Various - Harvard Psychological Studies, Volume 1

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All of the subjects except _R_ were conscious of more or less of a
_strain_, which varied during the intervals, and was by some felt to
be largely a tension of the chest and other muscles, while others felt
it rather indefinitely as a 'strain of attention.' The characteristics
of this tension feeling were almost always different in the second
interval from those in the first, the tension being usually felt to be
more _constant_ in the second interval. In experiments of the third
group a higher degree of tension was felt in awaiting a light tap than
in awaiting a heavy one.

Evidently, in all these cases, the effect of a _difference_ between
two stimulations was to introduce certain changes in sensation
_during_ the interval which they limited, owing to the fact that the
subject expected the difference to occur. Thus in the third group of
experiments there were, very likely, in all cases changes from
sensations of high tension to sensations of lower, or vice versa. It
is probable that, in the experiments of the second group, there were
also changes in muscular sensations, partly those of eye muscles,
partly of chest and arm muscles, introduced by the change of attention
from one point to another. At any rate, it is certain that there were
certain sensation changes produced during the intervals by changes of
locality.

If, then, we assume that the introduction of additional sensation
change into an interval lengthens it, we are led to the conclusion
that psychological time (as distinguished from metaphysical,
mathematical, or transcendental time) is perceived simply as the
quantum of change in the sensation content. That this is a true
conclusion is seemingly supported by the fact that when we wish to
make our estimate correspond as closely as possible with external
measurements, we exclude from the content, to the best of our ability,
the general complex of external sensations, which vary with extreme
irregularity; and confine the attention to the more uniformly varying
bodily sensations. We perhaps go even further, and inhibit certain
bodily sensations, corresponding to activity of the more peripherally
located muscles, that the attention may be confined to certain others.
But attention to a dermal stimulation is precisely the condition which
would tend to some extent to prevent this inhibition. For this reason
we might well expect to find the error in estimation more variable,
the 'constant error' in general greater, and the specific effects of
variations which would affect the peripheral muscles, more marked in
'tactual' time than in either 'auditory' or 'optical' time. Certainly
all these factors appear surprisingly large in these experiments.

It is not possible to ascertain to how great an extent subject _Sh_
inhibited the more external sensations, but certainly if he succeeded
to an unusual degree in so doing, that fact would explain the absence
of effect of stimulation difference in his case.

Explanation has still to be offered for the variable effect of
intensity difference upon the _second_ interval. According to all
subjects except _Sn_, there is a radical difference in attitude in the
two intervals. In the first interval the subject is merely observant,
but in the second he is more or less reproductive. That is, he
measures off a length which seems equal to the standard, and if the
stimulation does not come at that point he is prepared to judge the
interval as 'longer,' even before the third stimulation is given. In
cases, then, where the judgment with equal intensities would be
'longer,' we might expect that the actual strengthening or weakening
of the final tap would make no difference, and that it would make very
little difference in other cases. But even here the expectation of the
intensity is an important factor in determining tension changes,
although naturally much less so than in the first interval. So we
should still expect the lengthening of the second interval.

We must remember, however, that, as we noticed in discussing the
experiments of Group 2, there is complicated with the lengthening
effect of a change the _bare constant error_, which appears even when
the three stimulations are similar in all respects except temporal
location. Compare _WWW_ with _SSS_, and we find that with all five
subjects the constant error is decidedly changed, being even reversed
in direction with three of the subjects.

Now, what determines the direction of the constant error, where there
is no pause between the intervals? Three subjects reported that at
times there seemed to be a slight loss of time after the second
stimulation, owing to the readjustment called for by the change of
attitude referred to above, so that the second interval was begun, not
really at the second stimulation, but a certain period after it. This
fact, if we assume it to be such, and also assume that it is present
to a certain degree in all observations of this kind, explains the
apparent overestimation of the first interval. Opposed to the factor
of _loss of time_ there is the factor of _perspective_, by which an
interval, or part of an interval, seems less in quantity as it recedes
into the past. The joint effect of these two factors determines the
constant error in any case where no pause is introduced between _ST_
and _CT_. It is then perfectly obvious that, as the perspective factor
is decreased by diminishing the intervals compared, the constant error
must receive positive increments, _i.e._, become algebraically
greater; which corresponds exactly with the results obtained by
Vierordt, Kollert, Estel, and Glass, that under ordinary conditions
long standard intervals are comparatively underestimated, and short
ones overestimated.

On the other hand, if with a given interval we vary the loss of time,
we also vary the constant error. We have seen that a change in the
intensity of the stimulations, although the relative intensity of the
three remains constant, produces this variation of the constant error;
and the individual differences of subjects with regard to sensibility,
power of attention and inhibition, and preferences for certain
intensities, lead us to the conclusion that for certain subjects
certain intensities of stimulation make the transition from the
receptive attitude to the reproductive easiest, and, therefore, most
rapid.

Now finally, as regards the apparent failure of the change in _SSW_ to
lengthen the second interval, for which we are seeking to account; the
comparatively great loss of time occurring where the change of
attitude would naturally be most difficult (that is, where it is
complicated with a change of attention from a strong stimulation to
the higher key of a weak stimulation) is sufficient to explain why
with most subjects the lengthening effect upon the second interval is
more than neutralized. The individual differences mentioned in the
preceding paragraph as affecting the relation of the two factors
determining the constant error, enter here of course to modify the
judgments and cause disagreement among the results for different
subjects.

