42 



BRAIN MECHANISMS AND LEARNING 



that there is some structural modification, in the sense defined above (in 

 addition to ■whatever activity trace there may be). 



Fig. I 



/5 



I? 



II 



Zf 



Number of subjects (out of forty) successfully repeating nine digits on each of twenty-four 

 trials, when every third set of digits is the same ('repeated series') ; non-correction method. 



The results show clearly that cumulative learning occurs. Fig. i illustrates 

 the data for one procedure. Here the subject's errors are not corrected, and 

 the record is made in terms of the number of trials in wliich the nine digits 



3.5 



-I — I — I — I- 



IZ 



Fig. 2 



/5 



z/ 



Z¥ 



Mean number of digits correctly repeated on each of twenty-four trials, by twenty-five sub- 

 jects, when every third set of digits is the same ('repeated series'); correction method. 



are repeated without error. Fig. 2 shows the similar result that is obtained 

 when the subject is stopped as soon as he gives one digit out of the proper 



