380 JOHN LINCK ULRICH 



establish neural arcs, sensory excitations appear again to be 

 primarily of importance, not the responses themselves; for exci- 

 tations in the external senses originally select or establish paths, 

 or reflex arcs, through definite regions of the nervous system. 

 Accordingly, all such theories are fundamentally based upon the 

 establishment of " sensory associations," or " sensory-motor con- 

 nections," and the repetition or recurrence of familiar successful 

 stimuli are just as important as the repetition of the successful 

 act or movements. Learning, then, is a question of obtaining 

 successful stimuli, or of obtaining successful excitations, so that 

 the successful movement can take place, and the unsuccessful 

 stimuli, or unsuccessful excitations, may not produce unsuccess- 

 ful movements. Thus, in the organism there must in all cases 

 be established exact " sensory associations." 



On the principle of the repetition of some definite movement 

 have resulted theories of the kind generally outlined above. 

 These theories have developed along the same line of reasoning, 

 and start with the assumption of the existence of an antithetical 

 division of movements. These theories are of interest because of 

 their relation to traditional psychology. 



The explanations of learning offered by Carr (1) supplemented 

 by Watson (2) show a transformation of the original working 

 concept of " trial and error" and " pleasure-pain" with the tra- 

 ditional division of all movements into successful and unsuccess- 

 ful with which this concept is inseparably bound. Both these 

 investigators disregard the " pleasure-pain" concept and start 

 then- theories with the usual acceptance of an antithetical divi- 

 sion of all movements into successful and unsuccessful. The con- 

 cept of "trial and error" still remains in its very foundation, for 

 the "successful" movement is selected or produced when a great 

 many movements are made. 



According to Carr it is the recency, the frequency, and the sen- 

 sory intensity of the final or the "successful" act or movements 

 that "stamps in" or fixates these movements. The exact nature 

 of these movements is left to conjecture. What is evidently 

 produced by the recency and the frequency of the final act is an 

 increase in sensory intensity or sensory excitations. The "sue- 



