E. A. ASRATYAN IO5 



recorded with a sensitive mechanographic device, and in some experi- 

 ments also by electromyography. His data show that when a combination 

 of a sound of moderate intensity with an electrical stimulation of the 

 animal's legs is used, a motor conditioned reflex is not elaborated if both 

 stimuli begin and cease to act strictly simultaneously within a period of 

 I to 5 seconds. According to Pakovich's fmdings, hundreds of combina- 

 tions of these stimuli do not lead to the formation of the conditioned 

 reflex even when sound precedes the electric current within a limit of 

 about 100 msec, and when they cease to act simultaneously. The picture 

 does not change if the intensity of the stimulating current is considerably 

 increased. A conditioned reflex becomes elaborated only when the 

 interval between the onset of the sound and that of the electrical stimula- 

 tion of the skin exceeds this time-limit. This is illustrated in Fig. 6. Other 

 data obtained by Pakovich show that the time fictor expressed in such 

 micro-values makes itself felt also at a certain distance from the above- 

 mentioned peculiar demarcation line. Pakovich established in particular 

 that the latent period of the newly formed conditioned reflex, as well as 

 its strength, duration, stability and other properties, depends to a con- 

 siderable degree on the interval between the onset of action of the two 

 stimuli, the indifferent and the unconditioned. 



Pakovich established another very interesting fact: a firmly established 

 and regularly evoked clcctro-detensive motor reflex disappears in the dog 

 if the conditioned stimulus is applied synchronously with the uncondi- 

 tioned one in the course of a series of experiments. The same occurs also 

 when the interval between onset of the conditioned and of the un- 

 conditioned stimulus is reduced to less than lOO msec. The conditioned 

 reflex reappears only when these conditions of combined action of both 

 stimuli arc changed and when the interval between the onset of the two 

 stimuli again exceeds lOO msec. The restoration of the conditioned reflex 

 proceeds more rapidly and is more complete when this interval is some- 

 what higher than its threshold value. 



Recently, Pakovich carried out an experimental analysis of the dis- 

 appearance of the established conditioned reflex when conditioned and 

 unconditioned stimuli were applied synchronously. 



He found that this phenomenon is due to the sporadic application in the 

 course of his experiment of the conditioned stimulus alone for the purpose 

 of testing its conditioned effect. It seems, therefore, that simultaneous 

 application of the conditioned and unconditioned stimuli leads to such a 

 weakening of the conditioned reflex that it disappears even after a few 

 extinction trials. 



