Attention Capture by Angry Faces Depends on the Distribution of Attention

The threat-capture hypothesis posits a threat-detection system that automatically directs visual attention to threat-related stimuli (e.g., angry facial expressions) in the environment. Importantly, this system is theorised to operate preattentively, processing all input across the visual field in parallel, prior to the operation of selective attention. The threat-capture hypothesis generates two predictions. First, because the threat-detection system directs attention to threat automatically, threat stimuli should capture attention when they are task-irrelevant and the observer has no intention to attend to them. Second, because the threat-detection system operates preattentively, threat stimuli should capture attention even when it is engaged elsewhere. This thesis tested these predictions using behavioural measures of attention capture in conjunction with the N2pc, an event-related potential (ERP) index of attention selection. Experiment 1 tested the first prediction of the threat-capture hypothesis – that threat stimuli capture attention when they are task-irrelevant. Participants performed a dot-probe task in which pairs of face cues – one angry and one neutral – preceded a lateral target. On some trials, the faces were Fourier phase-scrambled to control for low-level visual properties. Consistent with the threat-capture hypothesis, an N2pc was observed for angry faces, suggesting they captured attention despite being completely task-irrelevant. Interestingly, this effect remained when faces were Fourier phase-scrambled, suggesting it is low-level visual properties that drive attention capture by angry faces. Experiments 2A and 2B tested the second prediction of the threat capture hypothesis – that threat stimuli capture attention when it is engaged elsewhere. Participants performed a primary task in which they searched a column of letters at fixation for a target letter. The perceptual load of this task was manipulated to ensure that attentional resources were consumed by this task. Thus there were high and low perceptual load conditions in these experiments. Task-irrelevant angry faces interfered with task performance when the perceptual load of the task was high but not when it was low (Experiment 2A). Similarly, angry faces elicited an N2pc, indicating that they captured attention, but only when perceptual load was high and when faces were phase-scrambled (Experiment 2B). These experiments further suggest that low-level visual factors are important in attention capture by angry faces. These results appear to be inconsistent with the threat-capture hypothesis, and suggest that angry faces do not necessarily capture attention when it is engaged elsewhere.