ORIGINAL PAPER

Abstract The accessory optic system and pretectum are highly conserved brainstem visual pathways that process the visual consequences of self-motion (i.e. optic flow) and generate the optokinetic response. Neurons in these nuclei have very large receptive fields in the contalateral eye, and exhibit direction-selectivity to large-field mov-ing stimuli. Previous research on visual motion path-ways in the geniculostriate system has employed ‘‘plaids’ ’ composed of two non-parallel sine-wave grat-ings to investigate the visual system’s ability to detect the global direction of pattern motion as opposed to the direction of motion of the components within the plaids. In this study, using standard extracellular techniques, we recorded the responses of 47 neurons in the nucleus of the basal optic root of the accessory optic system and 49 cells in the pretectal nucleus lentiformis mesencephali of pigeons to large-field gratings and plaids. We found that most neurons were classified as pattern-selective (41– 49%) whereas fewer were classified as component-selective (8–17%). There were no striking differences between nucleus of the basal optic root and lentiformis mesencephali neurons in this regard. These data indicate that most of the input to the optokinetic system is ori-entation-insensitive but a small proportion is orienta-tion-selective. The implications for the connectivity of the motion processing system are discussed