Power Law of Practice

Power Law of Practice

Subject universality is often considered necessary evidence of architectural mechanisms of behavior. One such universal observation from psychology is the power law of practice. This law simply states that the logarithm of the reaction time for a particular task decreases linearly with the logarithm of the number of practice trials taken. Qualitatively, the law simply says only that practice improves performance. However, the quantitative statement of the law and its applicability to a wide-variety of different human behaviors -- immediate-response tasks, motor-perceptual tasks, recall tests, text editing, and more high-level, deliberate tasks such as game-playing -- have suggested it as an architectural result of learning. For example, the power of law of practice has been called upon repeatedly to demonstrate the psychological validity of Soar's learning mechanism, chunking.

Rational Analysis

As an application of rational analysis, Anderson argues that the power law of practice is an environmental and not architectural constraint.


  1. Need probabilities are distributed according to Zipf's law.
  2. Desirability is a gamma function.
  3. Usage decays exponentially. This is a mechanistic assumption and is made with a priori notions of mechanism.
  4. Retrievals are a Poisson process.
(Several of these assumptions are
discussed by Simon in a response to this work.)

List of Theories
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