Effects of distractor load and temporal target-distractor separation on numerical comparison performance: a stimulus-competition approach.

Effects of distractor load and temporal separation between target and distractor onset were studied in a selective attention task. Two experiments required 128 participants to decide as quickly and accurately as possible which of two spatially separated one-digit numerals was larger. Targets were either preceded or succeeded by distractors with intervals of 0, 33, 83, 133, 183, and 233 msec. In Exp. 1, the target digits could appear with 0, 1, 2, or 3 one-digit distractors numerals, representing four levels of distractor load. In Exp. 2, three asterisks were used as distractors. Interference effects of digit distractors varied with distractor load and temporal separation between target and distractor onsets. Moreover, the effects of distractors preceding the target differed from distractors succeeding the target. The pattern of results provided evidence that distractor-interference effects originated from stimulus competition for selection in visual short-term memory. The results were interpreted in terms of attentional engagement theory of Duncan and Humphreys.