During visual search, attentional templates guide the allocation of attention to objects with template-matching features. When targets are defined by a conjunction of two colours, these guidance processes appear to operate independently for each of these features. As a result, there is no effective attentional guidance when targets defined by a particular configuration (e.g., blue above red) are accompanied by a distractor with the reverse configuration (e.g., red above blue) in the same display. This has been demonstrated recently with ERP markers of attentional selectivity (N2pc components; Berggren & Eimer, 2016). The present study investigated attentional guidance in tasks where targets were defined by the configuration of two different shapes (e.g., hourglass above circle). Participants reported the presence or absence of such combined-shape targets while ignoring non-target items that could be non-matching (e.g. hexagon above cross), partially-matching (e.g., cross above circle) or fully-matching in the reverse configuration (e.g., circle above hourglass). The pattern of N2pc components measured for target-present and target-absent displays again revealed evidence for independent attentional guidance by each of the two target-defining shapes. However, and in contrast colour configuration search, attention was also guided by shape configuration. When a target and a reverse-configuration nontarget appeared in the same display, an N2pc was triggered by the target, although it was delayed and attenuated relative to the target N2pc triggered in the absence of a template-matching distractor. Similar N2pc results were observed when the two shapes were adjacent (thus forming a single object) and when they appeared in different quadrants, demonstrating that guidance by shape configuration was not simply based on search templates for fused target objects. Results show that in contrast to colour, conjunction search in the shape domain can be guided by target templates for spatial configurations.
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