ATTENTION AS A CONDITION OF SEEING 67 



other factors in the process, which we call " seeing," besides 

 the duration of the retinal impression or excitation. These 

 are, first, attention, and second, judgment. We are apt to 

 think that "seeing" is a simple, straightforward sort of 

 thing, whereas it is really a strangely complex and delusive 

 process. " I did not see it, therefore it was not there," or 

 " You must have seen it ; it was right in front of you," are 

 common assertions, and the belief that such assertions 

 are justified leads to miscarriage of justice in courts of law. 

 Yet everyone knows that he may stare out of the window 

 of a railway carriage and have a long panorama pass before 

 his eyes, or may walk along a crowded street and look his 

 acquaintances in the face, and in neither case will he have 

 " seen " or recognised anything, or be able to give an 

 account of the scene that was pictured on the back of his 

 eye. Attention, the direction of the mind to the sensation, 

 is necessary ; and it appears that it is very difficult (to 

 some more than to others) to hold the attention alert, and 

 to give it to the unexpected. In fact, to a very large 

 extent we can only " see " (using the word to signify the 

 ultimate mental condition) that which we are prepared to 

 see or that which we expect to see. In the absence of 

 such expectation, a very strongly illuminated or well- 

 marked, outstanding object is far more readily " seen " 

 than less marked objects. Accordingly, the outstretched 

 legs of the galloping horse, now in front and now behind, 

 are " seen," whilst the rest of the phases are not observed. 

 Moreover, it is a fact that the swinging pendulum of a 

 clock is " seen " at the extreme position of the swing on 

 each side, and not in the intermediate sp ace. This is 

 because the image is formed very quickly, twice in the 

 space where the bob of the pendulum is coming to the 

 limit of its swing and is again returning on its course. 

 For the same reason, the outstretched legs of the horse 

 going up to their limit and at once returning give in very 



