e nervous process underlying a
sensation occupies the same central region as that which underlies the
corresponding image. According to this theory, the two processes differ
in their degree of energy only, this difference being connected with the
fact that the former involves, while the latter does not involve, the
peripheral region of the nervous system. Accepting this view as on the
whole well founded, I shall speak of an ideational, or rather an
imaginational; and a sensational nervous process, and not of an
ideational and a sensational centre.[12]

The special force that belongs to the representative element in a
percept, as compared with that of a pure "perceptional" image,[13] is
probably connected with the fact that, in the case of actual perception,
the nervous process underlying the act of imaginative construction is
organically united to the initial sensational process, of which indeed
it may be regarded as a continuation.

For the physical counterpart of the two stages in the interpretative
part of perception, distinguished as the passive stage of preperception,
and the active stage of perception proper, we may, in the absence of
certain knowledge, fall back on the hypothesis put forward by Dr. J.
Hughlings Jackson, in the articles in _Brain_ already referred to,
namely, that the former answers to an action of the right hemisphere of
the brain, the latter to a subsequent action of the left hemisphere. The
expediting of the process of preperception in those cases where it has
frequently been performed before, is clearly an illustration of the
organic law that every function is improved by exercise. And the
temporary disposition to perform the process due to recent imaginative
activity, is explained at once on the physical side by the supposition
that an actual perception and a perceptional image involve the activity
of the same nervous tracts. For, assuming this to be the case, it
follows, from a well-known organic law, that a recent excitation would
leave a temporary disposition in these particular structures to resume
that particular mode of activity.

What has here been said about visual perception will apply, _mutatis
mutandis_, to other kinds. Although the eye is the organ of perception
_par excellence_, our other senses are also avenues by which we intuit
and recognize objects. Thus touch, especially when it is finely
developed as it is in the blind, gives an immediate knowledge of
objects--a more imm