Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 07 table of contents.
In a famous analysis of the pecking movement carried out by birds, Hailman (1969) pointed out that even a simple motor behavior is actually quite complex and creative. The peck is stereotyped in form. One might assume it is the same every time it occurs. But a close analysis shows the peck is slightly different each time it is executed. A bird adjusts its aim in subtle ways and can peck the same spot from a variety of starting positions. Hailman's work reminds us that there is just as much creative variation in motor activity as there is in perception or language.
What did Hailman point out about pecking? In what sense is there "no such thing as a behavior which is repeated"?
There is, in fact, no such thing as "a behavior" which is "repeated" at different times, unless you take care to define behavior by its effect or consequence in the environment (as behaviorists define operants). If you define behavior by the exact sequence of muscles activated, each repetition of a behavior is different. Bartlett (1932) expressed this well when he wrote:
What did Bartlett write in 1932, concerning a tennis stroke?
Suppose I am making a stroke in a quick game, such as tennis or cricket. How I make the stroke depends on the relating of certain new experiences, most of them visual, to other immediately preceding visual experiences and to my posture, or balance of postures, at the moment... When I make the stroke I do not, as a matter of fact, produce something absolutely new, and I never merely repeat something old. The stroke is literally manufactured out of the living visual and postural "schemata" of the moment and their interrelations. I may say, I may think that I reproduce exactly a series of textbook movements, but demonstrably I do not... (pp. 201-202)
Handwriting is an example of a complex motor production that naturally varies each time it is produced. This predictable variation was an important clue for handwriting expert Charles Hamilton Jr. when he debunked the fake "Hitler Diaries" sold to the German magazine Stern in 1983. He knew the diaries were not actually written by Hitler because the handwriting was too consistent.
Why was Hamilton skeptical of the Hitler diaries?
"If Hitler had written these spontaneously, each letter would be a little different," he said, "whereas a forger would copy the way Hitler formed his 'a' and would be afraid to vary it." (McFadden 1983)
How is speech a complex motor production?
Human speech is also a motor act that requires extremely complex coordination.
In the space of 30 milliseconds it may be necessary for the brain to switch off a noise generator at the front of the mouth, switch on the larynx vibration, move the soft palate, change the configuration of the tongue, modify the lip shape, and initiate a certain pattern of frequency change by the vocal folds. These actions are not synchronized but must be carried out with various specified leads and lags [i.e. careful timing]. (Fry, 1979)
To summarize, motor activity is much like other cognitive activity: (1) based on schemata, but (2) subject to great variation and (3) showing great creativity.
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