An increasing body of evidence is revealing a considerable degree of plasticity of receptive field properties and functional architecture in adult visual cortex. These dynamic properties are seen even at the earliest stages of cortical processing. We propose to study both short and long term effects of manipulating the visual environment, determining the stages along the visual pathway at which the changes first take place, finding which classes of intrinsic cortical connections are responsible, and exploring the underlying synaptic mechanisms. The characteristics of visual stimuli that lead to modification of receptive field properties will be explored, and documented with both electrophysiology and optical recording. The dynamic nature of visual cortex has implications for the way in which observers adapt to changes in visual input, induced either by environmental change (leading to perceptual constancies) or by changes within the observer (associated with, for example, changes in the optics of the eye). Longer term changes may account for recovery of function after lesions at various points along the visual pathway. There appears to be, throughout adulthood, a continuing calibration and normalization of the cortex to different visual attributes, which may in turn be related to normal processes such as scene segmentation and visual learning, and to abnormal processes such as amblyopia.