Clear speech production of Korean stops: changing phonetic targets and enhancement strategies.

The proposal that phonological contrast is enhanced through greater approximation of phonetic targets was investigated by comparing clear speech to conversational and citation-form speech produced by Korean speakers. The stop system of Korean is undergoing a sound change in which younger speakers produce the aspirated-lenis stop contrast differently from previous generations. Older speakers differentiate this contrast primarily with the acoustic correlate of voice onset time (VOT) and secondarily with F0. Younger speakers are merging VOT values for this contrast. As a result, the primary acoustic correlate is now F0 for younger speakers. These production differences likely indicate that younger speakers have developed different phonetic targets for stop production. These different phonetic targets were predicted to result in different enhancement patterns in clear speech: Younger speakers were predicted to enhance F0 differences, whereas older speakers were predicted to enhance VOT differences in clear speech. Results indicated that the older group solely used VOT to enhance the contrast in clear speech, whereas the younger group primarily used F0 but also demonstrated small VOT enhancement. These results indicate that clear speech enhancement strategies reflect phonetic targets. Older and younger speakers have different F0 and VOT targets and these different targets conditioned different enhancement strategies.