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Blindness for Unchanging Targets in the Absence of Motion Filtering

In the January 2004 issue of Psychological Science, Theeuwes reported new findings that may challenge current interpretations of change blindness, the inability of normal observers to detect a changing object among other unchanging stimuli (e.g., Rensink, 2000; Simons 2000). In an ingenious reversal of the usual conditions, Theeuwes examined visual search for unchanging targets among nontargets that did change. In the most important cases, target and nontargets were presented in a preview display and then in a second display, which followed the preview immediately. All nontargets changed their orientation (or orientation and position) in the second display relative to the preview, whereas the target did not. Theeuwes found efficient search (little effect of the number of nontargets on reaction time, or RT) for the targets, indicative of parallel processing. The exciting feature of Theeuwes’ findings is that they cannot be due to a transient (a visual response often elicited by rapid stimulus change) having cued attention to the target’s location—no transient arose there, as the target did not change. Theeuwes concluded that observers are able to detect a ‘‘no-transient signal’’ pertaining to the target in parallel vision. However, whereas Theeuwes’ conclusion concerned unchanging targets among changing nontargets generally, his experiments examined only the specific case of moving nontargets (which rotated even when changing orientation alone), raising a potential ambiguity of interpretation. Previous studies had already found efficient search for static targets among moving nontargets, concluding that a motion filter inhibited moving nontargets on the basis of their motion signals, leaving only static items to be searched (e.g., McLeod, Driver, Dienes, &Crisp, 1991). This same process might account for Theeuwes’ results without the need to assume that unchanging targets can, in general (via no-transient signals), be detected efficiently among changing nontargets. To distinguish Theeuwes’ account from this alternative view, we conducted two experiments completed by the same 8 observers (5 female, 3 male; ages 24–35 years), in counterbalanced order.