EXCITATORY-INHIBITORY NETWORK IN THE VISUAL-CORTEX - PSYCHOPHYSICAL EVIDENCE

At early stages in visual processing cells respond to local stimuli wi th specific features such as orientation and spatial frequency, Althou gh the receptive fields of these cells have been thought to be local a nd independent, recent physiological and psychophysical evidence has a ccumulated, indicating that the cells participate in a rich network of local connections, Thus, these local processing units can integrate i nformation over much larger parts of the visual field; the pattern of their response to a stimulus apparently depends on the context present ed, To explore the pattern of lateral interactions in human visual cor tex under different context conditions we used a novel chain lateral m asking detection paradigm, in which human observers performed a detect ion task in the presence of different length chains of high-contrast-f lanked Gabor signals, The results indicated a nonmonotonic relation of the detection threshold with the number of flankers. Remote flankers had a stronger effect on target detection when the space between them was filled with other flankers, indicating that the detection threshol d is caused by dynamics of large neuronal populations in the neocortex , with a major interplay between excitation and inhibition, We conside red a model of the primary visual cortex as a network consisting of ex citatory and inhibitory cell populations, with both short-and long-ran ge interactions, The model exhibited a behavior similar to the experim ental results throughout a range of parameters, Experimental and model ing results indicated that long-range connections play an important ro le in visual perception, possibly mediating the effects of context.