LECTURE X

§ I. Influence of Ocular Movement on Spatial Vision. § 2.
Geometrical Optical Illusions. § 3. Spatial Perceptions
OF the Sense of Touch. § 4. Accidental and Congenital
Blindness. § 5. Why .are not Visual Objects Inverted .'
§ 6. Concluding Remarks upon the Theory of Space-con¬
struction.

§  I

ALL our previous considerations have been based upon em¬
pirical facts. The laws of reflex movement, the muscular
sensibility, the local differences in sensations of light and touch,
the exhaustion consequent upon long exposure to sense-stimu¬
lus,—all these are phenomena which may be verified in experi¬
ence. But at the conclusion of these considerations we seem to
have left the firm ground of experience far behind us. We have
ventured upon a psychological construction of space, from the
associative co-operation of the specified factors. Is that not more
than experience can ever achieve ? Is not space a connate pos¬
session of the mind ? Or, if not that, is it not at least an en¬
tirely new element in our knowledge, which is sui generis, and
therefore not a derivative from anything else ?

It is certainly true that the perception of space is a new ele¬
ment in our knowledge. But in this sense every psychological
fact is new which arises from some particular combination of the
elements of our mental life. The laws of this composition are
such that the properties of the mental resultants to which they
give rise can never be predicted from the properties of the ele¬
ments which enter into them, although we are afterwards able to
see the connection of these elements and their combinations in
the complex result. Thus, e.g., after we have completed a com¬
plicated process of inference, we recognise that the conclusion
follows  necessarily from the premises.    But still it is, as con-

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