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Cybernetics: Closed-loop control

Cybernetics is defined as ``[...] the study of control and communication in the machine or in the animal [...]'' [362]. In the current context, we will use the term cybernetics in a narrower sense, i.e., as referring to the study of control systems. The communication and information-theoretical aspects that were originally partly embedded in cybernetics, are currently studied in a different field, called informatics or computer science. The name cybernetics comes from the Greek word for steersman (), and in fact does not have connotations with respect to communication or information. More specifically, even, we will only speak of systems controlling a physical parameter. The following quotation clarifies how Wiener himself envisaged the control problem:

``[...] what we will is to pick the pencil up. Once we have determined on this, our motion proceeds in such a way that [...] the amount by which the pencil is not yet picked up is decreased at each stage [...]''
[362, page 14,]
Since the development of technical servo systems [362], the interest in cybernetics as a paradigm has been increasing and fading in a number of fields, varying from engineering, biology and psychology to economics. Research in cybernetics has led to powerful mathematical tools and theoretical concepts, gathered under the heading of Control Theory.

In theories on motor control, this ``Closed loop model'' considers the sensorial feedback (tactile and/or acoustic) to be the intrinsic source of control, e.g., of the articulatory activities during speech or handwriting production. The articulatory trajectories are planned on-line depending on the measured feed-backs until the target (spatial or acoustic) is reached. Although this model can explain a number of phenomena in motor control, its basic shortcoming is the fact that propagation delays in the biological system are substantial, necessitating other concepts to explain principles like feedforward, predictive control. Tables 3.1 and 3.2 show a number of typical biological reaction and delay times.

Table 3.1 : Typical reaction times

Table 3.2 : Typical delay times

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Next: Open-loop models Up: Human Output Channels Previous: Human Output Channels

Esprit Project 8579/MIAMI (Schomaker et al., '95)
Thu May 18 16:00:17 MET DST 1995