We analyze palatalization from /z/ to [ʒ] at word boundaries in UK English. Previous research has investigated palatalization in the context of /s#j/, showing that lexical frequency influences its occurrence across word boundaries. Palatalization by voiced coronal fricatives is less well-understood, particularly in naturalistic speech, which we study using the Audio BNC (http://www.phon.ox.ac.uk/AudioBNC). We hypothesize that palatalization across word boundaries is subject to the Production Planning Hypothesis. That is, palatalization should be modulated by the extent to which phonological information for the second word is available when the first word is planned. We analyze spectral center of gravity (CoG) in fricatives from 7,134 word pairs across four phonological contexts, comparing test tokens subject to palatalization, /z#j/ (e.g., “is you ”), to control pairs containing non-alternating /z#V/ (e.g., “was only ”), or /ʒ/ (e.g., “rouge it ”, “precision ”). Although significant correlates of CoG vary by speaker gender, the acoustics of /z#j/ are predicted by factors related to production planning, including fricative duration, speech rate, presence and length of inter-word pause or sentence boundary, word-pair frequency, and following vowel acoustics. A supervised classification task using acoustics and lexical frequency metrics also distinguishes /z#j/ from /z#V/ and /ʒ#V/ with above-chance accuracy, illustrating automatic detection of palatalization.

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