A basic question in understanding the development and plasticity of the brain is: what determines the functional specificity of a structure during development? Recent investigations suggest that many fundamental features of sensory cortex are regulated developmentally by the pattern of their input activity. It has been demonstrated that single cells in auditory cortex can be made visually responsible by routing, through appropriate surgery, their retinal projections into auditory cortical targets. It is now proposed to demonstrate experimentally that global features, for example orientation selective patches and ocular dominance columns, typical of visual cortex develop in auditory cortex of such rewired animals. Retinal projections in newborn ferret kits will be routed into the auditory thalamus (MGN) by surgically ablating central retinal targets and by creating alternative terminal space in MGN. After rearing to adulthood intect cortex in these animals will be optically mapped for their intrinsic signals' generated in response to specific visual stimuli. Signals will be digitally processed and compared with those of visual cortex of normal ferrets. In addition, it is proposed to mathematically model generation of columnar geometry in 'visually responsive' auditory cortex of rewired animals and predict its role in visual signal processing.