Differences in Behavior 265 



Individual differences in sensitiveness to visual, auditory, 

 tactual, and olfactory stimuli have been revealed by many 

 of my experiments. The brightness discrimination tests 

 conclusively proved that a degree of difference in illumination 

 which is easily detectable by one dancer may be beyond the 

 discriminating sensitiveness of another. Both the tests with 

 gray papers and those with the Weber's law apparatus fur- 

 nished striking evidence of individual differences in the kind 

 of visual sensitiveness which throughout this book has been 

 called brightness vision. I suspect that certain of the differ- 

 ences which were observed should be referred to the experi- 

 ence of the individuals rather than to the capacity of the visual 

 organs, for training improves visual discrimination to a much 

 greater extent than would ordinarily be thought possible. To 

 the truth of this .statement the results of the Weber's law 

 experiments with No. 51 bear witness. Likewise in color 

 discrimination there are individual differences, examples of 

 which may be discovered by the examination of the results 

 given in Chapters IX and X. 



No differences in auditory sensitiveness appeared in my 

 adult dancers, for in none of them was there definite response 

 to sounds, but among the young individuals differences were 

 prominent. I may call attention to the data on this subject 

 which Table 5, p. 89, contains. The mice in four out of 

 twelve litters gave no indications of hearing any sounds that 

 I was able to produce ; the remaining individuals responded 

 with varying degrees of sensitiveness. I made no attempt 

 to measure this sensitiveness, but it obviously differed from 

 mouse to mouse. I feel justified, therefore, hi stating that 

 the young dancers exhibit extreme individual difference in 

 sensitiveness to sounds. 



My observations of differences in sensitiveness to other 

 forms of stimulation were made in connection with training 



