Evidence for efficiency in vowel production

Speaking is generally considered efficient in that less effort is spent articulating more redundant items. With efficient speech production, less reduction is expected in the pronunciation of phonemes that are more important (distinctive) for word identification. The importance of a single phoneme in word recognition can be quantified as the information (in bits) it adds to the preceding word onset to narrow down the lexical search. In our study, segmental information showed to correlate consistently with two measures of reduction: vowel duration and formant reduction. This correlation was found after accounting for speaker and vowel identity, speaking style, lexical stress, modeled prominence, and position of the syllable in the word. However, consistent correlations are only found in high−frequency words. Furthermore, the correlation is strongest in normal reading and weaker in spontaneous and anomalous read speech. Combined, these facts suggest that this type of efficiency in production might rely on retrieving stored words from memory. Efficiency in vowel production seems to be less or absent when words have to be assembled on−line.