Supplementary data for the paper 'A role of peripheral vision in chess? Evidence from a gazecontingent method'

Chunking theory and previous eye-tracking studies suggest that expert chess players use peripheral vision to judge chess positions and determine the best moves to play. However, the role of peripheral vision in chess has largely been inferred rather than tested through controlled experimentation. In this study, we used a gaze-contingent paradigm in a reconstruction task, similar to the one initially used by De Groot (1946). It was hypothesized that the smaller the gaze-contingent window while memorizing a chess position, the smaller the differences in reconstruction accuracy between novice and expert players. Participants viewed 30 chess positions for 20 seconds, after which they reconstructed this position. This was done for four different window sizes as well as for full visibility of the board. The results, as measured by Cohen’s d effect sizes between experts and novices of the proportion of correctly placed pieces, supported the above hypothesis, with experts performing much better but losing much of their performance advantage for the smallest window size. A complementary find-the-best-move task and additional eye-movement analyses showed that experts had a longer median fixation duration and more spatially concentrated scan patterns than novice players. These findings suggest a key contribution of peripheral vision and are consistent with the prevailing chunking theory.