The Stroop effect, in its classical form, is an effect found when attention-grabbing word meaning interferes with the naming of the ink the words are printed in. For example, if the word "red" is printed in the ink color green, then it is harder to name the ink color than if it had been printed in red (or black). It typically takes longer to name the ink color when it doesn't match the word meaning. One possible explanation of this effect is that the meaning of the word captures attention and thereby distracts us from the task we are supposed to carry out.
Figure 1: The word ‘red’ is here displayed in the color black (left) and the color green (right). It takes longer for subjects to name the color of the ink when the word is printed in green than when it is printed in black or red. Image credit: Berit Brogaard and Kristian Marlow.
The Stroop effect, or "Stroop-like effect," has been reported in many other cases. For example, studies indicate that words denoting body shapes may trigger a similar interference in people who are at risk of having an eating disorder (the effect reported in these studies remains controversial).
Even more fascinating, perhaps, is that the effect apparently shows up in perceptual learning cases. A quintessential case of perceptual learning (that has been extensively studied) is that of expert chess players. Whereas novices are only able to encode the position of the individual chess pieces in long-term memory, expert chess players apparently encode chess configurations.
Reingold et al. (2001) carried out a study that indicates that expert chess players may in fact be subject to a Stroop-like effect. A minimized 5x5 chessboard was displayed to novice, intermediate and expert chess players. In the first part of the study configurations fell into two types: one figuration with two or three pieces in a check setup (e.g., the bishop in one corner and the king in the diagonal corner). This is the ‘yes’ condition. Another configuration with two or three pieces in a no-check setup (e.g., the rook in one corner and the king in the diagonal corner). This is the ‘no’ condition. In the second part of the study, only the two attacker positions (e.g., the bishop/rook and the king) from the first part were used, and double-check positions were added to create four possible combinations of checking for both attackers (i.e., yes/yes, yes/no, no/yes, and no/no). Non-check is the congruent condition, whereas check is the incongruent condition. On half of the trials, one of the attackers was colored red as a cue (e.g. the rook) (Fig. 2).
Figure 2. Examples of the check configurations The top row demonstrates yes (check) versus no (non-check) conditions with two or three pieces The bottom row illustrates the no-cue condition (‘no’ trials) and conditions in which a cued nonchecking attacker appeared together with an attacker that was either congruent (i.e., nonchecking) or incongruent (i.e., checking). From Reingold et al. (2001)
In the first part of the study, the players were told to determine as quickly and accurately as they could whether or not the black king was in check. Here the results showed that novices and intermediate players responded more slowly when there were two attackers (three pieces) than one attacker, whereas the extra piece didn’t affect expert players. This indicates holistic processing for experts but non-holistic processing for novices and intermediate players, who would need to evaluate each chess piece independently.
In the second part of the study, the participants were instructed to proceed as before if there was no cue but if a cue was present they should ignored the non-colored attacker. If processing of chess relations is serial (piece by piece), the cuing in the congruent (no-chess) condition should improve performance, as compared with the no-cue condition, because the player doesn’t need to examine non-cued checking relation. If, on the other hand, the processing of the chess relations is parallel (holistic), the cuing should not improve performance. The results showed that cueing helped novices and intermediate players but didn’t help expert, suggesting that unlike non-experts, experts process the chess configurations holistically rather than piece by piece.
Experts were faster in the congruent (non-check) versus the incongruent (check) condition, when a cue was present. A plausible explanation of this is that there is a Stroop-like interference that is generated because the incongruent (check) relation that is supposed to be ignored grabs the expert’s attention. This type of interference found in experts but not in novices supports the hypothesis that novice and expert chess players perceptually encode chess board configurations differently.
Reingold, E. M., Charness, N., Pomplun,M., & Stampe, D. M. (2001). “Visual span in expert chess players: Evidence from eye movements,” Psychological Science, 12, 49-56.