Visual search for redundantly defined target in pigeons: The effects of trialwise search difficulty on redundancy gain.

The redundant signals effect was examined in a visual search task with pigeons. In Experiment 1, pigeons searched for a fixed target among homogeneous, identical distractors that differed from the target on one of two dimensions. Target-distractor discriminability varied across trials, resulting in trial-by-trial changes in search difficulty. When set size increased at test, the relationship between response time and difficulty followed an inverted U-shaped function: Pigeons responded quickly but inaccurately on the most difficult trials, most slowly on trials of intermediate difficulty, and quickly and accurately on easy trials. With smaller set sizes, response time remained flat despite large variation in difficulty. In Experiment 2, the target differed redundantly from distractors on both dimensions, and performance was compared with that on single-cue trials. On difficult trials, redundant cues produced slower but more accurate search than single-cue trials, indicating a time-investing enhancement consistent with a speed-accuracy tradeoff. On trials of intermediate difficulty, redundant cues reduced response time while maintaining high accuracy, demonstrating the typical time-saving enhancement. However, this time-saving benefit diminished as the cues were more salient and the search difficulty on the corresponding single-cue trials decreased. Search efficiency, measured as the slope of response time as a function of set size, was determined solely by the most salient cue. These findings suggest that the two forms of redundancy enhancement arise from distinct processing loci and emerge automatically when individually learned cues are combined. (PsycInfo Database Record (c) 2026 APA, all rights reserved).