Spatial Sense

SPATIAL SENSE, the general name for a very complex set of sensorimotor mechanisms that provide the subject with orientation in space. S. s. cannot be placed alongside the sense of sight, touch, hearing, etc., since it does not have a special specific receptor - an 'organ of sense.' It widely uses impulses received from various receptors, with the greatest significance for the formation of spatial representations being the tactile, visual, labyrinthine, and proprioceptive apparatuses. To a lesser degree, the sense of hearing and the apparatuses of deep sensitivity participate in the formation and activity of S. s. In connection with such a complex synthetic structure of S. s., it is understandable that this sense develops and begins to function correctly later than all other receptor systems.--Upon receiving receptor impulses from the entire periphery of the body, thus utilizing the activity of almost all terminal sensory apparatuses, the S. s. system in turn affects the centers associated with these terminal apparatuses, modifying and shaping their responses. As a result of such interaction of each individual receptor system with the organized and centralized collection of all other receptor systems, a certain spatial ordering of the receptor impulses received from the outside is developed in these individual systems; so to speak, a spatial coordinate grid is developed, on which the sets of sensations received from the outside by this system are placed. This spatial ordering is generally called the spatial-sensory field or simply the field of a given sense. These complex relationships are best explained by an example taken from the activity of one of the sense organs participating in the general S. s. system. The primary sensations given by the visual organ, by themselves, contain no signs of their mutual location in space. From the testimony of persons who received sight already as adults (after removal of operable cataracts), it is known that their initial visual impressions after removal of the bandage represent a chaos of light spots, devoid not only of objective differentiation but also of signs characterizing their mutual location in the field of vision. The ordering of the visual field, i.e., the visual assimilation of the concepts 'right,' 'left,' 'near,' 'between,' and even more so optical concepts of the simplest geometric forms, is established far from immediately. Such ordering requires immediately the auxiliary activity of receptors of other orders. First of all, (conditional) connections are established between the sensations given by the retina and the muscular (proprioceptive) sensations from the eye muscles, since the movement of this or that element of the visual field into the area of clear vision (fovea centralis) is accompanied by a certain sensation of tension in certain eye muscles. At the same time, since the sensations from these muscles are also not yet 'calibrated,' a corresponding calibration of their readings is carried out with the help of turns of the head and body. Then the hands are introduced into the visual field and correspondence is established between certain objective elements of the visual field and the set of tactile and kinesthetic concepts of the same objects. Further, gradual establishment of connections occurs between the muscular sensations of convergence and the concepts of distance to objects along the ray of vision, again obtained through the medium of tactile and proprioceptive sensitivity. To what extent the synthetic 'visual' concept obtained by these paths differs from what is actually perceived by the visual centers is best clarified by the following examples. We are accustomed to complete confidence that our optical perception contains within itself elements of all three coordinates of space: height, width, and depth; even a physiologist, knowing that depth stereoscopic vision is the result of the combination of vision with both eyes with muscular sensations of convergence, cannot rid himself of the impression that as a result of such combination the depth coordinate is still perceived optically, is contained in the visual perception itself. In reality, however, the latter contains no elements of the depth coordinate, which is perceived completely and solely by muscles; we therefore attribute or project into the visual field and endow with sensory-visual properties an object which by itself undoubtedly does not possess these properties. A second example, perhaps even more expressive. The set of strictly visual sensations given by the retina represents a perspective image of the visible world, quite similar to that given by a camera. Meanwhile, for an ordinary person there is nothing more difficult than to draw some simplest object in perspective - this art must be learned, i.e., in fact to unlearn to entangle visual perception, by its nature perspective, with all sorts of additional foreign introductions. A child or primitive can draw a person in profile, but with two eyes, and no one will suspect imperfection in his visual field; an adult and civilized person will not draw such an obvious absurdity, but can draw, for example, a barrel with both bottoms visible, or a vehicle with both sides visible, not to mention less striking errors. Thus, the developed, fully developed spatial-visual field essentially and sharply differs from the primary purely sensory visual contents, and this difference is the result of the long evolutionary interaction of the visual apparatus with the synthetic activity of the S. s. mechanisms. The close connection of the tactile and proprioceptive receptor apparatuses, both between themselves and with the entire S. s. system, is well known, and apparently these two receptors are the main basis for constructing the entire S. s. system. It is possible that even in the tactile receptor itself the foundation is laid for the spatial localization of tactile concepts in the form of so-called local or spatial signs, i.e., sensory differences inherent in each individual tactile point, characterizing its location relative to adjacent points. However, unlike the psychophysiologists of the 19th century (Wundt, Ziehen), it is now generally accepted that local signs are not primary elements of tactile sensations themselves, but secondarily related characteristics developed on the basis of interaction with the S. s. system as a whole, and in particular with the muscle-joint sense and vision. It is difficult to say whether sense organs such as hearing and smell participate in any way in the development of the S. s. system. On the other hand, the reverse influence of S. s. on the shaping of the activity of these sense organs is beyond doubt. Determining the direction from which a sound comes ('sound ranging') is performed by man with fairly satisfactory accuracy, with an error of about 10 degrees. Cats, which have the possibility of using the mobility of the auricles for sound ranging, undoubtedly have a highly developed spatial-hearing field. The same can be said about the spatial-olfactory field of a dog (orientation in space by smell). Finally, the labyrinthine (and otolithic) apparatus has colossal significance as the supreme control over the S. s. system. If all the previously mentioned receptors contribute to the organization and ordering of spatial elements of sensation in relation to the subject's own body, its parts and movements, then the labyrinthine apparatus is the main receptor binding these spatial elements to external physical space, in particular to the earth's gravitational field. Through the medium of labyrinthine sensations, the S. s. system and the synthetic sensory spatial field created by it are brought into correspondence with external space, with fixed coordinate systems associated with the earth's surface. This circumstance makes the role of the labyrinthine apparatus particularly significant in all kinds of locomotions, especially in those when the possibility of controlling the connection with external space from other receptors decreases. Such locomotions include swimming and flying; in this connection, it should be noted the enormous development of labyrinths in flying birds, as well as the decisive importance attached to the perfection of the labyrinthine system in the professional profile of pilots. The complexity and multifaceted nature of S. s. fully explains the fact that to the present day there is not only a sufficiently developed system for studying and quantitatively assessing an individual's S. s., but even a well-established classification of its functions. The task of studying S. s. is further complicated by the fact that, as stated in the initial definition of this term, S. s. is a sensorimotor activity, most closely connected with spatial coordination of movements.

The synthetic spatial-sensory field of Spatial Sense is completely inseparable from the spatial-motor field, which is no less synthetic and serves as the basis of all motor coordination. Therefore, it is almost impossible to devise tests that would demonstrate the state of Spatial Sense in its pure form, isolating it from motor coordination. Thus, for example, the task of touching with the fingertip, with eyes closed, a point just previously seen, is undoubtedly a task for Spatial Sense, but at the same time it is also a task of coordination, and failure in performing such a task may depend on the imperfection of either system. In general, test and experimental research on Spatial Sense is conducted along the following lines: A. Metric (measurable) properties of Spatial Sense 1. Evaluation of object sizes (visual estimation, evaluation by palpation). 2. Evaluation of distances to objects (visual and kinesthetic). B. Topical properties of Spatial Sense--evaluation of object location. 1. Evaluation of the mutual location of objects (differentiation of spatial figures and bodies, evaluation of displacements of points relative to each other, etc.). 2. Evaluation of the location of objects relative to one's own body. C. Vector properties of Spatial Sense--evaluation of direction.