Measuring the allocation of attention in the Stroop task: evidence from eye movement patterns

Attention plays a crucial role in the Stroop task, which requires attending to less automatically processed task-relevant attributes of stimuli and the suppression of involuntary processing of task-irrelevant attributes. The experiment assessed the allocation of attention by monitoring eye movements throughout congruent and incongruent trials. Participants viewed two stimulus arrays that differed regarding the amount of items and their numerical value and judged by manual response which of the arrays contained more items, while disregarding their value. Different viewing patterns were observed between congruent (e.g., larger array of numbers with higher value) and incongruent (e.g., larger array of numbers with lower value) trials. The direction of first saccades was guided by task-relevant information but in the incongruent condition directed more frequently towards task-irrelevant information. The data further suggest that the difference in the deployment of attention between conditions changes throughout a trial, likely reflecting the impact and resolution of the conflict. For instance, stimulus arrays in line with the correct response were attended for longer and fixations were longer for incongruent trials, with the second fixation and considering all fixations. By the time of the correct response, this latter difference between conditions was absent. Possible mechanisms underlying eye movement patterns are discussed.