Modification by Experience 257 



reach full expansion after having contracted at a touch, will 

 respond to the second touch just as it did to the first ; the 

 stimuli, to exert any influence on later reactions, must come 

 in quick succession. On the other hand, in the responses oi 

 moUusks to shadows, the experiences of one day appear to ] 

 extend their effects to the followiijg day (520, 588, 590). 

 Here we are dealing with a new type of modification by 

 experience, though one which develops directly out of sen- 

 sory adaptation ; namely, the relatively permanent dropping] 

 off of useless movements. 



§ 73. Modifications Due to Relatively Permanent Effects 



of Stimuli 



In true learning, the conscious experience and the be4 

 havior of an animal suffer changes so lasting, relativem 

 speaking, that they cannot be set down as due merely to j 

 adaptation of the sense organ, muscular fatigue, hunger, I 

 satiety, or any other variable physiological state of the/ 

 organism. On the other hand, as we saw in Chapter II\ 

 the modifications must occur rapidly enough so that there] 

 is not time for actual changes in the animal's muscular 

 structure to be produced. In animals which possess nerv-» 

 ous systems, true learning is probably always the result\ 

 of alterations in the coimections between the elements of j 

 that system, such that the nervous process is able to pass/ 

 ea^ly in a direction where it originally encountered high' 

 resistances. 



The fundamental law of all learning is the Law of Repeti- \ 

 lion, whereby when a nervous process traverses a certain 1 

 pathway in the nervous system, it leaves the resistances in ' 

 that pathway less than it found them. This is the law 

 in accordance with which, when we wish to learn anything, 



