James, William, ‘Principles
of Psychology,’ New York, II.,
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 of experiments to report, which seems to me to prove beyond the possibility of a doubt the correctness of my position. These experiments were made with the apparatus shown in Fig. 10. The subjects proceeded precisely as before. The finger-tip was passed over the filled space, and then out over the open space, until an equivalent distance was measured off. But while the subject was drawing his fingers over the spaces, the block A was moved in either direction by means of the lever B. The subjects were all the while kept ignorant of the fact that the block was being moved. They all expressed great surprise on being told, after the experiments were over, that the block had been moved under the finger-tip through such long distances without their being able to detect it. The block always remained stationary as the finger passed over one space, but was moved either with or against the finger as it passed over the other space.
A B C D E 4 7.1 2.6 2.4 6.5 5 8.3 3.1 3.3 8.7 6 8.2 3.3 4.1 9.2 7 9.7 3.6 3.7 10.1 8 10.5 3.7 4.5 10.6 9 12.4 4.8 5.1 11.5 10 13.1 4.7 5.3 13.2 11 13.3 5.3 6.1 14.6 12 13.7 6.9 7.2 12.7 13 14.6 7.5 8.1 13.2 14 15.3 8.2 9.4 15.6 15 15.7 8.7 10.3 14.9
Column A contains the
filled spaces, columns B, C, D,
E the open spaces that were judged equal. In B the block
was moved with the finger, and in C against the finger as it
traversed the filled space, and in D and E the block was
moved with and against the finger respectively as it passed
over the open space. The block was always moved approximately
one-half the distance of the filled space.
I have given some of the results for one subject in Table XII. These results show at a glance how potent a factor the time element is. The quantity of tactual sensations received by the finger-tip enters into the judgment of space to no appreciable extent. With one subject, after he had passed his finger over a filled space of 10 cm. the block was moved so as almost to keep pace with the finger as it passed over the open space. In this way the subject was forced to judge a filled space of 10 cm. equal to only 2 cm. of the open space. And when the block was moved in the opposite direction he was made to judge a distance of 10 cm. equal to an open distance of 16 cm.