Attention does not always help: The role of expectancy, divided, and spatial attention on illusory conjunctions

Humans have the subjective impression of a rich perceptual experience, but this perception is riddled with errors that might be produced by top-down expectancies or failures in feature integration. The role of attention in feature integration is still unclear. Some studies support the importance of attention in feature integration, whereas others suggest that feature integration does not require attention. Understanding attention as a heterogeneous system, in this study, we explored the role of divided (as opposed to focused-Experiment 1) attention, and endogenous-exogenous spatial orienting (Experiments 2 and 3) in feature integration. We also explored the role of feature expectancy, by presenting stimulus features that were completely unexpected to the participants. Results demonstrated that both endogenous and exogenous orienting improved feature integration whereas divided attention did not. Moreover, a strong and consistent feature expectancy effect was observed, demonstrating perceptual completion when an unexpected perceptual feature was presented in the scene. These results support the feature confirmation account, which proposes that attention is important for top-down matching of stable representations.