We are also told that he could not recognize by sight the objects which he knew by touch. But this only proves that not having been able to compare the two orders of sensations, he could not know what corresponded in one to the impressions of the other. By touch he would have known a spherical body; but as he was still ignorant of the impression which a globe makes on the eye, it is clear that if any one should show him a ball which he had handled a thousand times, he would not even have suspected that the object seen was the same which he had touched. This leads me to another observation which I consider very important.
77. The child on whom these experiments were made was obliged to express his sensations in the visual order, in a language which he did not understand. For any one who is deprived of one of the senses must be absolutely ignorant of all the ideas which have their origin in that sensation. Hence it follows that he knows nothing of the language relating to that sense, and the ideas which he joins to the words are entirely different from what those who possess that sense mean to express. The blind man will speak of colors and the impressions produced by sight, because he hears others speak of these things; but for him the word to see does not mean to see, light is not light, nor color color, as we understand them, but they express different ideas which he has formed according to the circumstances, in conformity with the explanations he has heard. What importance then should we attach to what a child may say who, besides the thoughtlessness natural to his age, is placed in a situation new to him, and required to express his ideas in a language which he does not know? He is asked, for example, if he can distinguish a greater object from another which is smaller, without considering that the words greater and smaller as he understood them, inasmuch as they expressed abstract ideas, or were referred to the sensations of touch, were altogether new to him when applied to objects seen, since he had no means of knowing what was meant when referred to a sensation which he experienced for the first time. If within a circle, a number of smaller circles of a different color were described, he would see the smaller circles within the circumference of the greater; but if asked if one appeared greater than the rest, or if he could distinguish the limits which, separated the smaller circles from each other, he could not but give very absurd answers, which the observers might perhaps take as the expression of curious phenomena. They speak to him of figures, lines, extremities, size, position, and distances in relation to sight, and as he is ignorant of this language, yet knows not that he is ignorant of it, he must necessarily talk in a very strange manner. A more attentive and profound observer would have perceived the same misunderstanding as when a deaf man disputes without hearing what was said.
These remarks are further confirmed by the contradiction in the account of Cheselden. The oculist tells us that the child could not distinguish the objects, even those which differed most in form and size: but that he found those most agreeable which were the most regular. He must then have distinguished them; for otherwise, the sensation could not have been more or less pleasing. And here in choosing an alternative in this contradiction, we must hold that he distinguished the objects, since there is a strong argument in its favor. When two objects, the one regular, the other irregular, were presented to him, and he was questioned as to their resemblance and difference, he must have answered so absurdly as to create the suspicion that he could not distinguish them. The reason of this is, that besides the confusion of sensations, to which he was always more or less subject, he was also ignorant of the language, and although he distinguished the objects plainly, still he could not understand what he was asked, nor express what he felt. But when examined as to the nature of the impression and whether it was pleasing or otherwise, he found himself on a field common to all sensations, the ideas of pleasure and displeasure were not new to him, and he could say without confusion, this pleases me; that is displeasing to me.
To sum up what I have said, I believe that the phenomena of Cheselden's blind man, only prove that sight, like all the other senses, needs a certain education, that its first impressions are necessarily confused, that the organ acquires the proper strength and precision only after long practice, and finally, that the judgments formed in consequence, must be very incorrect until comparison, joined with reflection, has taught how to rectify inaccuracies.[37]
[CHAPTER XIV.]
CAN SIGHT GIVE US THE IDEA OF A SOLID?
78. It has been asserted that sight can not give us the idea of size or of a solid, but that this can be obtained only by the help of touch. I believe the contrary may be proved with convincing certainty.
What is a solid? It is the union of three dimensions. If sight can give us the idea of surfaces which consist of two, why not also of solids which consist of three dimensions? This one reflection is enough to show that it has been denied without reason; but I shall not stop with this, but shall prove, by the most rigorous observation, and the analysis of its phenomena, that sight can give us the idea of a solid.
79. I willingly agree, that if we suppose a man deprived of all the other senses, to have his eyes immovably fixed on an immovable object, he would never be able to distinguish between what is solid and what is merely perspective in the object; or, in other words, that all the objects permanently painted on the retina will appear to be projected on a plane. The reason of this is founded on the very laws of the organ of this sense, and of the transmission of its impressions to the brain.
The soul refers the sensation to the extremity of the visual ray; and since in the present instance it has been unable to make any comparisons, it can have no motive for placing these extremities at unequal distances, which constitutes the third dimension.