Visual search for dimensionally redundant pop-out targets: Redundancy gains in compound tasks

Abstract

Two visual search experiments investigated the detection of odd-one-out feature targets redundantly defined on multiple dimensions. Targets differed from the distractors in either orientation or colour or both (redundant targets). In Experiment 1, the three types of target were presented either in separate trial blocks or randomized within blocks, and the task involved either a simple target detection response or a “compound” response based on the position of dials inside the target. Mean reaction times (RTs) were faster to redundant targets than to singly defined targets, with greater gains in simple detection than in compound tasks. Further, simple detection RTs to redundant targets were faster than the fastest RTs to singly defined targets, violating Miller's (1982) “race model inequality” (RMI). Experiment 2 showed that, with compound tasks, mean RT redundancy gains (and violations of the RMI) depend on practice. The results suggest that separate colour and orientation feature contrast signals coactivate perceptual mechanisms involved in target detection.