During the mid sixties De Groot made a ground breaking study in expertise using chess players.

As one of the experiments used for the study has been widely repeated and discussed it is worth to go through it here so that the reader is familiar with it.

During the study De Groot presented players of different strength (from amateurs to, GMs, including a World Champion) several piece setups over a chess board (for a restricted amount of time, 5 seconds).

The masters showed:

This showed a great remarkable short term memory for LEGAL chess positions in masters.

Strikingly, this was not the only experiment conducted, but for all other tasks and processes evaluated (i.e. number of moves evaluated, thought process, search depth, etc.) masters showed the same performance that amateurs, weaker players.

From that moment on chess mastery has been tied to perception and memory enconding.