ABSTRACT

Processes designed to cope with the inevitable variability of the retinal images of even one and the same scene or object are thus essential for any visual system. In the human-research literature these have been reported as perceptual invariance phenomena and are seen as contributing to what is termed the subjective constancy of objects and scenes. This chapter presents the results relating to the size invariance of shape recognition. Again, most visual systems, whether natural or artificial, have to cope with the fact that the size of the image of an object on the phototransductive surface varies with the viewing distance. Pigeons, which have a brain much smaller than humans, might accordingly be expected to be short of processing capacity even though, as fast-moving animals, sizeinvariance capacities are likely to be essential for their fitness.