The perception of speech gestures.

Two experiments examined the effects of temporal overlap of speech gestures on the perception of stop consonant clusters. Sequences of stop consonant gestures that exhibit temporal overlap extreme enough to potentially eliminate the acoustic evidence of (at least) one of the consonants were obtained from x-ray microbeam data. Subjects were given a consonant monitoring task using stimuli containing stop sequences as well as those containing single stops. Results showed that (1) the initial consonant in the stop sequences was detected significantly less often than in the single stops; (2) bilabial gestures were considerably more effective at obscuring a preceding alveolar than the reverse; and (3) the detection rate correlated with an index of overlap between lip and tongue tip gestures. Experiment 2 employed stimuli that were truncated during the closure for the critical stop or stop sequence, so as to eliminate any information occurring in the acoustic signal at the stop release. This experiment showed that removing release information decreased detectability of the consonants generally. However, consistent with the observed gestural patterns, removing the release did not decrease detection of the alveolar stop when it was the first consonant of a sequence, indicating that there was no information about the alveolar stop present in acoustic realization of the second stop release. These experiments show that certain gestural patterns actually produced by English speakers may not be completely recoverable by listeners, and further, that it is possible to relate recoverability to particular metric properties of the gestural pattern.