One of the most fascinating and impressive aspects of skilled performance is the ability of the experienced eye to encode at a glance the essence of briefly presented stimulus material, which is related to the domain of expertise (henceforth, domain-specific knowledge). For example, Kundel and Nodine (1975) showed expert radiologists X-ray films for 200 msec. The experts were able to detect and name 70% of the abnormalities in the films.Crucial to this process of rapid perception, particularly for visual displays that require multiple fixations for encoding, is the ability to encode large clusters of related information-that is, chunks-and to locate the most relevant areas, or identify the salient locations, on which to focus attention. In order to examine these early perceptual encoding processes, we required chess players at different skill levels to choose the best move for simple, tactically active chess positions while we monitored their eye-fixation patterns. If more skilled players can extract relational information about piece clusters more efficiently than less skilled players (e.g., in parallel, as seen in Reingold, Charness, Pomplun, & Stampe, 2001; Reingold, Charness, Schultetus, & Stampe, 2001), we hypothesize that skilled players' first few seconds of fixations will be characterized by a greater likelihood of fixating on empty squares (in order to maximize information extraction from surrounding piece-occupied squares). Also, when more skilled players fixate squares occupied by pieces, they should be more likely to fixate salient pieces.The most influential investigation of the perceptual aspects of skilled performance originated from the pioneering work on chess by de Groot (1946Groot ( /1978 and Simon (1973a, 1973b). De Groot presented chess positions briefly (2-15 sec) and then removed them from view. Even after such a brief exposure, the best chess players were able to reproduce the locations of the chess pieces almost perfectly (about 93% correct for positions containing about 25 pieces). More generally, performance in this task systematically varied as a function of skill. De Groot concluded that perception and memory were more important differentiators of chess expertise than was the ability to think ahead in the search for good moves. In a classic study, Simon (1973a, 1973b) replicated and extended de Groot's findings demonstrating that after viewing chess positions for 5 sec, chess masters were able to reproduce these positions much more accurately than less-skilled players. However, there was little difference as a function of expertise when random board configurations were used instead of game positions, indicating that the superior immediate memory performance of the skilled players was not attributable to the general superiority of their memory systems or processes (i.e., hardware aspects of memory). More recently, a very small but reliable advantage in recall for random configurations has been shown for expert players, although this is probably attributable to the occasional presenc...