Colour-specific differences in attentional deployment for equiluminant pop-out colours: Evidence from lateralised potentials Vincent Jetté Pomerleau a , Ulysse Fortier-Gauthier a , Isabelle Corriveau a , Roberto Dell'Acqua b , Pierre Jolicœur a, ⁎ a Université de Montréal, Montréal, Québec, Canada b University of Padova, Padova, Italy abstract article info Article history: Received 9 March 2013 Received in revised form 20 October 2013 Accepted 28 October 2013 Available online 1 November 2013 Keywords: Colour vision ERP N2pc Ppc Ptc Multiframe presentation We investigated how target colour affected behavioural and electrophysiological results in a visual search task. Perceptual and attentional mechanisms were tracked using the N2pc component of the event-related potential and other lateralised components. Four colours (red, green, blue, or yellow) were calibrated for each participant for luminance through heterochromatic flicker photometry and equated to the luminance of grey distracters. Each visual display contained 10 circles, 1 colored and 9 grey, each of which contained an oriented line segment. The task required deploying attention to the colored circle, which was either in the left or right visual hemifield. Three lateralised ERP components relative to the side of the lateral coloured circle were examined: a posterior contralateral positivity (Ppc) prior to N2pc, the N2pc, reflecting the deployment of visual spatial attention, and a temporal and contralateral positivity (Ptc) following N2pc. Red or blue stimuli, as compared to green or yellow, had an earlier N2pc. Both the Ppc and Ptc had higher amplitudes to red stimuli, suggesting particular selectivity for red. The results suggest that attention may be deployed to red and blue more quickly than to other colours and suggests special caution when designing ERP experiments involving stimuli in different colours, even when all colours are equiluminant. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Colour is an effective cue for attentional selection and as such is often used in experiments probing attentional mechanisms (Bacon and Egeth, 1994; Clark, 1969; Jolicoeur et al., 2008; Posner, 1980; Von Wright, 1972; Woodman and Luck, 2003). Attentional selection enables us to concentrate our limited attentional resources on a subset of the visual information reaching the visual cortex. Selection is required to avoid the loss of relevant information at later stages of processing because higher-level visual areas can only process and/or store a finite number of relevant objects (Cowan, 2000; Dell'Acqua et al., 2012). Visual spatial attention mechanisms are believed to process visual items serially (whether individually or in small groups) at some point in the visual processing stream in order to be identified in more detail and to control further processing (Sperling, 1960; Treisman and Gelade, 1980). 1.1. Colors and visual spatial attention Usually, colours are used as a discriminative tool for segregating visual targets from distracters. This section provides a brief overview of the results of a few key studies in which chromaticity was shown to have an experimental effect in attentional tasks. Additional discussion can be found in a number of more detailed studies (for which we sug- gest key studies e.g. Carter, 1982; Treisman and Gelade, 1980; Wolfe, 1994). Two recent papers evaluate the contributions of colour to visual spa- tial attention (see also Ansorge and Becker, 2013; Lennert et al., 2011, for additional evidence). The first study addresses the contribution of colour to motion processing in automatic target selection (Tchernikov and Fallah, 2010). The authors measured smooth pursuit eye move- ments that occur spontaneously immediately following a saccade to a circular region containing dots moving coherently either left or right. The dots were red, green, blue, or yellow (with luminance equated across colours). In two experiments, pursuit movements were initiated earlier for red dots. In Experiment 1, this was evaluated with one colour at a time. The participant's task was to move their eyes in the general direction of the colored stimulus after the disappearance of a white fix- ation cross. In Experiment 2, different colours were put in opposition and red tended to win over other colours (if two sets of dots moved in the region in different directions, the spontaneous pursuit movements were in the same direction as the moving red dots). Overall, a hierarchy of colours was found, from red (strongest), to green, to yellow, to blue (weakest). A second paper also evaluated reaction times (RTs) to targets of different desaturated colours (Lindsey et al., 2010). In this study, International Journal of Psychophysiology 91 (2014) 194–205 ⁎ Corresponding author at: Département de Psychologie Université de Montréal C.P. 6128, succursale Centre-ville Montréal QC H3C 3J7, Canada. Tel.: +1 514 343 6511; fax: +1 514 343 2285. E-mail address: vincent.jette.pomerleau@umontreal.ca (P. Jolicœur). 0167-8760/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijpsycho.2013.10.016 Contents lists available at ScienceDirect International Journal of Psychophysiology journal homepage: www.elsevier.com/locate/ijpsycho