Listening to recordings of clearly pronounced repeated syllables can produce quite different perceptual effects depending upon whether observations are perstimulatory (during stimulation) or poststimulatory (after stimulation ceases). Poststimulatory changes involve migration of category boundaries separating speech sounds—for example a shift in the /t/–/d/ voice onset time (VOT) boundary toward that of a previously repeated consonant–vowel syllable such as “to” or “do”. Studies of the perstimulatory changes called “verbal transformations” usually employ phonetically complex stimuli, and consist of abrupt illusory changes in what is heard, frequently accompanied by considerable phonetic distortion. The present study examined verbal transformations reported while listening to alternating statements of “to” and “do” (“to, do, to, do …”)for which the adaptational VOT boundary changes produced by one syllable opposed that of the other. The perstimulatory reports were inconsistent with adaptational category boundary shifts. It is suggested that although poststimulatory changes reflect a criterion shift rule applicable to perceptual judgments in general, perstimulatory verbal transformations involve perceptual cleavage into organizational units, some of which mutate before recombining to yield a different linguistic form. Verbal transformations provide information concerning linguistic processing which differs from that furnished by poststimulatory changes.
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