Bauhaus-Universität Weimar

Titel:
Experimental Psychology: A Manual of Laboratory Practice, Vol. I: Qualitative Experiments, part 2: Instructor's Manual
Person:
Titchener, Edward B.
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit11938/71/
§ 13- Negative After-images 
37 
the window, shall declare the contrast-colour to be the richer, 
more saturated and more positive colour of the two. 
On discs for the demonstration of contrast, see Helmholtz, 
Phys. Optik, 544 f. ; Sanford, Course, 158; Aubert, Phys. Optik, 
497- 
Hering (Pflüger’s Arch., xli., 1887, 358) describes an instru¬ 
ment (Rothe, Mk. 28) for experiments upon mirror contrast 
(‘ Ragona Scinà’s experiment : ’ see D. R. Scinà, Atti dell’ Acad. 
Palermit., iii., 1859; Helmholtz, Phys. Optik, 557; Wundt, 
Phys. Psych., i., 424; Sanford, Course, 155 f.). Two other in¬ 
struments of Hering’s for the demonstration of simultaneous 
contrast are sold by Rothe at Mk. 50 and Mk. 30 respectively. 
EXPERIMENT IV 
§ 13. Visual After-images. (1) Negative.—This experiment 
follows Hering, whose Zur Lehre vom Lichtsinne should be read 
(or lectured upon) alongside of the laboratory work. The alter¬ 
native theory is that of Fechner: that the phenomena of negative 
after-images are explicable in terms of retinal fatigue (verminderte 
Reizempfänglichkeit). This hypothesis is adopted by Helmholtz, 
in the Physiol. Optik ; and the student should be told that 
Helmholtz asserts, in his 2d edition : “ I have so far been unable 
to discover any phenomenon that is distinctly irreconcilable with 
Fechner’s principles of explanation.” A strong statement, and 
a statement made after full survey of “ dieses äusserst verwirrte 
Gebiet der mannigfaltigsten Erscheinungen”! Nevertheless, 
the author has become convinced by repeated experiments that 
Hering’s account of simultaneous and successive contrast, and 
simultaneous and successive light-induction, is very much more 
adequate to the phenomena, taken as a whole, than is the treat¬ 
ment in the Physiol. Optik. James speaks truly, when he says 
of the book: “It seems to me that Helmholtz’s genius moves 
most securely when it keeps close to particular facts.” If, then, 
the student is to theorise his facts as he goes, if he is not merely 
to ‘ observe ’ the after-images and have done with them, the 
Instructor has, in the author’s judgment, no choice but to follow 
Hering.
        

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