CORTICAL SYNCHRONIZATION AND PERCEPTUAL FRAMING

How does the brain group together different parts of an object into a coherent visual object representation? Different parts of an object ma y be processed by the brain at different rates and may thus become des ynchronized. Perceptual framing is a process that resynchronizes corti cal activities corresponding to the same retinal object. A neural netw ork model is presented that is able to rapidly resynchronize desynchro nized neural activities. The model provides a link between perceptual and brain data. Model properties quantitatively simulate perceptual fr aming data, including psychophysical data about temporal order judgmen ts and the reduction of threshold contrast as a function of stimulus l ength. Such a model has earlier been used to explain data about illuso ry contour formation, texture segregation, shape-from-shading, 3-D vis ion, and cortical receptive fields. The model hereby shows how many da ta may be understood as manifestations of a cortical grouping process that can rapidly resynchronize image parts that belong together in vis ual object representations. The model exhibits better synchronization in the presence of noise than without noise, a type of stochastic reso nance, and synchronizes robustly when cells that represent different s timulus orientations compete. These properties arise when fast long-ra nge cooperation and slow short-range competition interact via nonlinea r feedback interactions with cells that obey shunting equations.