Likova L T, Tyler C W, 2006, "A cortical network mediating perceptual organisation for temporally defined form" Perception 35 ECVP Abstract Supplement
A cortical network mediating perceptual organisation for temporally defined form
L T Likova, C W Tyler
Figure/ground categorisation is a key factor for theories of perceptual organisation, shape, and object recognition. To study the categorisation process underlying figure - ground organisation, we used spatial form produced solely by temporal asynchronies in subregions of random-dot fields (temporally defined form). These stimuli were contrasted with uniformly synchronous null-stimuli, generating no form. The response throughout the brain was assessed by functional magnetic resonance imaging (fMRI). In experiment 1 figure/ground was generated by an asynchrony between a central region (figure) and its surroundings. In experiment 2, figure/ground organisation was eliminated by asynchronous segmentation into multiple equivalent stripes. In experiment 3 cue-invariance tests of experiments 1 and 2 were replicated in a novel paradigm of asynchronous unidirectional apparent motion of the visual noise. All experiments were done with equated test/null attention. Our data show dramatic reorganisation of the cortical activation pattern with the perceptual switch from figure/ground to non-figural segmentation. Consistent figure/ground-specific activation was seen only in V5/hMT+, while background-specific suppression occurred in V1/V2, but both were abolished by eliminating the figure/ground organisation in the multiple-stripes condition, when the activation shifted to higher retinotopic areas. These data identify V5/hMT+ as the source driving retinotopic suppression in the V1/V2 representations of the ground regions. This is the first demonstration in the human brain of figure - ground categorisation through top - down suppression from V5/hMT+ to the V1/V2 ground representation.
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