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

the filled space was a most important factor in producing an illusory

judgment of distance.

The overestimation of these filled spaces is evidently due in a large

measure to æsthetic motives. The space that is filled with agreeable

sensations is judged shorter than one which is filled with

disagreeable sensations. In other words, the illusions in judgments on

cutaneous space are not so much dependent on the quality of sensations

that we get from the outer world through these channels, as from the

amount of inner activity that we set over against these bare

sense-perceptions.

I have already spoken of the defects of this method of measuring off

equivalent distances as a means of getting at the quantitative amount

of the illusion. The results that have come to light thus far have,

however, amply justified the method. I had no difficulty, however, in

adapting my apparatus to the other way of getting the judgments. I had

a short curved piece of wire inserted in the handle, which could be

held across the line traversed, and thus the end of the open space

could be marked out. Different lengths were presented to the subject

as before, but now the subject passed his finger in a uniform motion

over the spaces, after which he pronounced the judgment ‘greater,’

‘equal,’ or ‘less.’ The general result of these experiments was not

different from those already given. The short, filled spaces were

overestimated, while the longer ones were underestimated. The only

difference was found to be that now the transition from one direction

to the other was at a more distant point. It was, of course, more

difficult to convert these qualitative results into a quantitative

determination of the illusion.

Before passing to the experiments in which the open spaces were

presented first, I wish to offer an explanation for the divergent

tendencies that were exhibited through all the experiments of the last

two sections, namely, that the short filled spaces are overestimated

and the long spaces underestimated. Let us take two typical judgments,

one in which a filled space of 3 cm. is judged equal to an open space

of 4.2 cm., and then one in which the filled space is 9 cm., and is

judged equal to an open space of 7.4 cm. In the case of the shorter

distance, because of its shortness, after the finger leaves it, it is

held in a present state of consciousness for some moments, and does

not suffer the foreshortening that comes from pastness. This is,

however, only a part of the reason for its overestimation. After the

finger-tip has left the filled space, and while it is traversing the

first part of the open space, there is a dearth of sensations. The

tactual sensations are meager and faint, and muscular tensions have

not yet had time to arise. It is not until the finger has passed over

several centimeters of the distance, that the surprise of its

barrenness sets up the organic sensations of muscular strain. One

subject remarked naïvely at the end of some experiments of this kind,

that the process of judging was an easy and comfortable affair so long

as he was passing over the filled space, but when he set out upon the

open space he had to pay far more strict attention to the experiment.

By a careful introspection of the processes in my own case, I came to

the conclusion that it is certainly a combination of these two

illusions that causes the overestimation of the short filled

distances. In the case of the long distances, the underestimation of

the filled space is, I think, again due to a combination of two

illusions. When the finger-tip leaves the filled space, part of it,

because of its length, has already, as it were, left the specious

present, and has suffered the foreshortening effect of being relegated

to the past. And, on the other hand, after the short distance of the

open space has been traversed the sensations of muscular strain become

very pronounced, and cause a premature judgment of equality.

One subject, who was very accurate in his judgments, and for whom the

illusion hardly existed, said, when asked to explain his method of

judging, that after leaving the filled space he exerted a little more

pressure with his finger as he passed over the open space, so as to

get the same quantity of tactual sensations in both instances. The

muscular tension that was set up when the subject had passed out over

the open space a short way was very plainly noticeable in some

subjects, who were seen at this time to hold their breath.

I have thus far continually spoken of the space containing the tacks

as being the filled space, and the smooth surface as the open space.

But now we see that in reality the name should be reversed, especially

for the longer distances. The smooth surface is, after the first few

centimeters, very emphatically filled with sensations arising from the

organism which, as I have already intimated, are of the most vital

importance in our spatial judgments. Now, according to the most

generally accepted psychological theories, it is these organic

sensations which are the means whereby we measure time, and our

spatial judgments are, in the last analysis, I will not for the

present say dependent on, but at any rate fundamentally related to our

time judgments.

VIII.

In the last section I attempted to explain the overestimation of short

filled spaces, and the underestimation of long filled spaces by active

touch, as the result of a double illusion arising from the differences

in the manner and amount of attention given to the two kinds of

spaces when they are held in immediate contrast. This explanation was

of course purely theoretical. I have thus far offered no experiments

to show that this double illusion of lengthening, on the one hand, and

shortening, on the other, does actually exist. I next made some simple

experiments which seemed to prove conclusively that the phenomenon

does not exist, or at least not in so important a way, when the time

factor is not permitted to enter.

