326 WALTER S. HUNTER 



tone 896 d.v. If we count the difference between that tone 

 and the present chord as sub-limnal, these 2 rats were given 

 1350 trials with no evidence of discrimination. 

 B. Evidence Bearing Upon Tone Sensitivity Which While Not 

 In Itself Crucial Is Yet Of The Greatest Significance: 



(1) Four rats trained to react to a whistle tone of 3906.17 

 d.v. would not react to a tuning fork chord (1152 d.v. plus 1280 

 d.v.), or to the fork 1280 d.v. when these were each substituted 

 for the standard stimulus. When a whistle of the same pitch 

 was sounded in an adjoining room so that distance probably 

 eliminated the noise factor, the rats failed; although they made 

 a significantly larger per cent of correct reactions when the 

 standard stimulus was decreased in intensity to match the in- 

 tensity of the distant whistle. 



Further these same rats reacted properly when either of the 

 following noises were substituted for the standard whistle; (a) 

 the rush of air through the whistle; (b) sound of "rush of air" 

 made with lips; and (c) clapping of hands. The rats reacted 

 successfully to 1280 d.v. on the standard whistle but failed when 

 the same pitch was sounded on a tuning fork. 



(2) Three rats trained to react to hand clapping reacted 

 successfully to the following noises when these were substituted: 

 rattling of paper, dropping sunflower seed on tin, scratching 

 on wood, drumming on the table with the fingers, rubbing two 

 pieces of board together, hissing through the teeth, and rattling 

 nails in a glass. These rats failed when the following tones were 

 sounded in place of the hand claps: (a) 1024 d.v. on fork; (b) 

 256 d.v. on organ pipe sounded steadily; (c) b sounded in toots; 

 (d) 1024 d.v. sounded steadily on organ pipe; (e) d sounded 

 in toots; and (f) 341.3 d.v. on the organ pipe sounded steadily. 



(3) Six untrained rats failed (after from 575-800 trials) to 

 discriminate a very intense from a very faint sounding of the 

 fork 256 d.v. 



(4) Rats trained to localize a tapping noise ignored: the 

 fork 256 d.v.; and the same pitch tooted upon an organ pipe. 

 They responded to a noise made by tapping with the rubber 

 end of a lead pencil upon the resonator box of the fork 256 d.v. 

 This gave an interrupted noise of the same predominant pitch 

 as the fork. 



