title: Event-related brain potentials and the efficiency of visual search for vertically and horizontally oriented stimuli.
abstract: Reports that visual search is more efficient for vertically than for horizontally shaded objects suggested that search is influenced by a priori knowledge about the source of light. In this study, we examined search for targets defined by the orientation of luminance gradients and measured event-related brain potentials (ERPs). In Experiment 1, we examined search for stimuli that comprised gradual luminance differences. Response times showed the expected orientation anisotropy effect. ERP amplitudes in the P1 latency range were slightly more positive in response to horizontally oriented stimuli, whereas P3 amplitudes were more positive in response to nonsingleton vertically oriented stimuli. Experiment 2 compared search for stimuli that comprised gradual versus step differences in luminance. All the anisotropies that we observed in Experiment 1 could be replicated in Experiment 2. Moreover, these anisotropies were not dependent on the type of the luminance gradient. This finding is inconsistent with the view that search efficiency is influenced by a priori knowledge about the source of light. The behavioral and electrophysiological data are consistent with a context model of visual search. We propose that contextual modulation reduces redundancy and contributes to computing the saliency of visual information by implementing divisive normalization and multiplicative filtering.
authors.affiliation: University of Technology Carolo-Wilhelmina Braunschweig, Germany. b.kopp@klinikum-braunschweig.de
authors.forename: Bruno
authors.initials: B
authors.lastname: Kopp
authors.forename: Jasmin
authors.initials: J
authors.lastname: Kizilirmak
authors.forename: Carolin
authors.initials: C
authors.lastname: Liebscher
authors.forename: Julia
authors.initials: J
authors.lastname: Runge
authors.forename: Karl
authors.initials: K
authors.lastname: Wessel
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001288:Attention / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005133:Eye Movements; D005260:Female; D006801:Humans; D008297:Male; D008960:Models, Psychological; D009949:Orientation / Q000502:physiology*; D010364:Pattern Recognition, Visual; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D055815:Young Adult