Lexical frequency and voice assimilation.

Acoustic duration and degree of vowel reduction are known to correlate with a word's frequency of occurrence. The present study broadens the research on the role of frequency in speech production to voice assimilation. The test case was regressive voice assimilation in Dutch. Clusters from a corpus of read speech were more often perceived as unassimilated in lower-frequency words and as either completely voiced (regressive assimilation) or, unexpectedly, as completely voiceless (progressive assimilation) in higher-frequency words. Frequency did not predict the voice classifications over and above important acoustic cues to voicing, suggesting that the frequency effects on the classifications were carried exclusively by the acoustic signal. The duration of the cluster and the period of glottal vibration during the cluster decreased while the duration of the release noises increased with frequency. This indicates that speakers reduce articulatory effort for higher-frequency words, with some acoustic cues signaling more voicing and others less voicing. A higher frequency leads not only to acoustic reduction but also to more assimilation.