Instantaneous stimulus paradigm: cortical network and dynamics of figure-ground organization

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TitleInstantaneous stimulus paradigm: cortical network and dynamics of figure-ground organization
Publication TypeConference Paper
Year of Publication2007
AuthorsLikova, LT, Tyler, CW
Conference NameElectronic Imaging XII, 64921E
Date Published03/2007
PublisherInternational Society for Optics and Photonics
KeywordsAsynchrony, BOLD Waveform., Cerebral cortex, Figure/ground, Neural response, Perceptual Organization, Structure-from transients, Transients

To reveal the cortical network underlying figure/ground perception and to understand its neural dynamics, we

developed a novel paradigm that creates distinct and prolonged percepts of spatial structures by instantaneous refreshes

in random dot fields. Three different forms of spatial configuration were generated by: (i) updating the whole stimulus

field, (ii) updating the ground region only (negative-figure), and (iii) updating the figure and ground regions in brief

temporal asynchrony. FMRI responses were measured throughout the brain. As expected, activation by the

homogenous whole-field update was focused onto the posterior part of the brain, but distinct networks extending

beyond the occipital lobe into the parietal and frontal cortex were activated by the figure/ground and by the negativefigure

configurations. The instantaneous stimulus paradigm generated a wide variety of BOLD waveforms and

corresponding neural response estimates throughout the network. Such expressly different responses evoked by

differential stimulation of the identical cortical regions assure that the differences could be securely attributed to the

neural dynamics, not to spatial variations in the hemodynamic response function. The activation pattern for

figure/ground implies a widely distributed neural architecture, distinct from the control conditions. Even where

activations are partially overlapping, an integrated analysis of the BOLD response properties will enable the functional

specificity of the cortical areas to be distinguished.


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