Pop-out without awareness: unseen feature singletons capture attention only when top-down attention is available.

Visual pop-out occurs when a unique visual target (e.g., a feature singleton) is present in a set of homogeneous distractors. However, the role of visual awareness in this process remains unclear. In the experiments reported here, we showed 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 conscious visual awareness of a feature singleton is not necessary for it to attract attention. Furthermore, the subliminal pop-out effect disappeared when subjects diverted their attention toward a rapid sequential visual presentation task while presented with the same subliminal pop-out display. These results suggest that top-down attention is necessary for the subliminal pop-out effect and that the cognitive processes underlying attention and awareness are somewhat independent.