Publication Type: Journal Article
Authors: Lora T Likova; Christopher W Tyler
Publication: Experimental Brain Research, Volume 189, p.257–267 (2008)
Abstract:
To study the cortical mechanism of figure/
ground categorization in the human brain, we employed
fMRI and the temporal-asynchrony paradigm. This paradigm
is able to eliminate any diferential activation for local
stimulus features, and thus to identify only global perceptual
interactions. Strong segmentation of the image into
diferent spatial configurations was generated solely from
temporal asynchronies between zones of homogeneous
dynamic noise. The figure/ground configuration was a single
geometric figure enclosed in a larger surround region. In
a control condition, the figure/ground organization was
eliminated by segmenting the noise field into many identical
temporal-asynchrony stripes. The manipulation of the
type of perceptual organization triggered dramatic reorganization
in the cortical activation pattern. The figure/ground
configuration 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
figure/ground organization was eliminated. These results
suggest that figure/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
architecture incorporating suppressive feedback that
operates in a topographic manner, forming a figure/ground
categorization network distinct from that for “pure” scene
segmentation and thus underlying the perceptual organization
of dynamic scenes into cognitively relevant components.
Keywords: Contextual interactions, Figure and ground, hMT+, Perceptual Organization, Salience, Suppression, Temporal asynchrony, Top-down feedback, V1, V2, Visual cortex