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

a difference. The subjects seem to feel very uncertain about their

answers, and it looks very much like guess-work, but something caused

the guesses to go more in one direction than in the other.

Two were called less than one …. 16% of the times given.

” ” ” equal to …. 48% ” “

” ” ” greater than …. 36% ” “

Approximately half of the time two were called equal to one, and if

there had been no difference in the sensations half of the remaining

judgments should have been that two was smaller than one, but two were

called larger than one more than twice as many times as one was called

larger than two. There was such uniformity in the reports of the

different subjects that no one varied much from this average ratio.

This experiment seems to indicate a very slight power of

discrimination of stimulations within the threshold. In striking

contrast to this is the power to perceive variations of distance

between two points outside the threshold. To test this the

æsthesiometer was spread enough to bring the points outside the

threshold. The back of the hand was then stimulated with the two

points and then the distance varied slightly, the hand touched and the

subject asked to tell which time the points were farther apart. A

difference of 2 mm. was usually noticed, and one of from 3 to 5 mm.

was noticed always very clearly.

I wondered then what would be the result if small cards set parallel

to each other were used in place of the knobs of the æsthesiometer. I

made an æsthesiometer with cards 4 mm. long in place of knobs. These

cards could be set at any angle to each other. I set them at first 10

mm. apart and parallel to each other and asked the subjects to compare

the contact made by them with a contact by one card of the same size.

The point touched by the one card was always between the points

touched by the two cards, and the one card was put down so that its

edge would run in the same direction as the edges of the other cards.

The result of this was that:

Two were called less, 14 per cent.

” ” ” equal, 36 ” “

” ” ” greater, 50 ” “

I then increased the distance of the two cards to 15 mm., the other

conditions remaining the same, and found that:

Two were called less, 11 per cent.

” ” ” equal, 50 ” “

” ” ” greater, 39 ” “

It will be noticed that the ratio in this last series is not

materially different from the ratio found when the two knobs of the

æsthesiometer were compared with one knob. The ratio found when the

distance was 10 mm., however, is somewhat different. At that distance

two were called greater half of the time, while at 15 mm. two were

called equal to one half of the time. The explanation of the

difference, I think, is found in the comments of one of my subjects. I

did not ask them to tell in what way one object was larger than the

other—whether longer or larger all around or what—but simply to

answer ‘equal,’ ‘greater,’ or ‘less.’ One subject, however, frequently

added more to his answers. He would often say ‘larger crosswise’ or

‘larger lengthwise’ of his hand. And a good deal of the time he

reported two larger than one, not in the direction in which it really

was larger, but the other way. It seems to me that when the two cards

were only 10 mm. apart the effect was somewhat as it would be if a

solid object 4 mm. wide and 10 mm. long had been placed on the hand.

Such an object would be recognized as having greater mass than a line

4 mm. long. But when the distance is 15 mm. the impression is less

like that of a solid body but still not ordinarily like two objects.

In connection with the subject of diffusion the Vexirfehler is of

interest. An attempt was made to develop the Vexirfehler with the

æsthesiometer. Various methods were tried, but the following was most

successful. I would tell the subject that I was going to use the

æsthesiometer and ask him to close his eyes and answer simply ‘one’ or

‘two.’ He would naturally expect that he would be given part of the

time one, and part of the time two. I carefully avoided any suggestion

other than that which could be given by the æsthesiometer itself. I

would begin on the back of the hand near the wrist with the points as

near the threshold as they could be and still be felt as two. At each

successive putting down of the instrument I would bring the points a

little nearer together and a little lower down on the hand. By the

time a dozen or more stimulations had been given I would be working

down near the knuckles, and the points would be right together. From

that on I would use only one point. It might be necessary to repeat

this a few times before the illusion would persist. A great deal seems

to depend on the skill of the operator. It would be noticed that the

first impression was of two points, and that each stimulation was so

nearly like the one immediately preceding that no difference could be

noticed. The subject has been led to call a thing two which ordinarily

he would call one, and apparently he loses the distinction between the

sensation of one and the sensation of two. After going through the

procedure just mentioned I put one knob of the æsthesiometer down one

hundred times in succession, and one subject (Mr. Meakin) called it

two seventy-seven times and called it one twenty-three times. Four of

the times that he called it one he expressed doubt about his answer

and said it might be two, but as he was not certain he called it one.

