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

opening, it is clear that the 9 cm. of exposure become more than 9°

11’ of eye-movement. Therefore the eye and the fixation-points are so

placed that EA (Fig. 5) = 26 cm. and PP’ = 18 cm. The total

eye-movement is thus 38° 11’, of which the nine-centimeter distance of

exposure is 19° 38’. Now the eye is found to move very well through

19° 38’ in 275[sigma], although, again, this is much more than a

proportionate part of the total time (99.9[sigma]) given by Dodge and

Cline for a movement of the eye through 40°. The eye is in this case

also moving slowly. As before, it is permissible to let the pendulum

run down till it swings too slowly for the eye to move with it; since

any lessened speed of the pendulum only makes the reddish-orange phase

more prominent.

As in the experiment with the dumb-bell, we have also here three

cases: the control, the case of the eye moving, and again a control.

Case 1. T swings with the pendulum. I is placed in the front

groove, and the eye looks straight forward without moving. The

pendulum falls from 9.5° at one side, and the illumination is so

adjusted that the phase in which the band is reddish-orange, is

unmistakably perceived before that in which it is straw-yellow. The

appearance must be 3 followed by 5 (Fig. 8).

Case 2. T is fixed in the background, I on the pendulum, and the

phenomena are observed with the eye moving.

Case 3. A repetition of case 1, to make sure that no different

adaptation or fatigue condition of the eye has come in to modify the

appearance of the two successive phases as at first seen.

The possible appearances to the moving eye are closely analogous to

those in the dumb-bell experiment. If the eye moves too soon or too

late, so that it is at rest during the exposure, the image is like T

itself (Fig. 8) but somewhat fainter and localized midway between the

points P and P’. If the eye moves reflexly at the rate of the

pendulum, the image is of the shape i and shows the two phases (3

followed by 5). It is localized in the middle and appears to move

across the nine-centimeter opening.

A difficulty is met here which was not found in the case of the

dumb-bell. The eye is very liable to come to a full stop on one of the

colored surfaces, and then to move quickly on again to the final

fixation-point. And this happens contrary to the intention of the

subject, and indeed usually without his knowledge. This stopping is

undoubtedly a reflex process, in which the cerebellar mechanism which

tends to hold the fixation on any bright object, asserts itself over

the voluntary movement and arrests the eye on the not moving red or

green surface as the exposure takes place. A comparable phenomenon was

found sometimes in the experiment with the dumb-bell, where an

eye-movement commenced as voluntary would end as a reflex following of

the pendulum. In the present experiment, until the subject is well

trained, the stopping of the eye must be watched by a second person

who looks directly at the eyeball of the subject during each

movement. The appearances are very varied when the eye stops, but the

typical one is shown in Fig. 8:1. The red strip AB is seldom longer

and often shorter than in the figure. That part of it which is

superposed on the green seldom shows the orange phase, being almost

always of a pure straw-yellow. The localization of these images is

variable. All observations made during movements in which the eye

stops, are of course to be excluded.

If now the eye does not stop midway, and the image is not localized in

the center, the appearance is like either 2, 4, or 5, and is localized

over the final fixation-point. 2 is in all probability the case of the

eye moving very much faster than the pendulum, so that if the movement

is from left to right, the right-hand side of the image is the part

first exposed (by the uncovering of the left-hand side of T), which

is carried ahead by the too swift eye-movement and projected in

perception on the right of the later portion. 3 is the case of the eye

moving at very nearly but not quite the rate of the pendulum. The

image which should appear 2 cm. wide (like the opening i) appears

about 3 cm. wide. The middle band is regularly straw-yellow, extremely

seldom reddish, and if we could be sure that the eye moves more slowly

than the pendulum, so that the succession of the stimuli is even

slower than in the control, and the red phase is surely given, this

appearance (3) would be good evidence of anæsthesia during which the

reddish-orange phase elapses. It is more likely, however, that the eye

is moving faster than the pendulum, but whether or not so

inconsiderably faster as still to let the disappearance of the reddish

phase be significant of anæsthesia, is not certain until one shall

have made some possible but tedious measurements of the apparent width

of the after-image. Both here and in the following case the _feeling

of succession_, noticeable between the two phases when the eye is at

rest, has disappeared with the sensation of redness.

The cases in which 5 is seen are, however, indisputably significant.

