EXPLANATION OF OBSERVATIONS 165 



ing out and bringing forth pieces of colored cloth there 

 is involved the perception of an object at rest, viz.: 

 the direction of the questioner who is standing quietly;^ 

 whereas in the case of responses by means of tapping the 

 stimulus is the horse's perception of the questioner's 

 movements. Now, the construction of the horse's eye, 

 as described above, is not favorable for the perception 

 of objects (so-called acuity of vision). This may partly 

 account for the slight success of the horse in those tests i 

 in which he was required to select a piece of cloth of a! 

 designated color, in so far as these commands were not ' 

 accompanied by calls or exhortations. Where human 

 observers averaged eighty per cent correct responses 

 (page 135), Hans, under similar conditions was suc- 

 cessful in only one-third of the tests'. In his errors he 

 was also wider of the mark than were the human obser- 

 vers (page 82). The object perceived, to be sure, is 

 a large one, viz. : the questioner, and he at close range. 

 We must therefore consider more specifically what are 

 the determining factors that make for success or failure 

 of the response. 1 First of all, the innocent questioner 

 very often did not designate thT'difection with sufficient 

 cleaiuess. Furthermore, ^Hans presumably was not 

 able to discriminate sufficiently between the direction of 

 the experimenter's eye and that of his head, which two 

 directions did not always coincide. "^ Finally the horse's 

 attention was often diverted, while he was running toward 

 the piece indicated, by the other pieces lying to the right 

 and to the left, and for this reason the addition of a single 

 piece to the otherwise unchanged row of five pieces 

 tended to decrease greatly the chances of success. 



The case is different with the perception of the direct- 

 ive signs for tapping, for nodding and shaking the head. 



