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

firstly, the separation of resident, or organic, from transient, or

objective, factors; secondly, the determination of the special organic

factors which enter into the mechanism of judgment and their several

values; and thirdly, within this latter field, the resolution of the

problem of a special mechanism of spatial orientation, the organ of

the static sense.

The special problem with which we are here concerned relates to the

group of factors upon which depends one’s judgment that any specified

object within the visual field lies within the horizontal plane of the

eyes, or above or below that plane, and the several functions and

values of these components. The method of procedure has been suggested

by the results of preceding investigations in this general field.

The first aim of the experiments was to separate the factors of

resident and transient sensation, and to determine the part played by

the presence of a diversified visual field. To do so it was necessary

to ascertain, for each member of the experimental group, the location

of the subjective visual horizon, and the range of uncertainty in the

observer’s location of points within that plane. Twelve observers in

all took part in the investigation. In the first set of experiments no

attempt was made to change the ordinary surroundings of the observer,

except in a single point, namely, the provision that there should be

no extended object within range of the subject’s vision having

horizontal lines on a level with his eyes.

The arrangements for experimentation were as follows: A black wooden

screen, six inches wide and seven feet high, was mounted between two

vertical standards at right angles to the axis of vision of the

observer. Vertically along the center of this screen and over pulleys

at its top and bottom passed a silk cord carrying a disc of white

cardboard, 1 cm. in diameter, which rested against the black surface

of the screen. From the double pulley at the bottom of the frame the

two ends of the cord passed outward to the observer, who, by pulling

one or the other, could adjust the disc to any desired position. On

the opposite side of the screen from the observer was mounted a

vertical scale graduated in millimeters, over which passed a light

index-point attached to the silk cord, by means of which the position

of the cardboard disc in front was read off. The observer was seated

in an adjustable chair with chin and head rests, and a lateral

sighting-tube by which the position of the eyeball could be vertically

and horizontally aligned. The distance from the center of the eyeball

to the surface of the screen opposite was so arranged that, neglecting

the radial deflection, a displacement of 1 mm. in either direction was

equal to a departure of one minute of arc from the plane of the eyes’

horizon.

The observer sat with the light at his back, and by manipulation of

the cords adjusted the position of the white disc freely up and down

the screen until its center was judged to be on a level with the eye.

Its position was then read off the vertical scale by the conductor

(who sat hidden by an interposed screen), and the error of judgment

was recorded in degrees and fractions as a positive (upward) or

negative (downward) displacement. The disc was then displaced

alternately upward and downward, and the judgment repeated. From the

time of signalling that the point had been located until this

displacement the observer sat with closed eyes. These determinations

were made in series of ten, and the individual averages are in general

based upon five such series, which included regularly the results of

sittings on different days. In some cases twice this number of

judgments were taken, and on a few occasions less. The number of

judgments is attached to each series of figures in the tables. In that

which follows the individual values and their general averages are

given as minutes of arc for (a) the constant error or position of

the subjective horizon, (b) the average deviation from the objective

horizon, and (c) the mean variation of the series of judgments.

TABLE I.

Observer. Constant Error. Average Deviation. Mean Variation.

A (100) -19.74 38.78 10.67

C (90) -18.18 23.89 10.82

D (100) -19.84 33.98 7.95

E (50) - 4.28 72.84 6.90

F (100) +46.29 46.29 2.05

G (50) +14.96 35.40 8.40

H (50) -27.22 27.46 5.78

I (50) + 6.62 53.34 7.45

K (50) + 1.08 30.26 6.59

L (20) -56.70 56.70 10.39

Average: -7.70 41.89 7.69

The average subjective horizon shows a negative displacement, the

exceptional minority being large. No special facts could be connected

with this characteristic, either in method of judgment or in the past

habits of the reactor. The average constant error is less than an

eighth of a degree, and in neither direction does the extreme reach

the magnitude of a single degree of arc. Since the mean variation is

likewise relatively small, there is indicated in one’s ordinary

judgments of this kind a highly refined sense of bodily orientation in

space.

II.

In order to separate the resident organic factors from those presented

by the fixed relations of the external world, an adaptation of the

mechanism was made for the purpose of carrying on the observations in

a darkened room. For the cardboard disc was substituted a light

carriage, riding upon rigid parallel vertical wires and bearing a

miniature ground-glass bulb enclosing an incandescent electric light

of 0.5 c.p. This was encased in a chamber with blackened surfaces,

having at its center an aperture one centimeter in diameter, which was

covered with white tissue paper. The subdued illumination of this

disc presented as nearly as possible the appearance of that used in

the preceding series of experiments. No other object than this spot of

moving light was visible to the observer. Adjustment and record were

made as before. The results for the same set of observers as in the

preceding case are given in the following table:

TABLE II.

