It's a Jungle in There: How Competition and Cooperation in the Brain Shape the Mind by Rosenbaum David A

Author:Rosenbaum, David A. [Rosenbaum, David A.]
Language: eng
Format: epub
Publisher: Oxford University Press, USA
Published: 2014-01-17T00:00:00+00:00

Typing

The final class of phenomena I’d like to consider in this chapter on action concerns the parallel, interactive nature of action control. Consider typewriting. For typewriting to work, your fingers must land on the keys in the right order. The sentence I just typed, for example, required that I hit the shift key first, the “f” key second, the “o” key third, and so on. If you think about how this behavior is managed, you might suppose that a typist’s fingers start moving toward their respective keys in the same order as the keys are pressed. The first finger to move might be the one that hits the first key, the second finger to move might be the one that hits the second key, and so on. This expectation is reasonable, except that it turns out to be wrong. As shown in movies of skilled typists, their fingers start heading toward their respective targets as soon as they can.54 Each finger seems to be driven by a little demon that’s intent on moving its finger to that finger’s next target as soon as possible. Saying this another way, each target tries to attract its associated finger as soon as it can, wooing it like a Greek-myth siren.

What’s to prevent the fingers from colliding? Why don’t the fingers just launch en masse to wherever they must go? The answer, according to a model of the serial ordering of behavior that I find particularly compelling, is that behaviors that are supposed to occur late are inhibited more than behaviors that are supposed to occur early (Figure 10). According to the model, it’s the degree of inhibition among behaviors that defines their serial order.55 In the model, the last element is inhibited by the element before it, by the element before that, by the element before that, and so on. The penultimate element is inhibited by all the elements preceding it but not by the one to come afterward. Similarly, the element before the penultimate element is inhibited only by the elements preceding it but not by the two last elements.56

This model is elegant because its principal assumption is that serial order is embodied in patterns of inhibition. It doesn’t say that response elements are linked to serial position tags, such as “position number 1,” “position number 2,” and so on. Claiming that there are position tags begs the question of how serial positions are represented. So does saying that keystrokes are defined by their positions in a hierarchical control structure, such as a tree whose bottom nodes can be read from left to right. That symbolism might be helpful for teaching, but it leaves unanswered the question of how the behaviors are actually controlled.57

Building on this inhibitory model of behavioral control, David Rumelhart and Donald Norman, working together at the time at the University of California (San Diego), modeled the timing of keystrokes in typing.58 The details of their model are less important than its general flavor, which, again, is “jungle-like.” Each

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