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

But the image 2 or 3 may indeed be localized quite over the final

fixation-point. In this case the light is to be looked to. It is too

bright, as it probably was in the case of Dodge’s experiments. It must

be further reduced; and with the eye at rest, the control (case I)

must be repeated. In the experiments here described it was always

found possible so to reduce the light that the distinct, entire image

of the dumb-bell (2, Fig. 7) never appeared localized on the final

fixation-point, although in the control, H, of Fig. 7:1, was always

distinctly visible.

With these two precautions taken, the image on the final

fixation-point is like either 3, 4, or 5. Shape 5 very rarely appears,

while the trained subject sees 4 and 3 each about one half the times;

and either may be seen for as many as fifteen times in succession.

Shape 4 is of course exactly the appearance which this experiment

takes to be crucial evidence of a moment of central anæsthesia, before

the image is perceived and during which the stimulation of the handle

h completely elapses. Eight subjects saw this phenomenon distinctly

and, after some training in timing their eye-movements, habitually.

The first appearance of the handleless image was always a decided

surprise to the subject (as also to the writer), and with some

eagerness each hastened to verify the phenomenon by new trials.

The two ends (e, e) of the dumb-bell seem to be of the same

intensity as in shape 2 when seen in reflex movement. But there is no

vestige whatsoever of a handle. Two of the subjects stated that for

them the place where the handle should have been, appeared of a

velvety blackness more intense than the rest of the background. The

writer was not able to make this observation. It coincides

interestingly with that of von Kries,[21] who reports as to the phases

of fading after-images, that between the disappearance of the primary

image and the appearance of the ‘ghost,’ a moment of the most intense

blackness intervenes. The experiments with the pendulum, however,

brought out no ghost.

[21] Von Kries, J., _Zeitschr. f. Psych, u. Physiol. d.

Sinnesorgane_, 1896, XII., S. 88.

We must now enquire why in about half the cases shape 3 is still seen,

whereas shape 5 occurs very rarely. Some of the subjects, among whom

is the writer, never saw 5 at all. We should expect that with the

intensity of H sufficiently reduced 4 and 5 would appear with equal

frequency, whereas 3 would be seen no oftener than 2; shape 5

appearing when the eye did not, and 4 when it did, move at just the

rate of the pendulum. It is certain that when 4 is seen, the eye has

caught just the rate of the pendulum, and that for 3 or 5 it has moved

at some other rate. We have seen above (p. 27) that to move with the

pendulum the eye must already move decidedly more slowly than Dodge

and Cline find the eye generally to move. Nothing so reliable in

regard to the rate of voluntary eye-movements as these measurements of

Dodge and Cline had been published at the time when the experiments on

anæsthesia were carried on, and it is perhaps regrettable that in the

‘empirical’ approximation of the natural rate of the eye through 40°

the pendulum was set to move so slowly.

In any case it is highly probable that whenever the eye did not move

at just the rate of the pendulum, it moved more rapidly rather than

more slowly. The image is thus horizontally elongated, by an amount

which varies from the least possible up to 9 cm. (the width of the

opening in T), or even more. And while the last of the movement

(O to P, or N to P’), in which the stimulation of H’ is

supposed to subside, is indeed executed, it may yet be done so

rapidly that after all H’ cannot subside, not even although it is

now less intense by being horizontally spread out (that is, less

concentrated than the vanished h of shape 4). This explanation is

rendered more probable by the very rare appearance of shape 5, which

must certainly emerge if ever the eye were to move more slowly than

the pendulum.

The critical fact is, however, that shape 4 does appear to a trained

subject in about one half the trials—a very satisfactory ratio when

one considers the difficulty of timing the beginning of the movement

and its rate exactly to the pendulum.

Lastly, in some cases no image appears at all. This was at first a

source of perplexity, until it was discovered that the image of the

dumb-bell, made specially small so as to be contained within the area

of distinct vision, could also be contained on the blind-spot. With

the pendulum at rest the eye could be so fixed as to see not even the

slight halo which diffuses in the eye and seems to lie about the

dumb-bell. It may well occur, then, that in a movement the image

happens to fall on the blind-spot and not on the fovea. That this

accounts for the cases where no image appears, is proved by the fact

that if both eyes are used, some image is always seen. A binocular

image under normal convergence can of course not fall on both

blind-spots. It may be further said that the shape 4 appears as well

when both eyes are used as with only one. The experiment may indeed as

well be carried on with both eyes.

