Sixteen Experimental Investigations from the Harvard Psychological Laboratory by Hugo Münsterberg (100 books to read .txt) 📕

easily detached from the upright rods at K and L. Each of the

points by which the contacts were made moved easily along the sliding

rule, and could be also raised or lowered for accommodation to the

unevenness of the surface of the skin. These latter were the most

valuable two features of the apparatus. There were two sets of points,

one of hard rubber, the other of metal. This enabled me to take into

account, to a certain extent, the factor of temperature. A wide range

of apparent differences in temperature was secured by employing these

two stimuli of such widely different conductivity. Then, as each point

was independent of the rest in its movements, its weight could also be

changed without affecting the rest.

In the first series of experiments I endeavored to reproduce for touch

the optical illusion in its exact form. There the open and the filled

spaces are adjacent to each other, and are presented simultaneously

for passive functioning of the eye, which is what concerns us here in

our search for the analogue of passive touch. This was by no means an

easy task, for obviously the open and the filled spaces in this

position on the skin could not be compared directly, owing to the lack

of uniformity in the sensibility of different portions of the skin. At

first, equivalents had to be established between two collinear open

spaces for the particular region of the skin tested. Three points were

taken in a line, and one of the end points was moved until the two

adjacent open spaces were pronounced equal. Then one of the spaces was

filled, and the process of finding another open space equivalent to

this filled space was repeated as before. This finding of two

equivalent open spaces was repeated at frequent intervals. It was

found unsafe to determine an equivalent at the beginning of each

sitting to be used throughout the hour.

Two sets of experiments were made with the illusion in this form. In

one the contacts were made simultaneously; the results of this series

are given in Table I. In the second set of experiments the central

point which divided the open from the filled space touched the skin

first, and then the others in various orders. The object of this was

to prevent fusion of the points, and, therefore, to enable the subject

to pronounce his judgments more rapidly and confidently. A record of

these judgments is given in Table II. In both of these series the

filled space was always taken near the wrist and the open space in a

straight line toward the elbow, on the volar side of the arm. At

present, I shall not undertake to give a complete interpretation of

the results of these two tables, but simply call attention to two

manifest tendencies in the figures. First, it will be seen that the

short filled distance of four centimeters is underestimated, but that

the long filled distance is overestimated. Second, in Table II., which

represents the judgments when the contacts were made successively, the

tendency to underestimate the short distance is less, and at the same

time we notice a more pronounced overestimation of the longer filled

distances. I shall give a further explanation of these results in

connection with later tables.

TABLE I.

4 cm. 6 cm. 8 cm.

Filled. Open. Filled. Open. Filled. Open.

F. 5.3 4.7 7.8 7.6 9.3 10.5

F. 5.7 4.4 6.5 7.3 9.2 11.7

F. 6.0 5.6 8.2 7.3 8.7 10.8

– – – – – –-

Av. 5.7 4.9 7.5 7.4 9.1 11.0

R. 5.7 5.1 6.7 6.8 9.3 10.2

R. 5.4 5.4 7.2 7.1 8.5 10.7

R. 4.6 4.2 8.1 8.1 9.1 11.4

– – – – – –-

Av. 5.2 4.9 7.3 7.3 9.0 10.8

K. 5.6 5.1 6.8 6.7 8.1 9.6

K. 5.0 5.1 7.3 7.5 8.2 11.2

K. 4.9 4.9 8.2 8.1 10.1 10.1

– – – – –- –-

Av. 5.2 5.0 7.4 7.4 8.8 10.3

TABLE II.

4 cm. 6 cm. 8 cm.

Filled. Open. Filled. Open. Filled. Open.

F. 5.1 5.0 8.0 8.3 9.2 10.3

F. 5.8 4.7 7.2 7.9 8.7 10.9

F. 5.6 5.5 6.9 9.1 9.1 11.1

– – – – – –-

Av. 5.5 5.1 7.4 8.4 9.0 10.8

R. 6.0 4.8 8.2 7.5 9.4 10.6

R. 5.7 5.4 6.5 7.4 10.1 9.4

R. 5.0 5.2 7.7 7.8 8.6 11.2

– – – – –- –-

Av. 5.6 5.1 7.5 7.6 9.4 10.4

K. 4.8 4.8 8.2 8.3 8.1 9.8

K. 5.1 5.3 7.1 7.7 10.0 10.8

K. 4.7 5.0 8.1 8.6 8.6 9.4

– – – – –- –-

Av. 4.9 5.0 7.8 8.2 8.9 10.0

The first two numbers in the first line signify that when an

open distance of 4 cm. was taken, an adjacent open distance of

4.7 cm. was judged equal; but when the adjacent space was

filled, 5.3 cm. was judged equal. Each number in the column of

filled distances represents an average of five judgments. All

of the contacts in Table I. were made simultaneously; in Table

II. they were made successively.

In the next series of experiments the illusion was approached from an

entirely different point of view. The two points representing the open

space were given on one arm, and the filled space on a symmetrical

part of the other arm. I was now able to use a much wider range of

distances, and made many variations in the weights of the points and

the number that were taken for the filled distance.

