Les mecanismes nerveux de l'orientation spatiale chez l'homme

Abstract

Under the expression “spatial orientation” is meant the perception of the spatial relations between surrounding objects and between the perceiving individual and these objects, followed by the performance of oriented movements towards these objects. Spatial orientation of man in an environment is, according to the prevailing opinion of physiologists and psychologists, carried out mainly by visual and kinesthetic perception. At the same time we have shown by the experiments on animals that the stimulation of labyrinthine receptors together with visual ones is the main factor in spatial orientation. Analogous experiments on normal children and also on deaf-mute and blind children led us to the same conclusion. Normal children about 6–7 years old were blindfolded and led on foot or carried on a chair from one place to another and then told to walk the same traversed route. We drew on the floor different figures: semicircle, triangle, the letters U, Z etc. along which the children were led or carried. All of the blindfolded children examined by us walked by themselves more or less correctly along those figures after they had been led or carried on them. Also, they could come to a terminal point not only by the traversed route but also by other shorter routes. Thus, blindfolded normal children perceive the traversed distance and turning points by means of labyrinthine receptors and create the images of them projected in space. Analogous experiments were performed on deaf-mute children. At a deaf-mute school children were chosen with destroyed non-functioning labyrinths. When blindfolded none of these children were able to walk the route along which they had been led or carried on one or several occasions. However, deaf-mute children with intact labyrinths could walk along the traversed route even blindfolded. From these experiments it is clear that blindfolded deaf-mutes wirth destroyed labyrinthine functions are not able to orient in space, similar to labyrinthless animals. However, if deaf-mute children with destroyed labyrinths are led for many times along the same figure, then they become able to walk along that figure though less precisely that the normal children do. In this case we have elaboration of conditioned reflex movements on the basis of proprioceptive and interoceptive stimulations taking place during the movement. We have investigated the spatial orientation in blind children who lost their vision in early childhood. On them we performed the same experiments as on blindfolded normal children. The experiments have shown that the blind children orient in space on the basis of acoustic and labyrinthine impressions much better than the blindfolded normal children. This obviously depends upon the fact that these receptions are more trained in blind children than in normal children. As we know, the blind feel solid objects at a distance if they are at the level of their face and they go round without hitting them. They feel solid objects as small as a book at the level of their head at a distance of 20–30 cm, and large objects, as for example a wall, at a distance of up to 1m. The blind persons themselves insist that they sense big objects by means of stimulation of cutaneous receptors of the upper part of the face, especially of the forehead; they feel something like a slight touching or pressure. However, the blind children feel solid objects at a distance, even when the whole head is covered by a leather cap. These sensations at a distance disappear after stopping up the ears with wet cotton or after putting sounding headphones on the ears. We suppose that the observed cutaneous sensation on the face of the blind appear a second time as a result of cutaneous stimulation through conditioned contraction of smooth muscle cells in response to the subliminal auditory stimulation. This so-called subsensory stimulation depends on sound waves reflected by solid obstacles; it precedes the pain stimulus to the skin of the face when it encounters obstacles. This pain stimulation provokes reflex contraction of smooth muscle cells of the face. That is why a subsensory auditory stimulus becomes a conditioned signal for the contraction of these smooth muscle cells which produce the mechanical stimulation of cutaneous receptors. This stimulation of skin receptors is perceived by blind children as a light touch or pressure. However, these sensations at a distance do not play any significant part in establishment of spatial relation between objects. This is entirely determined by labyrinthine reception.