Search

We investigated whether spatial filtering can restrict attentional selectivity during visual search to a currently task-relevant attentional window. While effective filtering has been demonstrated during singleton search, feature-based attention is believed to operate spatially globally across the entire visual field. To test whether spatial filtering depends on search mode, we assessed its efficiency both during feature-guided search with colour-defined targets and during singleton search tasks. Search displays were preceded by spatial cues. Participants responded to target objects at cued/relevant locations, and ignored them when they appeared on the uncued/irrelevant side. In four experiments, electrophysiological markers of attentional selection and distractor suppression (N2pc and PD components) were measured for relevant and irrelevant target-matching objects. During singleton search, N2pc components were triggered by relevant target singletons, but were entirely absent for singletons on the irrelevant side, demonstrating effective spatial filtering. Critically, similar results were found for feature-based search. N2pcs to irrelevant target-colour objects were either absent or strongly attenuated (when these objects were salient), indicating that the feature-based guidance of visual search can be restricted to relevant locations. The presence of PD components to salient objects on the irrelevant side during feature-based and singleton search suggests that spatial filtering involves active distractor suppression. These results challenge the assumption that feature-based attentional guidance is always spatially global. They suggest instead that when advance information about target locations becomes available, effective spatial filtering processes are activated transiently not only in singleton search, but also during search for feature-defined targets.

It is well established that directing goal-driven attention to a particular stimulus property (e.g. red), or a conceptual category (e.g. toys) can induce powerful involuntary capture by goal-matching stimuli. Here we tested whether broad affective search goals (e.g. for anything threat-related) could similarly induce a generalised capture to an entire matching affective category. Across four experiments, participants were instructed to search for threat-related images in a Rapid Serial Visual Presentation (RSVP) stream, while ignoring threat-related distractors presented in task-irrelevant locations. Across these experiments we found no evidence of goal-driven attentional capture by threat distractors when participants adopted a general ‘threat detection’ goal encompassing multiple sub-categories of threat (Experiments 1a, 1b). This was true even when there was partial overlap between the threat distractors and the search goal (i.e. subset of the targets matched the distractor; Experiment 2). However, when participants adopted a more specific goal for a single sub-category of threat (e.g. fearful faces), robust goal-driven capture occurred by distractors matching this sub-category (Experiment 3). These findings suggest that while affective criteria can be used in the guidance of attention, attentional settings based on affective properties alone may not induce goal-driven attentional capture. We discuss implications for recent goal-driven accounts of affective attentional biases.

To investigate the time course of attentional object selection processes in visual search tasks where targets are defined by a combination of features from the same dimension, we measured the N2pc component as an electrophysiological marker of attentional object selection during colour/colour conjunction search. In Experiment 1, participants searched for targets defined by a combination of two colours, while ignoring distractor objects that matched only one of these colours. Reliable N2pc components were triggered by targets and also by partially matching distractors, even when these distractors were accompanied by a target in the same display. The target N2pc was initially equal in size to the sum of the two N2pc components to the two different types of partially matching distractors and became superadditive from approximately 250 ms after search display onset. Experiment 2 demonstrated that the superadditivity of the target N2pc was not due to a selective disengagement of attention from task-irrelevant partially matching distractors. These results indicate that attention was initially deployed separately and in parallel to all target-matching colours, before attentional allocation processes became sensitive to the presence of both matching colours within the same object. They suggest that attention can be controlled simultaneously and independently by multiple features from the same dimension and that feature-guided attentional selection processes operate in parallel for different target-matching objects in the visual field.