Just-Noticeable Differences for Phoneme Duration in Natural Speech

A tracking method [Levitt, J. Acoust. Soc. Amer. 43, 65 (1968)] was used to measure both the incremental and the decremental jND's for the durations of sound segments in naturally spoken sentences. Measurements were made for an unvoiced stop /p/ in word-initial, -medial, and -final positions, in symmetrical vowel context, and the first two also in asymmetric vowel context, and also for a stressed vowel /ɔ/, a fricative /∫/, a nasal /m/, and a lateral /l/. Four subjects served. The results show clearly that psychological time is not homogeneous during the perception of speech, which is equivalent to saying that the input sound wave has been “chunked” by the perceptual processing. [Research supported by the Science Research Council.]