Abstract: The purpose of this experiment is to clarify the question whether a dog can discriminate two simultaniously presented geometrical figures, as well as to explain the dog's physiological mechanisms of simultaneous differentiation according to the fundamental principles of Pavlov's theory. The experiment was carried out with two dogs on a conditioned motor running reflex. The stimuli consisted of two white figures on a black background, one being a rectangle and the other, a triangle of equal area. The results show that: (1) the dogs succeeded in discriminating the simultaneously presented stimuli of two geometrical figures, (2) in response to these paired stimuli, the dogs reacted not only to the absolute stimuli——the rectangle served as a positive signal for food, and triangle, merely as a negative signal, but also to their combined effect as a compound stimulus.

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