262 PSYCHOLOGY. 



latter being quite overlooked and, as it were, eliminated from perception. 

 It may even come to pass that instead of these parts eliminated by elec- 

 tion a feeling of entirely different elements comes to consciousness — 

 elements not objectively contained in the stimulus. A group of sensa- 

 tions, namely, for which a strong tendency to reproduction has become, 

 by frequent repetition, ingrained in the nervous system will easily revive 

 as a whole when, not its whole retinal image, but only an essential part 

 thereof, returns. In this case we get some sensations to which no ade- 

 quate stimulus exists in the retinal image, and which owe their being 

 solely to the reproductive power of the nervous apparatus. This is 

 complementary (ergdnzende) reproduction. 



"Thus a few points and disconnected strokes are sufficient to make 

 ns see a human face, and without specially directed attention we fail to 

 note that we see much that really is not drawn on the paper. Attention 

 will show that the outlines were deficient in spots where we thought 

 them complete. . . . The portions of the percept supplied by comple- 

 mentary reproduction depend, however, just as much as its other por- 

 tions, on the reaction of the nervous apparatus upon the retinal image, 

 indirect though this reaction may, in the case of the supplied portions, 

 be. And so long as they are present, we have a perfect right to call 

 them sensations, for they differ in no wise from such sensations as cor- 

 respond to an actual stimulus in the retina. Often, however, they are 

 not persistent ; many of them may be expelled by more close observa- 

 tion, but this is not proved to be the case with all. ... In vision with 

 one eye . . . the distribution of parts within tbe third dimension is 

 essentially the work of this complementary reproduction, i.e. of former 

 experience. . . . AVhen a certain way of localizing a particular group 

 of sensations has become with us a second nature, our better knowl- 

 edge, our judgment, our logic, are of no avail. . . . Things actually 

 diverse may give similar or almost identical retinal images; e.g., an 

 object extended in three dimensions, and its flat perspective picture. 

 In such cases it often depends on small accidents, and especially on our 

 will, whether the one or the other group of sensations shall be excited. 

 . . . We can see a relief hollow, as a mould, or tyice versa; for a relief 

 illuminated from the left can look just like its mould illuminated from 

 the right. Reflecting upon this, one may infer from the direction of 

 the shadows that one has a relief before one, and the idea of the relief 

 will guide the nerve-processes into the right path, so that t\iQ feeling of 

 the relief is suddenly aroused. . . . Whenever the retinal image is of 

 such a nature that two diveVse modes of reaction on the part of the 

 nervous apparatus are, so to speak, equally, or nearly equally, immi- 

 nent, it must depend on small accidents whether the one or the other 

 reaction is realized. In these cases our previous knowledge often has a 

 decisive effect, and helps the correct perception to victory. The bare 

 idea of the right object is itself a feeble reproduction which with the 

 help of the proper retinal picture develops into clear and lively sensa- 

 tion. But if there be not already in the nervous apparatus a disposi- 



