title: Electrophysiological correlates of top-down effects facilitating natural image categorization are disrupted by the attenuation of low spatial frequency information.
abstract: The modulatory effects of low and high spatial frequencies on the posterior C1, P1 and N1 event-related potential (ERP) amplitudes have long been known from previous electrophysiological studies. There is also evidence that categorization of complex natural images relies on top-down processes, probably by facilitating contextual associations during the recognition process. However, to our knowledge, no study has investigated so far how such top-down effects are manifested in scalp ERPs, when presenting natural images with attenuated low or high spatial frequency information. Twenty-one healthy subjects participated in an animal vs. vehicle categorization task with intact grayscale stimuli and images predominantly containing high (HSF) or low spatial frequencies (LSF). ERP scalp maps and amplitudes/latencies measured above occipital, parietal and frontocentral sites were compared among the three stimulus conditions. Although early occipital components (C1 and P1) were modulated by spatial frequencies, the time range of the N1 was the earliest to show top-down effects for images with unmodified low spatial frequency spectrum (intact and LSF stimuli). This manifested in ERP amplitude changes spreading to anterior scalp sites and shorter posterior N1 latencies. Finally, the frontocentral N350 and the centroparietal LPC were differently influenced by spatial frequency filtering, with the LPC being the only component to show an amplitude and latency modulation congruent with the behavioral responses (sensitivity index and reaction times). Our results strengthen the coarse-to-fine model of object recognition and provide electrophysiological evidence for low spatial frequency-based top-down effects within the first 200 ms of visual processing.
authors.affiliation: Doctoral School of Education, Faculty of Arts, University of Szeged, Petőfi Sándor sgt. 30-34, 6722 Szeged, Hungary.
authors.forename: Adrienn Aranka
authors.initials: AA
authors.lastname: Rokszin
authors.affiliation: Doctoral School of Education, Faculty of Arts, University of Szeged, Petőfi Sándor sgt. 30-34, 6722 Szeged, Hungary.
authors.forename: Dóra
authors.initials: D
authors.lastname: Győri-Dani
authors.affiliation: Department of Image Processing and Computer Graphics, Faculty of Science and Informatics, University of Szeged, Árpád tér 2, 6720 Szeged, Hungary.
authors.forename: László G
authors.initials: LG
authors.lastname: Nyúl
authors.affiliation: Department of Cognitive and Neuropsychology, Institute of Psychology, Faculty of Arts, University of Szeged, Egyetem u. 2, 6722 Szeged, Hungary. Electronic address: gaborcsifcsak@yahoo.co.uk.
authors.forename: Gábor
authors.initials: G
authors.lastname: Csifcsák
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology; D013028:Space Perception / Q000502:physiology*; D055815:Young Adult
keywords: Categorization; ERP; Spatial frequency; Top-down facilitation