Fig. 10.
In order to enable the subject to make proper connections with the first point in the filled space, when the open space was presented first, a slight depression was put in the smooth surface. This depression amounted merely to the suggestion of a groove, but it sufficed to guide the finger.
The general results of the first series of experiments with this apparatus were similar to those already given, but were based on a very much larger number of judgments. They show at once that the short filled spaces are overestimated, while the longer spaces are underestimated. The uniformity of this law has seemed to me one of the most significant results of this entire investigation. In the results already reported from the experiments with the former apparatus, I have mentioned the fact that the judgments upon the distances fluctuate more widely when one is filled and the other open, than when both are open. This fluctuation appeared again in a pronounced way in the present experiments. I now set about to discover the cause of this variation, which was so evidently outside of the limits of Weber's law.
TABLE XI.
| I. | II. | ||||||
|---|---|---|---|---|---|---|---|
| Filled Spaces. | Subjects | R. | B. | A. | R. | B. | A. |
| 2= | 3.1 | 3.2 | 3.7 | 2.7 | 2.5 | 3.1 | |
| 3= | 4.5 | 4.4 | 4.1 | 4.1 | 4.0 | 3.6 | |
| 4= | 5.3 | 5.0 | 4.3 | 4.2 | 4.6 | 4.6 | |
| 5= | 6.0 | 5.1 | 5.8 | 5.9 | 5.2 | 4.3 | |
| 6= | 6.8 | 5.6 | 6.2 | 6.9 | 5.3 | 6.0 | |
| 7= | 7.4 | 7.2 | 6.9 | 7.6 | 7.3 | 6.8 | |
| 8= | 8.1 | 8.4 | 7.3 | 8.3 | 9.7 | 7.8 | |
| 9= | 9.3 | 9.0 | 8.5 | 9.5 | 8.9 | 8.7 | |
| 10= | 10.1 | 10.0 | 8.1 | 10.3 | 10.0 | 9.2 | |
| 11= | 10.5 | 9.3 | 9.7 | 10.6 | 8.7 | 9.6 | |
| 12= | 11.7 | 10.6 | 10.6 | 11.8 | 9.7 | 10.2 | |
| 13= | 12.3 | 10.9 | 10.9 | 11.1 | 10.2 | 9.6 | |
| 14= | 12.2 | 11.5 | 12.2 | 10.4 | 9.6 | 11.3 | |
| 15= | 13.6 | 12.3 | 11.9 | 13.1 | 10.1 | 9.6 | |
| 16= | 14.1 | 13.5 | 14.1 | 12.3 | 13.2 | 13.3 | |
| 17= | 14.9 | 12.9 | 14.6 | 14.1 | 12.6 | 13.7 | |
| 18= | 15.0 | 15.3 | 14.9 | 15.0 | 15.3 | 13.8 | |
| 19= | 15.2 | 14.6 | 15.2 | 14.1 | 13.9 | 14.2 | |
| 20= | 17.1 | 16.5 | 15.7 | 16.1 | 16.4 | 14.7 | |
The first line of group I. reads: 'When the finger-tip was passed over a filled space of 2 cm., the subject R measured off 3.1 cm. on the open space, the subject B 3.2 cm., and the subject A 3.7.' In group II., the numbers represent the distance measured off when both spaces were unfilled.
In my search for the cause of the variations reported previously I first tried the plan of obliging the subject to attend more closely to the filled space as his finger was drawn over it. In order to do this, I held a piece of fine wire across the line of the filled space, and after the subject had measured off the equal open space he was asked to tell whether or not he had crossed the wire. The wire was so fine that considerable attention was necessary to detect it. In some of the experiments the wire was inserted early in the filled space, and in some near the end. When it was put in near the beginning, it was interesting to notice, as illustrating the amount of attention that was being given to the effort of finding the wire, that the subject, as soon as he had discovered it, would increase his speed, relax the attention, and continue the rest of the journey more easily.
The general effect of this forcing of the attention was to increase the apparent length of the filled space. This conclusion was reached by comparing these results with those in which there was no compelled attention. When the obstacle was inserted early, the space was judged shorter than when it came at the end of the filled space. This shows very plainly the effect of continued concentration of attention, when that attention is directed intensely to the spot immediately under the finger-tip. When the attention was focalized in this way, the subject lost sight of the space as a whole. It rapidly faded out of memory behind the moving finger-tip. But when this concentration of attention was not required, the subject was able to hold together in consciousness the entire collection of discrete points, and he overestimated the space occupied by them. It must be remembered here that I mean that the filled space with the focalized attention was judged shorter than the filled space without such concentration of attention, but both of these spaces were judged shorter than the adjacent open space. This latter fact I shall attempt to explain later. Many other simple devices were employed to oblige the subject to fix his attention on the space as it was traversed by the finger. The results were always the same: the greater the amount of attention, the longer the distance seemed.
In another experiment, I tried the plan of tapping a bell as the subject was passing over the filled space and asking him, after he had measured off the equivalent open space, whether the sound had occurred in the first half or in the second half of the filled space.
When the finger-tip was drawn over two adjacent open spaces, and during the first a bell was tapped continuously, this kind of filled space was underestimated if the distance was long and overestimated if the distance was short. So, too, if a disagreeable odor was held to the nostrils while the finger-tip was being drawn over one of the two adjacent open spaces, the space thus filled by the sensations of smell followed the law already stated. But if an agreeable perfume was used, the distance always seemed shorter than when an unpleasant odor was given.