| Abstract | [Introduction]
There are over 792 muscles and 100 joints in the human body, while, according to my eldest son’s biology textbooks, the elephant’s trunk contains over 40000 muscles and tendons. Thus, any activity of the human body or the elephant’s trunk involves the cooperative effort of very many degrees of freedom. But what form do principles of cooperation in multivariate movements take? For some years now, my colleagues and I have viewed this question as continuous with the general issue of understanding the emergence of order and regularity in complex systems (see, e.g., Yates 1979, for defining characteristics of complexity). The core idea that we have pursued is that the collective action among multiple neuromuscular components is fundamentally task-related, and that the significant units of control and coordination are functional groupings of muscles and joints which we call coordinative structures or functional synergies (e.g. Fowler et al. 1980; Kelso et al. 1979; Kelso and Tuller 1984a; Kugler et al. 1980; Saltzman and Kelso 1985b; Turvey 1977). The hallmark of a coordinative structure is the temporary marshalling of several articulators into a task-specific pattern.
This notion of functional units of action, or coordinative structures differs in significant says from conventional treatments of movement control that are based on either the neurophysiological notion of a central pattern generator or the information processing notion of a motor program. First, unlike the notion of a hard “prewired” central pattern generator, the coordinative structure construct underscores the soft of flexible nature of action units that are functionally specific, not automatically specific. One of the goals of this paper is to buttress this claim using examples from recent research on the motor control of speech and limb movements. Second, contrary to the motor program formulation that relies on symbol-string manipulation familiar to computer technology, the coordinative structure construct highlights the analytic tools of qualitative (nonlinear) dynamics (e.g. Kelso et al. 1981, 1985a; Saltzman and Kelso 1985b) and the physical principles of cooperative phenomena (e.g. Kelso and Tuller 1984a, b; Kugler et al. 1980, 1982).
Thus, the problem of pattern formation for skilled actions is couched as a specific aspect of the more general topic of cooperative phenomena in nonlinear, open systems (see, e.g. Haken 1975, 1977, 1983). Such systems display ordered states that are not imposed by programs, but that actively evolve from the dynamic interplay of processes, in a so-called “self-organized” fashion. Although the present theoretical approach is in preliminary form as far as biological movements are concerned (see Kelso 1981a; Kelso and Tuller, 1984a; Kugler et al. 1980, 1982), this paper attempts to convey the flavor of the approach, not only theoretically, but in terms of the kinds of experiments that it motivates. In the following sections I shall briefly address four questions drawing from out own and others’ experimental work on limb movements and speech articulators involving many degrees of freedom.
1. The cooperativity question. What kind of unitary organization is formed by an ensemble of neuromuscular components?
2. The control question. What kind of control structure underlies the generation of certain movement patterns? What are the essential control parameters and how are parameter values specified?
3. The stability question. What characterizes the stability of a movement pattern, and what is the informational basis for the stability? Colloquially speaking, what holds a pattern together?
4. The change question. What are the necessary and sufficient conditions that give rise to change in an articulatory pattern? |
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