More on the motor organization of speech gestures

Abstract

Observations have been reported of reorganization of motor commands to muscles whose increased contraction will further narrow some portion of the upper vocal tract [Bell-Berti and Harris, J. Acoust. Soc. Am. 55, 384(A) (1974)]. This reorganization manifests itself as a merging of EMG activity for two contiguous speech gestures in some contexts but not in others. We have postulated a rule to predict this reorganization: commands to muscles that close the vocal tract will merge in sequences of gestures in which the vocal tract is being closed. Data have now been recorded from muscles that open the vocal tract to determine if the rule for motor command reorganization for these muscles is the converse of the rule for the closers: commands to muscles that open the vocal tract will merge in sequences of gestures in which the vocal tract is being opened. (Another expression of these rules might be: when a muscle must be shorter for the second element in a sequence than for the first, activity will merge into one continuous burst; when a muscle must be lengthened for the second element of a sequence, activity will be suppressed between commands for the two gestures.) This information may be correlated with the limits of coarticulation at the movement level. Acoustic records will be checked to examine this hypothesis.