integrate multiple sources of evidence in making phoneme category judgments.
The aim i s to learn how closely listeners approximate optimal informational weightings in such tasks when different stimulus properties are degraded in either predictable or unpredictable ways. In the fifth set of experiments, natural phoneme distributions will be used to estimate optimal trajectories between a set of native language (L1) phoneme contrasts and a competing set of contrasts in a second language (L2). Perception data of L2 learners at varying stages of proficiency will be compared to the estimated optimal trajectories. The techniques developed and tested in the proposed studies can serve as important tools for the study of speech perception in listeners with varying degrees of hearing loss, including those with cochlear implants. In particular, the derivation of ideal classifiers whose auditory input is restricted to mimic that of particular hearing-impaired individuals may allow investigators to distinguish between limits on performance due to sensory factors and those attributable to non-optimal categorization strategies.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Language and Communication Study Section (LCOM)
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Shekim, Lana O
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University of Texas Austin
Schools of Arts and Sciences
United States
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Lindblom, Björn; Diehl, Randy; Creeger, Carl (2009) Do 'Dominant Frequencies' explain the listener's response to formant and spectrum shape variations? Speech Commun 51:622-629
Garcia-Sierra, Adrian; Diehl, Randy L; Champlin, Craig (2009) Testing the double phonemic boundary in bilinguals. Speech Commun 51:369-378
Kingston, John; Diehl, Randy L; Kirk, Cecilia J et al. (2008) On the internal perceptual structure of distinctive features: The [voice] contrast. J Phon 36:28-54
Diehl, Randy L (2008) Acoustic and auditory phonetics: the adaptive design of speech sound systems. Philos Trans R Soc Lond B Biol Sci 363:965-78
Hay, Jessica S F; Diehl, Randy L (2007) Perception of rhythmic grouping: testing the iambic/trochaic law. Percept Psychophys 69:113-22
Hay, Jessica F; Sato, Momoko; Coren, Amy E et al. (2006) Enhanced contrast for vowels in utterance focus: a cross-language study. J Acoust Soc Am 119:3022-33
Molis, Michelle R (2005) Evaluating models of vowel perception. J Acoust Soc Am 118:1062-71
Holt, Lori L; Lotto, Andrew J; Diehl, Randy L (2004) Auditory discontinuities interact with categorization: implications for speech perception. J Acoust Soc Am 116:1763-73
Diehl, Randy L; Lotto, Andrew J; Holt, Lori L (2004) Speech perception. Annu Rev Psychol 55:149-79
Wong, Patrick C M; Parsons, Lawrence M; Martinez, Michael et al. (2004) The role of the insular cortex in pitch pattern perception: the effect of linguistic contexts. J Neurosci 24:9153-60

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