BRAIN MECHANISMS AND LEARNING 



one of them) called forth effects which could be recorded objectively. 

 Moreover, as shown in the course of the experiments, the new stimulus, a 

 puff of air in the animal's eye, applied in the given combination, proved 

 to be stronger than the stimulus (sound) applied in the previous combina- 

 tion. With this technique, it proved possible to demonstrate the elabora- 

 tion of direct and reverse connections in a more distinct, graphic and what 

 is particularly important, direct form. This was possible both when one 

 of the combined stimuli was applied first in stereotyped sequence, and 



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Fig. 2 

 A two-way connection resulting from the combination of a passive lifting of the leg with the 

 blowing of air into the eye. {a) A conditioned motor reflex arising when the combination is 

 applied in the stereotyped sequence — 'blowing of air into the eye — passive lifting of the leg'. 

 In response to the blowing of air into the eye [d) the dog blinks and lifts the leg which is 

 testified to by the disappearance of action potentials in the gastrocnemius muscle. The lifting 

 of the leg (p.p.) is again accompanied by blinking which testifies to a reverse connection; 

 (/)) A conditioned eyelid reflex arising when the combination is applied in the stereotype 

 sequence 'passive lifting of the leg — blowing of air into the eye'. In response to the passive 

 lifting of the leg (p.p) the dog blinks. After the blowing of air into the eye ((/) there is observed, 

 along with the blinking, a disappearance of action potentials in the gastrocnemius muscle, 

 which testihes to a reverse connection. 



I. — action potentials of the gastrocnemius muscle; i. — movement of the eyelids; 3. — 

 marks of stimulation (long line — passive lifting of the leg; short line — blowing of air into the 

 eye). 



when the other stimulus was applied first (Fig. 2). As a puff of air in the 

 animal's eye proved to be a stronger stimulus than sound, the direct 

 conditioned connections were much more stable than when sound was 

 combined with a passive lifting ot the animal's leg. To some extent this 

 also applies to reverse conditioned connections. 



II. New facts related to this problem were established by Lyan-Chi-an, 

 who continued the investigation of a very pressing problem which 

 Varga (1953) had previously studied in our laboratory. 



Using dogs, Varga combined in a strictly alternating sequence two 



