THE DURATION OF CUTANEOUS SENSATION (I) AND THE IMPROVEMENT OF ITS SENSIBLE DISCRIMINATION BY PRACTICE (II)

BY K. C. MUKHERJEE

Dacca University

The experiment consists of two parts. The part chosen for the two experiments is the same i.e. a small area—say b—of the left forearm about 50 mm from the wrist on its palmary side. An electro-magnetic pointer with an hair at- tached to its end was used for the experiment. It was then, through electric connection, attached to a metronome. So the rapidity of successive contacts was determined by the beats of the metronome and was gradually increased till they fused to an unitary sensation. By the application of this method it is observed that only two or three contacts in the sec. are felt as just separate, and so the duration of the sensa- tion of moderate intensity varies from .5 to .3 sec. But when the intensity of the stimulus is greatly increased or it becomes rather painful the duration is much altered. Not only the sensitivity of the areas but also the intensity of the stimuli employed affects considerably the duration: At the tip of the finger the number of the separately felt contacts increases per second and so the duration decreases while the intensity of contact is moderately felt. The objective intensity of con- tact varies subjectively in different areas of the skin. As the felt intensity of the stimulas is greater, the lingering sensation continues longer and so the duration increases. The results of this experiment given by other observers are widely divergent.1 The subjective difference of the intensity of con- tact may have caused greatly this varying result. The sub- ject A observes that though the continuity of contact is quite clear, but still a vague feeling of succession seems to be mixed

1 Kulpe, Outlines of Psychology, p. 383.

339

340 K. C. MUKHERJEE

in it. It appears that the stimulation spreads over to the neighbouring points in varying intensity and subsides therein earlier than in the point directly stimulated—thus causing the vague feeling of succession inter-mingling with the fusion. The wide divergence of results may also be due to the want of proper discrimination on this point.

II The same area which was explored for the duration of the

contact sensation was used to determine the improvement of its discriminative delicacy by practice. In making this ex- periment Spearmann’s aesthesiometer was used. The experi- ment was each day taken twice almost at the same time with two subjects—one male and the other female, and was con- tinued over a month. At each sitting thirty observations were made with each subject. The subject remained blind- fold with the arm comfortably placed on a ‘felt.’ The aesthe- siometer was applied to the skin uniformly and the distance between the points of contact was gradually increased or de- creased as required for the method. In order to put off the effect of fatigue, too many observations at one sitting were carefully avoided by dividing the series into three parts—and allowing a pause of ten minutes after the completion of each part. The regularity of the interval of 3 seconds between the successive applications of the aesthesiometer was throughout maintained. The following table will show the space limen in mm of each subject.

There is practically no difference of discrimination which can be marked in the observations of the subjects in their morning and evening sittings. It is also difficult to say, on the basis of a single instance that the variability of space limen, as shown in the table, is greater for the woman than for the man. The table shows that the discriminative delicacy im- proves greatly in the third and the fourth weeks of the ex- periment. Now the question arises—whether this improve- ment is particularly peripheral or central; that is to say whether the improvement is only of the particular part exer- cised or it is an improvement of sensible discrimination of

CUTANEOUS SENSATION

I

341

Date Subject I (Woman)

M

Subject II (Man)

M

November 3 November 4 November 5 November 6 November 7 November 8 November 9 Av. space limen 1st week

November 10 November 11 November 12 November 13 November 14 November 15 November 16 Av. sp. limen 2d week

November 17 November 18 November 19 November 20 November 21 November 22 November 23 Av. sp. limen or av. senst 3d week

November 24 November 25 November 26 November 27 November 38 November 29 November 30 Av. sp. limen 4th week

20 mm 16 mm 12 mm 20 mm 10 mm 9 mm 9 mm

13.7 mm

21 mm 19 mm 17 mm 15 mm 9 mm 9 mm 8 mm

14 mm

14 mm 16 mm 15 mm IS mm 12 mm 13 mm 13 mm 14 mm

15 mm 13 mm 17 mm 14 mm 15 mm 14 mm 12 mm

14.2 mm

9 mm 12 mm 10 mm 9 mm S mm 8 mm 8 mm

8.7 mm

9 mm 10 mm 9 mm 8 mm 9 mm 8 mm 6 mm

8.4 mm

12 mm 14 mm 10 mm 10 mm 11 mm 9 mm 9 mm

10.7 mm

10 mm 15 mm 9 mm

10 mm 9 mm

10 mm 9 mm

10.2 mm

S mm 3 mm 4 mm 3 mm 4 mm 3 mm 3 mm

3.5 mm

3 mm 4 mm 4 mm 4 mm 4 mm 3 mm 4 mm

3.7 mm

8 mm 6 mm 5 mm 6 mm 5 mm 4 mm 6 mm

5.5 mm

8 mm 7 mm 7 mm 6 mm 6 mm S mm S mm

6.2 mm

3 mm 3 mm 4 mm 3 mm 4 mm 3 mm 2 mm 3 mm

3 mm 3 mm S mm 3 mm 3 mm 3 mm 3 mm

3.2 mm

S mm 5 mm 6 mm S mm 7 mm 4 mm 5 mm

5.2 mm

5 mm 6 mm S mm 5 mm S mm 7 mm S mm

5.4 mm

contact in general and so its effect is to be found also in distant parts of the skin. Wundt views “the difference in the structure of the sense organ is the chief cause of the different quality of the sensation. . . .” So all the qualitative dif- ferences which belong to any single organ have their necessary basis in the smaller variations, which may appear in the structure, or in the arrangement of the end organ. This view may not be much directly related to the question, but its indirect bearing on it is quite clear. It is a peripheral account of the local sign and suggests, on that basis an ex- planation of the improvement in which the local sign is also

342 K. C. MUKHERJEE

involved. Dressier believes definitely that the improvement is local i.e. to the exercised part alone. But he admits he has not observed experimentally whether the sensibility is as a result raised outside.2

For proper investigation on this point the discriminative sensibility of three different points on each of the two forearms of each subject was, at the beginning recorded and then compared with the sensibility as afterwards found of the points after the completion of the experiment. The results are given in the table II for comparison.

II

Subject I

Before practice After practice

Subject II

Before practice After practice

a

19 4

a

16 7

Left fore-ann

b

20 3.2

6

14 5.2

c

22 5

c

12 8

d

21 4

d

16 9

Right fore-ann

b”

22 4

b”

IS 7

e

18 S-3

e

IS 6

b is the exercised part of the left forearm and b” its sym- metrical part of the right forearm while a, c; and d, e; are the non-symmetrical parts taken on them. The table shows that the improvement is most in the exercised part but its effect is greatly noticeable also in other parts. It cannot here be said definitely that the symmetrical parts evince any greater effect of the improvement. After a week’s interval the experiment was again made, but it was then found that the improved sensibility was greatly lost.

s Dressier, Psychology of touch, Arner. J. Psych., 1893, p. 329.