In most of my experiments, however, I did not insist on rapid and
naïve judgments; but by a close observation of the subject as he was
about to make a judgment I could tell quite plainly which judgments
were spontaneous and which were deliberate. By keeping track of these
with a system of marks, I was able to collect them in the end into
groups representing fairly well the different degrees of attention.
The illusion is always greatest for the group of spontaneous
judgments, which points to the conclusion that all illusions, tactual
as well as visual, are very largely a function of attention.

In Section II. I told of my attempt to reproduce the optical illusion
upon the skin in the same form in which we find it for sight, namely,
by presenting the open and filled spaces simultaneously, so that they
might be held in a unitary grasp of consciousness and the judgment
pronounced on the relative length of these parts of a whole. However,
as I have already said, the filled space appears longer, not only when
given simultaneously, but also when given successively with the open
space. In the case of the optical illusion I am not so sure that the
illusion does not exist if the two spaces are not presented
simultaneously and adjacent, as Münsterberg asserts. Although, to be
sure, for me the illusion is not so strong when an interval is allowed
between the two spaces, I was interested to know whether this was true
also in the case of a touch illusion. My previous tables did not
enable me to compare the quantitative extent of the illusion for
successive and simultaneous presentation. But I found in two series
which had this point directly in view, one with the subject _F_ and
one in which _G_ served as subject, that the illusion was emphatically
stronger when the open and filled spaces were presented simultaneously
and adjacent. In this instance, the illusion was doubtless a