Research report Attention selection, distractor suppression and N2pc Veronica Mazza a,b, *, Massimo Turatto a,b and Alfonso Caramazza a,c a Center for Mind/Brain Sciences (CIMeC), University of Trento, Italy b Department of Cognitive Sciences and Education, University of Trento, Italy c Cognitive Neuropsychology Laboratory, Harvard University, Cambridge, USA article info Article history: Received 10 April 2008 Reviewed 13 August 2008 Revised 27 October 2008 Accepted 31 October 2008 Action editor Gus Buchtel Published online 14 November 2008 Keywords: Attentional orienting N2pc Distractor suppression Visual search Event-related brain potentials abstract N2pc is generally interpreted as the electrocortical correlate of the distractor-suppression mechanisms through which attention selection takes place in humans. Here, we present data that challenge this common N2pc interpretation. In Experiment 1, multiple distractors induced greater N2pc amplitudes even when they facilitated target identification, despite the suppression account of the N2pc predicted the contrary; in Experiment 2, spatial proximity between target and distractors did not affect the N2pc amplitude, despite resulting in more interference in response times; in Experiment 3, heterogeneous dis- tractors delayed response times but did not elicit a greater N2pc relative to homogeneous distractors again in contrast with what would have predicted the suppression hypothesis. These results do not support the notion that the N2pc unequivocally mirrors distractor- suppression processes. We propose that the N2pc indexes mechanisms involved in iden- tifying and localizing relevant stimuli in the scene through enhancement of their features and not suppression of distractors. ª 2008 Elsevier Srl. All rights reserved. 1. Introduction What is attention and why do we need it? Theories of visual attention postulate that because of the limited computational resources of the human brain, these need to be selectively dedicated to some stimuli at the expense of others (e.g., Desimone and Duncan, 1995). Attention appears to be the way the visual system limits the analysis of unwanted stimuli, but the mechanism(s) underlying this function still remain controversial. For instance, does attention act through enhancement of the relevant stimulus or through suppression mechanisms that filter out irrelevant information? Several behavioral and neuroimaging studies in humans (e.g., Awh et al., 2003; Caputo and Guerra, 1998; Mounts, 2000; Serences et al., 2004) have been interpreted to support the view that attention solves ambiguities during target analysis by sup- pressing irrelevant stimuli, and their corresponding features, in order to prevent erroneous coding or binding (Treisman and Schmidt, 1982). Some neurophysiological studies in monkeys provided evidence consistent with the filtering role of atten- tion, showing that in V4 and IT cortex the neuron’s prefer- ential response to a given stimulus was physiologically suppressed when the stimulus was not attended (Moran and Desimone, 1985; Chelazzi et al., 1993; Desimone and Duncan, 1995; Reynolds et al., 1999). In humans, event-related potentials (ERPs) studies of attention have been used to build a bridge between theories of visual selection and single neuron responses in monkeys. * Corresponding author. Corso Bettini 31, 38068 Rovereto, Italy. E-mail address: veronica.mazza@unitn.it (V. Mazza). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/cortex 0010-9452/$ – see front matter ª 2008 Elsevier Srl. All rights reserved. doi:10.1016/j.cortex.2008.10.009 cortex 45 (2009) 879–890