138 POPULAR SCIENCE MONTHLY 



render for the soul the clue, by following which it transposes the same red, 

 now to one, now to another spot, or simultaneously to different spots in the 

 space intuited by it. 



In order, however, that this may take place in a methodical way, these 

 accessory impressions must be completely different from the main impressions, 

 the colors, and must not disturb the latter. They must be, however, not merely 

 of the same kind among themselves, but wholly definite members of a series 

 or system of series ; so that for every impression " r " there may be assigned, 

 by the aid of this adjoined " local sign," not merely a particular, but a quite 

 definite spot among all the rest of the impressions. The foregoing is the 

 theory of " Local Signs." * 



The best anatomical and physiological researches fail tu reveal 

 spatial order as inherent in sensation; and, even if this ignorance be 

 due to the impossibility of following up the evolutionary regress, it is 

 a real difficulty. Lotze therefore concluded that " localization in 

 space belongs to the unconscious product of the soul's action through 

 the mechanism of its internal states." 8 We gain a field of vision from 

 an ensemble of local signs, and, as concerns tactile sense, the same 

 thing happens, the functions of the corpuscles of touch being like 

 those of the cones and rods of the retina in sight. As a result, our 

 notion of the extended originates in a perception of qualitative differ- 

 ences, from which the mind, by its own power of transformation, con- 

 structs extensive relations. Later researches into the structure of the 

 peripheral nerve terminations seem to confirm, rather than undermine, 

 the hypothesis. That it is a typical example of the limitations of 

 hypothesis Lotze acknowledged quite frankly. But he claimed, with 

 justice, that it explained the actual phenomena better than any other 

 theory. As a consequence, even if modified, it has been incorporated 

 in physiological psychology, and, especially as regards vision and touch, 

 must be reckoned with still. 9 To sum up — the point is this: Lotze 

 held that every sensation, say, of color, was accompanied by an " acces- 

 sory impression " of locality. The facts made it necessary to assume 

 this " accessory impression." Now, just because it happens to be an 

 assumption, it lies open to several interpretations. In other words, 

 the principle of the hypothesis may stand, but opinions as to the way 

 in which it may be read can differ widely. However this may be, more 

 than any other psychologist, he has laid bare the numerous pitfalls sur- 

 rounding the explanation of a psychological fact so obvious and com- 

 mon as space perception. 



Nascent sciences present a certain family likeness in their life 



7 "Grundziige d. Psychologie " (1881); Eng. trans, (from ed. of 1884), 

 pp. 51 ff. 



8 " Med. Psych.," Bk. II., Sect. 294. 



9 Cf . " Elements of Physiological Psychology," Ladd, pp. 396 ff . ; " Prin- 

 ciples of Psychology," James, Vol. II., pp. 157 f. ; "German Psychology of 

 To-day," Ribot, p. 95 (Eng. trans.). 