Subject. Constant Error. Average Deviation. Mean Variation.

A (50) - 52.76 55.16 30.08

C (30) - 7.40 42.00 35.31

D (50) - 14.24 38.60 30.98

E (50) - 43.12 86.44 30.19

F (100) - 2.01 72.33 20.27

G (100) - 21.89 47.47 32.83

H (50) - 1.62 59.10 29.95

I (50) - 32.76 41.60 24.40

K (50) - 61.70 100.02 52.44

L (40) -128.70 128.90 27.83

Average: - 36.62 67.16 31.43

Changes in two directions may be looked for in the results as the

experimental conditions are thus varied. The first is a decrease in

the certainty of judgment due to the simple elimination of certain

factors upon which the judgment depends. The second is the appearance

of definite types of error due to the withdrawal of certain

correctives of organic tendencies which distort the judgment in

specific directions. The loss in accuracy is great; the mean variation

increases from 7.69 to 31.43, or more than 400 per cent. This large

increase must not, however, be understood as indicating a simple

reduction in the observer’s capacity to locate points in the

horizontal plane of the eyes. The two series are not directly

comparable; for in the case of the lighted room, since the whole

visual background remained unchanged, each determination must be

conceived to influence the succeeding judgment, which becomes really a

correction of the preceding. To make the two series strictly parallel

the scenery should have been completely changed after each act of

judgment. Nevertheless, a very large increase of uncertainty may

fairly be granted in passing from a field of visual objects to a

single illuminated point in an otherwise dark field. It is probable

that this change is largely due to the elimination of those elements

of sensation depending upon the relation of the sagittal axis to the

plane against which the object is viewed.

The change presented by the constant error can here be interpreted

only speculatively. I believe it is a frequently noted fact that the

lights in a distant house or other familiar illuminated object on

land, and especially the signal lights on a vessel at sea appear

higher than their respective positions by day, to the degree at times

of creating the illusion that they hang suspended above the earth or

water. This falls in with the experimental results set forth in the

preceding table. It cannot be attributed to an uncomplicated tendency

of the eyes of a person seated in such a position to seek a lower

direction than the objective horizon, when freed from the corrective

restraint of a visual field, as will be seen when the results of

judgments made in complete darkness are cited, in which case the

direction of displacement is reversed. The single illuminated spot

which appears in the surrounding region of darkness, and upon which

the eye of the observer is directed as he makes his judgment, in the

former case restricts unconscious wanderings of the eye, and sets up a

process of continuous and effortful fixation which accompanies each

act of determination. I attribute the depression of the eyes to this

process of binocular adjustment. The experience of strain in the act

of fixation increases and decreases with the distance of the object

regarded. In a condition of rest the axes of vision of the eyes tend

to become parallel; and from this point onward the intensity of the

effort accompanying the process of fixation increases until, when the

object has passed the near-point of vision, binocular adjustment is no

longer possible. In the general distribution of objects in the visual

field the nearer, for the human being, is characteristically the

lower, the more distant the higher, as one looks in succession from

the things at his feet to the horizon and vice versa. We should,

therefore, expect to find, when the eyes are free to move in

independence of a determinate visual field, that increased convergence

is accompanied by a depression of the line of sight, decreased

convergence by an elevation of it. Here such freedom was permitted,

and though the fixed distance of the point of regard eliminated all

large fluctuations in convergence, yet all the secondary

characteristics of intense convergence were present. Those concerned

in the experiment report that the whole process of visual adjustment

had increased in difficulty, and that the sense of effort was

distinctly greater. To this sharp rise in the general sense of strain,

in coöperation with the absence of a corrective field of objects, I

attribute the large negative displacement of the subjective horizon in

this series of experiments.

III.

In the next set of experiments the room was made completely dark. The

method of experimentation was adapted to these new conditions by

substituting for the wooden screen one of black-surfaced cardboard,

which was perforated at vertical distances of five millimeters by

narrow horizontal slits and circular holes alternately, making a scale

which was distinctly readable at the distance of the observer.

Opposite the end of one of these slits an additional hole was punched,

constituting a fixed point from which distances were reckoned on the

scale. As the whole screen was movable vertically and the observer

knew that displacements were made from time to time, the succession of

judgments afforded no objective criterion of the range of variation in

the series of determinations, nor of the relation of any individual

reaction to the preceding. The method of experimentation was as

follows: The observer sat as before facing the screen, the direction

of which was given at the beginning of each series by a momentary

illumination of the scale. In the darkness which followed the observer

brought the