Abstract
Background: While previous studies have shown that it is possible to proactively suppress attentional capture by a singleton distractor in a visual search task, this suppression disappears in larger set size conditions. One possible explanation for these findings is that the singleton has higher local feature contrast in the larger set size conditions, which increases its physical saliency and makes suppression impossible. However, increasing the number of items also affects target and singleton distractor location uncertainty and the number of possible display configurations, which might provide an alternative explanation for these findings. Methods: We performed a visual search study with 8-item search displays, where occasional probe trials tested the perception of letters at each location in the search display. In a series of online experiments, we manipulated singleton and target location uncertainty by limiting the locations they appeared at, and manipulated the number of possible display configurations by fixing part of the display. We compared probe letter recall in these conditions to performance in normal 4-item and 8-item display conditions. In a follow-up experiment, participants performed 2 sessions of the task, where only a subset of all possible search display configurations were used. Results: Recall of letters at singleton locations remains higher than at non-singleton distractor locations under reduced location uncertainty, but when configuration uncertainty was reduced, either by fixing the display or after two sessions of the restricted configuration condition, this difference disappeared. Currently, we are examining the interaction between longer learning and context uncertainty, by training participants with a limited set of configurations in 3 sessions over 3 days, and testing whether the reduced early attentional capture we observed in our previous experiment only applies to learned configurations. Conclusions: Our findings suggest that configuration uncertainty, but not location uncertainty, influences early attentional capture by singletons in visual search.