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

cutaneous distances made indirectly

by means of localization, and judgments that are pronounced directly

upon the subjective experience of the distance.

 

In the first of these experiments, in which two points of different

weight were used, the points were always taken safely outside of the

threshold for the discrimination between two points in the particular

region of the skin operated on. An inspection of the results shown in

Figs. 2 and 3 will indicate the marked tendency of the heavier point

to attract the lighter. In Figs. 2 and 3 the heavy curves were plotted

from judgments where both heavy and light points were given together.

The dotted curve represents the localization of each point when given

alone. The height of the curves at any particular point is determined

by the number of times a contact was judged to be directly under that

point. The fact that the curves are higher over the heavy points shows

that, when two points were taken as one, this one was localized in the

vicinity of the heavier point. When points were near the threshold for

any region, it will be observed that the two points were attracted to

each other. But when the points were altogether outside the threshold,

they seemed strangely to have repelled each other. As this problem lay

somewhat away from my main interest here, I did not undertake to

investigate this peculiar fluctuation exhaustively. My chief purpose

was satisfied when I found that the lighter point is displaced toward

the heavier, in short distances. A further explanation of these

figures will be given in connection with similar figures in the next

section.

 

[Illustration: FIG. 2. Back of hand.]

 

[Illustration: FIG. 3. Forearm.]

 

This attraction of the heavier for the lighter points is, I think, a

sufficient explanation for the variations in judgments upon filled

distances where changes are made in the place at which the pressure is

applied. I furthermore believe that an extension of this principle

offers an explanation for the underestimation of cutaneous

line-distances, which has been frequently reported from various

laboratories. Such a straight line gives a subjective impression of

being heavier at the center. I found that if the line is slightly

concave at the center, so as to give the ends greater prominence and

thereby leave the subjective impression that the line is uniform

throughout its entire length, the line will be overestimated in

comparison with a point distance. Out of one hundred judgments on the

relative length of two hard-rubber lines of 5 cm. when pressed against

the skin, one of which was slightly concave, the concave line was

overestimated eighty-four times. For sight, a line in which the shaded

part is concentrated at the center appears longer than an objectively

equal line with the shading massed towards the ends.

 

IV.

 

In the last section, I gave an account of some experiments in the

localization of touch sensations which were designed to show how,

under varying pressure, the points in the filled distance are

displaced or fused and disappear entirely from the judgment. Our

earliest experiments, it will be remembered, yielded unmistakable

evidence that short, filled distances were underestimated; while all

of the secondary experiments reported in the last section have pointed

to the conclusion that even these shorter distances will follow the

law of the longer distances and be overestimated under certain

objective conditions, which conditions are also more nearly parallel

with those which we find in the optical illusion. I wish now to give

the results of another and longer set of experiments in the

localization of a manifold of touch sensations as we find them in this

same illusion for filled space, by which I hope to prove a direct

relation between the function of localization and the spatial

functioning proper.

 

These experiments were made with the same apparatus and method that

were used in the previous study in localization; but instead of two

points of different weights, four points of uniform weight were

employed. This series, therefore, will show from quite another point

of view that the fusion which takes place, even where there is no

difference in the weight, is a very significant factor in judgments of

distance on the skin.

 

[Illustration: Fig. 4.]

 

I need hardly say that here, and in all my other experiments, the

subjects were kept as far as possible in complete ignorance of the

object of the experiment. This and the other recognized laboratory

precautions were carefully observed throughout this work. Four

distances were used, 4, 8, 12 and 16 cm. At frequent intervals

throughout the tests the contact was made with only one of the points

instead of four. In this way there came to light again the interesting

fact which we have already seen in the last section, which is of great

significance for my theory—that the end points are located

differently when given alone than when they are presented

simultaneously with the other points. I give a graphic representation

of the results obtained from a large number of judgments in Figs. 4, 5

and 6. These experiments with filled spaces, like the earlier

experiments, were made on the volar side of the forearm beginning near

the wrist. In each distance four points were used, equally distributed

over the space. The shaded curve, as in the previous figures,

represents the results of the attempts to localize the points when all

four were given simultaneously. In the dotted curves, the end points

were given alone. The height of the curve at any place is determined

by the number of times a point was located immediately underneath that

particular part of the curve. In Fig. 4 the curve which was determined

by the localization of the four points when given simultaneously,

shows by its shape how the points appear massed towards the center. In

Fig. 5 the curve AB shows, by its crests at A and B, that the

end points tended to free themselves from the rest in the judgments.

