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

backward until finally they relapse into confusion.

But let the rate of the rod be not decreased but always steadily

increased. The bands will reappear, this time three of each color with

six transition-bands. As before, the system at first rotates backward,

then lies still, and then moves forward until it is dissolved. As the

rod moves still faster, another system appears, two bands of each

color forming a diameter and the two diameters lying at right angles.

This system goes through the same cycle of movements. When the

increased velocity of the rod destroys this system, another appears

having one band of each color, the two lying on opposite sides of the

center. The system goes through the same phases and is likewise

dissolved. Now, at this point the rod will be found to be rotating at

the same speed as the disc itself.

The explanation of the phenomenon is simple. The bands are not

produced by a single interruption of the vision of a sector by a rod,

but each band is made up of successive superpositions on the retina of

many such single-interruption bands. The overlapping of bands has been

already described (cf. Fig. 10 and pp. 196-198); superposition depends

of course on the same principle.

At the moment when a system of four bands of either color is seen at

rest, the rod is moving just one fifth as rapidly as the disc; so

that, while the rod goes once around, either sector, say the green

one, will have passed behind it exactly four times, and at points

which lie 90° apart. Thus, four red bands are produced which lie at

right angles to one another. But the disc is revolving at least 24

times in a second, the rod therefore at least 4.8 times, so that

within the interval of time during which successive stimuli still

contribute to the characteristic effect the rod will have revolved

several times, and with each revolution four red bands at right angles

to one another will have been formed. And if the rod is moving

exactly one fifth as fast as the disc, each new band will be

generated at exactly that position on the disc where was the

corresponding band of the preceding four. The system of bands thus

appear motionless on the disc.

The movement of the system arises when the rate of the rod is slightly

less or more than one fifth that of the disc. If slightly less, the

bands formed at each rotation of the rod do not lie precisely over

those of the previous rotation, but a little to the rear of them. The

new set still lies mostly superposed on the previous sets, and so

fuses into a regular appearance of bands, but, since each new

increment lags a bit behind, the entire system appears to rotate

backward. The apparatus is actually a cinematograph, but one which

gives so many pictures in the second that they entirely fuse and the

strobic movement has no trace of discontinuity.

If the rod moves a trifle more than one fifth as fast as the disc, it

is clear that the system of bands will rotate forward, since each new

set of bands will lie slightly ahead of the old ones with which it

fuses. The farther the ratio between the rates of rod and disc departs

from exactly 1:5, whether less or greater, the more rapid will the

strobic movement, backward or forward, be; until finally the

divergence is too great, the newly forming bands lie too far ahead or

behind those already formed to fuse with them and so be apperceived as

one system, and so the bands are lost in confusion. Thus the cycle of

movement as observed on the disc is explained. As the rate of the rod

comes up to and passes one fifth that of the disc, the system of four

bands of each color forms in rapid backward rotation. Its movement

grows slower and slower, it comes to rest, then begins to whirl

forward, faster and faster, till it breaks up again.

The same thing happens as the rate of the rod reaches and exceeds just

one fourth that of the disc. The system contains three bands of each

color. The system of two bands of each color corresponds to the ratio

1:3 between the rates, while one band of each color (the two lying

opposite) corresponds to the ratio 1:2.

If the rod and the disc rotate in opposite directions, the phenomena

are changed only in so far as the changed geometrical relations

require. For the ratio 1:3 between the two rates, the strobic system

has four bands of each color; for 1:2, three bands of each color;

while when the two rates are equal, there are two bands of each color,

forming a diameter. As would be expected from the geometrical

conditions, a system of one band of each color cannot be generated

when rod and disc have opposite motions. For of course the rod cannot

now hide two or more times in succession a sector at any given point,

without hiding the same sector just as often at the opposite point,

180° away. Here, too, the cycle of strobic movements is different. It

is reversed. Let the disc be said to rotate forward, then if the rate

of the rod is slightly less than one fourth, etc., that of the disc,

the system will rotate forward; if greater, it will rotate backward.

So that as the rate of the rod increases, any system on its appearance

will move forward, then stand still, and lastly rotate backward. The

reason for this will be seen from an instant’s consideration of where

the rod will hide a given sector.

It is clear that if, instead of using as ‘rod’ a single radial sector,

one were to rotate two or more such sectors disposed at equal angular

intervals about the axis, one would have the same strobic phenomena,

although they would be more complicated. Indeed, a large number of

rather narrow sectors can be used or, what is the same thing, a second

disc with a row of holes at equal intervals about the circumference.

The disc used by the writer had a radius of 11 inches, and a

concentric ring of 64 holes, each 3/8 of an inch in diameter, lying 10

inches from the center. The observer looks through these holes at the

color-disc behind. The two discs need not be placed concentrically.

