AGE-RELATED CHANGES IN THE PERCEPTION OF SPEECH

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The aim of this three-year project is continue, extend and augment the line of research we began with our original NIA proposal. Our general goal has been to examine possible age-related changes in the speech perception abilities of older subjects at several different linguistic levels. These include auditory/phonetic processing in segment identification and discrimination, the processing of dynamic acoustic cues in the perception of phonetic segments, and top-down processes in word recognition. Basic questions addressed include: * Are there age-related changes in the use of auditory/phonetic memory (or its processing counterparts) in the identification and discrimination of speech sounds? We will be focusing on the age-related differences in the processing of voice onset time distinctions; perception of syllable-initial fricatives; and the identification of stops in intervocalic and syllable-final position. *Are there age-related changes in how listeners phonetically process rapidly changing acoustic information (such as formant frequencies) in order to make vowel or consonant identifications? We will be focusing on the processing of rapid vs. slow onset of acoustic energy in the fricative/affricate distinction; the perception of glides vs. stops; and use ability of listeners to utilize dynamic information in the identi- fication of vowels. *Do older individuals make greater (or lesser) use of top-down information in word recognition and segment identification than do younger listeners? Using the gating procedure, we will be examining the extent to which older listeners may make greater utilization of top-down information in recognizing words in semantically predictable, neutral or inhibiting phrasal contexts and in phonotactically constraining contexts. *Can significant age differences associated with higher level linguistic/cognitive processes be seen in measures of electrophysiologic activity? We will examine age-related differences in cortical activity (by measuring P3 latencies) during the processing of sounds exhibiting a representative range of linguistic/phonetic distinctions. The results of our experiments will be evaluated in terms of both the relevant aging literature and the relevant theoretical models of speech production and word recognition. These data should allow a more accurate understanding of the aging process, in general, and the types of speech processing difficulties the older individual may face, in particular.