Mental imagery and chunks: empirical and computational findings.

To investigate experts' imagery in chess, players were required to recall briefly presented positions in which pieces were placed on the intersections between squares (intersection positions). Position types ranged from game positions to positions in which both the piece distribution and the location were randomized. Simulations were run with the CHREST model (Gobet & Simon, 2000). The simulations assumed that pieces had to be centered back, one by one, to the middle of the squares in the mind's eye before chunks could be recognized. Consistent with CHREST's predictions, chess players (N = 36), ranging from weak amateurs to grandmasters, exhibited much poorer recall for intersection positions than for standard positions (pieces placed on the centers of the squares). For the intersection positions, the skill difference in recall was larger for game positions than for the randomized positions. The participants recalled bishops better than they recalled knights, suggesting that Stroop-like interference impairs recall of the latter. The data supported both the time parameter in CHREST for shifting pieces in the mind's eye (125 msec per piece) and the seriality assumption. In general, the study reinforces the plausibility of CHREST as a model of cognition.