Simply shapely: relative, not absolute shapes are primed in pop-out search

Visual search is typically faster when the target from the previous trial is repeated than when it changes. This priming effect is commonly attributed to a selection bias for the target feature value or against the nontarget feature value that carries over to the next trial. By contrast, according to a relational account, what is primed in visual search is the target-nontarget relationship-namely, the feature that the target has in relation to the features in the nontarget context (e.g., larger, darker, redder)-and switch costs occur only when the target-nontarget relations reverse across trials. Here, the relational account was tested against current feature-based views in three eye movement experiments that used different shape search tasks (e.g., geometrical figures varying in the number of corners). For all tested shapes, reversing the target-nontarget relationships produced switch costs of the same magnitude as directly switching the target and nontarget features across trials ("full-switch"). In particular, changing only the nontargets produced large switch costs, even when the target feature was always repeated across trials. By contrast, no switch costs were observed when both the target and nontarget features changed, such that the coarse target-nontarget relations remained constant across trials. These results support the relational account over feature-based accounts of priming and indicate that a target's shape can be encoded relative to the shapes in the nontarget context.