Timing factors in the coordination of speech movements

Abstract

Speech movement coordination involves substantial timing adjustments among multiple degrees of muscles and movement freedom. The present investigation examined the kinematic and muscle timing adjustments associated with the production of select speech movements. For oral closing movements, the timing of the upper lip, lower lip, and jaw peak velocities were found to be tightly coupled, apparently reflecting a coordinative strategy. In contrast, oral opening movements demonstrated reduced temporal coupling and inconsistent sequencing across subjects. Overall, it appears that the temporal organization of speech movements varies with the specific movement goals. In order to evaluate the coordinative patterns for oral closing in detail, the temporal adjustments of multiple perioral muscles associated with the systematic closing peak velocity relations were examined. The relative timing of muscle onsets and peak EMG amplitudes was found to be predictably related to the peak velocity timing variations, suggesting that the motor commands are temporally scaled to generate changes in speaking conditions. It was also found that the mechanical properties of the speech articulators influence movement coordination and can be exploited to maximize movement efficiency. The systematic change in muscle timing characteristics for all synergistic muscles apparently reduces the degrees of freedom to control, thereby facilitating the coordination process.

Limb versus Speech Motor Control: A Conceptual Review

“…Differences in inter-articulatory coordination and timing between opening and closing gestures were reported by Gracco (1988) (2000) who investigated speech acquisition and explained it in terms of the preferred co-occurrences between certain consonant and vowel places of articulations in human languages. According to MacNeilage and Davis, bilabials would be simpler to produce than coronals, since the first require only a cyclical jaw motion as in babbling and mastication, whereas the latter need an active motion of the tongue which is independent of jaw motion.…”

Speech Production in People Who Stutter: Testing the Motor Plan Assembly Hypothesis

“…In this re-j spect, it is important to notice the between-subject variabil-1 ity in the interlip interval data for both groups (see Figure 5). I However, Gracco (1988) also indicated that at the same time I the individual muscle onsets are adjusted in a consistent I manner. This was taken as evidence that synergistic mus-| cles are initiated by a common control signal, reflecting a 1 functional relationship between individual articulators as I part of a coordinative structure (see also Gracco, 1994;I Saltzman & Munhall, 1989), In the present study, it was ; shown that across subjects (Table 3) there were co-varia tions in the onset of IEMG of synergistic articulators (upper lip and lower lip).…”

Interarticulator cohesion within coronal consonant production

“…For example, for the bilabial closure a very consistent advancement of the upper lip velocity peak for the closing movement relative to the lower lip and jaw velocity peaks has been found ͑see, e.g., Gracco and Abbs, 1986;Gracco, 1988;van Lieshout, 1995;Kollia et al, 1995͒. The stability of such relatively time-locked interarticulator cohesion has been experimentally tested by varying external parameters such as speech rate and stress placement.…”

“…In former studies the strength of cohesion has been found to vary with several aspects, e.g., closing movements are more tightly coupled than opening movements ͑e.g., Gracco, 1988;Hertrich and Ackermann, 2000͒. Furthermore, articulators controlled by different tract variables such as the vocal folds and velum exhibit a smaller degree of interarticulator cohesion with the jaw than articulators controlled by a single tract variable such as upper lip and jaw ͑see, e.g., Gracco and Löfqvist, 1994;Kollia et al, 1995͒ as measured by a greater variability in timing parameters.…”