Speech is considered an efficient communication channel. This implies that the organization of utterances is such that more speaking effort is directed towards important parts than towards redundant parts. Based on a model of incremental word recognition, the importance of a segment is defined as its contribution to word-disambiguation. This importance is measured as the segmental information content, in bits. On a labeled Dutch speech corpus it is then shown that crucial aspects of the information structure of utterances partition the segmental information content and explain 90% of the variance. Two measures of acoustical reduction, duration and spectral center of gravity, are correlated with the segmental information content in such a way that more important phonemes are less reduced. It is concluded that the organization of conventional information structure does indeed increase efficiency.
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