Unconscious pop-out: Attentional capture by unseen feature singletons only when top-down attention is available

Visual “pop-out” occurs when a unique visual target (e.g. a feature singleton) is present among a set of homogeneous distractors. However, the role of visual awareness in this process remains unclear. Here we show that, even though subjects were not aware of a suppressed pop-out display, their subsequent performance on an orientation discrimination task was significantly better at the pop-out location than at a control location. These results indicate that visual awareness of a feature singleton is not necessary for it to attract attention. Furthermore, our results show that the subliminal pop-out effect disappeared when subjects diverted their attention toward an RSVP task while viewing the same subliminal pop-out display, suggesting that the availability of top-down attention is necessary for the subliminal pop-out effect, and that the cognitive processes underlying attention and awareness are somewhat independent. Visual “pop-out” refers to the phenomenon in which a unique visual target (e.g. a feature singleton) can be rapidly detected among a set of homogeneous distractors (Treisman, 1985; Wolfe, 1994). Here we inquire about the roles of visual awareness and attention in this process. Specifically, what actually makes a feature singleton pop out? Is awareness of the feature singleton necessary for the stimulus to attract attention? Or can a feature singleton be processed and summon attention without the subject ever being aware of the stimulus?1 We investigated (1) whether visual awareness of a feature singleton is necessary for that stimulus to capture attention and (2) whether top-down attention is necessary to elicit such a subliminal response. Using the continuous flash suppression paradigm (Tsuchiya and Koch, 2005), we presented a pop-out display (a feature singleton among several distractors) subliminally and demonstrated that, even though subjects were not aware of the display, their subsequent performance on an orientation discrimination task was significantly better at the pop-out location than at a control location (Experiment 1). Furthermore, we showed that this effect disappeared when subjects diverted their attention toward a rapid serial visual presentation (RSVP) task while viewing the same subliminal pop-out display (Experiment 2). Together, these findings suggest that (1) awareness of a feature singleton is not necessary for it to summon attention and that (2) top-down attention is necessary for this subliminal effect to occur. *To whom correspondence should be addressed. hsieh.pj@gmail.com. 1Awareness is operationalized here as reportability (Dehaene et al., 2006). Top-down attention has been related to spatial, featural, temporal, and object-based variants of attention behaviorally, and neuronal ‘versions’ of top-down attention also include ‘shrinking receptive fields’ (Bundesen et al., 2005). For our purposes, top-down attention here only refers to the spatial and featural variants of attention. NIH Public Access