The influence of the visual wulst on the optic tectum of Columba livia were studied. Analysis of the surface field potential evoked by optic nerve stimulation showed that it is composed of two presynaptic waves (pr1 and pr2) a negative monosynaptic wave (N) and a late, positive component (P) due to activation of deeply located neurons. Single shock visual wulst stimulation elicited a surface-positive field potential the depth profile of which showed that it is due to the activation of neurons of the deep tectal layers, probably different from those responsible for the P wave. Visual wulst stimulation depresses the positive component of the field potential elicited by optic nerve stimulation. It is suggested that this effect is mediated by intratectal inhibitory interneurons.