Abstract
An object that suddenly appears among other objects is given perceptual priority, even when it seems irrelevant and non-predictive of the task of searching for a particular shape. There has been considerable debate over whether attentional capture of this kind is a function of the control settings the viewer is using to perform the task (e.g., carefully monitoring a display for changes in luminance may make the viewer vulnerable to the onset of new objects) or whether there is truly task-independent attentional capture. Recent evidence favoring the task-independent position shows that capture occurs when a pre-existing object looms (grows in size) but not when it recedes (shrinks in size), suggesting that attentional capture may index the rapid visual evaluation of task-irrelevant behavioral threat (Franconeri & Simons, 2003).
Here, we report on several new tests of the behavioral threat hypothesis. In Experiment 1, we found that search for targets near the center of a display was disrupted more by looming in the periphery than looming near the center. In Experiment 2, we manipulated the direction of looming relative to the participant, finding that attentional capture was stronger for looming objects when they were on a collision path with the viewer than when they were not. An unexpected finding consistent with the behavioral threat hypothesis was the finding of strong capture when looming objects were moving away from the viewer's head but toward the viewer's torso. In Experiment 3, we compared the capture strength of objects that loomed or receded predictably versus unpredictably to evaluate the role of top-down expectations in attentional capture for looming objects.
These results imply that perceptual priority is not solely determined by task-relevant features of a task, suggesting that task-irrelevant actions of objects in displays are constantly monitored with regards to their possible threat to the viewer.