title: Radial Frequency Analysis of Contour Shapes in the Visual Cortex.
abstract: Cumulative psychophysical evidence suggests that the shape of closed contours is analysed by means of their radial frequency components (RFC). However, neurophysiological evidence for RFC-based representations is still missing. We investigated the representation of radial frequency in the human visual cortex with functional magnetic resonance imaging. We parametrically varied the radial frequency, amplitude and local curvature of contour shapes. The stimuli evoked clear responses across visual areas in the univariate analysis, but the response magnitude did not depend on radial frequency or local curvature. Searchlight-based, multivariate representational similarity analysis revealed RFC specific response patterns in areas V2d, V3d, V3AB, and IPS0. Interestingly, RFC-specific representations were not found in hV4 or LO, traditionally associated with visual shape analysis. The modulation amplitude of the shapes did not affect the responses in any visual area. Local curvature, SF-spectrum and contrast energy related representations were found across visual areas but without similar specificity for visual area that was found for RFC. The results suggest that the radial frequency of a closed contour is one of the cortical shape analysis dimensions, represented in the early and mid-level visual areas.
authors: Institute of Behavioural Sciences, Division of Cognitive and Neuropsychology, University of Helsinki, Helsinki, Finland.|Advanced Magnetic Imaging Centre, Aalto NeuroImaging, Aalto University School of Science, Espoo, Finland.
authors: Viljami R
authors: VR
authors: Salmela
authors: Advanced Magnetic Imaging Centre, Aalto NeuroImaging, Aalto University School of Science, Espoo, Finland.|Department of Neuroscience and Biomedical Engineering, Aalto University, Espoo, Finland.
authors: Linda
authors: L
authors: Henriksson
authors: Advanced Magnetic Imaging Centre, Aalto NeuroImaging, Aalto University School of Science, Espoo, Finland.|Clinical Neurosciences, Neurology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.
authors: Simo
authors: S
authors: Vanni
mesh_terms: D019295:Computational Biology; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011601:Psychophysics / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology*