12. 



THE QUARTERLY REVIEW OF BIOLOGY 



hand has been adequately set and that 

 sufficient motivation has been brought to 

 bear upon its solution. 



We are not at all inclined to belittle 

 the dog's olfactory acuity and feel that 

 the bulk of the evidence shows it to be 

 far superior to our own. 



Auditory capacity 



Experimental evidence on hearing in ' 

 dogs appears to indicate that they are at 

 least as sensitive as man in this respect, 

 while their capacity for auditory discrim- 

 ination is less certainly known. 



Only one study of intensity discrimi- 

 nation has been made, that by Tihomirov, 

 a student of Pavlov. He used an organ 

 pipe with an arrangement for damping the 

 sound as desired. The results seem too 

 good to be true and are perhaps best 

 covered by quoting from Pavlov (35, 

 p. 135): "... it was found that an 

 intensity very closely approaching the 

 one employed as a positive conditioned 

 stimulus could be differentiated by the 

 dog with an absolute precision even when 

 a pause of 17 hours was made between the 

 two stimuli. The experimenter found 

 himself able to detect a difference between 

 these two intensities of the sound only 

 when they succeeded each other immedi- 

 ately. ... In the continuation of these 

 experiments the intensity of the inhibitory 

 tone was brought still nearer to the in- 

 tensity used for the positive conditioned 

 stimulus, and an absolute differentiation 

 was obtained even after a pause of three 

 hours between the stimuli. Unfortu- 

 nately these experiments were conducted 

 in our old laboratory where the effect of 

 the inhibitory stimulus was easily dis- 

 turbed, and it must be left to the future 

 to repeat these experiments under more 

 perfect conditions in our new laboratory. 



The bulk of the experiments on pitch 

 discrimination leave much to be desired in 



the way of technique. The experimenter 

 has usually been present, and pure tones 

 have seldom if ever been used. All in- 

 vestigators but Johnson have found some 

 degree of pitch discrimination. Johnson's 

 work was inspired by reports of some of 

 the earlier work done in Pavlov's labora- 

 tory (by Selionyi and by Beliakov) in 

 which it was claimed that dogs could 

 discriminate differences of one quarter and 

 even one eighth of a tone. Johnson 

 justly criticizes this work in the article 

 reporting his own results (zo). He used 

 the Yerkes-Watson discrimination appa- 

 ratus employing both punishment and 

 reward. The experimenter was elimi- 

 nated. The sounds were produced by 

 electrically driven tuning forks. To one 

 note the dog was required to turn to the 

 right to be rewarded, to the other he was 

 required to turn to the left. Although 

 the dogs were given a prolonged training 

 series there was no evidence that they 

 could learn to make the discrimination. 

 Pavlov set Anrep on the problem of re- 

 peating the earlier work of Selionyi, 

 which had not been accepted by American 

 investigators. Anrep (1) criticizes John- 

 son's work on two grounds. The first 

 criticism is methodological. It is his 

 opinion that the problem as set by John- 

 son is far too complicated. The animal 

 is rewarded for both sounds, although 

 at different places and, similarly, when it 

 makes a wrong choice it is punished while 

 both sounds are being given. We are 

 forced to agree that the Pavlov method 

 presents the animal with a far simpler 

 learning problem. The one note is con- 

 tinually reenforced by food, the other 

 note is never so reenforced . 



Anrep 's second criticism relates to the 

 production of the tones, it being his 

 claim that it is impossible to eliminate 

 entirely the noise of the "make and 

 break" when using electrically driven 



