[Estimation by toads of the distance to the moving objects and their true size: neuroethological and comparative aspects].

In two sets of experiments, studies have been made on the parameters by which the toad Bufo bufo estimates the neighbour and remote moving objects. In absence of the structural surrounding, a dark target with a diameter 17.2 degrees (3 cm at a distance of 10 cm) and with the rate of movement 36, 72 and 145 degrees/sec evoked in toads only feeding turns; at the rates 72 and 145 degrees/sec, together with these turns, animals usually fired with their tongues to the direction of the target, revealing evident underestimation of the distance and real size of the object. Under the same experimental conditions, a target with a diameter 1.2 degrees (0.25 cm at a distance of 12 cm) and the rate of movement 0.6 and 3 degrees/sec produced mainly frightful reaction, which indicates overestimation of the distance to the object and its size. The same object moving at a structural background evoked only feeding reactions, i.e. the animals correctly estimated the distance to the target and its size.