Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 07 table of contents.
The information processing approach to motor behavior began after World War II. Norbert Weiner's influential book Cybernetics proposed a general theory of control systems and guided movement with clear relevance to motor control. In principle, the flight of a guided missile and the reaching movement of an arm toward a target are similar, both involving the same sorts of information processing.
A guided missile and a reaching arm both use negative feedback. To an engineer, negative feedback does not mean criticism. A negative feedback process is one that reduces deviation of a system from a goal state.
What is negative feedback and how does it relate to motor movement?
For example, a guided missile control system feeds back information about the direction of a heat source (its target) to the guidance system. The information is used to adjust the fins on the missile, turning it so it points at the heat source. As the missile travels, it reduces the deviation (distance) between itself and the target. The word "negative" in "negative feedback" refers to this reduction in the distance between (1) the present state of the system, and (2) the goal state. So a negative feedback system is a deviation-reducing system, which is to say, a system that pursues goals. That turns out to be important for psychology, because almost all the motor behavior of interest to psychologists is directed at goals.
A synonym for negative feedback is deviation-reducing feedback. Negative or deviation-reducing feedback is involved in all goal-directed activity, from eye movements to building a house or solving math problems. In motor movements, often there are two distinct components:
What are two components of many guided movements?
1. A ballistic component in which there is a large movement in the right general direction (like launching a missile)
2. A zeroing in component during which negative feedback processes take over control of the system and guide it to a precise destination (like guiding the missile to its target)
Why do eye movements, when diagrammed, often look like canes?
Jerky eye movements called saccades are the most common variety of eye movement, and they have both ballistic and zeroing-in components. First the eye movement is launched toward a target (the ballistic component) then a network of muscles perform tiny adjustments (the zeroing in component) so that the important part of the visual image lands on the fovea centralis, the most sensitive receptor surface in the eye. As a result of the two components, a diagram of a saccade often looks like a cane, with a long straight jump followed by a little hook.
All movements require some form of aiming to achieve accuracy. The faster a person executes a movement, the less time there is to aim. In 1954 Paul Fitts-a leading researcher in the field-outlined equations describing the speed-accuracy trade-off. The basic idea is that the faster you perform a motor movement, the more mistakes you make. The trade-off was summarized in an equation called Fitts' Law.
What relationship did Fitts's Law express?
Paul Fitts died unexpectedly in 1965. Although the death of one researcher should not be enough to damage a whole field of research, the death of Paul Fitts seemed to symbolize what happened to motor research over the next few years. Federal funding support for research into motor behavior, generous in the post-war period of the 1950s, disappeared in the 1960s. Soon conditions were so unfavorable for researchers that an "academic funeral" for the discipline of motor research was held at Tulane University. "Renowned motor behavior psychologists gathered to read the last rites and bid each other farewell, as each moved on to other related topics in psychology." (Schmidt, 1982)
What caused a new interest in motor research?
But the field of motor research was not dead. The resurgence of cognitive psychology in the late 1960s and 1970s stimulated new research on motor behavior. Soon psychologists were looking at motor behavior as a form of cognition or information processing. As it turned out, motor tasks (such as teaching a robot to navigate a crowded room) involved all sorts of cognitive processes, such as pattern recognition and problem solving. Motor research fit right in with perceptual research and language research as a form of information processing suitable for study by psychologists.
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