[Illustration: FIG. 1.--In order to see the lion's
head, look at the above cut upside down, and the
head will be discovered facing the left, as above
outlined. It is clearer on the coin itself than in this
representation.]
[Illustration: FIG. 2.--These letters should not be
seen at all until they have been observed at a distance
of eight to twelve feet. An interesting method of
testing the activity of the mind's eye with these
letters is described in the text.]
[Illustration: FIG. 2_a_.]
[Illustration: FIG. 2_b_.]
[Illustration: FIG. 3.--For description, see text, page
282.]
The importance of the mind's eye in ordinary vision is also well
illustrated in cases in which we see or seem to see what is not
really present, but what for one cause or another it is natural to
suppose is present. A very familiar instance of this process is the
constant overlooking of misprints--false letters, transposed letters,
and missing letters--unless these happen to be particularly striking.
We see only the general physiognomy of the word, and the detailed
features are supplied from within; in this case it is the expected
that happens. In a series of experiments by Professor Münsterberg a
word was briefly shown, while just before a certain idea or train of
thought was suggested. Under these circumstances the word shown was
often misread in accordance with the suggested idea; if the idea of
future is suggested, part may be read as past; if vegetable is the
suggested line of thought, fright may be read as fruit, and so on.
Reading is thus done largely by the mental eye; and entire words,
obviously suggested by the context, are sometimes read in, when they
have been accidentally omitted. This is more apt to occur with the
irregular characters used in manuscript than in the more distinct
forms of the printed alphabet, and is particularly frequent in
reading over what one has himself written. In reading proof, however,
we are eager to detect misprints, and this change in attitude helps
to make them visible. It is very difficult to illustrate this process
intentionally, because the knowledge that one's powers of observation
are about to be tested places one on one's guard, and thus suppresses
the natural activity of the mind's eye and draws unusual attention
to objective details. Let the reader at this point hold the page
at some distance off--say, eight or twelve feet--and draw an exact
reproduction of the letters shown in Fig. 2. He should not look at
Fig. 2 at close range nor read further in the text until this has
been done; and _perhaps_ he may find that he has introduced strokes
which were not present in the original. If this is not the case, let
him try the test upon those who are ignorant of its nature, and he
will find that most persons will supply light lines to complete the
contours of the letters, which in the original are suggested but not
really present; the original outline, Fig. 2_a_, becomes something
like Fig. 2_b_, and so on for the rest of the letters. The physical
eye sees the former, but the mental eye sees the latter. I tried
this experiment with a class of some thirty University students of
Psychology, and, although they were disposed to be quite critical
and suspected some kind of an illusion, only three or four drew
the letters correctly; all the rest filled in the imaginary light
contours; some even drew them as heavily as the real strokes. I
followed this by an experiment of a similar character. I placed
upon a table a figure (Fig. 3) made of light cardboard, fastened to
blocks of wood at the base, so that the pieces would easily stand
upright. The middle piece, which is rectangular and higher than the
rest, was placed a little in front of the rest of the figure. The
students were asked to describe precisely what they saw; and with
one exception they all described, in different words, a semicircular
piece of cardboard with a rectangular piece in front of it. In
reality there was no half-circle of cardboard, but only portions
of two quarter-circles with the portion back of the middle piece
omitted. The students, of course, were well aware that their physical
eyes could not see what was behind the middle cardboard, but they
inferred, quite naturally, that the two side pieces were parts of one
continuous semicircle. This they saw, so far as they saw it at all,
with their mind's eye.