our instantaneous perceptions these two stages are indistinguishable to
consciousness. Thus, in most cases, the recognition of size, distance,
etc., takes place so rapidly that it is impossible to detect the two
phases here separated. But in the classification of an object, or the
identification of an individual thing, there is often an appreciable
interval between the first reception of the impression and the final
stage of complete recognition. And here it is easy to distinguish the
two stages of preperception and perception. The interpretative image is
slowly built up by the operation of suggestion, at the close of which
the impression is suddenly illumined as by a flash of light, and takes a
definite, precise shape.

Now, it is to be noted that the process of preperception will be greatly
aided by any circumstance that facilitates the construction of the
particular interpretative image required. Thus, the more frequently a
similar process of perception has been performed in the past, the more
ready will the mind be to fall into the particular way of interpreting
the impression. As G.H. Lewes well remarks, "The artist sees details
where to other eyes there is a vague or confused mass; the naturalist
sees an animal where the ordinary eye only sees a form." This is but one
illustration of the seemingly universal mental law, that what is
repeatedly done will be done more and more easily.

The process of preperception may be shortened, not only by means of a
_permanent_ disposition to frame the required interpretative scheme, the
residuum of past like processes, but also by means of any _temporary_
disposition pointing in the same direction. If, for example, the mind of
a naturalist has just been occupied about a certain class of bird, that
is to say, if he has been dwelling on the _mental image_ of this bird,
he will recognize one at a distance more quickly than he would otherwise