City Research Online

Abstract

To study the cortical mechanism of Wgure/ ground categorization in the human brain, we employed fMRI and the temporal-asynchrony paradigm. This paradigm is able to eliminate any di Verential activation for local stimulus features, and thus to identify only global perceptual interactions. Strong segmentation of the image into diVerent spatial conWgurations was generated solely from temporal asynchronies between zones of homogeneous dynamic noise. The Wgure/ground conWguration was a single geometric Wgure enclosed in a larger surround region. In a control condition, the Wgure/ground organization was eliminated by segmenting the noise Weld into many identical temporal-asynchrony stripes. The manipulation of the type of perceptual organization triggered dramatic reorganization in the cortical activation pattern. The Wgure/ground conWguration generated suppression of the ground representation (limited to early retinotopic visual cortex, V1 and V2) and strong activation in the motion complex hMT+/ V5+; conversely, both responses were abolished when the Wgure/ground organization was eliminated. These results suggest that Wgure/ground processing is mediated by topdown suppression of the ground representation in the earliest visual areas V1/V2 through a signal arising in the motion complex. We propose a model of a recurrent cortical rchitecture incorporating suppressive feedback that operates in a topographic manner, forming a Wgure/ground categorization network distinct from that for “pure” scene segmentation and thus underlying the perceptual organization of dynamic scenes into cognitively relevant components.

Publication Type:	Article
Additional Information:	The final publication is available at Springer via http://dx.doi.org/10.1007/s00221-008-1417-6
Publisher Keywords:	Perceptual organization · Figure/ground, Contextual interactions, Temporal asynchrony, Visual cortex, Suppression, Salience, Top-down feedback, V1, V2, hMT+
Subjects:	R Medicine
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences
SWORD Depositor:	Symplectic Administrator

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