E. A. ASRATYAN 97 



above-mentioned properties — fragility and instability — are characteristic 

 for both conditioned connections between the brain points of two stimuli, 

 they are not inherent in these reflexes in an equal measure. When sound 

 and passive lifting of the animal's leg are combmed in a variable sequence, 

 the conditioned connections arising between them are almost equivalent 

 in their rate of formation, consolidation, stability, resistance to extinction, 

 etc. But when these stimuli are combined in a stereotyped sequence, the 

 resulting conditioned connections essentially difi^er from each other in all 

 of the above-mentioned criteria. A direct or forward conditioned connec- 

 tion, i.e. a connection leading from the preceding stimulus (P) to the 



/ iii»i w >h>i ) iiit " 'i ^.i^ M >^^ *>iiit->41ii4»>iHi 



Z ZZZ^ZZI 



I 



Fig. I 

 Conditioned connections resulting from various combinations of a sound and a passive lilting 

 of the dog's leg. (a) Active lifting of the leg (indicated by the rarefiction or disappearance of 

 electrical potentials in the extensor of the leg, i.e. in the gastrocnemius muscle) in response to 

 the application of a tone after its thirty-seven combinations with a passive lifting of the leg in 

 the stereotyped sequence: 'tone — passive lifting of the leg' ; (fo) reaction to a tone after twenty- 

 eight combinations of a passive lifting of the leg with this tone in experiments with a reverse 

 sequence, i.e. 'passive lifting of the leg — tone'. 



I. — clectromyogram of the gastrocnemius muscle; 2. — mark of conditioned stimulation. 



subsequent one (S) becomes elaborateci more easily and is more powerful 

 and resistant to extinction and other altering factors, than a reverse or 

 backward conditioned ct^nnection, i.e. a connection leading from S to P. 

 Further, a direct connection recovers more rapidly than a reverse one 

 after an acute extinction or when, following their natural disappearance, 

 a break is made in the experiment, or when one of the combined stimuli 

 turns into an alimentary conditioned signal. Essentially similar results 

 were obtained by Varga and Pressman in a series of experiments on other 

 dogs in which they combined passive lifting of the animal's leg with the 

 blowing of air into the animal's eye which evoked the blink reflex. The 

 advantage of the combination of these two stimuli over those applied in 

 the previously described experiments was that both stimuli (and not only 



