T indicates that the shaded portion of Fig. 16 in this
view represents the top of a block; B that in the other
view it represents the bottom.]
This collection of diagrams serves to illustrate the principle
that when the objective features are ambiguous, we see one thing
or another according to the impression that is in the mind's eye;
what the objective factors lack in definiteness the subjective
ones supply, while familiarity, prepossession, as well as other
circumstances influence the result. These illustrations show
conclusively that seeing is not wholly an objective matter depending
upon what there is to be seen, but is very considerably a subjective
matter, depending upon the eye that sees. To the same observer a
given arrangement of lines now appears as the representation of one
object and now of another; and from the same objective experience,
especially in instances that demand a somewhat complicated exercise
of the senses, different observers derive very different impressions.
[Illustration: FIG. 19.--Do you see a duck or a rabbit,
or either? (From _Harper's Weekly_, originally in
_Fliegende Blätter_.)]
Not only when the sense-impressions are ambiguous or defective, but
when they are vague--when the light is dim or the forms obscure--does
the mind's eye eke out the imperfections of physical vision. The
vague conformations of drapery and make-up that are identified and
recognized in spiritualistic _séances_ illustrate extreme instances
of this process. The whitewashed tree or post that momentarily
startles us in a dark country lane takes on the guise that expectancy
gives it. The mental predisposition here becomes the dominant factor,
and the timid see as ghosts what their more sturdy companions
recognize as whitewashed posts. Such experiences we ascribe to the
action of suggestion and imagination--the cloud "that's almost in
shape like a camel," or "like a weasel," or "like a whale." But
throughout our visual experiences there runs this double strain, now
mainly outward and now mainly inward, from the simplest excitements
of the retina up to the realms where fancy soars free from the
confines of sense, and the objective finds its occupation gone.