However, before I began this second series, in which one of the chief

variations was to be in the weights of the different points, I made a

brief preliminary series of experiments to determine in a general way

the influence of pressure on judgments of point distances. Only three

distances were employed, four, six and twelve centimeters, and three

weights, twelve, twenty and forty grams. Table III. shows that, for

three men who were to serve as subjects in the main experiments that

are to follow, an increase in the weight of the points was almost

always accompanied by an increase in the apparent distance.

TABLE III.

Distances. 4 cm. 6 cm. 12 cm.

Weights

(Grams). 12 20 40 12 20 40 12 20 40

R. 3.9 3.2 3.0 6.2 5.6 5.3 11.4 10.4 9.3

F. 4.3 4.0 3.6 6.1 5.3 5.5 12.3 11.6 10.8

B. 4.1 3.6 3.1 6.0 5.7 5.8 12.0 10.2 9.4

P. 4.3 4.1 3.7 5.9 5.6 5.6 13.1 11.9 10.7

In the standard distances the points were each weighted to 6

grams. The first three figures signify that a two-point

distance of 4 cm., each point weighing 6 grams, was judged

equal to 3.9 cm. when each point weighed 12 grams. 3.2 cm.

when each point weighed 20 grams, etc. Each figure is the

average of five judgments.

Now the application of this principle in my criticism of Parrish’s

experiments, and as anticipating the direction which the following

experiments will take, is this: if we take a block such as Parrish

used, with only two points in it, and weight it with forty grams in

applying it to the skin, it is plain that each point will receive one

half of the whole pressure, or twenty grams. But if we put a pressure

of forty grams upon a block of eight points, each point will receive

only one eighth of the forty, or five grams. Thus, in the case of the

filled space, the end points, which play the most important part in

the judgment of the distance, have each only five grams’ pressure,

while the points in the open space have each twenty grams. We should,

therefore, naturally expect that the open space would be

overestimated, because of the decided increase of pressure at these

significant points. Parrish should have subjected the blocks, not to

the same pressure, but to a pressure proportional to the number of

points in each block. With my apparatus, I was easily able to prove

the correctness of my position here. It will be seen in Tables IV. to

VIII. that, when the sum of the weights of the two end points in the

open space was only just equal to the sum of the weights of all the

points in the filled space, the filled space was underestimated just

as Parrish has reported. But when the points were all of the same

weight, both in the filled and the open space, the filled space was

judged longer in all but the very short distances. For this latter

exception I shall offer an explanation presently.

Having now given an account of the results of this digression into

experiments to determine the influence of pressure upon point

distances, I shall pass to the second series of experiments on the

illusion in question. In this series, as has been already stated, the

filled space was taken on one arm and the open on the other, and then

the process was reversed in order to eliminate any error arising from

a lack of symmetry between the two regions. Without, for the present,

going into a detailed explanation of the statistics of this second

series of experiments, which are recorded in Tables IV., V., VI.,

VII. and VIII., I may summarize the salient results into these general

conclusions: First, the short filled distance is underestimated;

second, this underestimation of the filled space gradually decreases

until in the case of the filled distance of 18 cm. the judgments pass

over into pronounced overestimations; third, an increase in the number

of points of contact in the shorter distances increases the

underestimation, while an increase in the number of points in the

longer distance increases the overestimation; fourth, an increase of

pressure causes an invariable increase in the apparent length of

space. If a general average were made of the results given in Tables

IV., V., VI., VII. and VIII., there would be a preponderance of

evidence for the conclusion that the filled spaces are overestimated.

But we cannot ignore the marked tendencies in the opposite direction

for the long and the short distances. These anomalous results, which,

it will be remembered, were also found in our first series, call for

explanation. Several hypotheses were framed to explain these

fluctuations in the illusion, and then some shorter series of

experiments were made in different directions with as large a number

of variations in the conditions as possible, in the hope of

discovering the disturbing factors.

TABLE IV.¹

4 Centimeters.

A B D E

less = gr. less = gr. less = gr. less = gr.

R. (a) 7 2 1 8 1 1 6 2 2 5 1 4

(b) 7 3 0 7 1 2 6 2 2 6 1 3

F. (a) 6 3 1 7 1 2 7 0 3 6 0 4

(b) 7 0 3 9 1 0 6 1 3 5 2 3

––- ––— ––— ––—

27 8 5 31 4 5 25 5 10 22 4 14

¹In columns A, B, and C the filled spaces were made up

of 4, 5 and 6 points, respectively. The total weight of the

filled space in A, B and C was always just equal to the

weight of the two points in the open space, 20 gr. In (a)

the filled distance was given on the right arm first, in (b)

on the left arm. It will be observed that this reversal made

practically no difference in the judgments and therefore was

sometimes omitted. In D the filled space consisted of four

points, but here the weight of each point was 10 gr., making a

total