Abstract
In numerous psychological experiments, participants classify stimuli by pressing response keys. According to Lakens, Schneider, Jostmann, and Schubert (2011), classification performance is affected by physical distance between response keys – indicating a cognitive tendency to represent categories in spatial code. However, previous evidence for a key distance effect (KDE) from a color-naming Stroop task is inconclusive as to whether: (a) key separation automatically leads to an internal spatial representation of non-spatial stimulus characteristics in participants, or if the KDE rather depends on physical spatial characteristics of the stimulus configuration; (b) the KDE attenuates the Stroop interference effect. We therefore first adopted the original Stroop task in Experiment 1, confirming that wider key distance facilitated responses, but did not modulate the Stroop effect as was previously found. In Experiments 2 and 3 we controlled potential mediator variables in the original design. When we did not display instructions about stimulus-response mappings, thereby removing the unintended spatial context from the Stroop stimuli, no KDE emerged. Presenting the instructions at a central position in Experiment 4 confirmed that key separation alone is not sufficient for a KDE, but correspondence between spatial configurations of stimuli and responses is also necessary. Evidence indicates that the KDE on Stroop performance is due to known mechanisms of stimulus-response compatibility and response discriminability. The KDE does, however, not demonstrate a general disposition to represent any stimulus in spatial code.
Highlights
Almost any undergraduate student of Psychology has earned course credits by completing one variation or another of the following task: identifying the color of a visual stimulus, while ignoring the meaning of a color word that itself carries the color or that is presented at another time or position in the stimulus array
After controlling several possible mediators of the key distance effect (KDE) other than perceived key separation in Experiment 2, that is, without SR mapping instructions on the screen and with un-labeled response keys at three different distances, we found no indication that key distance affected performance
Error rate showed a main effect of Stroop congruency (F(2,38) = 6.52, e = .76, p = .008, gp2 = .26): participants made more errors in incongruent than in congruent conditions (t(19) = 3.14, p = .005, d = 0.7; M = 7 vs. 2.5%, 95% CI [1.5, 7.5])
Summary
Almost any undergraduate student of Psychology has earned course credits by completing one variation or another of the following task: identifying the color of a visual stimulus, while ignoring the meaning of a color word that itself carries the color or that is presented at another time or position in the stimulus array. Lakens, Schneider, Jostmann, and Schubert [3] reported an interesting finding from a two-choice key-press version of the Stroop task. They tested whether the spatial distance between response keys on a computer keyboard influenced the performance in this task. Average reaction time (RT) was shorter when participants used the response keys that were located far apart on the keyboard, compared to when keys were close together (approximately 33 ms) This key distance effect (KDE) was more pronounced in incongruent trials (close-far = 61 ms) than in congruent (15 ms) or in neutral trials (22 ms). In their replication (Experiment 1), Proctor and Chen [4] obtained a similar RT pattern
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