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1 Department of Neurology, Charite Humboldt University of Berlin, Berlin, Germany; Department of Human Neurobiology, University of Bremen, Bremen, Germany
2 Department of Human Neurobiology, University of Bremen, Bremen, Germany
3 Department of Neurology, Charite Humboldt University of Berlin, Berlin, Germany
* To whom correspondence should be addressed. E-mail: stephan.brandt{at}charite.de.
We investigated contour processing and figure-ground detection within human retinotopic areas using event-related functional magnetic resonance imaging (fMRI) in 6 healthy and naive subjects. A figure (6° side length) was created by a second order texture contour. An independent and demanding foveal letter discrimination task prevented subjects from noticing this more peripheral contour stimulus. The contour subdivided our stimulus into a figure and a ground. Using localizers and retinotopic mapping stimuli we were able to subdivide each early visual area into three eccentricity regions corresponding to i) the central figure, ii) the area along the contour and iii) the background. In these subregions we investigated the hemodynamic responses to our stimuli and compared responses with or without the contour defining the figure. No contour related BOLD-modulation in early visual areas V1, V3, VP and MT+ was found. Significant signal modulation in the contour subregions of V2v, V2d, V3a and LO occurred. This activation pattern was different from comparable studies, which might be due to the letter discrimination task reducing confounding attentional modulation. In V3a but not in any other retinotopic area signal modulation corresponding to the central figure could be detected. Such contextual modulation will be discussed in light of the recurrent processing hypothesis and the role of visual awareness.
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