[Constancy of color perception in the gray toad (Bufo bufo L.): role of the surrounding background in recognition of stimulus color].

The paper continues the previous study (1) on some aspects of toad colour vision. It deals with signs which allow the visual system of toad to recognize blue stimuli. The behavioural experiments were performed during the breeding season when males exhibited the clasping of stationary blue stimuli. It is shown that in spite of some variety of spectral compositions of light sources males clasp only blue stimuli on white surrounding background. Under fixed illumination on white background males clasp blue stimuli, while on red and/or yellow background they clasp grey stimuli as well. These responses appear explicable if it is assumed that the surrounding background is the main sign of a spectral composition of illumination with "the simultaneous colour contrast" being a part of the constant colour perception mechanism (2).