Exp Brain Res (1995) 104:493-501 9 Springer-Verlag 1995 Anne Smith 9 Lisa Goffman 9 Howard N. Zelaznik Goangshiuan Ying 9 Clare McGillem Spatiotemporal stability and patterning of speech movement sequences Received: 25 July 1994 / Accepted: 10 February 1995 Abstract In order to examine the stability and pattern- ing of speech movement sequences, movements of the lip were recorded as subjects produced a phrase at nor- mal, fast, and slow rates. Three methods of analysis were employed. First, a new index of spatiotemporal stability was derived by summing the standard deviations com- puted across amplitude- and time-normalized displace- ment records. This index indicated that normal and fast rates of speech production result in more stable move- ment execution compared to slow rates. In the second analysis, the relative time of occurrence of the peak ve- locity of the three middle opening movements of the ut- terance was measured. For each of the three peaks, the preservation of relative timing was assessed by applying Genter's (1987) slope test. The results clearly indicate that the relative timing of these events does not remain constant across changes in speech rate. The relative tim- ing of the middle opening gestures shifted, becoming la- ter as utterance duration increased. In a third analysis, pattern recognition techniques were applied to the nor- malized displacement waveforms. A classification algo- rithm was highly successful in sorting waveforms into normal, fast, and slow rate conditions. These findings were interpreted to suggest that, within a subject, three distinct patterns or movement templates exist, one for each rate of production. Speech rate appears to be a global parameter, one that affects the entire command se- quence for the utterance. A. Smith ( ~ ) - L. Goffman Department of Audiology and Speech Sciences, Purdue University, West Lafayette, Indiana 47907, USA; Tel: 317-494-7743, Fax no: 317-494-0771, e-mail: asmith@ sage.cc.purdue.edu H. N. Zelaznik Department of Health, Kinesiology and Leisure Studies, Purdue University, West Lafayette, Indiana 47907, USA G. Ying - C. McGillem Department of Electrical Engineering, Purdue University, West Lafayette, Indiana 47907, USA Key words Speech 9 Motor control 9 Kinematics. Human Introduction A normal, adult speaker produces 3-5 syllables/s; thus, the nervous system must simultaneously control and co- ordinate the movements of a large number of effectors to produce rapid sequences of vocal tract configurations. Given the rapidity of speech production and its highly practiced nature, it is reasonable to suggest that moto- neuron pool activity in speaking may be largely driven by stored, centrally generated commands that interact with a wide array of sensory signals. As in the study of other motor behaviors, such as locomotion, respiration, and mastication, investigators have sought invariances in speech motor output as evidence of central patterning of movement. Unlike these rhythmic, repetitive behaviors, however, speech does not have an obvious unit of analy- sis. Thus, there has been limited success in describing the fundamental characteristics of movement patterning for speech, or in determining which features of move- ments remain invariant in the face of changes in parame- ters such as rate or stress. Recent investigations of speech employing kinematic measures have focused on the organization of single movements and have explored the hypothesis that a set of fundamental movement units comprise the basic orga- nizational components of speech production. Gracco and Abbs (1986, 1988; Gracco 1988) determined the relative timing of lip and jaw kinematic and electromyographic events in the utterance, 'sapapple.' In their initial study, Gracco and Abbs (1986) found that lip and jaw move- ments were characterized by single-peaked velocity pro- files, and that peak velocities of oral closing movements of the upper lip, lower lip, and jaw for 'p' occurred in a fixed sequence. A later study (Gracco and Abbs 1988) indicated that this sequence was maintained following perturbations of the lower lip. In contrast, the magnitude of movements and muscle activity varied greatly across