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

might be into the plane of the horizontal, when, upon a simple signal,

the perforated scale was instantly and noiselessly illuminated by the

pressure of an electrical button, and the location of the point of

regard was read off the vertical scale by the observer himself, in

terms of its distance from the fixed point of origin described above.

The individual and general averages for this set of experiments are

given in the following table:

TABLE III.

Observer. Constant Error. Average Deviation. Mean Variation.

A (50) + 7.75 20.07 19.45

C ” + 14.41 25.05 2.94

D ” + 14.42 34.54 29.16

E ” +108.97 108.97 23.13

F ” - 5.12 23.00 2.02

G ” + 20.72 34.80 10.23

H ” + 35.07 53.60 33.95

I ” + 25.52 30.68 22.49

K ” - 8.50 40.65 21.07

Average: + 23.69 41.26 17.16

The point at which the eyes rest when seeking the plane of the horizon

in total darkness is above its actual position, the positive

displacement involved being of relatively large amount.

In addition to the removal of the whole diversified visual field there

has now been eliminated the final point of regard toward which, in the

preceding set of experiments, the sight was strained; and the factor

of refined visual adjustment ceases longer to play a part in the

phenomenon. The result of this release is manifested in a tendency of

the eyes to turn unconsciously upward. This is their natural position

when closed in sleep. But this upward roll is not an uncomplicated

movement. There takes place at the same time a relaxation of binocular

convergence, which in sleep may be replaced by a slight divergence.

This tendency of the axes of vision to diverge as the eyes are raised

is undoubtedly connected biologically with the distribution of

distances in the higher and lower parts of the field of vision, of

which mention has already been made. Its persistence is taken

advantage of in the artificial device of assisting the process of

stereoscopic vision without instruments by holding the figures to be

viewed slightly above the primary position, so that the eyes must be

raised in order to look at them and their convergence thereby

decreased. It is by the concomitance of these two variables that the

phenomena of both this and the preceding series of experiments are to

be explained. In the present case the elimination of a fixed point of

regard is followed by a release of the mechanism of convergence, with

a consequent approximation to parallelism in the axes of vision and

its concomitant elevation of the line of sight.

The second fact to be noted is the reduction in amount of the mean

variation. The series of values under the three sets of experimental

conditions hitherto described is as follows: I. 7’.69; II. 31’.42;

III. 17’.16. This increase of regularity I take to be due, as in the

case of the lighted room, to the presence of a factor of constancy

which is not strictly an element in the judgment of horizontality.

This is a system of sensory data, which in the former case were

transient—the vision of familiar objects; and in the latter

resident—the recognition of specific experiences of strain in the

mechanism of the eye. The latter sensations exist under all three sets

of conditions, but they are of secondary importance in those cases

which include the presence of an objective point of regard, while in

the case of judgments made in total darkness the observer depends

solely upon resident experiences. Attention is thus directed

specifically toward these immediate sensational elements of judgment,

and there arises a tendency to reproduce the preceding set of

eye-strains, instead of determining the horizon plane afresh at each

act of judgment upon more general data of body position.

If the act of judgment be based chiefly upon sensory data connected

with the reinstatement of the preceding set of strains, progressions

should appear in these series of judgments, provided a constant factor

of error be incorporated in the process. This deflection should be

most marked under conditions of complete darkness, least in the midst

of full illumination. Such a progression would be shown at once by the

distribution of positive and negative values of the individual

judgments about the indifference point of constant error. As instances

of its occurrence all cases have been counted in which the first half

of the series of ten judgments was uniformly of one sign (four to six

being counted as half) and the second half of the opposite sign. The

percentages of cases in which the series presented such a progression

are as follows: In diffused light, 7.6%; in darkness, point of regard

illuminated, 18.3%; in complete darkness, 26.1%. The element of

constant error upon which such progressions depend is the tendency of

the eye to come to rest under determinate mechanical conditions of

equilibrium of muscular strain.

The relation of the successive judgments of a series to the

reinstatement of specific eye-strains and to the presence of an error

of constant tendency becomes clearer when the distribution of those

series which show progression is analyzed simultaneously with

reference to conditions of light and darkness and to binocular and

monocular vision respectively. Their quantitative relations are

presented in the following table:

TABLE IV.

Illumination. Per Cent. Showing Progress. Binocular. Monocular.

In light. 7.6 % 50 % 50 %

In darkness. 18.3 34.2 65.8

Among judgments made in daylight those series which present

progression are equally distributed between binocular and monocular

vision. When, however, the determinations are of a luminous point in

an otherwise dark field, the preponderance in monocular vision of the

tendency to a progression becomes pronounced. That this is not a

progressive rectification of the judgment, is made evident by the

distribution of the directions of change in the several experimental

conditions shown in the following table:

TABLE V.

Light. Darkness.

Direction of Change. Binocular. Monocular. Binocular. Monocular.

