The associated non-targets effect: evidence of nontarget processing at and beyond the level of letter recognition.

In four visual search tasks participants were asked to make a target response if either of two targets was present and to make a nontarget response if neither target was present. Some target-absent displays included only nontarget stimuli or features that never occurred in the same displays as targets, whereas other target-absent displays included nontarget stimuli or features that did sometimes occur with targets. Nontarget responses were reliably faster in the former case than in the latter. This "associated non-targets effect" indicates that non-targets are not simply classified as non-targets but in addition are discriminated from one another. Current visual search models may underestimate the degree to which non-targets are processed during search.