Sixteen Experimental Investigations from the Harvard Psychological Laboratory, Hugo Münsterberg [top fiction books of all time TXT] 📗

a curious negative displacement of the subjective horizon

took place when one looked across a downward slope to a distant cliff,

the altitude (in relation to the observer’s own standpoint) of

specific points on the wall of rock being largely overestimated.

Attributing the illusion to a reconstruction of the sensory data upon

an erroneous interpretation of the objective relations of the

temporary plane of the landscape, Dr. Münsterberg later made a series

of rough experiments by stretching an inclined cord from the eye

downward to a lower point on an opposite wall and estimating the

height above its termination of that point which appeared to be on a

level with the observing eye. He found an illusion present similar to

the case of an extended slope of country.

 

The first experiments of this group repeated those just described. The

previous mechanical conditions were varied only by the introduction of

a slender cord which was stretched from just below the eyes to the

bottom of the vertical screen. Full results were obtained from only

two observers, which are given in the following table:

 

TABLE XI.

 

Observer. Const. Err. Av. Dev. Mean Var. Exp. Conds.

 

C (30) +123.92 123.92 11.94 Cord present and

G (30) +66.47 66.47 15.56 consciously referred to.

C (30) +126.90 126.90 6.31 Cord not present.

G (30) +83.20 83.20 6.31

C (30) +126.93 126.93 6.39 Cord present but not

G (30) +86.63 86.63 9.40 consciously referred to.

 

Averages. I +95.19 95.19 13.75

” II +105.05 105.05 6.31

” III +106.78 106.78 7.89

 

The effect of introducing such an objective plane of reference is

twofold: the mean variation is increased, and the plane of the

subjective horizon is displaced downwards. First, then, it acts as a

simple factor of disturbance; it distracts from those habitual

adjustments upon which the accuracy of the judgment depends. Secondly,

it enters as a source of constant error into the determination of the

subjective horizon, which is attracted toward this new objective

plane. In the third section of the table are given the results of

judgments made in the presence of such a plane but without conscious

reference to it.[2] The figures here are of intermediate value in the

case of the mean variation and of slightly greater value than the

first in that of the constant error. In other words, the introduction

of such a plane cannot be wholly overlooked, though it may be greatly

abstracted from.

 

[2] In the preceding experiments the cord was definitely to be taken

into account in making the judgment. The method of so doing was by

running the eye back and forth over the cord preliminary to

determining the location of the point.

 

The single cord was next replaced by a plane of blackened wood six

inches wide and extending from the observer to the vertical screen.

This strip was arranged in two ways: first, from the observer’s chin

to the bottom of the screen, and secondly, from the feet of the

observer to a point on the screen a short distance below the plane of

the objective horizon. The individual and average results are given in

the following table:

 

TABLE XII.

 

Observer. Descending Plane. Ascending Plane.

 

A. (10) +18.80 18.80 5.24 +35.10 35.10 8.27

E. (20) +79.30 79.30 11.56 +131.67 131.67 12.07

H. (10) -37.50 37.50 16.80 -46.90 46.90 7.90

K. (30) +71.40 71.40 12.85 +48.05 48.05 5.11

Average: +33.00 51.75 11.61 +41.95 65.43 8.34

 

The introduction of a descending plane lowers the apparent horizon;

that of an ascending plane elevates it. The general disturbance of

judgment appears distinctly greater in the case of a downward than in

that of an upward incline.

 

The results of a third variation of the experimental conditions may be

presented at once. In it the location of the subjective horizon under

normal conditions was compared with the results of adjustments made

when the screen bearing the white disc was rotated backward from the

observer through an angle of varying magnitude. The averages for each

of the two subjects are as follows:

 

TABLE XIII.

 

Observer Const. Err. Av. Dev. Mean Var. Rotation.

F (20) +130.50 130.50 3.20 20°

” ” +115.50 115.50 1.10 50°

J (20) +443.10 443.10 9.47 45°

 

These experiments were carried on in the presence of the definitely

figured visual field of the lighted room, and the observers were

conscious of taking these permanent features into account as

correctives in making their judgments. Before proceeding, this defect

was remedied as far as possible by enclosing the apparatus of

experimentation, including the observer, between two walls of black

fabric. Nothing was to be seen but these two walls, and the inclined

plane which terminated the observer’s view. The position of the screen

remained constant at an inclination of 45°. The upper bounding lines

of the enclosing walls, on the contrary, were adjusted in three

different relations to the plane of the gravity horizon. In the first

arrangement these lines were horizontal; in the second the ends next

to the observer were depressed five degrees; while in the final

arrangement these ends were elevated through a like angular distance.

 

The inclined position of the screen was of course observed by every

reactor, but of the changes in the enclosing walls no subject was

informed, and none discerned them on any occasion. Each observer was

questioned as to alterations in the experimental conditions after the

use of each arrangement, and at the close of the whole series inquiry

was made of each as to the planes of the upper boundaries of the

walls. On various occasions, but not customarily, the observer was

aware of a change of some kind in the whole set of conditions, but the

particular feature altered was not suspected. The results for all

three arrangements are given in the following table; of the sections

of this table the third is incomplete, full results having been

reached in the cases of only three observers:

 

TABLE XV.

