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

the Vexirfehler. According to this definition, when the

Vexirfehler appears we should have to say that one point is above

the threshold for twoness, which is a queer contradiction, to say the

least. It follows that all of the elaborate and painstaking

experiments to determine a threshold are useless. That is, the

threshold determinations do not lead us beyond the determinations

themselves.

In order to explain the fact that a person sometimes fails to

distinguish between one point and two points near together, it has

been suggested that the sensations fuse. This, I suppose, means either

that the peripheral processes coalesce and go to the center as a

single neural process, or that the process produced by each stimulus

goes separately to the brain and there the two set up a single

activity. Somewhat definite ‘sensory circles,’ even, were once

believed in.

If the only fact we had to explain was that two points are often

thought to be one when they are near together, ‘fusion’ might be a

good hypothesis, but we have other facts to consider. If this one is

explained by fusion, then the mistaking of one point for two must be

due to diffusion of sensations. Even that might be admissible if the

Vexirfehler were the only phenomenon of this class which we met. But

it is also true that several contacts are often judged to be more than

they actually are, and that hypothesis will not explain why certain

arrangements of the stimulating objects are more likely to bring about

that result than others. Still more conclusive evidence against

fusion, it seems to me, is found in the fact that two points, one on

each hand, may be perceived as one when the hands are brought

together. Another argument against fusion is the fact that two points

pressed lightly may be perceived as one, and when the pressure is

increased they are perceived as two. Strong pressures should fuse

better than weak ones, and therefore fusion would imply the opposite

results. Brückner[1] has found that two sensations, each too weak to

be perceived by itself, may be perceived when the two are given

simultaneously and sufficiently near together. This reënforcement of

sensations he attributes to fusion. But we have a similar phenomenon

in vision when a group of small dots is perceived, though each dot by

itself is imperceptible. No one, I think, would say this is due to

fusion. It does not seem to me that we need to regard reënforcement as

an indication of fusion.

[1] Brückner, A.: ‘Die Raumschwelle bei Simultanreizung,’

Zeitschrift für Psychologie, 1901, Bd. 26, S. 33.

My contention is that the effects sometimes attributed to fusion and

diffusion of sensations are not two different kinds of phenomena, but

are identical in character and are to be explained in the same way.

Turning now to the explanation of the special experiments, we may

begin with the Vexirfehler.[2] It seems to me that the Vexirfehler

is a very simple phenomenon. When a person is stimulated with two

objects near together he attends first to one and then to the other

and calls it two; then when he is stimulated with one object he

attends to it, and expecting another one near by he hunts for it and

hits upon the same one he felt before but fails to remember that it is

the same one, and hence thinks it is another and says he has felt two

objects. Observers agree that the expectation of two tends to bring

out the Vexirfehler. This is quite natural. A person who expects two

and receives one immediately looks about for the other without waiting

to fixate the first, and therefore when he finds it again he is less

likely to recognize it and more likely to think it another point and

to call it two. Some observers[3] have found that the apparent

distance of the two points when the Vexirfehler appears never much

exceeds the threshold distance. Furthermore, there being no distinct

line of demarcation between one and two, there must be many sensations

which are just about as much like one as they are like two, and hence

they must be lumped off with one or the other group. To the

mathematician one and two are far apart in the series because he has

fractions in between, but we perceive only in terms of whole numbers;

hence all sensations which might more accurately be represented by

fractions must be classed with the nearest whole number. A sensation

is due to a combination of factors. In case of the Vexirfehler one

of these factors, viz., the stimulating object, is such as to suggest

one, but some of the other conditions—expectation, preceding

sensation, perhaps blood pressure, etc.—suggest two, so that the

sensation as a whole suggests one-plus, if we may describe it that

way, and hence the inference that the sensation was produced by two

objects.

[2] Tawney, Guy A.: ‘Ueber die Wahrnehmung zweier Punkte

mittelst des Tastsinnes mit Rücksicht auf die Frage der Uebung

und die Entstehung der Vexirfehler,’ Philos. Stud., 1897, Bd.

XIII., S. 163.

[3] See Nichols: ‘Number and Space,’ p. 161. Henri, V., and

Tawney, G.: Philos. Stud., Bd. XI., S. 400.

