Visual search for dimensionally redundant pop-out targets: Evidence for parallel-coactive processing of dimensions

In two visual search experiments, the detection of singleton feature target s redundantly defined on multiple dimensions was investigated. Targets diff ered from the distractors in orientation, color, or both (redundant targets ). In Experiment 1, the various target types were presented either in separ ate blocks or in random order within blocks. Reaction times to redundant ta rgets significantly violated the race model inequality (Miller, 1982), but only when there was constancy of the target-defining dimension(s) within tr ial blocks. In Experiment 2, there was dimensional variability within block s. Consistent with Experiment 1, constancy of the target-defining dimension (s), but this time across successive trials (rather than within blocks), wa s critical for observing violations of the race model inequality. These res ults provide evidence for parallel-coactive processing of multiple dimensio ns, consistent with the dimension-weighting account of Muller, Heller, and Ziegler (1995).