Some objections must be answered. It may be said that the image of h

happens to fall on the blind-spot, e and e being above and below

the same. This is impossible, since the entire image and its halo as

well may lie within the blind-spot. If now h is to be on the

blind-spot, at least one of the end-circles e, e will be there

also, whereas shape 4 shows both end-circles of the dumb-bell with

perfect distinctness.

Again, it cannot properly be urged that during the movement the

attention was distracted so as not to ‘notice’ the handle. The shape

of a dumb-bell was specially chosen for the image so that the weaker

part of the stimulation should lie between two points which should be

clearly noticed. Indeed, if anything, one might expect this central,

connecting link in the image to be apperceptively filled in, even when

it did not come to consciousness as immediate sensation. And it

remains to ask what it is which should distract the attention.

In this connection the appearance under reflex eye-movement compares

interestingly with that under voluntary. If the wall WONW (Fig. 5)

is taken from before the pendulum, and the eye allowed to move

reflexly with the swinging dumb-bell, the entire image is seen at each

exposure, the handle seeming no less bright than the end-circles.

Moreover, as the dumb-bell opening swings past the place of exposure

and the image fades, although the handle must fade more quickly than

the ends, yet this is not discernible, and the entire image disappears

without having at any time presented the handleless appearance.

B. Another test for this anæsthesia during movement is offered in the

following experiment. It is clear that, just as a light-stimulation is

not perceived if the whole retinal process begins and ends during a

movement, so also a particular phase of it should not be perceived if

that phase can be given complete within the time of the movement. The

same pendulum which was used in the previous experiment makes such a

thing possible. If in place of the perforated dumb-bell the pendulum

exposes two pieces of glass of nearly complementary colors, one after

the other coming opposite the place of exposure, the sensations will

fuse or will not fuse according as the pendulum swings rapidly or

slowly. But now a mean rate of succession can be found such as to let

the first color be seen pure before the second is exposed, and then to

show the second fused with the after-image of the first. Under some

conditions the second will persist after the first has faded, and will

then itself be seen pure. Thus there may be three phases in

consciousness. If the first color exposed is green and the second red,

the phases of sensation will be green, white, and perhaps red. These

phases are felt to be not simultaneous but successive. A modification

of this method is used in the following experiment. (See Fig. 8, Plate

IV.)

T and I here correspond to the cards T and I of Fig. 6.

T consists of a rectangular opening, 9×5 cm., which contains three

pieces of glass, two pieces of green at the ends, each 2.8 cm. wide

and 7 cm. high, and a piece of red glass in the middle 3.4 cm. wide

and only 1.5 cm. high, the space above and below this width being

filled with opaque material. The shape of the image is determined as

before by the hole in I, which now, instead of being a dumb-bell, is

merely a rectangular hole 2 cm. wide and 5 cm. high. Exactly as

before, T is fixed in the background and I swings with the

pendulum, the eye moving with it.

The speed of the pendulum must be determined, such that if I lies in

the front groove (Fig. 5, x) and the eye is at rest, the image will

clearly show two phases of color when T swings past on the pendulum.

With T and I as described above, a very slow pendulum shows the

image green, red (narrow), and green, in succession. A very fast

pendulum shows only a horizontal straw-yellow band on a green field

(Fig. 8:5). There is but one phase and no feeling of succession.

Between these two rates is one which shows two phases—the first a

green field with a horizontal, reddish-orange band (Fig. 8:3), the

second quickly following, in which the band is straw-yellow (5). It

might be expected that this first phase would be preceded by an

entirely green phase, since green is at first exposed. Such is however

not the case. The straw-yellow of the last phase is of course the

fusion-color of the red and green glasses. It would be gray but that

the two colors are not perfectly complementary. Since the arrangement

of colors in T is bilaterally symmetrical, the successive phases are

the same in whichever direction the pendulum swings.

[Illustration: MONOGRAPH SUPPLEMENT 17. PLATE IV.

Fig. 8.

HOLT ON EYE-MOVEMENT.]

It is desirable to employ the maximum rate of pendulum which will give

the two phases. For this the illumination should be very moderate,

since the brighter it is, the slower must be the pendulum. With the

degree of illumination used in the experiments described, it was found

that the pendulum must fall from a height of only 9.5° of its arc: a

total swing of 19°. The opening of T, which is 9 cm. wide, then

swings past the middle point of I in 275[sigma].

Now when the eye moves it must move at this rate. If the eye is 56 cm.

distant from the opening, as in the previous case, the 9 cm. of

exposure are 9° 11’ of eye-movement, and we saw above that 9° 11’ in

110[sigma] is a very slow rate of movement, according to the best

measurements. Now it is impossible for the eye to move so slowly as 9°