THE QUARTERLY REVIEW OF BIOLOGY 



mental, as well as the physical side. He 

 merely insists more emphatically than 

 formerly that evidences of this character 

 must run the usual gauntlet of scientific 

 criticism; that claims of this sort must 

 first be established by the most painstak- 

 ing and defensible scientific methodology. 

 Much of what the average man 

 "knows" about his own dog, and about 

 dogs in general is, of course, quite un- 

 known to the animal psychologist. For 

 no animal has a richer heritage of lore, 

 sentimental and lofty, representing an 

 accumulation of the long ages since primi- 

 tive man first made the dog his hunting 

 companion and his domestic ally. It is 

 difficult for any of us to escape entirely 

 this traditional influence; most difficult 

 indeed to observe with clarity of purpose 

 and uncompromising logic the behavior 

 of a dog, or other pet, to which we have 

 formed an attachment. Only a few dec- 

 ades ago, and even in certain circles now, 

 the method of anecdote with its unfailing 

 tendency toward anthropomorphic in- 

 terpretation stood in high favor, and 

 passed itself off under the guise of science. 

 Selecting cases to bolster up a theory may 

 be an interesting diversion but it is hardly 

 worthy of the trained mind in any field. 

 We have deliberately eliminated from the 

 following discussion all anecdote and 

 have meant to include only such observa- 

 tional and experimental results as ap- 

 peared to us to be worthy of the attention 

 of the serious scientist. 



I. SENSORY CAPACITIES AND INTELLIGENCE 



Visual capacity 



Consideration of the experimental lit- 

 erature on the visual capacity of dogs 

 indicates that the average dog has far 

 more faulty vision than most dog-lovers 

 suppose. Behavior evidence for this con- 

 clusion is supported by anatomical study 



of the eye. Slonaker (43) reports that 

 the dog possesses no fovea and that even 

 the so-called "sensitive areas" are only 

 vaguely defined. Numerous opaque nerve 

 fibres are said to penetrate the retina, and 

 these must be considered as blind spots. 

 The pupillary opening is always relatively 

 large and the pupillary response, while 

 rather quick, is not strong. Johnson (zi) 

 and others have demonstrated convergence. 

 The method ordinarily used in testing 

 the dog's eyesight has been called the 

 discrimination method, and in most cases 

 involves the use of the original ' 'discrimi- 

 nation box" designed by Yerkes and 

 Watson (58), or some modification of this. 

 The dog being tested is faced with a choice 

 of two alleyways, the one leading to a 

 compartment in which he will find food, 

 the other to a compartment where he is 

 usually given a light electric shock. 

 Whether or not the dog makes a fortunate 

 choice he is faced with this situation again 

 and again. Sometimes the reward is to 

 the right and the punishment to the left, 

 sometimes just the reverse. The only 

 way the animal can be sure of making a 

 correct choice is by attending to signals 

 or cues (stimulus patches) which are 

 presented at the entrance of the alleyways. 

 In testing for brightness discrimination, 

 for example, a very bright light may be 

 placed always at the entrance of which- 

 ever alley in that trial leads to the food, a 

 less bright light at the other alley entrance. 

 Many precautions must be taken to insure 

 the fact that there are no other stimuli 

 than the signals being studied which 

 might give the animal a clue as to which 

 alley to enter. Use of his nose to detect 

 the side of the box at which he will re- 

 ceive food will not help the dog for there 

 is food in both compartments, though 

 in the punishment compartment it is 

 screened off so as to be inaccessible. The 

 experimenter must be entirely eliminated 



