Previous work has demonstrated that when the target and distractors differ in two features across different dimensions (e.g., red and square), search can unfold in parallel in either a simultaneous or a sequential feature-guidance manner. However, the underlying mechanism of how two features within a single feature dimension guide search remains elusive. This study specifically aims to explore how two colors, arranged in a center-surround configuration (e.g., red center/green surround), guide search. Our investigation encompasses homogeneous (Experiments 1-3) and heterogeneous (Experiment 4) search displays. Experiment 1 demonstrated a parallel search mechanism with a two-color location-bound search template by using a search display containing distractors that have inverse color relation with the target. Experiments 2 revealed a strategic preference for using a single color to guide search without location binding when distractor types were intermixed across trials, and this preference persisted even when the template was emphasized by presenting it before each trial. Furthermore, Experiment 3 illustrated that, with fixed-distractor practice, participants can acquire a two-color location-bound search strategy. Once in place, this strategy persists, even when the distractor types become intermixed in subsequent blocks of trials. Experiments 4A-D used a computational modeling approach and found that two-color guidance search works in a parallel sequential manner in heterogeneous displays. Participants utilize one of the two target colors first in a location-bound manner to filter out one subset of distractors and then attended to the second target color (location bound) to reject the remaining distractors.
