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.

    95/446 page 77
    ness of objects as near or far from my body, as in front or behind, to right or to left of me — is of great biological sig¬ nificance. An animal able to react promptly and accurately to the sight, sound, or touch which reveals the presence of dangerous foe, of friend, or of mate is evidently favored in the struggle for existence. It follows that the localizing reactions, and the consciousness of them, must have been advanced by the extinction of poor localizers and by the preservation and propagation of good ones. Visual localization is conditioned by muscular changes, chiefly of two kinds. When (within certain limits) an object is moved nearer or farther from the eyes, there is first a change in ‘ accommodation,’ 8 that is, in the contraction of the ciliary muscle, such that the crystalline lens of the eye either bulges farther forward or is more flattened, thus becoming more or less refractive as the object is nearer or farther; there is, second, a change in the convergence of the two eyes such that the angle of convergence is more or less acute according as the object is farther or nearer.9 As I look, for example, from the sail on the horizon to the rosebush at my window¬ sill, my eyes converge. Other conditions of the consciousness of visual distance are, first, the occurrence of differing retinal images,* and second, a number of so-called ‘signs’ of distance, notably: (i) the distribution of shadows, (2) the apparent interference of inter¬ vening objects, and (3) mistiness of the atmosphere. The significance of these factors may be shown in many ways. Thus, a mask, hollow side to the observer, if so placed that * Cf. p. 75, above; and note that changes in accommodation and con¬ vergence may condition consciousness of the depth-form as well as of the posi¬ tion of an object in space.
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