228 The Animal Mind 



"Food," which was taken as indicating that he really was 

 paying attention to the look of the words (444). Such 

 observations, however, are very inconclusive when com- 

 pared with modern experimental studies where all the 

 sources of error, from smell, for example, are carefully 

 controlled. In Johnson's (386) study of the visual acuity of 

 the dog, while two chickens and a monkey learned to dis- 

 tinguish a striped from a plain field in from three hundred 

 to four hundred trials, dogs failed to learn in over a thousand 

 trials, although the stripes were made nearly six times as 

 wide. The dog could not distinguish between two visual 

 fields unless they differed in intensity. Thus his visual 

 images would seem to be far from clear. The eye of the 

 dog, it may be noted, does not possess a fovea. Johnson 

 thinks the dog's vision is useful chiefly for the perception 

 of moving objects. Szymansld (702) finds that when 

 dogs and cats have been trained to go to a box in a certain 

 corner to get food, and the box is moved, the dogs show 

 their lack of dependence on vision by displaying little 

 tendency, as compared with the cats, to use this sense in find- 

 ing the new situation of the box. Orbeli, however, obtained 

 evidence by Pawlow's method that dogs could appreciate 

 form and size differences (532 a). 



The dancing mouse could not learn to distinguish two 

 equal illuminated areas of different forms (820). Rac- 

 coons learned to discriminate a round card from a square 

 one (134). Thorndike taught the two Cebus monkeys 

 under his observation to come down to the bottom of the 

 cage for food when a card bearing the word "Yes" printed 

 on it was exposed, and to stay up when one bearing the 

 letter "N" was shown. The conditions seem to have 

 been complicated, however, by the fact that the two cards 

 were not placed in quite the same position. Further 



