The perception of visual stimuli is widely held to be supported through the activity of populations of neurons in visual cortex. Work in our laboratory seeks to record this population activity and to characterize its evolution in time. Our methods rely on optical imaging of voltage-sensitive dyes (Benucci et al, 2007) and on electrical imaging via multielectrode arrays (Nauhaus et al, 2009). Our results indicate that the visual cortex operates in a regime that depends on the strength of the visual stimulus: For large, high contrast stimuli, the cortex operates in a manner that emphasizes local computations, whereas for smaller or lower contrast stimuli the effect of lateral connections becomes predominant. In this interconnected regime, the population responses exhibit rich dynamics, with waves of activity that travel over 2-6 millimetres of cortex to influence distal locations. In the complete absence of a stimulus, these waves dominate, and are sufficient to explain the apparently erratic activity of local populations. These results indicate that two apparently contradictory views of visual cortex, one postulating computations that are entirely local and the other postulating strong lateral connectivity, are both correct. The cortex can operate in both regimes, and makes its choice of regime adaptively, based on the stimulus conditions.