Abstract
In visual search for a singleton target among two or more homogeneous distractors, pop out is usually observed, in which RTs to detect or locate the singleton do not increase with the number of items in the display. We have found several displays where the element that appears to pop out is not the singleton but rather one of the homogeneous distractors. Here we review these cases and provide evidence that such False Pop Out (FPO) results from grouping taking place among the separate elements in the display. For example, in searching a display containing two identical distractors and a single odd target, if that target groups with one of the distractors, this will leave the other distractor perceptually isolated, and so it will be the one to pop out. Researchers often assume that jittering positions of the elements in the display will prevent such grouping, but rarely is independent confirmation provided to show this technique works. FPO serves as a new diagnostic criterion for grouping and reminds us that subjects may perceive our displays quite differently from how we intend.