The spatially global control of attentional target selection in visual search

Glyn Humphreys and his co-workers have made numerous important theoretical and empirical contributions to research on visual search. They have introduced the concept of attentional target templates and investigated the nature of these templates and how they are involved in the control of search performance. In the experiments reported here, we investigated whether feature-specific search templates for particular colours can guide target selection independently for different regions of visual space. We employed behavioural and electrophysiological markers of attentional selection in tasks with targets defined by specific colour/location combinations. In Experiment 1, participants searched for pairs of colour targets in a particular spatial configuration (e.g., red in the upper and blue in the lower visual field). In Experiment 2, they searched for single colour-defined targets at specific locations (e.g., red on the left or blue on the right). Target displays were preceded by non-informative cues containing target-colour items at taskset matching or mismatching locations. Contingent attentional capture was observed only for matching cues. However, both matching and mismatching cues elicited identical N2pc components, indicating equivalent attentional capture. This shows that the rapid deployment of attention towards target features is spatially non-selective, and that selection of colour/location combinations occurs at later post-perceptual stages. This was further corroborated in search displays where targets were accompanied by target-colour distractors at nonmatching locations. Here, spatial biases towards the target emerged late and were strongly attenuated relative to displays without such distractors. These results demonstrate that attentional templates for target-defining features operate in a spatially-global fashion. Feature-based guidance of visual search cannot be restricted to particular locations even when this is required by the demands of an attentional selection task.