Sixteen Experimental Investigations from the Harvard Psychological Laboratory - Hugo Münsterberg (best life changing books txt) 📗
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and Fechner in one essential respect. This difference, I think, is
sufficient to explain the different results. In my experiments the
two-point distance was held on the skin, while the stylus was moved
from one point to the other. In their experiments the line was drawn
without the points. This of course changes the objective conditions.
In simply drawing a line on the skin the subject rapidly loses sight
of the starting point of the movement. It follows, as it were, the
moving point, and hence the entire distance is underestimated. I made
a small number of tests of this kind, and found that the line seemed
shorter than the point distance as Fechner and Vierordt declared. But
when the point distance is kept on the skin while the stylus is being
drawn, the filling is allowed its full effect in the judgment,
inasmuch as the end points are perceived as stationary landmarks. The
subjects at first found some difficulty in withholding their judgments
until the movement was completed. Some subjects declared that they
frequently made a preliminary judgment before the filling was
inserted, but that when the moving point approached the end point,
they had distinctly the experience that the distance was widening. In
these experiments I used five sorts of motion, quick and heavy, quick
and light, slow and heavy, slow and light, and interrupted. I made no
attempt to determine either the exact amount of pressure or the exact
rate. I aimed simply at securing pronounced extremes. The slow rate
was approximately 3, and the fast approximately 15 cm. per second.
[7] ‘Zeitsinn,’ Tübingen, 1858.
[8] Fechner, G. Th., ‘Elem. d. Psychophysik,’ Leipzig, 1889; 2.
Theil, S. 328.
I have already said that these filled spaces were invariably
overestimated and that the slower the movement, the greater, in
general, is the overestimation. In addition to the facts just stated I
found also, what Hall and Donaldson[9] discovered, that an increase in
the pressure of a moving point diminishes the apparent distance.
[9] Hall, G. St., and Donaldson, H.H., ‘Motor Sensations on the
Skin,’ Mind, 1885, X., p. 557.
Nichols,[10] however, says that heavy movements seem longer and light
ones shorter.
[10] Op. citat., p. 98.
V.
There are several important matters which might properly have been
mentioned in an earlier part of this paper, in connection with the
experiments to which they relate, but which I have designedly omitted,
in order not to disturb the continuity in the development of the
central object of the research. The first of these is the question of
the influence of visualization on the judgments of cutaneous
distances. This is in many ways a most important question, and
confronts one who is making studies in tactual space everywhere. The
reader may have already noticed that I have said but little about the
factor of visualization in any of my experiments, and may have
regarded it as a serious omission. It might be offered as a criticism
of my work that the fact that I found the tactual illusions to exist
in the same sense as the optical illusions was perhaps due to the
failure to exclude visualization. All of the subjects declare that
they were unable to shut out the influence of visualizing entirely.
Some of the subjects who were very good visualizers found the habit
especially insistent. I think, however, that not even in these latter
cases does this factor at all vitiate my conclusions.
It will be remembered that the experiments up to this time fall into
two groups, first, those in which the judgments on the cutaneous
distances were reached by direct comparisons of the sensations
themselves; and secondly, those in which the sensations were first
localized and then the judgment of the distance read from these
localizations. Visualizing, therefore, entered very differently into
the two groups. In the first instance all of the judgments were made
with the eyes closed, while all of the localizations were made with
the eyes open. I was uncertain through the whole of the first group of
experiments as to just how much disturbance was being caused in the
estimation of the distance by visualizing. I therefore made a series
of experiments to determine what effect was produced upon the illusion
if in the one set of judgments one purposely visualized and in the
other excluded visualizing as far as possible. In my own case I found
that after some practice I could give very consistent judgments, in
which I felt that I had abstracted from the visualized image of the
arm almost entirely. I did not examine these results until the close
of the series, and then found that the illusion was greater for those
judgments in which visualization was excluded; that is, the filled
space seemed much larger when the judgment was made without the help
of visualization. It is evident, therefore, that the tactual illusion
is influenced rather in a negative direction by visualization.
In the second group of experiments, where the judgments were obtained
through the localization of the points, it would seem, at first sight,
that the judgments must have been very largely influenced by the
direct vision used in localizing the points. The subject, as will be
remembered, looked down at a card of numbered points and named those
which were directly over the contacts beneath. Here it should seem
that the optical illusion of the overestimation of filled spaces,
filled with points on the card, would be directly transmitted to the
sensation on the skin underneath. Such criticism on this method of
getting at the illusion has already been made orally to me. But this
is obviously a mistaken objection. The points on the card make a
filled space, which of course appears larger, but as the points
expand, the numbers which are attached to them expand likewise, and
the optical illusion has plainly no influence whatever upon the
tactual illusion.
