Distractor–Distractor Interactions in Visual Search for Oriented Targets Explain the Increased Difficulty Observed in Nonlinearly Separable Conditions

The linear separability effect refers to a benefit in search performance observed in a feature-search task, where target and distractor features vary along a continuous feature dimension: Search performance is best when there is a boundary in feature space that separates the distractor features from the target fea-ture. However, the role that distractor heterogeneity plays in this effect is not well understood. Here, we reexamined this effect in the context of a new predictive procedure from Lleras et al. (2019) that quanti-fies the impact of distractor heterogeneity on search performance. Experiments 1A and 1B measured people’s performance in homogeneous search conditions where they searched for the target among one type of distractor. The parameters observed in Experiments 1A and B were then used to predict search times in Experiments 2 and 3, where the target was presented in heterogeneous displays containing two types of distractors. The results show that total variance accounted for was 95% to 98%, without includ-ing any factor indexing the linear separability rule. The results demonstrate that heterogeneous search in orientation space is a function of target-distractor similarity and interitem interactions. The study high-lights the robustness of the predictive procedure and demonstrates the generalizability of the method to estimate interitem interactions to new stimulus types.