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

had no finger. A moment’s reflection would usually tell him it must be

an illusion, but the sensation of this illusory finger was as definite

as that of any of his real fingers. In such cases the subject seemed

to perceive the relation of the points to each other, but failed to

connect them with the right fingers. For instance, if contacts were

made on the first, second and third fingers, the first might be

located on the first finger, the third on the second finger, and then

the second would be located in between.

So far my attention had been given almost entirely to fusion, but the

tendency on the part of all subjects to report more contacts than were

actually given was so noticeable that I concluded that diffusion was

nearly as common as fusion and about as easy to produce. It also

seemed that the element of weight might play some part, but just what

effect it had I was uncertain. I felt, too, that knowledge of the

apparatus gained through sight was giving the subjects too much help.

The subjects saw the apparatus every day and knew partly what to

expect, even though the eyes were closed when the contacts were made.

A more efficient apparatus seemed necessary, and, therefore, before

taking up the work again in 1900, I made a new apparatus.

Not wishing the subjects to know anything about the nature of the

machine or what could be done with it, I enclosed it in a box with an

opening in one end large enough to allow the subject’s hand to pass

through, and a door in the other end through which I could operate. On

the inside were movable wooden levers, adjustable to hands of

different width. These were fastened by pivotal connection at the

proximal end. At the outer end of each of these was an upright strip

with a slot, through which was passed another strip which extended

back over the hand. This latter strip could be raised or lowered by

means of adjusting screws in the upright strip. On the horizontal

strip were pieces of wood made so as to slide back and forth. Through

holes in these pieces plungers were passed. At the bottom of each

plunger was a small square piece of wood held and adjusted by screws.

From this piece was suspended a small thimble filled with shot and

paraffine. The thimbles were all equally weighted. Through a hole in

the plunger ran a thread holding a piece of lead of exactly the weight

of the thimble. By touching a pin at the top this weight could be

dropped into the thimble, thus doubling its weight. A screw at the top

of the piece through which the plunger passed regulated the stop of

the plunger. This apparatus had three important advantages. It was

entirely out of sight, it admitted of rapid and accurate adjustment,

and it allowed the weights to be doubled quickly and without

conspicuous effort.

For the purpose of studying the influence of weight on the judgments

of number I began a series of experiments to train the subjects to

judge one, two, three, or four contacts at once. For this the bare

metal thimbles were used, because it was found that when they were

covered with chamois skin the touch was so soft that the subjects

could not perceive more than one or two with any degree of accuracy,

and I thought it would take entirely too long to train them to

perceive four. The metal thimbles, of course, gave some temperature

sensation, but the subject needed the help and it seemed best to use

the more distinct metal contacts.

In this work I had seven subjects, all of whom had had some experience

in a laboratory, most of them several years. Each one took part one

hour a week. The work was intended merely for training, but a few

records were taken each day to see how the subjects progressed. The

object was to train them to perceive one, two, three, and four

correctly, and not only to distinguish four from three but to

distinguish four from more than four. Hence five, six, seven, and

eight at a time were often given. When the subject had learned to do

this fairly well the plan was to give him one, two, three, and four in

order, then to double the weight of the four and give them again to

see if he would interpret the additional weight as increase in number.

This was done and the results were entirely negative. The subjects

either noticed no difference at all or else merely noticed that the

second four were a little more distinct than the first.

The next step was to give a number of light contacts to be compared

with the same number of heavy ones—the subject, not trying to tell

the exact number but only which group contained the greater number. A

difference was sometimes noticed, and the subject, thinking that the

only variations possible were variations of number and position, often

interpreted the difference as difference in number; but the light

weights were as often called more as were the heavy ones.

So far as the primary object of this part of the experiment is

concerned the results are negative, but incidentally the process of

training brought out some facts of a more positive nature. It was

early noticed that some groups of four were much more readily

recognized than others, and that some of them were either judged

correctly or underestimated while others were either judged correctly

or overestimated. For convenience the fingers were indicated by the

letters A B C D, A being the index finger. The thumb was not used.

