ACOUSTIC AND PERCEPTUAL INVARIANCE IN SPEECH

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The broad objectives of this proposal are to develop, test, and refine a theory of acoustic invariance in speech. We will extend our research on the acoustic properties for a number of phonetic features and phonetic contrasts. We will investigate fricative place of articulation by exploring the spectral patterns in the frication noise, the voicing of syllable-initial fricatives preceded by voiced and voiceless stops by exploring the characteristics of glottal excitation in the fricative noise and in the regions near the boundaries of the fricative onset and offset, the stop/glide manner of articulation by examining the patterns of amplitude change occurring in particular frequency regions in the vicinity of the stop-glide release, and nasal manner of articulation by examining the amplitude of the nasal murmur as well as the frequency characteristics of the murmur. We will investigate the effects of particular sources of variability on invariant properties, including the effects of the juxtaposition of consonantal properties on adjacent consonantal properties, the effects of the phonetic inventory of a particular language on the nature of acoustic properties, and the effects of speaker-rate on acoustic properties. Finally, we will explore the extent to which acoustic/phonetic properties affect word recognition and lexical access. We will investigate the extent to which sub-phonetic variations (voiceonset time) and phonological variations (syllable reduction) affect word recognition, we will explore whether an acoustic 'trace' associated with a particular phonetic feature is left in a phonetic segment that undergoes rule-governed phonetic and phonological processes and whether the 'trace' conforms to invariant properties associated with the phonetic feature; and, we will explore the extent to which the acoustic properties of a word affect lexical access and in particular semantic priming. Our general research strategy includes performing detailed acoustic analyses of natural speech tokens and conducting perception experiments using synthetic and computer-edited natural speech. The goals of the acoustic analyses are to identify those invariant properties relating to particular phonetic features, to devise algorithms for quantifying these properties, and to test the effectiveness of these measures by applying them to a new set of natural speech data. Perception experiments will be conducted to help us focus on potentially critical portions of the acoustic signal where invariant properties are likely to reside, and to explore the perceptual consequences of these properties for the identification of particular phonetic dimensions. Lexical decision experiments will be conducted to explore the effects of acoustic/phonetic properties on lexical access.