[Mechanisms of recognizing geometric figures and their elements--angles in fish (Cyprinus carpio)]

A study was made of the mechanisms of discrimination of geometrical figures and their angles by fish and of the influence of repeated presentation of stimuli on recognition time. The experiment was made by the conditioning method with the use of two variants of food-procuring technique: simultaneous and successive choice of stimuli. It was shown that discrimination of geomentrical figures is achieved at the fist stage by the mechanism of selection, and after long training, by the mechanism of camparison with a chosen standard. The selection mechanism is also used for recognition of angles by their size. Certain combinations of angles differentiated not by size, but by orientation of their sides, are recognized by the mechanism of comparison with a standard.