Multiple sources of conflict in the flanker task: Flanker interference can be decomposed into cumulative components

Interference created by incongruent stimuli in the classic Stroop task appears to be a complex phenomenon, attributed to multiple sources: task conflict (created by the possibility of engaging both word reading and color naming), semantic conflict (created by incompatibility between the concepts denoted by the word and the color), and response conflict (created when the word and the color are associated with two different possible responses). This composite view has seen little use in other conflict tasks, even though interference might reflect multiple sources of conflict in those tasks as well. The current pre-registered study attempted to decompose interference in the classic flanker task. A sample of 130 participants from two countries identified a centrally presented letter while ignoring flanking stimuli, which could be of ten different types (from least to most expected interference: no flanker, simple dots, patches of random visual noise, meaningless simple shapes, meaningless complex shapes, meaningful pictograms, digits, non-response set letters, and letters belonging to the response set; congruent trials were also included as a reference). The results clearly showed cumulative levels of interference as flankers became processable, meaningful, and identifiable as a possible response, indicating that different types of conflict do contribute to interference in the flanker task. The results broadly map onto the task, semantic, and response types of conflict identified in the Stroop task, with a few nuances. Our findings suggest that the presence of multiple sources of conflict may be a very general phenomenon in conflict tasks, extending well beyond Stroop interference.