Flanker Effect

The flanker effect is a finding in cognitive control research in which a person's speed and accuracy at identifying a central target stimulus, such as an arrow or letter, is measurably affected by irrelevant surrounding stimuli, called flankers, presented on either side of it, even though participants are explicitly instructed to ignore the flankers entirely. Responses are typically faster and more accurate when the flankers happen to call for the same response as the target, a congruent trial, and slower and more error-prone when the flankers call for a conflicting response, an incongruent trial, demonstrating that irrelevant nearby information is processed and can interfere with target identification even when a person is actively trying to suppress it. The psychologists Charles Eriksen and Barbara Eriksen introduced the now widely used flanker task that produces this effect in a 1974 study, and it has since become one of the standard experimental paradigms for studying selective attention and cognitive control, alongside related tasks such as the Stroop task documented elsewhere in this section. Because the size of the congruency-related slowdown can be measured precisely and varies systematically with factors such as the spacing between target and flankers and a person's attentional focus, the flanker effect is widely used in research on attentional filtering, response conflict, and the development or decline of cognitive control across the lifespan.