Effects on search speed of the probability of target-distractor combinations

Pigeons searched for a small target form (T) among 31 identical distractors (Ds). T and D came from the same small set, which differed by simple features. Each form appeared equally often as T or D. Search reaction time (RT) was measured. In Experiment 1, RT was lower to frequent than to infrequent pairs, whether or not frequency was consistently associated with a featural difference. In Experiment 2, detection of T in the location predicted by D was relatively fast. In Experiment 3, search transferred to new T-D pairs. In Experiment 4, probable T-D pairs and improbable T-D pairs were drawn from different sets. Again, T-D probability affected search RT. It was concluded that probability of T-D combinations, not just of targets, affects search speed; distractors may mediate this effect through within-trial priming of attention. The results are consonant with previous studies of repetition priming, cued search, transfer, and the search image.