Briefly stated, the most important points upon which this discussion
hinges are thus the following: We have shown--

1. That the introduction of either a local difference or a
difference of intensity in the tactual stimulations limiting
an interval has, in general, the effect of causing the
interval to appear longer than it otherwise would appear.

2. That the apparent exceptions to the above rule are, (_a_)
that the _increase_ of the local difference in the first
interval, the stimulated areas remaining unchanged, produces a
slight _decrease_ in the subjective lengthening of the
interval, and (_b_) that in certain cases a difference in
intensity of the stimulations limiting the second interval
apparently causes the interval to seem shorter than it
otherwise would.

3. That the 'constant error' of time judgment is dependent
upon the intensity of the stimulations employed, although the
three stimulations limiting the two intervals remain of equal
intensity.

To harmonize these results we have found it necessary to assume:

1. That the length of a time interval is perceived as the
amount of change in the sensation-complex corresponding to
that interval.

2. That the so-called 'constant error' of time estimation is
determined by two mutually opposing factors, of which the
first is the _loss of time_ occasioned by the change of
attitude at the division between the two intervals, and the
second is the diminishing effect of _perspective_.

It is evident, however, that this last assumption applies only
to the conditions under which the results were obtained,
namely, the comparison of two intervals marked off by three
brief stimulations.

* * * * *

PERCEPTION OF NUMBER THROUGH TOUCH.

BY J. FRANKLIN MESSENGER.

The investigation which I am now reporting began as a study of the
fusion of touch sensations when more than two contacts were possible.
As the work proceeded new questions came up and the inquiry broadened
so much that it seemed more appropriate to call it a study in the
perception of number.

The experiments are intended to have reference chiefly to three
questions: the space-threshold, fusion of touch sensations, and the
perception of number. I shall deny the validity of a threshold, and
deny that there is fusion, and then offer a theory which attempts to
explain the phenomena connected with the determination of a threshold
and the problem of fusion and diffusion of touch sensations.

The first apparatus used for the research was made as follows: Two
uprights were fastened to a table. These supported a cross-bar about
ten inches from the table. To this bar was fastened a row of steel
springs which could be pressed down in the manner of piano keys. To
each of these springs was fastened a thread which held a bullet. The
bullets, which were wrapped in silk to obviate temperature sensations,
were thus suspended just above the fingers, two over each finger. Each
thread passed through a small ring which was held just a little above
the fingers. These rings could be moved in any direction to
accommodate the bullet to the position of the finger. Any number of
the bullets could be let down at once. The main object at first was to
learn something about the fusion of sensations when more than two
contacts were given.

Special attention was given to the relation of the errors made when
the fingers were near together to those made when the fingers were
spread. For this purpose a series of experiments was made with the
fingers close together, and then the series was repeated with the
fingers spread as far as possible without the subject's feeling any
strain. Each subject was experimented on one hour a week for about
three months. The same kind of stimulation was given when the fingers
were near together as was given when they were spread. The figures
given below represent the average percentage of errors for four
subjects.

Of the total number of answers given by all subjects when the fingers
were close together, 70 per cent. were wrong. An answer was called
wrong whenever the subject failed to judge the number correctly. In
making out the figures I did not take into account the nature of the
errors. Whether involving too many or too few the answer was called
wrong. Counting up the number of wrong answers when the fingers were
spread, I found that 28 per cent. of the total number of answers were
wrong. This means simply that when the fingers were near together
there were more than twice as many errors as there were when they were
spread, in spite of the fact that each finger was stimulated in the
same way in each case.

A similar experiment was tried using the two middle fingers only. In
this case not more than four contacts could be made at once, and hence
we should expect a smaller number of errors, but we should expect
still to find more of them when the fingers are near together than
when they are spread. I found that 49 per cent. of the answers were
wrong when the fingers were near together and 20 per cent. were wrong
when they were spread. It happens that this ratio is approximately the
same as the former one, but I do not regard this fact as very
significant. I state only that it is easier to judge in one case than
in the other; how much easier may depend on various factors.

To carry the point still further I took only two bullets, one over the
second phalanx of each middle finger. When the fingers were spread the
two were never felt as one. When the fingers were together they were
often felt as one.

The next step was to investigate the effect of bringing together the
fingers of opposite hands. I asked the subject to clasp his hands in
such a way that the second phalanges would be about even. I could not
use the same apparatus conveniently with the hands in this position,
but in order to have the contacts as similar as possible to those I
had been using, I took four of the same kind of bullets and fastened
them to the ends of two aesthesiometers. This enabled me to give four
contacts at once. However, only two were necessary to show that
contacts on fingers of opposite hands could be made to 'fuse' by
putting the fingers together. If two contacts are given on contiguous
fingers, they are quite as likely to be perceived as one when the
fingers are fingers of opposite hands, as when they are contiguous
fingers of the same hand.

These results seem to show that one of the important elements of
fusion is the actual space relations of the points stimulated. The
reports of the subjects also showed that generally and perhaps always
they located the points in space and then remembered what finger
occupied that place. It was not uncommon for a subject to report a
contact on each of two adjacent fingers and one in between where he
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
aesthesiometer. 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
aesthesiometer 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
attention to the size there seems to be a slight tendency to perceive
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% " "