Perceptual context effects of speech and nonspeech sounds: the role of auditory categories

Williams [(1986). "Role of dynamic information in the perception of coarticulated vowels," Ph.D. thesis, University of Connecticut, Standford, CT] demonstrated that nonspeech contexts had no influence on pitch judgments of nonspeech targets, whereas context effects were obtained when instructed to perceive the sounds as speech. On the other hand, Holt et al. [(2000). "Neighboring spectral content influences vowel identification," J. Acoust. Soc. Am. 108, 710-722] showed that nonspeech contexts were sufficient to elicit context effects in speech targets. The current study was to test a hypothesis that could explain the varying effectiveness of nonspeech contexts: Context effects are obtained only when there are well-established perceptual categories for the target stimuli. Experiment 1 examined context effects in speech and nonspeech signals using four series of stimuli: steady-state vowels that perceptually spanned from /inverted ohm/-/I/ in isolation and in the context of /w/ (with no steady-state portion) and two nonspeech sine-wave series that mimicked the acoustics of the speech series. In agreement with previous work context effects were obtained for speech contexts and targets but not for nonspeech analogs. Experiment 2 tested predictions of the hypothesis by testing for nonspeech context effects after the listeners had been trained to categorize the sounds. Following training, context-dependent categorization was obtained for nonspeech stimuli in the training group. These results are presented within a general perceptual-cognitive framework for speech perception research.