THE AUDITORY SENSITIVITY OF THE WHITE RAT 221 



method of " general response " has convinced me more strongly 

 merely that there is a fundamental difference for the rat in noise 

 and tone. 



(5) It will be recalled that only three rats of set I were 

 tested immediately upon sensitivity to tone vs. no-tone. The 

 other three rats were tested as follows: In place of hand claps, 

 the following noises were each substituted for five trials from 

 time to time: (a) rattling of paper; (b) dropping sunflower 

 seed on tin; (c) scratching on wood; (d) drumming on the 

 table with the fingers ; (e) rubbing two pieces of board together ; 

 (f) hissing through the teeth; and (g) rattling of nails in a glass. 

 Pitch, volume and quality varied greatly, but a rough attempt 

 was made to keep the intensity values equal to that of the 

 tone. (See above, page 216.) The rats responded to all of these 

 stimuli as accurately as to the regular stimulus of hand claps, 

 i.e., never below 80% correct. Rat No. 5 failed to react cor- 

 rectly to noises e and f, i.e., although repeatedly tested, he 

 never made more than from 55% to (at most) 70% correct. 

 This was the rat tested later with set II, on tone vs. no-tone, 

 with negative results. In view of those tests, his failure to re- 

 spond correctly to the two noises is to be explained on the basis 

 of their dissimilarity to the standard noise rather than upon 

 their likeness to c' 512, which tone this rat seems not to hear. 



Tests were also made in which each of the following tones 

 were substituted for the original c' on the fork on enough occa- 

 sions to be sure that the reactions were not due to chance: 

 (1) c'" 2048 on the fork; (2) c' 512 v. s. on the organ pipe, sounded 

 steadily; (3) No. 2, sounded interruptedly, i.e., in toots; (4) c" 

 1024 on the organ pipe, sounded steadily; (5) No. 4 sounded 

 interruptedly; and (6) f 341.3 on the organ pipe, sounded 

 steadily. With no exception, the rats reacted to these tonal 

 stimuli as to the original tone which had been sounded steadily, 

 i.e., they ignored them. There are many suggestions as to in- 

 terpretation which arise from these results. The points that 

 can be definitely stated are these: (1) All of the tones given 

 were for some reason very different from the noises. (2) This 

 difference was not the fact of smoothness, i.e., lack of inter- 

 ruptedness. This point seems conclusively proved, because on 

 the same day with the interrupted noises were given trials with 

 the interrupted tones, yet the rats paid no more attention to 



