title: Cue-dependent circuits for illusory contours in humans.
abstract: Objects' borders are readily perceived despite absent contrast gradients, e.g. due to poor lighting or occlusion. In humans, a visual evoked potential (VEP) correlate of illusory contour (IC) sensitivity, the "IC effect", has been identified with an onset at ~90 ms and generators within bilateral lateral occipital cortices (LOC). The IC effect is observed across a wide range of stimulus parameters, though until now it always involved high-contrast achromatic stimuli. Whether IC perception and its brain mechanisms differ as a function of the type of stimulus cue remains unknown. Resolving such will provide insights on whether there is a unique or multiple solutions to how the brain binds together spatially fractionated information into a cohesive perception. Here, participants discriminated IC from no-contour (NC) control stimuli that were either comprised of low-contrast achromatic stimuli or instead isoluminant chromatic contrast stimuli (presumably biasing processing to the magnocellular and parvocellular pathways, respectively) on separate blocks of trials. Behavioural analyses revealed that ICs were readily perceived independently of the stimulus cue--i.e. when defined by either chromatic or luminance contrast. VEPs were analysed within an electrical neuroimaging framework and revealed a generally similar timing of IC effects across both stimulus contrasts (i.e. at ~90 ms). Additionally, an overall phase shift of the VEP on the order of ~30 ms was consistently observed in response to chromatic vs. luminance contrast independently of the presence/absence of ICs. Critically, topographic differences in the IC effect were observed over the ~110-160 ms period; different configurations of intracranial sources contributed to IC sensitivity as a function of stimulus contrast. Distributed source estimations localized these differences to LOC as well as V1/V2. The present data expand current models by demonstrating the existence of multiple, cue-dependent circuits in the brain for generating perceptions of illusory contours.
authors.affiliation: The Laboratory for Investigative Neurophysiology (The LINE), Department of Clinical Neurosciences, University Hospital Center and University of Lausanne, Lausanne, Switzerland.
authors.forename: Jacques
authors.initials: J
authors.lastname: Anken
authors.affiliation: The Laboratory for Investigative Neurophysiology (The LINE), Department of Radiology, University Hospital Center and University of Lausanne, Lausanne, Switzerland; Electroencephalography Brain Mapping Core, Center for Biomedical Imaging (CIBM) of Lausanne and Geneva, Switzerland.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Knebel
authors.affiliation: The Laboratory for Investigative Neurophysiology (The LINE), Department of Clinical Neurosciences, University Hospital Center and University of Lausanne, Lausanne, Switzerland.
authors.forename: Sonia
authors.initials: S
authors.lastname: Crottaz-Herbette
authors.affiliation: The Laboratory for Investigative Neurophysiology (The LINE), Department of Clinical Neurosciences, University Hospital Center and University of Lausanne, Lausanne, Switzerland; Attention, Brain and Cognition Group, Department of Experimental Psychology, Oxford, UK.
authors.forename: Pawel J
authors.initials: PJ
authors.lastname: Matusz
authors.affiliation: The Laboratory for Investigative Neurophysiology (The LINE), Department of Radiology, University Hospital Center and University of Lausanne, Lausanne, Switzerland; Toronto Western Research Institute, Toronto, Canada.
authors.forename: Jérémie
authors.initials: J
authors.lastname: Lefebvre
authors.affiliation: The Laboratory for Investigative Neurophysiology (The LINE), Department of Clinical Neurosciences, University Hospital Center and University of Lausanne, Lausanne, Switzerland; The Laboratory for Investigative Neurophysiology (The LINE), Department of Radiology, University Hospital Center and University of Lausanne, Lausanne, Switzerland; Electroencephalography Brain Mapping Core, Center for Biomedical Imaging (CIBM) of Lausanne and Geneva, Switzerland; Department of Ophthalmology, University of Lausanne, Jules-Gonin Eye Hospital, Lausanne, Switzerland; Department of Hearing and Speech Sciences, Vanderbilt University, Nashville, TN, USA. Electronic address: Micah.murray@chuv.ch.
authors.forename: Micah M
authors.initials: MM
authors.lastname: Murray
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D003463:Cues; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D055815:Young Adult
keywords: Event-related potential (ERP); Illusory contour; Kanizsa; Magnocellular; Object recognition; Parvocellular; Visual evoked potential (VEP)