Yerkes, Modifiahility of Behavior. 



251 



As it happens tlie averages for the age groups are precisely the same 

 for both the males and the females. This is a surprising result 

 which we could not expect to obtain by the repetition of so small 

 a number of tests. (3) Individual differences in sensitiveness are 

 much more marked, and in all likelihood more important, than either 

 sex or possible age differences. 



As there is no reason to suppose, in the light of these rough 

 determinations, that i)ossible changes in sensitiveness which ac- 

 company ageing account for any of the results of the jjlasticity 

 experiments, we may ask whether it is at all likely that the sex 



TABLE 8. 

 Measurements of Sensitiveness to Electbicax STiMxn:.us. 



Sex Differences. 



Position of secondary coil, First 



Day 



Position, Second Day 



Average Position 



F-!rtrpmp<j I Least sensitive 



H^xtremes | ^j^^^ sensitive 



Males (averages for 20). 



17.88+ cm. 



17.72— 



17.80* 



15.75 



19.25 



Females (averages for 20). 



17.41 cm. 



17.25 



17.33 



16.67 



18.00 



Age Differences. 



Not over 

 four months. 



Number of dancers tested 13 



Average age 2.5 mos. 



Position of secondary coil. First 



Day 17.73 cm 



Position, Second Day ' 17 .87 



Average Position I 17.80 



Over 

 four months. 



7 

 8.3 mos. 



18.17 cm. 



17.44 



17.80 



Not over 

 four months. 



12 

 2.4 mos. 



17.35 cm. 



17.30 



17.33 



Over 

 four months. 



8 mos. 



17.50 cm. 



17.17 



17.33 



* Difference in favor of males .47 cm., or about 10% of the value of the current. 



and individual differences in sensitiveness furnish the basis for 

 such differences in rapidity of habit-formation as the tables in- 

 dicate. 



Before this question can be answered satisfactorily, we must know 

 what relation strength of electric stimulus bears to rapidity of 

 learning. Does increase in the strengih of the stimulus from the 

 threshold value — or, what for our present purposes amounts to the 

 same thing, increase in sensitiveness — facilitate or retard the process 



