The Flanker Task, also sometimes called a Eriksen Task, is a choice reaction time task where there is dimensional overlap between the irrelevant stimulus and the relevant stimulus. In the dimensional overlap taxonomy, it is considered a Type 4 task. Other Type 4 tasks include the Stroop-like task and Cross-Modal tasks.
Charles Eriksen (Eriksen & Eriksen, 1974; see also Eriksen, 1995; Eriksen & Schultz, 1979; Cohen & Shoup, 1993, 1997; Miller, 1982, 1991) studied the effects of distracting “flanker” stimuli that appear around or near a relevant target stimulus. In a typical Eriksen task, subjects are shown a string of letters on a screen, and are told to press a left key or a right key depending on what letter appears in the center of the screen (the target letter). The surrounding flanker letters are irrelevant, but can be either consistent (“HHH”) or inconsistent (“SHS”) with the target. Responses are faster and more accurate for consistent stimuli than for inconsistent stimuli. The difference in reaction time is called the Eriksen effect or the flanker effect.
Targets and flankers are both defined as values along the same dimension: in the example above, it is letter. As a result, the relevant and irrelevant stimulus have perceptual and conceptual overlap. Moreover, because the overlap is between stimulus properties, consistency is a property of the stimuli themselves, and is independent of the mapping instructions. However, because different letters are usually assigned to different responses, a confound arises in most tasks: when the stimulus is S-S consistent, the response assigned to the flankers is different from the response assigned to the target. This confound is central to the debate about different explanations of the S-S consistency effect.
Eriksen tasks permit a large number of variations, while still producing the same effect. For example, although flankers and targets are generally letters, they can also be words or shapes or symbols (e.g. Hommel, 1995; Shaffer & LaBerge, 1979; Zhang & Kornblum, 1998). Also, although flankers are usually presented to the left and right of the target, they can also be presented above or below the target, or in other patterns around it (e.g. Eriksen & Hoffman, 1973; Eriksen & St. James, 1986; Eriksen & Murphy, 1987; Yantis & Johnston, 1990; Zhang & Kornblum, 1998).
The key factor that all flanker tasks have in common is the perceptual dimensional overlap between the irrelevant stimulus and the relevant stimulus.
NOTE: There are some times when you will see people use the term “Flanker task” to refer to tasks where left and right arrows are assigned to left and right key-presses, and each target arrow is flanked by irrelevant flanker arrows that are either consistent or inconsistent with the target arrow. In the Dimensional Overlap taxonomy, this is not a Type 4 task: it is a Type 8 task, like the Stroop task. Even though this task has flankers, the dimensional overlap model contends that cognitive processing in this task is fundamentally different from processing in the standard Eriksen task, because it adds overlap between the stimulus dimensions and the response dimension.