The principles of psychology . e ? and call the fovea to the spot. Most parts of the skin dobut perform the same office for the finger-tips. Of coursefinger-tips and fovea leave some power of direct perceptionto marginal retina and skin respectively. But it is worthyof note that such perception is best developed on the skin ofthe most movable parts (the labors of Vierordt and hispupils have well shown this) ; and that in the blind, whoseskin is exceptionally discriminative, it seems to have becomeso through the inveterate habit which most of them possessof twitching and moving it under whateve
The principles of psychology . e ? and call the fovea to the spot. Most parts of the skin dobut perform the same office for the finger-tips. Of coursefinger-tips and fovea leave some power of direct perceptionto marginal retina and skin respectively. But it is worthyof note that such perception is best developed on the skin ofthe most movable parts (the labors of Vierordt and hispupils have well shown this) ; and that in the blind, whoseskin is exceptionally discriminative, it seems to have becomeso through the inveterate habit which most of them possessof twitching and moving it under whatever object maytouch them, so as to become better acquainted with the con-formation of the same. Czermak was the first to notice may be easily verified. Of course movement of surfaceunder object is {for purposes of stimulation) equivalent to move-ment of object over surface. In exploring the shapes and mation of both sorts of difference ; whereof the natural eifect must be toproduce the most perfect discrimination of Fig. 53. In the left-hand figure let the dark spot B move, for example, fromright to left. At the outset there is the simultaneous contrast of black andwhite in B and A. When the motion has occurred so that the right-handfigure is produced, the same contrast remains, the black and the whitehaving changed places. But in addition to it there is a double suc-cessive contrast, first in A, which, a moment ago white, has now becomeblack; and second in B, which, a moment ago black, has now becomewhite. If we make each single feeling of contrast = 1 (a supposition tartoo favorable to the state of rest), the sum of contrasts in the case of motionwill be 3, as against 1 in the state of rest. That is, our attention will becalled by a treble force to the dilierence of color, provided the color be-gin to move.—(Cf. also Fleischl, Physiologische Optische Notizen, 2teJVIittheilung, Wiener Sitzungsberichte, 1882.) 176 PSYCHOLOGY. sizes of tilings by either eye or skin
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectpsychology, bookyear1
