Vision is active. It is a dynamic process, resulting from an interaction between context, perceptual learning and top-down influences. All cortical and thalamic levels of sensory processing are subject to powerful top-down influences, the shaping of lower level processes by higher order, more complex information and cognitive states. There is an expanding view of the kind of information that is conveyed in a top-down fashion, including attention, expectation, and perceptual task. As a consequence every cortical area acts as an adaptive processor, undergoing continuing cycles of state change and functional switching, with earlier states influencing the way in which the bottom up sensory information is interpreted in subsequent states. Recording from primary visual cortex (V1) while animals perform shape detection and discrimination tasks, we find that neurons develop different stimulus selectivities as animals learn these tasks. Moreover, neurons alter their functional properties along with the task requirements. The output from V1 therefore reflects both sensory and behavioral context, which may reflect an interaction between feedback pathways to V1 and local circuits within V1. We propose that during perceptual learning, both the encoding and recall of learned information involves a selection of the appropriate inputs that convey information about the stimulus being discriminated. In addition, experience alters cortical circuitry, with massive rapid sprouting and pruning of both excitatory and inhibitory axons. Modification and gating of cortical circuits therefore underlies the experience and task dependent dynamics of cortical function.