44 JOSEPH PETERSON 



not here enter into further consideration of this complex behavior, 

 except to point out that when the various stimulus-response 

 mechanisms have become sufficiently well associated with 

 certain muscular strains or neural excitations, the revival of the 

 latter by favorable stimuli will call out the acts themselves. 

 Thus a stimulus may have entirely ceased to play upon the 

 sense organs from without and long periods of time may have 

 elapsed, and yet, because of this acquired organization, the 

 recurrence of any significant aspect of the outer situation, even 

 such as a sound associated with it, may revive the crucial exci- 

 tation and thus call out the act. Something of this kind — 

 stimulated, however, by the original situation minus the light 

 when the animal is allowed to respond — likely takes place in 

 the delayed reactions of animals, though this assumption leaves 

 entirely open the question as to whether or not the animals 

 have ideas, a rather infertile question for science, it must be 

 confessed. More elaborate systems of acquired associations 

 make possible the continual thinking of absent situations which 

 we know that we ourselves experience. In these more advanced 

 forms of behavior groups of response systems may come so to 

 interact upon one another by associations and by stimulation 

 from the inward bodily conditions that rehearsal of a problem 

 mentally may take place long after actual practice has ceased, 

 thus changing behavior materially between practices. It is 

 yet_ questionable whether there are any such cases in animal 

 behavior. 22 



In the foregoing pages we have called into question the prin- 

 ciples of frequency, recency, and intensity of stimulation as 

 usually understood in relation to the fixing of associations, so 

 far as their value in explaining learning is concerned. They do 

 not seem to account for the change in successive trials called 

 learning. This seems to be true at any rate for maze learning; 

 probably it holds for all kinds of learning. All that these fac- 

 tors do is, likely, to make more and more easy any associations 

 and acts brought about by the real directing factors. That 

 is, they tend to fix any series of acts in the order that they are 

 gone through, not to change the order of the acts. Some other 

 directing f actors and some vis a tergo must be found to account 



22 Cf. Yerkes, R. M. The Mental Life of Monkeys and Apes: A Study of Idea- 

 tional Behavior. Behav. Mon., 1916, 3, No. 1. Yerkes thinks Julius, an orang- 

 utan, solved a problem ideationally; see particularly pp. 68 and 131. 



