title: Parallelism in the brain's visual form system.
abstract: We used magnetoencephalography (MEG) to determine whether increasingly complex forms constituted from the same elements (lines) activate visual cortex with the same or different latencies. Twenty right-handed healthy adult volunteers viewed two different forms, lines and rhomboids, representing two levels of complexity. Our results showed that the earliest responses produced by lines and rhomboids in both striate and prestriate cortex had similar peak latencies (40 ms) although lines produced stronger responses than rhomboids. Dynamic causal modeling (DCM) showed that a parallel multiple input model to striate and prestriate cortex accounts best for the MEG response data. These results lead us to conclude that the perceptual hierarchy between lines and rhomboids is not mirrored by a temporal hierarchy in latency of activation and thus that a strategy of parallel processing appears to be used to construct forms, without implying that a hierarchical strategy may not be used in separate visual areas, in parallel.
authors.affiliation: Wellcome Laboratory of Neurobiology, University College London, Gower Street, London, WC1E 6BT, UK.
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Shigihara
authors.forename: Semir
authors.initials: S
authors.lastname: Zeki
mesh_terms: D000328:Adult; D005260:Female; D005556:Form Perception; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D011930:Reaction Time; D014793:Visual Cortex / Q000502:physiology*
keywords: form perception; hierarchical model; orientation selective cells; prestriate cortex; striate cortex