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Abstract& Phonological processes map sound information onto higher levels of language processing and provide the mechanisms by which verbal information can be temporarily stored in working memory. Despite a strong convergence of data suggesting both left lateralization and distributed encoding in the anterior and posterior perisylvian language areas, the nature and brain encoding of phonological subprocesses remain ambiguous. The present study used functional magnetic resonance imaging (fMRI)

Several types of measurements were made to determine the acoustic characteristics that distinguish between voiced and voiceless fricatives in various phonetic environments. The selection of measurements was based on a theoretical analysis that indicated the acoustic and aerodynamic attributes at the boundaries between fricatives and vowels. As expected, glottal vibration extended over a longer time in the obstruent interval for voiced fricatives than for voiceless fricatives, and there were more extensive transitions of the first formant adjacent to voiced fricatives than for the voiceless cognates. When two fricatives with different voicing were adjacent, there were substantial modifications of these acoustic attributes, particularly for the syllable-final fricative. In some cases, these modifications leads to complete assimilation of the voicing feature. Several perceptual studies with synthetic vowel-consonant-vowel stimuli and with edited natural stimuli examined the role of consonant duration, extent and location of glottal vibration, and extent of formant transitions on the identification of the voicing characteristics of fricatives. The perceptual results were in general consistent with the acoustic observations and with expectations based on the theoretical model. The results suggest that listeners base their voicing judgments of intervocalic fricatives on an assessment of the time interval in the fricative during which there is no glottal vibration. This time interval must exceed about 60 ms if the fricative is to be judged as voiceless, except that a small correction to this threshold is applied depending on the extent to which the first-formant transitions are truncated at the consonant boundaries.

A production and a perception experiment were conducted to investigate the effect of speaking rate on the singleton/geminate consonant contrast in Italian. Acoustic analyses were performed of labial and dental singleton and geminate consonants produced in words spoken in isolation and in a sentential context at both a slow and a fast rate of speech. Closure duration was found to discriminate between the two categories of consonants within a given speaking rate. For one speaker, at a fast speaking rate the distribution of closure duration of geminate consonants was identical to the distribution of closure duration of singleton consonants produced in isolation. However, a measure reflecting the relation between two durations, the ratio between consonant duration and preceding vowel duration, discriminated between singletons and geminates both within and across speaking rates. The perception experiment tested whether manipulation of the consonant to vowel ratio would result in perceptual shifts. Results indicated that changing the ratio did affect perception of the geminate/singleton distinction. However, these effects varied greatly across listeners. Taken together, these findings provide support for the view that there are stable acoustic properties corresponding to phonetic features in that even though one type of temporal information, closure duration, is greatly affected by changes in speaking rate, a higher-order relational measure remains constant.

This study examines the extent to which acoustic parameters contribute to lexical effects on the phonetic categorization of speech. Experiment 1 was designed to replicate previous findings. Two test continua were created varying in voice onset time. Results of both identification and reaction time (RT) range data showed an effect of lexical status at the phonetic boundary, but only in the slowest RT ranges, suggesting that lexical effects on phonetic categorization are postperceptual. Experiment 2 explored whether the lexical effect would emerge when the stimulus continua more nearly approximated the parameter values of natural speech. Both identification and RT range data indicated that the lexical effect disappeared. These results suggest that without attention to the acoustic structure of the stimuli, the role of top-down processing in phonetic categorization may be overemphasized.