What do birds see in moving video images?

Ecological and physiological evidence suggests that motion should be very i mportant in the vision of birds, as it is in human vision. However, because of technical difficulties, and uncertainty about the suitability of curren t video and computer technology for presenting moving stimuli to birds, the re has been relatively little research on avian perceptual and cognitive pr ocessing of motion. The present article first reviews what we know about bi rds' processing of moving video images. Although the bird's eye view differ s from the human view, static video images are effective stimuli for birds, and pigeons can respond to apparent motion as though it was real motion. U sing video images, birds have been shown to discriminate still from moving images, between moving shapes, and between categories of movement. There is some but not complete evidence of transfer between moving video images and the real objects they represent. Movement may aid the process of feature i ntegration, and it gives rise to some but not all of the cognitive effects that it leads to in humans - for example birds do seem to track a temporari ly invisible moving object correctly, but they do not respond distinctively to causal movements. Secondly, the paper reviews some questions that are n ow open for research, but have not yet been properly addressed, for example the psychophysics of video images, the relative salience of movement cues in pattern discrimination, movement after effects and the role of movement in depth perception and individual recognition. There remain some things we can never know about how birds see video stimuli, because of problems that include the impossibility of sharing the subjective experience of any othe r individual, or of entering into the perceptions of animals whose perceptu al and cognitive processes and experience are different from our own.