Page:Mind (Old Series) Volume 12.djvu/340

 THE PERCEPTION OF SPACE, (ill.) 327 eye, the accommodation- and parallax-feelings are there, but fail to make us see it hollow, as it is. Our mental knowledge of the fact that human faces are always convex, overpowers them, and we directly perceive the nose to be nearer to us than the cheek instead of farther of. The other organic tokens of farness and nearness are proved by similar experiments (of which we shall ere long speak more in detail) to have an equally fluctuating import. They lose all their value whenever the collateral circum- stances favour a strong intellectual conviction that the object presented to the gaze contradicts their verdict cannot be either what or ivhcre they, if left to themselves, would make us perceive it to be. Now the query immediately arises : Can the feelings of these processes in the eye, if they are so easily neutralised and reversed by intellectual suggestions, ever have been direct sensations of distance at all?. Ought we not rather to assume, since the distances we see in spite of them are conclusions from past experience, that the distances we see by means of them are equally such conclusions ? Ought we not in short to say unhesitatingly that distance must be an intellectual and not a sensible content of consciousness ? and that each of these eye-feelings serves as a mere signal to awaken this content, our intellect being so framed that sometimes it notices one signal more readily and sometimes another ? Reid long ago (Inquiry, c. vi. sec. 17) said, " It may be taken for a general rule, that things which are produced by custom may be undone or changed by disuse or by contrary custom. On the other hand, it is a strong argument that an effect is not owing to custom, but to the constitution of nature, when a contrary custom is found neither to change nor to weaken it." More briefly, a way of seeing things that can be unlearned was presumably learned, and only what we cannot unlearn is instinctive. This seems to be Helmholtz's view, for he confirms Reid's maxim by saying in emphatic print, " No elements in our perception can be sensational which may be overcome or reversed by factors of demonstrably experimental origin. Whatever can be overcome by suggestions of experience must be regarded as itself a product of experience and custom. If we follow this rule it will appear that only qualities are sensational, whilst almost all spatial attributes are results of habit and experience." x 1 Physiol. OptiJc, p. 438. Helmholtz's reservation of 'qualities' is incon- sistent. Our judgments of light and colour vary as much as our judgments