212 PSYGHOLOOY. 



wafer or a black cross, the subject, although he denies that 

 he sees it wheu he h)oks strai<]fht at it, nevertheless gets a 

 ' negative after-image ' of it when he looks away again, 

 showing that the optical impression of it has been received. 

 Moreover reflection shows that such a subject must dis- 

 tinguish the object from others like it in order to be blind to 

 it. Make him blind to one person in the room, set all 

 the persons in a row, and tell him to count them. He will 

 count all but that one. But how can he tell tuhich one not 

 to count without recognizing who he is ? In like manner, 

 make a stroke on paper or blackboard, and tell him it is 

 not there, and he will see nothing but the clean paper or 

 board. Next (he not looking) surround the original stroke 

 with other strokes exactly like it, and ask him what he 

 sees. He will point out one by one all the new strokes, and 

 omit the original one every time, no matter how numerous 

 the new strokes ma}- be, or in what order they are 

 arranged. Similarly, if the original single stroke to which 

 he is blind be doubled by a prism of some sixteen degrees 

 placed before one of his ejes (both being kept open), he 

 will say that he now sees one stroke, and point in the direc- 

 tion in which the image seen through the 23rism lies, ignor- 

 ing still the original stroke. 



Obviously, then, he is not blind to the kind of stroke in 

 the least. He is blind only to one individual stroke of that 

 kind in a particular position on the board or paper — that 

 is to a particular complex object ; and, paradoxical as it 

 may seem to say so, he must distinguish it with great ac- 

 curacy from others like it, in order to remain blind to it 

 wheu the others are brought near. ITe discriminates it, as 

 a preliminary to not seeing it at all. 



Again, Avhen by a prism before one eye a previously in- 

 \dsible line has been made visible to that eye, and the other 

 eye is thereupon closed or screened, its closure makes no 

 ditfeience; the line still remains visible. But if then the 

 prism be removed, the line Avill disappear even to the eye 

 which a moment ago saw it, and both eyes will revert to 

 their original blind state. 



We have, then, to deal in these cases neither with a blind- 

 ness of the eye itself, nor with a mere failure to notice, but 



