at, when a child, he used to spend hours in discovering the
outlines of forms in the partly blackened and cracked stucco of the
house that stood opposite to his own.[50] Here it is plain that, while
experience and association are not wholly absent, but place certain wide
limits on this process of castle-building, the spontaneous activity of
the percipient mind is the great determining force.

So much as to the influence of a perfectly unfettered voluntary
attention on the determination of the stage of preperception, and,
through this, of the resulting interpretation. Let us now pass to cases
in which this direction of preperception follows not the caprice of the
moment, but the leading of some fixed predisposition in the
interpreter's mind. In these cases attention is no longer free, but
fettered, only it is now fettered rather from within than from without;
that is to say, the dominating preperception is much more the result of
an independent bent of the imagination than of some suggestion forced on
the mind by the actual impression of the moment.

_Involuntary Mental Preadjustment._

If we glance back at the examples of capricious selection just noticed,
we shall see that they are really limited not only by the character of
the impression of the time, but also by the mental habits of the
spectator. That is to say, we find that his fancy runs in certain
definite directions, and takes certain habitual forms. It has already
been observed that the percipient mind has very different attitudes with
respect to various kinds of impression. Towards some it holds itself at
a distance, while towards others it at once bears itself familiarly; the
former are such as answer to its previous habit and bent of imagination,
the latter such as do not so answer.

This bent of the interpretative imagination assumes, as we have already
seen, two forms, that of a comparatively permanent disposition, and that
of a temporary state of expectation or mental preparedness. Illusion may
arise in connection with either of these forms. Let us illustrate both
varieties, beginning with those which are due to a lasting mental
disposition.

It is impossible here to specify all the causes of illusion residing in
organized tendencies of the mind. The whole past mental life, with its
particular shade of experience, its ruling emotions, and its habitual
direction of fancy, serves to give a particular colour to new
impressions, and so to favour illusi