The Duration of Habits 255 



ability either to acquire or to retain a habit of distinguishing 

 spectral colors. Altogether, I made a large number of white- 

 black and black-white memory tests after rest intervals of 

 four, six, eight, or ten weeks. The results for the four-week 

 interval show extreme individual differences in memory. Num- 

 ber 1000, for example, was able to choose correctly every time 

 in a series of white-black tests after a rest interval of four 

 weeks, whereas No. 5 was wrong as often as she was right 

 after the same interval. I have placed the results for these 

 two individuals at the head of the table because they suggest 

 the variations which render averages undesirable. Number 

 1000 had a perfect habit at the end of four weeks of disuse ; 

 No. 5 had no habit whatever. I shall reserve further discus- 

 sion of age, sex, and individual differences in the permanency 

 of habits for the next chapter. 



With Nos. 7 and 998 memory tests were made after three 

 different rest intervals. At the end of two weeks the black- 

 white habit was present in both individuals, although it was 

 not perfect. After six and four weeks, respectively (see 

 Table 48), it still persisted ; in fact, it apparently had im- 

 proved as the result of additional training after the earlier 

 memory tests. At the expiration of ten weeks it had wholly 

 disappeared. In her first series of memory tests after the 

 ten- week interval No. 7 made only one error, but a chance 

 choice of the black (right) in the first test and the subsequent 

 choice of the box in which no shock had been received serve 

 to account for results which at first appear to be indicative 

 of memory. That this explanation is correct is proved by 

 the fact that a second memory series, in which the first choice 

 happened to be wrong, resulted in six mistakes. Evidently 

 she had lost the habit. 



In no instance have memory tests definitely indicated the 

 presence of a habit after a rest interval of more than eight 