But if the distance AB be taken to represent the average of the

judgments upon the filled space 1, 2, 3, 4, it will be seen to be

shorter than what may be regarded as the average of the judgments upon

the corresponding open space, namely, the distance A’B’, determined

by the localizations of the end points alone. The comparative

regularity of the curve indicates that the subject was unable to

discriminate among the points of the filling with any degree of

certainty. The localizations were scattered quite uniformly along the

line. In these short distances the subject often judged four points as

two, or even one.

 

[Illustration: Fig. 5.]

 

[Illustration: Fig. 6.]

 

Turning to Fig. 6, we notice that the tendency is now to locate the

end points in the filled distance outside of the localization of these

same points when given without the intermediate points. It will also

be seen from the irregularities in these two longer curves that there

is now a clear-cut tendency to single out the individual points. The

fact that the curves here are again higher over point 4 simply

signifies that at this, the wrist end, the failure to discover the

presence of the points was less frequent than towards the elbow. But

this does not disturb the relation of the two series of judgments. As

I have before said, the first two sets of experiments described in

Section II. showed that the shorter filled distances are

underestimated, while the longer distances are overestimated, and that

between the two there is somewhat of an ‘indifferent zone.’ In those

experiments the judgments were made directly on the cutaneous

distances themselves. In the experiments the results of which are

plotted in these curves, the judgment of distances is indirectly

reached through the function of localization. But it will be observed

that the results are substantially the same. The longer distances are

overestimated and the shorter distances underestimated. The curves in

Figs. 4, 5 and 6 were plotted on the combined results for two

subjects. But before the combination was made the two main tendencies

which I have just mentioned were observed to be the same for both

subjects.

 

It will be remembered also that in these experiments, where the

judgment of distance was based directly on the cutaneous impression,

the underestimation of the short, filled distance was lessened and

even turned into an overestimation, by giving greater distinctness to

the end points, in allowing them to come in contact with the skin just

before or just after the filling. The results here are again the same

as before. The tendency to underestimate is lessened by this device.

Whenever, then, a filled space is made up of points which are

distinctly perceived as discrete—and this is shown in the longer

curves by the comparative accuracy with which the points are

located—these spaces are overestimated.

 

In all of these experiments on localization, the judgments were given

with open eyes, by naming the visual points under which the tactual

points seemed to lie. I have already spoken of the other method which

I also employed. This consisted in marking points on paper which

seemed to correspond in number and position to the points on the skin.

During this process the eyes were kept closed. This may appear to be a

very crude way of getting at the illusion, but from a large number of

judgments which show a surprising consistency I received the emphatic

confirmation of my previous conclusion, that filled spaces were

overestimated. These experiments were valuable also from the fact that

here the cutaneous space was estimated by the muscle sense, or active

touch, as it is called.

 

In the experiments so far described the filling in of the closed space

was always made by means of stationary points. I shall now give a

brief account of some experiments which I regard as very important for

the theory that I shall advance later. Here the filling was made by

means of a point drawn over the skin from one end of a two-point

distance to the other.

 

These experiments were made on four different parts of the skin—the

forehead, the back of the hand, the abdomen, and the leg between the

knee and the thigh. I here forsook the plan which I had followed

almost exclusively hitherto, that of comparing the cutaneous distances

with each other directly. The judgments now were secured indirectly

through the medium of visual distances. There was placed before the

subject a gray card, upon which were put a series of two-point

distances ranging from 2 to 20 cm. The two-point distances were given

on the skin, and the subject then selected from the optical distances

the one that appeared equal to the cutaneous distance. This process

furnished the judgments on open spaces. For the filled spaces,

immediately after the two-point distance was given a blunt stylus was

drawn from one point to the other, and the subject then again selected

the optical distance which seemed equal to this distance filled by the

moving point.

 

The results from these experiments point very plainly in one

direction. I have therefore thought it unnecessary to go into any

further detail with them than to state that for all subjects and for

all regions of the skin the filled spaces were overestimated. This

overestimation varied also with the rate of speed at which the stylus

was moved. The overestimation is greatest where the motion is slowest.

 

Vierordt[7] found the same result in his studies on the time sense,

that is, that the more rapid the movement, the shorter the distance

seems. But lines drawn on the skin are, according to him,

underestimated in comparison with open two-point distances. Fechner[8]

also reported that a line drawn on the skin is judged shorter than the

distance between two points which are merely touched. It will be