Divided attention impairs detection of simple visual features

Covert spatial attention allows us to prioritize processing at relevant locations. There is substantial evidence that perception is poorer when attention is distributed across multiple locations than when attention is focused on a single location. However, recent work suggests that may not always be the case: divided attention does not appear to impair detection of simple visual features that are represented in primary visual cortex. Here, we re-examined this possibility. In two experiments, observers detected a simple target (a vertical Gabor), and we manipulated whether attention was focused at one location (focal-cue condition) or distributed across two locations (distributed-cue condition). In Experiment 1, targets could appear independently at each location. Thus, observers needed to judge target presence for each location separately in the distributed-cue condition. Under these conditions, we found a robust cost of dividing attention. In this experiment, the cost of dividing attention could reflect either a limit in perceptual processing or a limit in decision making. Therefore, in Experiment 2, we simplified the task to more directly test whether dividing attention impairs perceptual processing of the target. Specifically, only one target could appear on each trial, such that observers made the exact same decision in both conditions (“was a target present?”). Here, we found a marginal cost of dividing attention on performance, that was weaker than the cost in Experiment 1. Together, our results suggest that divided attention does impair detection of simple visual features, but that this cost is primarily due to limits in post-perceptual decision making.