Ontogenetic aspects on visual "size-constancy" phenomena in the midwife toad Alytes obstetricans (Laur.).

About 2 weeks after metamorphosis, midwife toads Alytes obstetricans judge the size of a prey object mainly in scales of visual angle. For distant objects they show a tendency to respond to absolute object size. About 6 months later the juvenile animals are able to judge absolute prey size in relation to the stimulus distance ("size constancy" phenomenon). This ability is not necessarily based on learning or previous experience.