SENSORY CAPACITIES AND INTELLIGENCE OF DOGS 



the use of vision as by their normal 

 companions and, furthermore, that normal 

 dogs worked in the dark almost as effi- 

 ciently as in the daylight. Hamilton (13), 

 Buytendijk and Hage (5), and others have 

 attempted to facilitate the solution of 

 problems by introducing prominent visual 

 cues, which one would expect to be of 

 real aid to the dogs, with but little or no 

 effect. 



Although there is little experimental 

 evidence on the subject of moving versus 

 still objects as visual stimuli, such as there 

 is agrees with casual observations of a 

 number of investigators to the effect that 

 the dog is extremely sensitive to objects 

 in motion. A preliminary study of the 

 subject has been made in the laboratory 

 of Pavlov, but no limits of discrimination 

 have been determined. 



Interesting indication of the great 

 sensitivity of the dog to slight movements 

 is to be found in the several examples of 

 the Clever Hans error — an error which is 

 as likely to occur in the study of dogs as 

 in the case of the famous horse after which 

 it was named. It seems probable that the 

 cues imperceptible to us which the animal 

 gets from the experimenter are chiefly 

 visual, although audition may be involved 

 here also. In the early experiments on 

 auditory discrimination made by Kalischer 

 (15), Rothmann (37), Swift (47 and 48), 

 and others it seems very probable that the 

 dogs obtained secondary cues from the 

 experimenter, who was always present. 

 Swift, for example, seems to give his case 

 away in the following statement (48): 

 ' 'I found at first he (the dog) was inclined 

 to react to motion rather than sound, and 

 watched me closely for the motion accom- 

 panying the low tone, and would react to 

 that." According to the conditions of 

 the experiment the dog was allowed to 

 take food from the experimenter's hand 

 when this low tone was sounded. In 



spite of the above-quoted statement that 

 the dog appeared at first to react to slight 

 movements of the experimenter no effort 

 seems to have been made to eliminate the 

 experimenter in this case, and the writer 

 goes on to assume the problem to have 

 been learned on the basis of auditory cues. 

 Johnson, studying the same problem (2.6), 

 apparently had evidence for pitch dis- 

 crimination in the earlier part of his work, 

 during which the experimenter was pres- 

 ent, but when the conditions were so 

 modified that the experimenter was en- 

 tirely concealed the discrimination could 

 not be made. This indicates rather con- 

 clusively that the dog had been reacting 

 not to sounds, but to slight movements 

 made by the experimenter. 



Olfactory capacity 



The dog is popularly accredited with 

 the possession of a remarkably efficient 

 nose. It is through his superiority to 

 man with respect to olfactory acuity that 

 he has most frequently been of practical 

 service to his master. He has been used 

 to trail and retrieve game, to find lost 

 articles and people, to detect fleeing and 

 hiding fugitives from justice. Very little 

 strictly laboratory work on the subject 

 has been reported. None such has ap- 

 peared from laboratories in this country. 

 No doubt the chief reason for the paucity 

 of work on olfaction, not only in dogs but 

 in almost all animal forms, lies in the rec- 

 ognition by investigators of the great 

 difficulty of controlling the stimuli in 

 question . 



An instance of the dog's olfactory acuity 

 and, incidentally, an illustration of the 

 difficulty of animal experimentation, is 

 to be found in an early study of Johnson's 

 (zz). This careful investigator, while 

 studying visual acuity in an English bull 

 terrier, obtained such a fine degree of 

 visual discrimination as to render him 



