Abstract
In efficient visual search tasks, response times increase logarithmically as a function of set size. This reflects an evidence accumulation process. The accumulation rate is indexed by the slope of this function. The less similar are the target and the item, the faster is the accumulation rate, the flatter is the slope. Here, we examined whether background complexity impacts search efficiency in parallel search in real-world scenes. In Experiment 1, a relatively unstructured background was studied. Observers searched for a green turtle presented against one of three unstructured backgrounds which varied in complexity: a solid-colored background (lowest complexity), a beach, and a phase-scrambled beach background (highest complexity). For half the participants, the distractors were yellow turtles (high target-distractor similarity). For the other half, the distractors were black turtles (low target-distractor similarity). Although background did not affect accumulation rates in the low-similarity condition, in the high-similarity condition, a significant but small reduction in accumulation rates was observed as background complexity increased. The magnitude of this effect on the log slope was relatively small (an increase of about 12.7%). In Experiment 2, a more structured background scene (a bedroom) was studied. Observers searched for a teddy bear presented against one of three backgrounds: the bedroom, a phase-scrambled version of the bedroom, and an upside-down version of the bedroom. For half the participants, the distractors were red dolls (high-similarity). For the other half, the distractors were white reindeers (low-similarity). In this experiment, the search slopes did not vary as a function of background. Overall, we concluded that background complexity does not have a meaningful effect on search efficiency, and when effects are observed, they tend to be small in magnitude.