 |
| Volume 8, Number 7, Article 15, Pages 1-12 |
doi:10.1167/8.7.15 |
http://journalofvision.org/8/7/15/ |
ISSN 1534-7362 |
From local to global: Cortical dynamics of contour integration
Topi Tanskanen |
Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland |
|
Jussi Saarinen |
Department of Psychology, University of Helsinki,
Helsinki, Finland |
|
Lauri Parkkonen |
Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland |
|
Riitta Hari |
Brain Research Unit, Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland, & Department of Clinical Neurophysiology, Helsinki University Central Hospital, Helsinki, Finland |
|
Abstract
Processing of global contours requires integration of local visual information. To study the involvement of different cortical areas and the temporal characteristics of their activity in such integration, we recorded neuromagnetic responses to arrays of Gabor patches in which a proportion of the patches was oriented either tangentially or radially with respect to a global circular contour; arrays with random patch orientations served as control stimuli. The first responses at 60–80 ms around the calcarine sulcus were similar to all stimuli. Starting from 130 ms, responses to the tangential contours differed significantly from responses to control stimuli, and the difference reached its maximum at 275 ms. The most pronounced differences emerged around the parieto-occipital sulcus, precuneus, cuneus, and superior and middle occipital gyri. This pattern of cortical activity was similar irrespective of whether the local elements were radial or tangential to the circle; however, the differences were smaller for the radial contours and tended to start 20–30 ms later. Correspondingly, discrimination reaction times were shortest for the contours consisting of tangential elements. These results demonstrate two spatially and temporally distinct stages of visual cortical processing, the first one limited to local features and the second one integrating information at a more global level.
|
|