The image is apparently of just the height and width of i, and there

is not the slightest trace of the reddish-orange phase. The image

flashes out over the final fixation-point, green and straw-yellow,

just as the end-circles of the dumb-bell appeared without their

handle. The rate of succession of the stimuli, green—red—green, on

the retina, is identical with that rate which showed the two phases to

the resting eye: for the pendulum is here moving at the very same

rate, and the eye is moving exactly with the pendulum, as is shown by

the absence of any horizontal elongation of the image seen. The

trained subject seldom sees any other images than 4 and 5, and these

with about equal frequency, although either is often seen in ten or

fifteen consecutive trials. As in the cases of the falsely localized

images and of the handleless dumb-bell, movements of both eyes, as

well as of the head but not the eyes, yield the same phenomena. It is

interesting again to compare the appearance under reflex movement. If

at any time during the experiments the eye is allowed to follow the

pendulum reflexly, the image is at once and invariably seen to pass

through its two phases as it swings past the nine-centimeter opening.

The frequent and unmistakable appearance of this band of straw-yellow

on a non-elongated green field _without the previous phase in which

the band is reddish-orange_, although this latter was unmistakable

when the same stimulation was given to the eye at rest, is

authenticated by eight subjects. _This appearance, together with that

of the handleless dumb-bell, is submitted as a demonstration that

during voluntary movements of the eyes, and probably of the head as

well, there is a moment in which stimulations are not transmitted from

the retina to the cerebral cortex, that is, a moment of central

anæsthesia_. The reason for saying ‘and probably of the head as

well,’ is that although the phenomena described are gotten equally

well from movements of the head, yet it is not perfectly certain that

when the head moves the eyes do not also move slightly within the

head, even when the attempt is made to keep them fixed.

Most of the criticisms which apply to this last experiment apply to

that with the dumb-bell and have already been answered. There is one

however which, while applying to that other, more particularly applies

here. It would be, that these after-images are too brief and

indistinct to be carefully observed, so that judgments as to their

shape, size, and color are not valid evidence. This is a perfectly

sensible criticism, and a person thoroughly convinced of its force

should repeat the experiments and decide for himself what reliance he

will place on the judgments he is able to make. The writer and those

of the subjects who are most trained in optical experiments find the

judgments so simple and easily made as not to be open to doubt.

In the first place, it should be remembered that only those cases are

counted in which the movement was so timed that the image was seen in

direct vision, that is, was given on or very near the fovea. In such

cases a nice discrimination of the shape and color of the images is

easily possible.

Secondly, the judgments are in no case quantitative, that is, they in

no case depend on an estimate of the absolute size of any part of the

image. At most the proportions are estimated. In the case of the

dumb-bell the question is, Has the figure a handle? The other

question, Are the end-circles horizontally elongated? has not to be

answered with mathematical accuracy. It is enough if the end-circles

are approximately round, or indeed are narrower than 9 cm.

horizontally, for at even that low degree of concentration the handle

was still visible to the resting eye. Again, in the experiment with

the color-phases, only two questions are essential to identify the

appearance 5: Does the horizontal yellow band extend quite to both

edges of the image? and, Is there certainly no trace of red or orange

to be seen? The first question does not require a quantitative

judgment, but merely one as to whether there is any green visible to

the right or left of the yellow strip. Both are therefore strictly

questions of quality. And the two are sufficient to identify

appearance 5, for if no red or orange is visible, images 1, 2, and 3

are excluded; and if no green lies to the right or left of the yellow

band, image 4 is excluded. Thus if one is to make the somewhat

superficial distinction between qualitative and quantitative

judgments, the judgments here required are qualitative. Moreover, the

subjects make these judgments unhesitatingly.

Finally, the method of making judgments on after-images is not new in

psychology. Lamansky’s well-known determination of the rate of

eye-movements[22] depends on the possibility of counting accurately

the number of dots in a row of after-images. A very much bolder

assumption is made by Guillery[23] in another measurement of the rate

of eye-movements. A trapezoidal image was generated on the moving

retina, and the after-image of this was projected on to a plane

bearing a scale of lines inclining at various angles. On this the

degree of inclination of one side of the after-image was read off, and

thence the speed of the eye-movement was calculated. In spite of the

boldness of this method, a careful reading of Guillery’s first article

cited above will leave no doubt as to its reliability, and the

accuracy of discrimination possible on these after-images.

[22] Lamansky, S., (Pflüger’s) Archiv f. d. gesammte

Physiologie, 1869, II., S. 418.

[23] Guillery, (Pflüger’s) Archiv f. d. ges. Physiologie, 1898,

LXXI., S. 607; and 1898, LXXIII., S. 87.

As to judgments on the color and color-phases of after-images, there

is ample precedent in the researches of von Helmholtz, Hering, Hess,

von Kries, Hamaker, and Munk. It is therefore justifiable to assume

the possibility of making accurately the four simple judgments of

shape and color described above, which are essential to the two proofs

of anæsthesia.

V. SUMMARY AND COROLLARIES OF THE EXPERIMENTS, AND A