Essays Towards a Theory of Knowledge | Page 6

our exertional Activity combined with the interruptions which that Activity perpetually encounters, and in which sensations arise. It would indeed be a useful work of psychological analysis if the conditions of exertional action were carefully and systematically investigated--much more useful than most of the trifling experiments to which psychological laboratories are usually devoted.
The principal elements of such a scheme would be--
(1) The force of gravity. This force constantly operating constrains the organism to be in constant contact with the earth on which we live. But, further, it gives us the definite idea of Direction. It is from the action of gravity that we derive our distinction between Up and Down from which as a starting-point we build up our conception of tridimensional Space. And in this respect it must be remembered that as the areas of spheres are proportional to the squares of their radii it necessarily follows that gravity if it acts uniformly in tridimensional Space must vary in intensity in proportion to the square of the distance of the point of application from the centre of origin. Gravity and tridimensionality are in short necessarily connected.
(2) The same law which determines the force of gravity seems to determine also the force of cohesion, and therefore the form of material bodies. These, therefore, are necessarily subject also to tridimensionality, and in the force which generates solid form we find a second source of our elementary spatial ideas.
Such form is the expression of an obstacle to action which determines all our movements, and in which we discover those forms of the limitations of activity which we call spatial characters.
(3) Organic Dualism is a third determinant of activity, and thus also a source of spatial ideas.
The structural dualism of the human body, its right and left, its front and back, etc., furnish our activity with a set of constant forms to which its action must conform, and which necessarily also partake of, and help us to conceive of tridimensional form. It is interesting to note that this dualism characterises the organs specially adapted to serve exertional action rather than those which serve our vegetal or nutrient life.
The way in which our spatial conceptions are ever extended and built up out of the data of action is also well illustrated in the case of the blind, and to this also M. Villey devotes an interesting chapter under the title La conqu��te des repr��sentations spatiales.
This is effected in their case by the high development of what we must call active touch. Just as we distinguish between hearing and listening, between seeing and looking, so must we distinguish between touching and palpation.
Mere passive touch gives a certain amount of information, but comparatively little. It is necessary to explore; that is what is done in active touch--palpation--of different degrees.
The sensitiveness of the skin varies at different places from the tongue downwards. Palpation by the fingers marks a further stage. The blind also, we are told, largely employ the feet in walking as a source of locative data.
To the concepts reached by such palpation with the hand, M. Villey gives the name of Manual Space. In this connection he thinks it necessary to distinguish between synthetic touch and analytic touch--the former resulting from the simultaneous application of different parts of the hand on the surface of a body, the latter that which we owe to the movements of our fingers when having only one point of contact with the object the fingers follow its contour. Various examples of the delicacy of the information thus obtainable are given. Following two straight lines with the thumb and index respectively, a blind man can acquire by practice a sensibility so complete as to enable him to detect the slightest divergence from parallelism.
The analysis passes on from the data of Space manual to those of Space brachial; then to the information derived from walking and other movements of the lower limbs, and then to the co-ordination of the information derived from the sensations of hearing, which is necessarily very important to the blind.
The conclusion of the whole matter is that our principal spatial ideas are common alike to the blind and the vident. Both can be taught and are taught the same geometry. Both understand one another in the description of spatial conditions. The common element cannot possibly be supplied either by the data of visual sensation which the blind do not possess, or by the data of passive tactual sensation which the vident hardly ever employ. Une ��tendue commune se retrouverait �� la fois dans les donn��es de la vue et dans celles du toucher. The common element is furnished by the common laws and forms of our exertional Activity by means of which and in terms of which we all construct our conceptions of the dynamic world of our