When produced in this way, the strobic illusion is exceedingly pretty.

Instead of straight, radial bands, one sees a number of brightly

colored balls lying within a curving band of the other color and

whirling backward or forward, or sometimes standing still. Then these

break up and another set forms, perhaps with the two colors changed

about, and this then oscillates one way or the other. A rainbow disc

substituted for the disc of two sectors gives an indescribably

complicated and brilliant effect; but the front disc must rotate more

slowly. This disc should in any case be geared for high speeds and

should be turned by hand for the sake of variations in rate, and

consequently in the strobic movement.

It has been seen that this stroboscope is not different in principle

from the illusion of the resolution-bands which this paper has aimed

to explain. The resolution-bands depend wholly on the purely

geometrical relations between the rod and the disc, whereby as both

move the rod hides one sector after the other. The only physiological

principles involved are the familiar processes by which stimulations

produce after-images, and by which the after-images of rapidly

succeeding stimulations are summed, a certain number at a time, into a

characteristic effect.

*

STUDIES IN MEMORY.

*

RECALL OF WORDS, OBJECTS AND MOVEMENTS.

BY HARVEY A. PETERSON.

Kirkpatrick,[1] in experimenting with 379 school children and college

students, found that 3-1/3 times as many objects were recalled as

visual words after an interval of three days. The experiment consisted

in showing successively 10 written names of common objects in the one

case and 10 objects in the other at the rate of one every two seconds.

Three days later the persons were asked to recall as many of each

series as possible, putting all of one series together. The averages

thus obtained were 1.89 words, 6.29 objects. The children were not

more dependent on the objects than the college students.

[1] Kirkpatrick, E.A.: PSYCHOLOGICAL, REVIEW, 1894, Vol. I., p.

Since the experiment just described was performed without laboratory

facilities, Calkins[2] repeated it with 50 college women, substituting

lantern pictures for objects. She obtained in recall, after two days,

the averages 4.82 words, 7.45 pictures. The figures, however, are the

number of objects or words remembered out of ten, not necessarily

correctly placed. Kirkpatrick’s corresponding figures for college

women were 3.22 words, 5.44 objects. The two experiments substantially

agree, Calkins’ higher averages being probably due to the shortening

of the interval to two days.

[2] Calkins, M.W.: PSYCHOLOGICAL, REVIEW, 1898, Vol. V., p.

Assuming, thus, that objects are better remembered than names in

deferred recall, the question arises whether this holds true when the

objects and names are coupled with strange and arbitrary symbols—a

question which is clearly of great practical interest from the

educational point of view, as it is involved in the pedagogical

problem whether a person seeking to acquire the vocabulary of a

foreign language ought to connect the foreign words with the familiar

words or with the objects themselves. And the further question arises:

what are the facts in the case of movements instead of objects, and

correspondingly in that of verbs instead of nouns. Both questions are

the problems of the following investigation.

As foreign symbols, either the two-figure numbers were used or

nonsense-words of regularly varying length. As familiar material,

nouns, objects, verbs and movements were used. The words were always

concrete, not abstract, by which it is meant that their meaning was

capable of demonstration to the senses. With the exception of a few

later specified series they were monosyllabic words. The nouns might

denote objects of any size perceptible to the eye; the objects,

however, were all of such a size that they could be shown through a

14×12 cm. aperture and still leave a margin. Their size was therefore

limited.

Concerning the verbs and movements it is evident that, while still

being concrete, they might be simple or complicated activities

consuming little or much time, and further, might be movements of

parts of the body merely, or movements employing other objects as

well. In this experiment complicated activities were avoided even in

the verb series. Simple activities which could be easily and quickly

imaged or made were better for the purpose in view.

THE A SET.

The A set contained sixteen series, A^{1}, A^{2}, A^{3}, etc.,

to A^{16}. They were divided as follows:

Numbers and nouns: A^{1}, A^{5}, A^{9}, A^{13}.

Numbers and objects: A^{2}, A^{6}, A^{10}, A^{14}.

Numbers and verbs: A^{3}, A^{7}, A^{11}, A^{15}.

Numbers and movements: A^{4}, A^{8}, A^{12}, A^{16}.

The first week A^{1-4} were given, the second week A^{5-8}, etc.,

so that each week one series of each of the four types was given the

subject.

In place of foreign symbols the numbers from 1 to 99 were used, except

in A^{13-15}, in which three-figure numbers were used.

Each series contained seven couplets, except A^{13-16}, which, on

account of the greater difficulty of three-figure numbers, contained

five. Each couplet was composed of a number and a noun,