the objective conditions here from what they are in the optical
illusion which has so often been called the analogue of this.
James[14] has said of this tactual illusion: 'This seems to bring
things back to the unanalyzable laws, by reason of which our feeling
of size is determined differently in the skin and in the retina even
when the objective conditions are the same.' I think that my
experiments have shown that the objective conditions are not the same;
that they differ in that most essential of all factors, namely, the
time element. Something very nearly the analogue of the optical
illusion is secured when we take very short open and filled tactual
spaces, and move over them very rapidly. Here the illusion exists in
the same direction as it does for sight, as has already been stated.
On the other hand, a phenomenon more nearly parallel to the tactual
illusion, as reported in the experiments of James and Dresslar, is
found if we take long optical distances, and traverse the open and
filled spaces continuously, without having both parts of the line
entirely in the field of view at any one moment. I made a few
experiments with the optical illusion in this form. The filled and
open spaces were viewed by the subject through a slot which was
passed over them. These experiments all pointed in the direction of an
underestimation of a filled space. Everywhere in this illusion, then,
where the objective conditions were at all similar for sight and
touch, the resulting illusion exists in the same direction for both
senses.

[14] James, William, 'Principles of Psychology,' New York, II.,
p. 250.

Throughout the previous experiments with the illusion for active touch
we saw the direct influence of the factor of time. I have yet one set