Stimulation outside the classical receptive field can alter drastically the response properties of simple neurons. Besides the well known phenomena of patch-suppression and contrast enhancement, Sillito and coworkers found cells which were sensitive for orientation contrasts, even if they were centrally stimulated with their non-preferred orientation. In this paper, we propose a simple mechanism for orientation contrast sensitivity. The two main ingredients are the long-range lateral connections linking cell populations of similar orientation preference, and the local microcircuits which introduce a differential interaction whose sign depends on the post- and presynaptic activation. We compare our analytical results for one spatial dimension to numerical simulations carried out in two dimensions, where we find a delicate interplay between the activity-dependant pattern formation and the boundary conditions introduced by the orientation preference of each cell population. Orientation ...