12. Besides our ideas of the position and movements of the various parts of our body, we have also an idea of the position and movement of our whole body. The former can never have anything but a relative significance; it is only when considered in connection with the latter that they become absolute. The organ of orientation for this general idea is the head. We always have a definite idea of the position of the head; the other organs are localized in our ideas, generally, indeed, very indefinitely, with reference to it, according to the particular complexes of inner and outer tactual sensations in each case. The specific organ of orientation in the head is the system of semicircular canals, to which are added as secondary aids the inner and outer tactual sensations resulting from the action of the muscles of the head. The function of these canals as an organ of orientation can be most easily understood by assuming that [p. 114] inner tactual sensations with especially marked differences in local signs, arise in them through the influence of the changing pressure of the fluid medium, which fills them. It is highly probable that dizziness, which comes from rapid rotation of the head, is due to the sensations caused by the violent movements of this fluid. This is in accord with the observations that partial derangements of the canals bring about constant illusions in localization, and complete derangement of the same is followed by an almost total suspension of the ability to localize.
12a. The antagonistic theories in regard to the psychical formation of spacial ideas, are generally called nativism and empirism. The nativistic theory seeks to derive localization in space from connate properties of the sense-organs and sense-centres, while the empiristic theory seeks to derive it from the influences of experience.
This discrimination does not give proper expression to the actual opposition that exists, for the assumption of connate spacial ideas may be attacked without affirming that these ideas arise through experience. This is the case when, as above, space-perceptions are regarded as products of psychical fusions due both to the physiological properties of the organs of sense and of movement, and to the general laws for the rise of psychical compounds.
Such processes of fusion and the arrangements of sense-impressions based upon them, are everywhere the substrata of our experience, but for this very reason it is inadmissible to call them "experience" itself. It is much more proper to point out the opposition that really exists, as that of nativistic and genetic, theories. It is to be noted that the widespread nativistic theories contain empirical elements, while, on the other hand, empirical theories contain nativistic elements, so that the difference is sometimes very small. Supporters of the nativistic view assume that the arrangement of impressions in space corresponds directly to the arrangement of sensitive points in the skin and retina. The special way in which the projection outward is effected, especially the ideas of the distance and magnitude of objects, and the reference of a plurality of specially [p. 115] separated impressions to a single object, are all regarded as dependent upon "attention", "will", or even "experience". Supporters of the empirical theory, on the other hand, generally presuppose space as given in some way or other, and then interpret each single idea as a localization in this space due to some empirical motive. In the theory of spacial ideas from sight, tactual space is generally regarded as this originally given space; in the theory of tactual ideas, original spacial qualities have sometimes been attributed to motor sensations. Thus, in the actual concrete theories empirism and nativism are very ill defined concepts. They agree in the use of the complex concepts of popular psychology, such as '"attentions", "will", and "experience", without any examination or analysis. In this respect they are different from the genetic theory, which seeks to show the elementary processes from which the ideas rise, by means of a psychological analysis of the ideas. In spite of their weaknesses, the nativistist and empiristic theories have served to set the psychological problem that exists here, clearly before us and to bring to light a great number of facts for its solution. B. SPACIAL SIGHT-IDEAS.
13. The general properties of the touch-sense are repeated in the visual sense, but in a more highly organized form. Corresponding to the sensory surface of the outer skin, we have here the retina with its rods and cones arranged in rows and forming an extraordinarily fine mosaic of sensitive points. Corresponding to the movements of the tactual organs, we have the movements of both eyes in fixating objects and following their bounding lines. Still, while tactual impressions are perceived only through immediate contact with the objects, the refractive media in front of the retina throw inverted, reduced images upon it. These images are so small that space is allowed for a large number of simultaneous impressions, and the ability of light to traverse space makes it possible for both neighboring and distant objects to yield [p. 116] impressions. Vision thus becomes a distance-sense in a much higher degree than hearing. Light can be perceived from incomparably greater distances than sound. Furthermore, only visual ideas are directly localized at different distances from the subject; for auditory ideas this localization is always indirect, through the aid of visual ideas of space.
14. With regard to its spacial attributes, every visual idea may be resolved into two factors: 1) the location of the single elements in relation to one another, and 2) their location in relation to the ideating subject.