Two weights were over each finger. The one near the base was called 1,

the one toward the end 2. Thus A12 B1 C2 means two contacts on the

index finger, one near the base of the second finger, and one near the

end of the third finger. The possible arrangements of four may be

divided into three types: (1) Two weights on each of two fingers, as

A12 B12, C12 D12, etc., (2) four in a line across the fingers, _A1

B1 C1 D1_ or A2 B2 C2 D2, (3) unsymmetrical arrangements, as _A1 B2

C1 D2_, etc. Arrangements of the first type were practically never

overestimated. B12 C12 was overestimated once and B12 D12 was

overestimated once, but these two isolated cases need hardly be taken

into account. Arrangements of the second type were but rarely

overestimated—A2 B2 C2 D2 practically never, A1 B1 C1 D1 a few

times. Once the latter was called eight. Apparently the subject

perceived the line across the hand and thought there were two weights

on each finger instead of one. Arrangements of the third type were

practically never underestimated, but were overestimated in 68 per

cent. of the cases.

These facts in themselves are suggestive, but equally so was the

behavior of the subject while making the answers. It would have hardly

done to ask the person if certain combinations were hard to judge, for

the question would serve as a suggestion to him; but it was easy to

tell when a combination was difficult without asking questions. When a

symmetrical arrangement was given, the subject was usually composed

and answered without much hesitation. When an unsymmetrical

arrangement was given he often hesitated and knit his brows or perhaps

used an exclamation of perplexity before answering, and after giving

his answer he often fidgeted in his chair, drew a long breath, or in

some way indicated that he had put forth more effort than usual. It

might be expected that the same attitude would be taken when six or

eight contacts were made at once, but in these cases the subject was

likely either to fail to recognize that a large number was given or,

if he did, he seemed to feel that it was too large for him to perceive

at all and would guess at it as well as he could. But when only four

were given, in a zigzag arrangement, he seemed to feel that he ought

to be able to judge the number but to find it hard to do so, and

knowing from experience that the larger the number the harder it is to

judge he seemed to reason conversely that the more effort it takes to

judge the more points there are, and hence he would overestimate the

number.

The comments of the subjects are of especial value. One subject (Mr.

Dunlap) reports that he easily loses the sense of location of his

fingers, and the spaces in between them seem to belong to him as much

as do his fingers themselves. When given one touch at a time and told

to raise the finger touched he can do so readily, but he says he does

not know which finger it is until he moves it. He feels as if he

willed to move the place touched without reference to the finger

occupying it. He sometimes hesitates in telling which finger it is,

and sometimes he finds out when he moves a finger that it is not the

one he thought it was.

Another subject (Dr. MacDougall) says that his fingers seem to him

like a continuous surface, the same as the back of his hand. He

usually named the outside points first. When asked about the order in

which he named them, he said he named the most distinct ones first.

Once he reported that he felt six things, but that two of them were in

the same places as two others, and hence he concluded there were but

four. This feeling in a less careful observer might lead to

overestimation of number and be called diffusion, but all cases of

overestimation cannot be explained that way, for it does not explain

why certain combinations are so much more likely to lead to it than

others.

In one subject (Mr. Swift) there was a marked tendency to locate

points on the same fingers. He made many mistakes about fingers B

and C even when he reported the number correctly. When B and D

were touched at the same time he would often call it C and D, and

when C and D were given immediately afterward he seemed to notice

no difference. With various combinations he would report C when B

was given, although C had not been touched at the same time. If B

and C were touched at the same time he could perceive them well

enough.

The next part of the research was an attempt to discover whether a

person can perceive any difference between one point and two points

which feel like one. A simple little experiment was tried with the

æsthesiometer. The subjects did not know what was being used, and were

asked to compare the relative size of two objects placed on the back

of the hand in succession. One of these objects was one knob of the

æsthesiometer and the other was two knobs near enough together to lie

within the threshold. The distance of the points was varied from 10 to

15 mm. Part of the time the one was given first and part of the time

both were given together. The one, whether given first or second, was

always given about midway between the points touched by the two. If

the subject is not told to look for some specific difference he will

not notice any difference between the two knobs and the one, and he

will say they are alike; but if he is told to give particular