title: Contextual effects on perceived contrast: figure-ground assignment and orientation contrast.
abstract: Figure-ground segregation is an important step in the path leading to object recognition. The visual system segregates objects ('figures') in the visual scene from their backgrounds ('ground'). Electrophysiological studies in awake-behaving monkeys have demonstrated that neurons in early visual areas increase their firing rate when responding to a figure compared to responding to the background. We hypothesized that similar changes in neural firing would take place in early visual areas of the human visual system, leading to changes in the perception of low-level visual features. In this study, we investigated whether contrast perception is affected by figure-ground assignment using stimuli similar to those in the electrophysiological studies in monkeys. We measured contrast discrimination thresholds and perceived contrast for Gabor probes placed on figures or the background and found that the perceived contrast of the probe was increased when it was placed on a figure. Furthermore, we tested how this effect compared with the well-known effect of orientation contrast on perceived contrast. We found that figure-ground assignment and orientation contrast produced changes in perceived contrast of a similar magnitude, and that they interacted. Our results demonstrate that figure-ground assignment influences perceived contrast, consistent with an effect of figure-ground assignment on activity in early visual areas of the human visual system.
authors: Department of Vision and Cognition, Netherlands Institute for Neuroscience, 1105BA, Amsterdam, The Netherlands.
authors: Matthew W
authors: MW
authors: Self
authors: Department of Vision and Cognition, Netherlands Institute for Neuroscience, 1105BA, Amsterdam, The Netherlands.
authors: Aart
authors: A
authors: Mookhoek
authors: Department of Vision and Cognition, Netherlands Institute for Neuroscience, 1105BA, Amsterdam, The Netherlands.
authors: Nienke
authors: N
authors: Tjalma
authors: Department of Vision and Cognition, Netherlands Institute for Neuroscience, 1105BA, Amsterdam, The Netherlands Department of Integrative Neurophysiology, Centre for Neurogenomics and Cognitive Research, Free University, Amsterdam, The Netherlands Psychiatry Department, Academic Medical Center, Amsterdam, The Netherlands.
authors: Pieter R
authors: PR
authors: Roelfsema
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009949:Orientation; D010364:Pattern Recognition, Visual / Q000502:physiology*
keywords: contextual modulation; contrast perception; figure–ground; orientation context; perceptual organization