This distortion of contrasted distances I have found in more than one case in this investigation—­not only in the case of distances in which there is a qualitative difference, but also in the case of two open distances.  In one experiment, in which open distances on the skin were compared with optical point distances, a distance of 10 cm. was given fifty times in connection with a distance of 15 cm., and fifty times in connection with a distance of 5 cm.  In the former instance the distance of 10 cm. was underestimated, and in the other it was overestimated.

The general conclusion of the entire investigation thus far may be summed up in the statement:  Wherever the objective conditions are the same in the two senses, the illusion exists in the same direction for both sight and touch.

VI.

Thus far all of my experiments were made with passive touch.  I intend now to pursue this problem of the relation between the illusions of sight and touch into the region of active touch.  I have yielded somewhat to the current fashion in thus separating the passive from the active touch in this discussion.  I have already said that I believe it would be better not to make this distinction so pronounced.  Here again I have concerned myself primarily with only one illusion, the illusion which deals with open and filled spaces.  This is the illusion to which Dresslar[12] devoted a considerable portion of his essay on the ‘Psychology of Touch,’ and which he erroneously thought to be the counterpart of the optical illusion for open and filled spaces.  One of the earliest notices of this illusion is that given by James,[13] who says, “Divide a line on paper into two equal halves, puncture the extremities, and make punctures all along one of the halves; then, with the finger-tip on the opposite side of the paper, follow the line of punctures; the empty half will seem much longer than the punctured half.”

   [12] Dresslar, F.B., Am.  Journ. of Psy., 1894, VI., p. 313.

   [13] James, W., ‘Principles of Psychology,’ New York, 1893,
   II., p. 250.

James has given no detailed account of his experiments.  He does not tell us how many tests were made, nor how long the lines were, nor whether the illusion was the same when the open half was presented first.  Dresslar took these important questions into consideration, and arrived at a conclusion directly opposite to that of James, namely, that the filled half of the line appears larger than the open half.  Dresslar’s conclusion is, therefore, that sight and touch function alike.  I have already said that I think that Parrish was entirely right in saying that this is not the analogue of the familiar optical illusion.  Nevertheless, I felt sure that it would be quite worth the while to make a more extensive study than that which Dresslar has reported.  Others besides James and Dresslar have experimented with this illusion.  As in the case of the illusion for passive touch, there are not wanting champions of both opinions as to the direction in which this illusion lies.