In these new experiments the filled and the open spaces were compared

separately with optical distances. After the finger-tip was drawn over

the filled path, judgment was given on it at once by comparing it

directly with an optical distance. In this way the foreshortening

effect of time was excluded. In all these experiments it was seen that

the filled space was judged longer when the judgment was pronounced on

it at once than when an interval of time was allowed, either by

drawing the finger-tip out over the open space, as in the previous

experiment, or by requiring the subject to withhold his judgment until

a certain signal was given. Any postponement of the judgment resulted

in the disappearance of a certain amount of the illusion. The

judgments that were made rapidly and without deliberation were subject

to the strongest illusion. I have already spoken of the unanimous

testimony which all who have made quantitative studies in the

corresponding optical illusions have given in this matter of the

diminution of the illusion with the lapse of time. The judgments that

were made without deliberation always exhibited the strongest tendency

to illusion.

I have already said that the illusion for passive touch was greatest

when the two spaces were presented simultaneously and adjacent.

Dresslar has mentioned in his studies on the ‘Psychology of Touch,’

that the time factor cannot enter into an explanation of this

illusion; but the experiments of which I have just spoken seem to

point plainly to a very intimate relation between this illusion and

the illusions in our judgments of time. We have here presented on a

diminutive scale the illusions which we see in our daily experience in

comparing past with present stretches of time. It is a well-known

psychological experience that a filled time appears short in passing,

but long in retrospect, while an empty time appears long in passing,

but short in retrospect. Now this illusion of the open and filled

space, for the finger-tip, is at every point similar to the illusion

to which our time judgment is subject. If we pronounce judgment on a

filled space or filled time while we are still actually living in it,

it seems shorter than it really is, because, while we pay attention to

the discrete sensations of external origin, we lose sight of the

sensations of internal origin, which are the sole means whereby we

measure lapse of time, and we consequently underestimate such

stretches of time or space. But when the sensations from the outer

world which enter into such filled spaces or times exist only in

memory, the time-measuring sensations of internal origin are allowed

their full effect; and such spaces and times seem much longer than

when we are actually passing through them.

I dwell on this illusion at a length which may seem out of proportion

to its importance. My object has been to show how widely different are

the objective conditions here from what they are in the optical

illusion which has so often been called the analogue of this.

James[14] has said of this tactual illusion: ‘This seems to bring

things back to the unanalyzable laws, by reason of which our feeling

of size is determined differently in the skin and in the retina even

when the objective conditions are the same.’ I think that my

experiments have shown that the objective conditions are not the same;

that they differ in that most essential of all factors, namely, the

time element. Something very nearly the analogue of the optical

illusion is secured when we take very short open and filled tactual

spaces, and move over them very rapidly. Here the illusion exists in

the same direction as it does for sight, as has already been stated.

On the other hand, a phenomenon more nearly parallel to the tactual

illusion, as reported in the experiments of James and Dresslar, is

found if we take long optical distances, and traverse the open and

filled spaces continuously, without having both parts of the line

entirely in the field of view at any one moment. I made a few

experiments with the optical illusion in this form. The filled and

open spaces were viewed by the subject through a slot which was

passed over them. These experiments all pointed in the direction of an

underestimation of a filled space. Everywhere in this illusion, then,

where the objective conditions were at all similar for sight and

touch, the resulting illusion exists in the same direction for both

senses.

[14] James, William, ‘Principles of Psychology,’ New York, II.,

p. 250.

Throughout the previous experiments with the illusion for active touch

we saw the direct influence of the factor of time. I have yet one set

of experiments to report, which seems to me to prove beyond the

possibility of a doubt the correctness of my position. These

experiments were made with the apparatus shown in Fig. 10. The

subjects proceeded precisely as before. The finger-tip was passed over

the filled space, and then out over the open space, until an

equivalent distance was measured off. But while the subject was

drawing his fingers over the spaces, the block A was moved in either

direction by means of the lever B. The subjects were all the while

kept ignorant of the fact that the block was being moved. They all

expressed great surprise on being told, after the experiments were

over, that the block had been moved under the finger-tip through such

long distances without their being able to detect it. The block always

remained stationary as the finger passed over one space, but was moved

either with or against the finger as it