Investigating the interactions between top-down and bottom-up visual processing: The influence of prior expectations on contour integration

Abstract

Event Abstract Back to Event Investigating the interactions between top-down and bottom-up visual processing: The influence of prior expectations on contour integration Marc Schipper1*, Udo Ernst2 and Manfred Fahle1 1 Institute for Human Neurobiology, Germany 2 Institute for Theoretical Neurophysics, Germany Contour integration is a process which links oriented edge elements that are aligned colinearily into a coherent percept. This process is thought to proceed in a mainly feed-forward and/or recurrent manner, making its percepts very salient and independent of top-down or on-going processes ("pop-out"). However, recent studies have shown that attention can strongly modulate contour integration, suggesting the confluence of bottom-up (sensory input) and top-down (prior expectations) processes might even be a necessary prerequisite for contour integration. To uncover neural substrates and mechanisms underlying the influence of prior expectations and attention on contour integration, we combine psychophysical with electrophysiological investigations: Participants had to carry out two experiments with identical visual stimuli but different behavioural tasks: a detection task (A) and a discrimination task (B). Stimuli consisted of vertical and horizontal ellipses formed by colinearily aligned Gabor elements, which were embedded in a field of Gabors with random orientations and positions. Each hemifield could contain either one vertical, one horizontal, or no ellipse. All combinations of these three basic configurations were possible, totalling to nine stimulus categories for the two hemifields. In experiment A participants had to give a yes response whenever one stimulus contained at least one ellipse, in experiment B observers had to give a yes response only when a target was present (this target could be either a horizontal or a vertical ellipse, in any hemifield of the stimulus). Our first results indicate that reaction times do not differ between stimuli in the detection task but are much faster for the target stimulus in the discrimination task. Event-related potentials (ERPs) for vertical and horizontal ellipses do not differ in the detection task, but start to differentiate after about 300ms in the discrimination task, where one of the ellipses was declared as the target. These results already indicate an influence of prior expectations on contour processing. Further acquisition of behavioral and electrophysiological data is carried out to support the assumption that top-down processes influence contour integration and to uncover underlying neural mechanisms. The final results are thought to build the basis for designing follow-up experiments adressing the question how bottom-up and top-down processes interact during contour integration and more complex tasks in visual perception. Conference: Bernstein Symposium 2008, Munich, Germany, 8 Oct - 10 Oct, 2008. Presentation Type: Poster Presentation Topic: All Abstracts Citation: Schipper M, Ernst U and Fahle M (2008). Investigating the interactions between top-down and bottom-up visual processing: The influence of prior expectations on contour integration. Front. Comput. Neurosci. Conference Abstract: Bernstein Symposium 2008. doi: 10.3389/conf.neuro.10.2008.01.108 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 17 Nov 2008; Published Online: 17 Nov 2008. * Correspondence: Marc Schipper, Institute for Human Neurobiology, Bremen, Germany, schipper.marc@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Marc Schipper Udo Ernst Manfred Fahle Google Marc Schipper Udo Ernst Manfred Fahle Google Scholar Marc Schipper Udo Ernst Manfred Fahle PubMed Marc Schipper Udo Ernst Manfred Fahle Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.