Increased perceptual and conceptual processing difficulty makes the immeasurable measurable: negative priming in the absence of probe distractors.

Negative priming (NP) refers to the finding that people's responses to probe targets previously presented as prime distractors are usually slower and more error prone than to unrepeated stimuli. In a typical NP experiment, each probe target is accompanied by a distractor. It is an accepted, albeit puzzling, finding that the NP effect depends on the presence of these probe distractors; for, without probe distractors, NP diminishes. This phenomenon causes severe problems for the majority of theoretical accounts of NP. In the present study, we follow a simple argument, namely that without probe distractors, the difficulty of responding to the probe is so low that NP becomes irrelevant. Hence, by increasing perceptual processing difficulty, as well as by increasing conceptual processing difficulty, significant NP effects with constantly absent probe distractors can be reliably observed. In addition, our results also show that NP without probe distractors can be found by exclusively manipulating probe display processing. This finding furthers our understanding of the processes causing NP.