This term refers to a group of response inhibition tests used in cognitive psychology to assess the ability to supress responses that are inappropriate in a particular context. In the flanker paradigm, a directional response (generally left or right) is made to a central target stimulus. The target is flanked by non-target stimuli which may corrrespond to the same directional response as the target (congruent flankers) or to the opposite response (incongruent flankers). Response times (RT) are slower for incongruent stimuli than for congruent stimuli.
In the original test descirbed by Eriksen and Eriksen in 1974 [1], letter stimuli were used. Testees were instructed to make a directional responses to certain letters, for example a right response to the letters H and K, and a left response to S and C. Each stimulus consisted of a set of seven letters, with the target in the central position. Examples of congruent stimuli would be HHHHHHH and CCCSCCC, as both the target and the flankers correspond to the same response. HHHSHHH and CCCHCCC are incongruent stimuli, as the central target letter and the flankers correspond to opposite responses. Other variants have used numbers [2], or colour patches [3] as stimuli.
These examples all use an arbitrary mapping between the stimulus and the response. Another possibility is to use a natural mapping, with arrows as stimuli. For example, Kopp et al. (1994)[4] used left and right arrows, with flanker stimuli above and below the target. The flankers could be arrows pointing in the same direction as the target (congruent) the opposite direction (incongruent) or squares (neutral). More commonly, flankers have been aranged in a horizontal array, as with letter stumuli, so <<<<< would be a congruent stimulus, <<><< an incongruent stimulus [5] .
The flanker paradigm was originally introduced as a way of studying the cognitive processes involved in detection and recognition of targets in the presence of distracting information, or "noise". Earlier work had used visual search [6], but this makes it difficult to separate the role of distraction from the search process. In the flanker paradigm, the position of the target is always known - there is no search process. Nonetheless interference still occurs, so it can be studied independently of search mechanisms. Eriksen and Schultz (1979)[7] varied a number of features of the flanker tests, for example the size and contrast of the letters, or the use of forward or backward masking. They proposed a continuous flow model of perception in which information is processed in parallel for different stimulus elements, and accumulates over time until sufficient information is available to determine a response. More recent work in this area has used neurophysiological measures such as event-related potentials [8] or imaging techniques such as fMRI[9].
Many studies have investigated the effects of acute drug administration on Eriksen flanker performance. For example, Ramaekers et al. (1992) [10] used an on-the-road driving tests, and several laboratory tests including the letter version of the Eriksen task to assess the effects of two antihistamines and alcohol on driving-related skills. The flanker test was considered relevant as dealing with distracting information is an important part of safe driving. Both alcohol and cetirizine impaired performance on the test measures, and their effects were additive. Loratidine had no effect on any of the measures studied. The arrows version of the flanker test has also been evaluated as a method of detecting impairment due to alcohol and drugs in drivers at the roadside [11].
Various psychiatric and neurological conditions affect performance on flanker tasks, for example acute schizophrenia [12] and Parkinson's disease [13].