Upward. 50 % 100 % 38.4 % 65.0 %

Downward. 50 00.0 61.6 35.0

Const. Err. -7.70 +11.66 -36.62 -3.38

When the visual field is illuminated the occurrence of progression in

binocular vision is accidental, the percentages being equally

distributed between upward and downward directions. In monocular

vision, on the contrary, the movement is uniformly upward and involves

a progressive increase in error. When the illuminated point is exposed

in an otherwise dark field the progression is preponderatingly

downward in binocular vision and upward in vision with the single eye.

The relation of these changes to phenomena of convergence, and the

tendency to upward rotation in the eyeball has already been stated.

There is indicated, then, in these figures the complication of the

process of relocating the ideal horizon by reference to the sense of

general body position with tendencies to reinstate simply the set of

eye-muscle strains which accompanied the preceding judgment, and the

progressive distortion of the latter by a factor of constant error due

to the mechanical conditions of muscular equilibrium in the resting

eye.

IV.

The influence of this factor is also exhibited when judgments made

with both eyes are compared with those made under conditions of

monocular vision. The latter experiments were carried on in alternate

series with those already described. The figures are given in the

following tables:

TABLE VI.

JUDGMENTS MADE IN DIFFUSED LIGHT.

Observer. Constant Error. Average Deviation. Mean Variation.

A (50) - 28.46 29.04 8.87

C ” + 7.54 14.86 8.01

D ” + 39.32 43.28 13.83

E ” + 50.46 65.26 9.86

F ” + 62.30 62.30 1.60

G ” 0.00 45.28 9.66

H ” + 22.92 79.12 5.07

I ” + 14.36 51.96 8.02

K ” + 9.26 38.10 9.55

L ” - 61.10 61.10 6.36

Average: + 11.66 49.03 8.18

TABLE VII.

JUDGMENTS IN ILLUMINATED POINT.

Observer. Constant Error. Average Deviation. Mean Variation.

A (50) - 38.42 51.96 32.64

C (30) - 29.03 41.23 35.75

D (20) - 30.87 34.07 17.24

E (50) + 65.30 75.86 29.98

F ” + 50.74 50.74 5.89

G ” + 66.38 88.10 44.98

H ” + 65.40 80.76 42.93

I ” - 0.02 80.22 47.53

K ” - 44.60 52.56 32.93

L ” - 71.06 73.30 31.86

Average: - 3.38 62.88 32.17

The plane of vision in judgments made with the right eye alone is

deflected upward from the true horizon to a greater degree than it is

depressed below it in those made with binocular vision, the respective

values of the constant errors being -7’.70 and +11’.66, a difference

of 19’.36. When the field of vision is darkened except for the single

illuminated disc, a similar reversion of sign takes place in the

constant error. With binocular vision the plane of the subjective

horizon is deflected downward through 36’.62 of arc; with monocular

vision it is elevated 3’.38, a difference of 40’.00, or greater than

in the case of judgments made in the lighted room by 20’.64. This

increase is to be expected in consequence of the elimination of those

corrective criteria which the figured visual field presents. The two

eyes do not, of course, function separately in such a case, and the

difference in the two sets of results is undoubtedly due to the

influence of movements in the closed eye upon that which is open; or

rather, to the difference in binocular functioning caused by shutting

off the visual field from one eye. The former expression is justified

in so far as we conceive that the tendency of the closed eye to turn

slightly upward in its socket affects also the direction of regard in

the open eye by attracting toward itself its plane of vision. But if,

as has been pointed out, this elevation of the line of sight in the

closed eye is accompanied by a characteristic change in the process of

binocular convergence, the result cannot be interpreted as a simple

sympathetic response in the open eye to changes taking place in that

which is closed, but is the consequence of a release of convergence

strain secondarily due to this act of closing the eye.

Several points of comparison between judgments made with binocular and

with monocular vision remain to be stated. In general, the process of

location is more uncertain when one eye only is used than when both

are employed, but this loss in accuracy is very slight and in many

cases disappears. The loss in accuracy is perhaps also indicated by

the range of variation in the two cases, its limits being for

binocular vision +46’.29 to -56’.70, and for monocular +62’.30 to

-61’.10, an increase of 20’.41. In the darkened room similar relations

are presented. The mean variations are as follows: binocular vision,

31’.42; monocular, 32’.17. Its limits in individual judgments are:

binocular, -1’.62 to -128’.70, monocular, +66’.38 to -71’.06, an

increase of 10’.36. In all ways, then, the difference in accuracy

between the two forms of judgment is extremely small, and the

conclusion may be drawn that those significant factors of judgment

which are independent of the figuration of the visual field are not

connected with the stereoscopic functioning of the two eyes, but such

as are afforded by adjustment in the single eye and its results.

VI.

The experimental conditions were next complicated by the introduction

of abnormal positions of the eyes, head and whole body. The results of

tipping the chin sharply upward or downward and keeping it so fixed

during the process of location are given in the following table, which

is complete for only three observers:

TABLE VIII.

Observer. Upward Rotation. Downward Rotation.

C.E. A.D. M.V. C.E. A.D. M.V.

L