title: The neural substrates and timing of top-down processes during coarse-to-fine categorization of visual scenes: a combined fMRI and ERP study.
abstract: Spatial frequencies in an image influence visual analysis across a distributed, hierarchically organized brain network. Low spatial frequency (LSF) information may rapidly reach high-order areas to allow an initial coarse parsing of the visual scene, which could then be "retroinjected" through feedback into lower level visual areas to guide finer analysis on the basis of high spatial frequency (HSF). To test this "coarse-to-fine" processing scheme and to identify its neural substrates in the human brain, we presented sequences of two spatial-frequency-filtered scenes in rapid succession (LSF followed by HSF or vice versa) during fMRI and ERPs in the same participants. We show that for low-to-high sequences (but not for high-to-low sequences), LSF produces a first increase of activity in prefrontal and temporo-parietal areas, followed by enhanced responses to HSF in primary visual cortex. This pattern is consistent with retroactive influences on low-level areas that process HSF after initial activation of higher order areas by LSF.
authors.affiliation: Laboratoire de Psychologie et NeuroCognition, CNRS-UMR 5105, Université Pierre Mendès-France, Grenoble, France. carole.peyrin@upmf-grenoble.fr
authors.forename: Carole
authors.initials: C
authors.lastname: Peyrin
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Michel
authors.forename: Sophie
authors.initials: S
authors.lastname: Schwartz
authors.forename: Gregor
authors.initials: G
authors.lastname: Thut
authors.forename: Mohamed
authors.initials: M
authors.lastname: Seghier
authors.forename: Theodor
authors.initials: T
authors.lastname: Landis
authors.forename: Christian
authors.initials: C
authors.lastname: Marendaz
authors.forename: Patrik
authors.initials: P
authors.lastname: Vuilleumier
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D003210:Concept Formation / Q000502:physiology*; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*