Another subject (Mr. George) called it two sixty-two times and one

thirty-eight times. A third subject (Dr. Hylan) called it two

seventy-seven times and one twenty-three times. At the end of the

series he was told what had been done and he said that most of his

sensations of two were perfectly distinct and he believed that he was

more likely to call what seemed somewhat like two one, than to call

what seemed somewhat like one two. With the fourth subject (Mr.

Dunlap) I was unable to do what I had done with the others. I could

get him to call one two for four or five times, but the idea of two

would not persist through a series of any length. He would call it two

when two points very close together were used. I could bring the knobs

within two or three millimeters of each other and he would report two,

but when only one point was used he would find out after a very few

stimulations were given that it was only one. After I had given up the

attempt I told him what I had been trying to do and he gave what seems

to me a very satisfactory explanation of his own case. He says the

early sensations keep coming up in his mind, and when he feels like

calling a sensation two he remembers how the first sensation felt and

sees that this one is not like that, and hence he calls it one. I pass

now to a brief discussion of what these experiments suggest.

It has long been known that two points near together on the skin are

often perceived as one. It has been held that in order to be felt as

two they must be far enough apart to have a spatial character, and

hence the distance necessary for two points to be perceived has been

called the ‘space-threshold.’ This threshold is usually determined

either by the method of minimal changes or by the method of right and

wrong cases.

If, in determining a threshold by the method of minimal changes—on

the back of the hand, for example, we assume that we can begin the

ascending series and find that two are perceived as one always until

the distance of twenty millimeters is reached, and that in the

descending series two are perceived as two until the distance of ten

millimeters is reached, we might then say that the threshold is

somewhere between ten and twenty millimeters. But if the results were

always the same and always as simple as this, still we could not say

that there is any probability in regard to the answer which would be

received if two contacts 12, 15, or 18 millimeters apart were given by

themselves. All we should know is that if they form part of an

ascending series the answer will be ‘one,’ if part of a descending

series ‘two.’

The method of right and wrong cases is also subject to serious

objections. There is no lower limit, for no matter how close together

two points are they are often called two. If there is any upper limit

at all, it is so great that it is entirely useless. It might be argued

that by this method a distance could be found at which a given

percentage of answers would be correct. This is quite true, but of

what value is it? It enables one to obtain what one arbitrarily calls

a threshold, but it can go no further than that. When the experiment

changes the conditions change. The space may remain the same, but it

is only one of the elements which assist in forming the judgment, and

its importance is very much overestimated when it is made the basis

for determining the threshold.

Different observers have found that subjects sometimes describe a

sensation as ‘more than one, but less than two.’ I had a subject who

habitually described this feeling as ‘one and a half.’ This does not

mean that he has one and a half sensations. That is obviously

impossible. It must mean that the sensation seems just as much like

two as it does like one, and he therefore describes it as half way

between. If we could discover any law governing this feeling of

half-way-between-ness, that might well indicate the threshold. But

such feelings are not common. Sensations which seem between one and

two usually call forth the answer ‘doubtful,’ and have a negative

rather than a positive character. This negative character cannot be

due to the stimulus; it must be due to the fluctuating attitudes of

the subject. However, if the doubtful cases could be classed with the

‘more than one but less than two’ cases and a law be found governing

them, we might have a threshold mark. But such a law has not been

formulated, and if it had been an analysis of the ‘doubtful’ cases

would invalidate it. For, since we cannot have half of a sensation or

half of a place as we might have half of an area, the subject regards

each stimulation as produced by one or by two points as the case may

be. Occasionally he is stimulated in such a way that he can regard the

object as two or as one with equal ease. In order to describe this

feeling he is likely to use one or the other of the methods just

mentioned.

We might say that when the sum of conditions is such that the subject

perceives two points, the points are above the threshold, and when the

subject perceives one point when two are given they are below the

threshold. This