Flanker negative priming from spatially unpredictable primes: an ERP study.

In a typical flanker task, a to-be-selected central target is flanked by two to-be ignored, identical distractors. The flanker negative priming (NP) effect denotes increased reaction time and error percent when the distractor of a first display serves as the target in the next. Most theories of NP are consistent with the idea that during processing of the first display, the identity of the distractors is inhibited. If the target of the subsequent display has the same identity, NP occurs because of persisting or retrieved inhibition. However, in the standard flanker task stimuli appear at the same screen locations for all trials, allowing for anticipatory spatial selection. No strong additional inhibition of stimulus identities may then be required. Therefore, besides the standard flanker task we employed a modified task in which the location of the stimulus triplet slightly differed across trials, thus disabling spatial pre-selection. Event-related potentials (ERPs) were recorded to identify brain correlates of NP in the two tasks. Behavioral NP was present in the modified task but absent in the standard task. An ERP correlate specific to NP in the modified task concerned larger amplitude of a left-posterior processing negativity. Results support the idea that stronger inhibition of distractor identities contributes to NP in the flanker task when spatial pre-selection is disabled.