35+ years of the additional singleton task: Design features and guidelines.

The additional singleton paradigm, introduced in the early 1990s, has become a cornerstone in attention research and the study of attentional capture. In this task, observers search for a unique target singleton while an irrelevant, but salient distractor singleton is also present. Decades of research have demonstrated that such distractors reliably slow responses, supporting a stimulus-driven account of attentional selection. This paper reviews the origins of the paradigm, key findings, and ongoing debates, with particular focus on design features that shape results. Critical factors include the consistency of target-distractor assignments, distractor prevalence, display size, target-distractor similarity, and the use of compound versus simple search tasks. Guidelines are presented to maximize the paradigm's utility and to avoid misinterpretation of attentional capture effects. The review concludes that the additional singleton task continues to provide unique leverage in distinguishing stimulus-driven selection from top-down control.