The adaptation and habituation characteristics produced by the repeated presentation of a moving visual stimulus were studied in single cells in the pigeon's optic tectum. Units located near the surface in the stratum opticum showed little adaptation. However, cells located in deeper layers exhibited varying rates and degrees of adaptation and recovery. Approximately two thirds of the units that adapted, individually showed different rates of adaptation to different directions of movement, thus revealing different receptive field profiles in their adapted and recovered states. Some units were described as habituating since a change in the path of the stimulus through the receptive field or a change in the type of stimulus, resulted in the reinstatement of the initial level of responsiveness.