Sixteen Experimental Investigations from the Harvard Psychological Laboratory - Hugo Münsterberg (best life changing books txt) 📗
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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
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