Abstract
When searching displays that can have more than one target, the detection of a second target is reduced relative to detection of the same target in a single target trial (Subsequent Search Misses). In addition, the second target deficit is magnified when the two targets are different objects. In order to explain this categorical effect, it has been suggested that detection of the first target activates that item’s search template in working memory, while the other target’s template become temporality deactivated. To test this theory, we eye tracked participants while they search for Ts and Os among L and Q distractors. The theory suggests that finding a T should produce a subsequent bias to fixate Ls (since they are similar to the T), while finding an O should bias subsequent fixations towards Qs. Our results failed to find such a bias. In addition, when we calculated second target detection rates using the conditional probability method that has been suggested for this type of work, we observed a significant second target deficit. However, this method neglects the fact that trials with two targets provide two opportunities for one of the targets to be a “difficult target”. We propose an alternative, and more appropriate, method for calculating the expected detection rate for the second target. When applied to our data, the apparent reduction in second target detection disappears. In short, the “second target deficit” we observed can be explained by simple probability theory, and thus does not require a cognitive explanation. This probability issue may not explain all prior findings of a second target deficit, but it may account for some of the findings, and may artificially increase the effect sizes when there are indeed effects. Researchers investigating multiple target searches should be aware of this issue.