A really serious objection to this indirect method of approaching the
illusion is, that the character of the cutaneous sensation is never so
distinctly perceived when the eyes are open as when they are closed.
Several subjects often found it necessary to close their eyes first,
in order to get a clear perception of the locality of the points;
they then opened their eyes, to name the visual points directly above.
Some subjects even complained that when they opened their eyes they
lost track of the exact location of the touch points, which they
seemed to have when their eyes were closed. The tactual impression
seems to be lost in the presence of active vision.
On the whole, then, I feel quite sure in concluding that the
overestimation of the filled cutaneous spaces is not traceable to the
influence of visualization. Parrish has explained all sporadic cases
of overestimation as due to the optical illusion carried over in
visualization. I have already shown that in my experiments
visualization has really the opposite effect. In Parrish’s experiments
the overestimation occurred in the case of those collections of points
which were so arranged as to allow the greatest differentiation among
the points, and especially where the end-points were more or less
distinct from the rest. This, according to my theory, is precisely
what one would expect.
Those who have made quantitative studies in the optical illusion,
especially in this particular illusion for open and filled spaces,
have observed and commented on the instability of the illusion.
Auerbach[11] says, in his investigation of the quantitative variations
of the illusion, that concentration of attention diminishes the
illusion. In the Zöllner figure, for instance, I have been able to
notice the illusion fluctuate through a wide range, without
eye-movements and without definitely attending to any point, during
the fluctuation of the attention. My experiments with the tactual
illusion have led me to the conclusion that it fluctuates even more
than the optical illusion. Any deliberation in the judgment causes the
apparent size of the filled space to shrink. The judgments that are
given most rapidly and naïvely exhibit the strongest tendency to
overestimation; and yet these judgments are so consistent as to
exclude them from the category of guesses.
[11] Auerbach, F., _Zeitsch. f. Psych. u. Phys. d.
Sinnesorgane_, 1874, Bd. VII., S. 152.
In most of my experiments, however, I did not insist on rapid and
naïve judgments; but by a close observation of the subject as he was
about to make a judgment I could tell quite plainly which judgments
were spontaneous and which were deliberate. By keeping track of these
with a system of marks, I was able to collect them in the end into
groups representing fairly well the different degrees of attention.
The illusion is always greatest for the group of spontaneous
judgments, which points to the conclusion that all illusions, tactual
as well as visual, are very largely a function of attention.
In Section II. I told of my attempt to reproduce the optical illusion
upon the skin in the same form in which we find it for sight, namely,
by presenting the open and filled spaces simultaneously, so that they
might be held in a unitary grasp of consciousness and the judgment
pronounced on the relative length of these parts of a whole. However,
as I have already said, the filled space appears longer, not only when
given simultaneously, but also when given successively with the open
space. In the case of the optical illusion I am not so sure that the
illusion does not exist if the two spaces are not presented
simultaneously and adjacent, as Münsterberg asserts. Although, to be
sure, for me the illusion is not so strong when an interval is allowed
between the two spaces, I was interested to know whether this was true
also in the case of a touch illusion. My previous tables did not
enable me to compare the quantitative extent of the illusion for
successive and simultaneous presentation. But I found in two series
which had this point directly in view, one with the subject F and
one in which G served as subject, that the illusion was emphatically
stronger when the open and filled spaces were presented simultaneously
and adjacent. In this instance, the illusion was doubtless a
combination of two illusions—a shrinking of the open space, on the
one hand, and a lengthening of the filled space on the other hand.
Binet says, in his studies on the well-known Müller-Lyer illusion,
that he believes the illusion, in its highest effects at any rate, to
be due to a double contrast illusion.
This distortion of contrasted distances I have found in more than one
case in this investigation—not only in the case of distances in which
there is a qualitative difference, but also in the case of two open
distances. In one experiment, in which open distances on the skin were
compared with optical point distances, a distance of 10 cm. was given
fifty times in connection with a distance of 15 cm., and fifty times
in connection with a distance of 5 cm. In the former instance the
distance of 10 cm. was underestimated, and in the other it was
overestimated.
The general conclusion of the entire investigation thus far may be
summed up in the statement: _Wherever the objective conditions are the
same in the two senses, the illusion exists in the same direction for
both sight and touch._
VI.
Thus far all of my experiments were made with passive touch. I
intend now to pursue this problem of the relation between the
illusions of sight and touch into the region of active touch. I have
yielded somewhat to the current fashion in thus separating the passive
from the active touch in this discussion. I have already said that I
believe it would be
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