A first book in psychology / by Mary Whiton Calkins.

  • Mary Whiton Calkins
Date:
1910
Catalogue details

Licence: Public Domain Mark

Credit: A first book in psychology / by Mary Whiton Calkins. Source: Wellcome Collection.

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    the inner layers of the retina, and excite the rod and cone layer. The activity of rods and cones stimulates the optic nerve, and the optic nerve, in turn, transmits this excitation to the occipital lobes of the cerebral hemispheres. The retinal processes which condition the color and the colorless-light consciousness are very probably the following:12 (i) Colored light— for example, red light (that is, ether waves four hundred and fifty billion to the second, six hundred and ninety millionths of a millimeter long) — partially decomposes a chemical substance on the cones of the retina. There are four possible phases of the decomposition of this cone-sub¬ stance, and corresponding to them are the sensational ex¬ periences of red, of yellow, of green, and of blue.13 (2) A mixture of colored lights totally decomposes this same cone- substance, and the consciousness of colorless light follows. (3) The consciousness of colorless light due to a single color- stimulus is excited by the decomposition of a similar, but less complex, chemical substance found on the rods of the retina. Any light stimulus suffices to break up this substance, and it is decomposable not in separate stages but only all at once. The three cases, already named, in which colored light excites colorless-light consciousness are thus explained: (a) When, as in twilight, the colorless-light stimulus is very faint, it lacks the intensity necessary to excite the processes of the cone-substance, whereas the rod-substance is particularly sensitive to faint light.14 (b) When a colored light falls on the outlying, or peripheral, part of the retina, it excites only the rod-substance, since this part of the retina contains no cones. (c) In partial color-blindness the cones of the retina may be supposed to be only partly developed, and the cone-substance to be decomposable in only two of the normal four stages.
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