340 



WALTER S. HUNTER 



The attempt was made to compel the rats to associate turning 

 to the right through the box with the tone produced by striking 

 the fork. In the six older rats, turning to the left was to be 

 associated with a noise produced by striking the fork with the 

 hammer while holding the prongs of the fork between the thumb 

 and finger. In this case the fork was struck at the same tempo 

 as when a tone was produced. Noises of two slightly different 

 kinds were present, although at one time the tone was absent and 

 at another it was absent. In the two younger rats (rats 7 and 8), 

 turning to the left was to be associated with silence. 



FIG. 1. T-SHAPED DISCRIMINATION Box 



0, the box containing the light; F, food bowl; S, alley stop; X, point above 

 which tuning forks and whistles were clamped. The dotted area indicates the 

 position of the sandpaper in certain tests. 



Table 1 gives the percentage of correct responses made by 

 each rat for each successive fifty trials of the learning period. 

 It will be seen from an examination of this table that rat 3 was 

 the only one who made significant progress toward the establish- 

 ment of the required habit. This rat made better than 70 per 

 cent of correct reactions for the last three groups of fifty trials. 

 It was therefore given certain control tests in order to determine 

 the nature of the cue guiding its response. 



It did not prove practical to eliminate noise by using electri- 

 cally driven forks because of the fork's small amplitude of vibra- 