 

Ascending Planes. Descending Planes.

Observer Const. Err. Av. Dev. M. Var. Const. Err. Av. Dev. M. V.

C (50) - 8.02 11.82 9.47 - 48.14 48.14 9.52

F (50) + 78.88 78.88 2.89 + 25.54 25.54 1.98

G (50) - 22.56 24.64 6.58 -101.20 101.20 7.39

H (50) - 83.84 83.84 11.78 -230.20 230.20 11.88

J (50) +315.64 315.64 18.16 +120.12 120.12 9.01

Average: + 55.96 102.96 9.78 -44.98 104.84 7.96

 

Horizontal Planes.

Observer. Const. Err. Av. Dev. Mean Var.

C (50) - 27.86 27.86 9.58

G (50) - 73.84 73.84 7.59

J (50) +243.72 243.72 18.52

 

For every individual observer, the position of the disc on the screen

has been affected by each change in the direction of these visible

lines. In every case, also, its location when these boundaries lay in

a horizontal plane was intermediate between the other two. The

importance of such relations in the objects of the visual field as

factors in our ordinary determination of the subjective horizon is

made evident by these experimental results. They become construction

lines having assumed permanence in the world of visual-motor

experience. The conception of unchanging spatial relations in the

fundamental lines of perspective vision receives constant

reinforcement from the facts of daily experience. The influence of the

above-described changes in experimental conditions is mediated through

their effect upon the location of the focus of the limiting and

perspective lines of vision. As the plane of the upper boundaries of

the enclosing walls was elevated and depressed the intersection of the

two systems of lines was correspondingly raised and lowered, and in

dependence upon the location of this imaginary point the determination

of the position of the white disc was made, and the plane of

perspective positively or negatively rotated.

 

Why such perspective lines should enter into the process of judgment

it is not difficult to infer. The plane of perspective for human

beings is characteristically horizontal, in consequence of the

distribution of important objects within the field of visual

perception. Roughly, the belt of the earth’s horizon contains the loci

of all human perspective planes. Both natural and artificial

arrangements of lines converge there. The systems of visual objects on

the earth and in the sky are there broken sharply off in virtue of

their practically vast differences in quality and significance for the

observer. The latter perspective probably never extends downward

illusorily to points on the earth’s surface; and the former system of

objects is carried continuously upward to skyey points only on

relatively rare occasions, as when one mistakes clouds for mountains

or the upper edge of a fog-belt on the horizon for the rim of sea and

sky. The point of convergence of the fundamental lines of perspective

thus becomes assimilated with the idea of the visual horizon, as that

concept has fused with the notion of a subjective horizon. There can

be little doubt that the disposition of such lines enters constantly

into our bodily orientation in space along with sensations arising

from the general body position and from those organs more specially

concerned with the static sense.

 

Upon the misinterpretation of such objective planes depends the

illusion of underestimation of the height or incline of a hill one is

breasting, and of the converse overestimation of one seen across a

descending slope or intervening valley. The latter illusion is

especially striking, and in driving over forest roads (in which case

the correction of a wider range of view is excluded) the stretch of

level ground at the foot of a hill one is descending is constantly

mistaken for an opposing rise. This illusion is put into picturesque

words by Stevenson when he describes the world, seen from the summit

of a mountain upon which one stands, as rising about him on every side

as toward the rim of a great cup. The fitness of the image may be

proved by climbing the nearest hill. In all such cases a

reconstruction of the sensory data of judgment takes place, in which

the most significant factor is the plane determined by the positions

of the observing eye and the perspective focus. In these judgments of

spatial relationship, as they follow one another from moment to

moment, this plane becomes a temporary subjective horizon, and

according as it is positively or negatively rotated do corresponding

illusions of perception appear.

 

*

 

THE ILLUSION OF RESOLUTION-STRIPES ON THE COLOR-WHEEL.

 

BY EDWIN B. HOLT.

 

If a small rod is passed slowly before a rotating disc composed of two

differently colored sectors, the rod appears to leave behind it on the

disc a number of parallel bands of about the width of the rod and of

about the colors, alternately arranged, of the two sectors. These

appear not to move, but gradually to fade away.

 

This phenomenon was first observed by Münsterberg, and by him shown to

Jastrow,[1] who, with Moorehouse, has printed a study, without,

however, offering an adequate explanation of it.

 

[1] Jastrow, J., and Moorehouse, G.W.: ‘A Novel Optical

Illusion,’ Amer. Jour. of Psychology, 1891, IV., p. 201.

 

I. APPARATUS FOR PRODUCING THE ILLUSION.

 

Any form of color-wheel may be used, but preferably one which is

driven by electricity or clock-work, so that a fairly constant speed

is assured. Several pairs of paper discs are needed, of the ordinary

interpenetrating kind which permit a ready readjustment of the ratios

between the two sectors, as follows: one pair consisting of a white

and a black disc, one of a light-and a dark-colored disc (light green

and dark red have been found admirably suited to the purpose), and a

pair of discs distinctly different in color, but equal in luminosity.

 

The rod should be black and not more than a quarter