This, it seems to me, may account for the appearance of the

Vexirfehler, but why should not the subject discover his error by

studying the sensation more carefully? He cannot attend to two things

at once, nor can he attend to one thing continuously, even for a few

seconds. What we may call continuous attention is only a succession of

attentive impulses. If he could attend to the one object continuously

and at the same time hunt for the other, I see no reason why he should

not discover that there is only one. But if he can have only one

sensation at a time, then all he can do is to associate that

particular sensation with some idea. In the case before us he

associates it with the idea of the number two. He cannot conceive of

two objects unless he conceives them as located in two different

places. Sometimes a person does find that the two objects of his

perception are both in the same place, and when he does so he

concludes at once that there is but one object. At other times he

cannot locate them so accurately, and he has no way of finding out the

difference, and since he has associated the sensation with the idea of

two he still continues to call it two. If he is asked to locate the

points on paper he fills out the figure just as he fills out the

blind-spot, and he can draw them in just the same way that he can draw

lines which he thinks he sees with the blind-spot, but which really

he only infers.

Any sensation, whether produced by one or by many objects, is one, but

there may be a difference in the quality of a sensation produced by

one object and that of a sensation produced by more than one object.

If this difference is clear and distinct, the person assigns to each

sensation the number he has associated with it. He gives it the name

two when it has the quality he has associated with that idea. But the

qualities of a sensation from which the number of objects producing it

is inferred are not always clear and distinct. The quality of the

sensation must not be confused with any quality of the object. If we

had to depend entirely on the sense of touch and always remained

passive and received sensations only when we were touched by

something, there is no reason why we should not associate the idea of

one with the sensation produced by two objects and the idea of two

with that produced by one object—assuming that we could have any idea

of number under such circumstances. The quality of a sensation from

which number is inferred depends on several factors. The number itself

is determined by the attitude of the subject, but the attitude is

determined largely by association. A number of facts show this. When a

person is being experimented on, it is very easy to confuse him and

make him forget how two feel and how one feels. I have often had a

subject tell me that he had forgotten and ask me to give him two

distinctly that he might see how it felt. In other words, he had

forgotten how to associate his ideas and sensations. In developing the

Vexirfehler I found it much better, after sufficient training had

been given, not to give two at all, for it only helped the subject to

perceive the difference between two and one by contrast. But when one

was given continually he had no such means of contrast, and having

associated the idea of two with a sensation he continued to do so. The

one subject with whom I did not succeed in developing the

Vexirfehler to any great extent perceived the difference by

comparing the sensation with one he had had some time before. I could

get him, for a few times, to answer two when only one was given, but

he would soon discover the difference, and he said he did it by

comparing it with a sensation which he had had some time before and

which he knew was two. By this means he was able to make correct

associations when otherwise he would not have done so. It has been

discovered that when a subject is being touched part of the time with

two and part of the time with one, and the time it takes him to make

his judgments is being recorded, he will recognize two more quickly

than he will one if there is a larger number of twos in the series

than there is of ones. I do not see how this could be if the sensation

of two is any more complex than that of one. But if both sensations

are units and all the subject needs to do is to associate the

sensation with an idea, then we should expect that the association he

had made most frequently would be made the most quickly.

If the feeling of twoness or of oneness is anything but an inference,

why is it that a person can perceive two objects on two fingers which

are some distance apart, but perceives the same two objects as one

when the fingers are brought near together and touched in the same

way? It is difficult to see how bringing the fingers together could

make a sensation any less complex, but it would naturally lead a

person to infer one object, because of his previous associations. He

has learned to call that one which seems to occupy one place. If two

contacts are made in succession he will perceive them as two because

they are separated for him by the time interval and he can perceive

that they occupy different places.

When two exactly similar contacts are given and are perceived as one,

we cannot be sure whether the subject feels only one of the contacts

and does not feel the other at all, or feels both contacts and thinks

they are in the same place, which is only another way of saying he

feels both as one. It is true that when asked to locate the point he

often locates it between the two points actually touched, but even

this he might do if he felt but one of the points. To test the matter

of errors of localization I have made a few experiments in the

Columbia University laboratory. In order to be sure that the