Identity Negative Priming: A Phenomenon of Perception, Recognition or Selection? Hecke Schrobsdorff 1,2,3 *, Matthias Ihrke 1,2,3 , Jo ¨ rg Behrendt 1,4 , J. Michael Herrmann 1,5 , Marcus Hasselhorn 1,6 1 Bernstein Center for Computational Neuroscience, Go ¨ ttingen, Germany, 2 Max-Planck-Institute for Dynamics and Self-Organization, Go ¨ ttingen, Germany, 3 Institute for Nonlinear Dynamics, University of Go ¨ ttingen, Go ¨ ttingen, Germany, 4 Georg-Elias-Mu ¨ ller Institute for Psychology, University of Go ¨ ttingen, Go ¨ ttingen, Germany, 5 Institute for Perception, Action and Behaviour, University of Edinburgh, Edinburgh, United Kingdom, 6 German Institute for International Educational Research (DIPF), Frankfurt/ Main, Germany Abstract The present study addresses the problem whether negative priming (NP) is due to information processing in perception, recognition or selection. We argue that most NP studies confound priming and perceptual similarity of prime-probe episodes and implement a color-switch paradigm in order to resolve the issue. In a series of three identity negative priming experiments with verbal naming response, we determined when NP and positive priming (PP) occur during a trial. The first experiment assessed the impact of target color on priming effects. It consisted of two blocks, each with a different fixed target color. With respect to target color no differential priming effects were found. In Experiment 2 the target color was indicated by a cue for each trial. Here we resolved the confounding of perceptual similarity and priming condition. In trials with coinciding colors for prime and probe, we found priming effects similar to Experiment 1. However, trials with a target color switch showed such effects only in trials with role-reversal (distractor-to-target or target-to-distractor), whereas the positive priming (PP) effect in the target-repetition trials disappeared. Finally, Experiment 3 split trial processing into two phases by presenting the trial-wise color cue only after the stimulus objects had been recognized. We found recognition in every priming condition to be faster than in control trials. We were hence led to the conclusion that PP is strongly affected by perception, in contrast to NP which emerges during selection, i.e., the two effects cannot be explained by a single mechanism. Citation: Schrobsdorff H, Ihrke M, Behrendt J, Herrmann JM, Hasselhorn M (2012) Identity Negative Priming: A Phenomenon of Perception, Recognition or Selection? PLoS ONE 7(3): e32946. doi:10.1371/journal.pone.0032946 Editor: Kevin Paterson, University of Leicester, United Kingdom Received September 21, 2011; Accepted February 2, 2012; Published March 12, 2012 Copyright: ß 2012 Schrobsdorff et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The funder, the Federal Ministry of Education and Research Germany (BMBF, http://www.bmbf.de/, grant numbers 01GQ0432 and 01GQ1005B), had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: hecke@nld.ds.mpg.de Introduction Selective attention is the process of extracting behaviorally relevant information from the environment which provides us with a permanent stream of sensory input. Successful processing of a stimulus involves the act of focusing on the relevant as well as ignoring the irrelevant information. Contradicting the early hypothesis that attending is active and ignoring is passive, the active nature of ignoring has been revealed experimentally [1]. Subjects had to process lists of colored words in a standard Stroop task where the stimulus cards were ordered such that the ignored meaning of a color word always became the color in which the next word was written and which was to be named. People were slower in responding to those lists compared to unrelated ink colors and color names. Even if the semantic meaning of the color words has been ignored to fulfill the task, it must have entered the cognitive system. These results showed that stimulus selection can be assessed by systematic variation of distracting information. An important approach to investigate the processing of distracting stimuli is provided by the so-called negative priming (NP) paradigm where always a pair of consecutive tasks, called the prime and probe trial, are considered. Those tasks present a relevant and irrelevant stimulus – the target and distractor – and require a response to the target. NP manifests in a slowdown of the reaction in response to a probe target that was presented as the prime distractor. NP is considered a well suited approach to assess the selective aspect of attentional processing, since the ignored stimuli can be shown to be actively processed [2,3]. Usually, NP is contrasted with the positive priming (PP) effect, a response- facilitation, which is observed when a target from the prime trial is repeated as target in the subsequent trial, the probe. The NP effect has been observed in a wide variety of experimental contexts and therefore is a reliable and general phenomenon, for reviews see [4,5]. In spite of this apparent robustness, many factors have been identified that can modulate, cancel or even reverse priming effects, e.g., the response stimulus interval [6–8], absence [7,9–12] or saliency of the probe distractor [13,14], task instructions [15], age [16–18], sex [19], perceptual load [4,15,20], composition of trials [21,22], stimulus presentation time [23], stimulus onset asynchrony [10] and prime awareness [24]. The complexity of the phenomenon is the reason for many different theoretical accounts that have been formulated over the years, e.g. [3,8,25–30]. Historically, the most influential explanation of NP is distractor inhibition theory, which assumes irrelevant stimulus representa- tions are actively suppressed, thereby supporting the selection of PLoS ONE | www.plosone.org 1 March 2012 | Volume 7 | Issue 3 | e32946