Research Report The electrophysiological correlate of saliency: Evidence from a figure-detection task Sirko Straube a, ⁎ , Manfred Fahle a,b a Department of Human Neurobiology, University of Bremen, Hochschulring 18, D-28359 Bremen, Germany b The Henry Wellcome Laboratories for Vision Sciences, Department of Optometry & Visual Science, City University, Northampton Square, London, EC1V 0HB, UK ARTICLE INFO ABSTRACT Article history: Accepted 16 October 2009 Available online 23 October 2009 Although figure-ground segregation in a natural environment usually relies on multiple cues, we experience a coherent figure without usually noticing the individual single cues. It is still unclear how various cues interact to achieve this unified percept and whether this interaction depends on task demands. Studies investigating the effect of cue combination on the human EEG are still lacking. In the present study, we combined psychophysics, ERP and time–frequency analysis to investigate the interaction of orientation and spatial frequency as visual cues in a figure detection task. The figure was embedded in a matrix of Gabor elements, and we systematically varied figure saliency by changing the underlying cue configuration. We found a strong correlation between the posterior P2 amplitude and the perceived saliency of the figure: the P2 amplitude decreased with increasing saliency. Analogously, the power of the θ-band decreased for more salient figures. At longer latencies, the posterior P3 component was modulated in amplitude and latency, possibly reflecting increased decision confidence at higher saliencies. In conclusion, when the cue composition (e.g. one or two cues) or cue strength is changed in a figure detection task, first differences in the electrophysiological response reflect the perceived saliency and not directly the underlying cue configuration. © 2009 Elsevier B.V. All rights reserved. Keywords: Cue combination ERP Figure-ground segregation Human Detection Time–frequency analysis 1. Introduction The first cue for object presence in a visual scene is the local difference of a visual feature (e.g. a difference in color, luminance, depth or motion). The detection of such basic differences at a glance is a powerful tool to rapidly evaluate which locations might contain objects and to start preparing appropriate actions. Accordingly, it has been suggested that a large amount of attention is caught by such bottom-up, image- based saliency cues (for reviews see e.g. Itti and Koch, 2001; Treue, 2003). But how is the saliency formed when figure- ground segregation can rely on multiple cues? Is the proces- sing of these cues independent or do cues interact? The answers to these questions seem to depend both on task and on cue type: The majority of studies observe cue interaction (Kubovy et al., 1999; Kubovy and Cohen, 2001; Meinhardt and Persike, 2003; Meinhardt et al., 2004, 2006; Nothdurft, 2000; Persike and Meinhardt, 2006; Rivest and Cavanagh, 1996; van BRAIN RESEARCH 1307 (2010) 89 – 102 ⁎ Corresponding author. Fax: +49 421 218 62985. E-mail address: sirko.straube@uni-bremen.de (S. Straube). Abbreviations: °, visual angle; cpd, cycles per degree; EEG, electroencephalogram; ERP, event-related potential; tsVEP, texture- segregation visual evoked potential; sd, standard deviation; MCS, method of constant stimuli; ANOVA, analysis of variance; QUEST, quick estimation by sequential testing 0006-8993/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2009.10.043 available at www.sciencedirect.com www.elsevier.com/locate/brainres