Proactive control mechanisms in visual search

Visual search tasks help unravelling cognitive processes for selecting target stimuli among distractors. However, whether any proactive control mechanisms guide selection during parallel search remains unresolved. Here, we combined a covert visual search task with the Distraction Context Manipulation (DCM) paradigm, a method for studying proactive control mechanisms (Marini et al., 2013, Journal of Experimental Psychology: General). Accordingly, blocks were of three types: Pure blocks (100% distractor-absent trials) and two types of Mixed blocks (33% distractor-absent and 66% distractor-present trials each). The two types of Mixed blocks differed in that the Parallel Search Mixed block included single-feature distractors, while the Serial Search Mixed block included featureconjunction distractors. In all block types, participants’ task was to indicate if a target (horizontally bisected black/gray disk) was present or absent on each trial. In the DCM paradigm, the comparison of distractor-absent trials of Mixed versus Pure blocks helps detecting proactive control mechanisms. Increases of detection sensitivity and slowing-down of reaction time (RT) were observed when distractors were expected, yet not presented (distractor-absent trials of Mixed versus Pure blocks). Thus, expectation of distractors recruited a proactive process that improved detection sensitivity and entailed a RT cost both in parallel and serial search tasks