 Expertise

Expertise is reliably superior performance in a particular domain of activity, acquired through substantial learning and practice. It involves effective recognition and use of task-relevant structure, rather than simply knowing many disconnected facts or being good at every unfamiliar task.

A classic experiment asked chess players of different strengths to reconstruct positions after a five-second view. Skilled players performed much better for meaningful game positions; the advantage greatly diminished when the same pieces were arranged randomly. William G. Chase and Herbert A. Simon interpreted reconstruction patterns in terms of learned groups of related pieces.^[ref]

The contrast is illuminating because the number of visible pieces need not change. What changes is whether prior learning supplies useful structure. Measuring expertise therefore requires specifying the task and the conditions under which an advantage is demonstrated.