Various - Harvard Psychological Studies, Volume 1

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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 deg. 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.
602.

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.
451.

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
14x12 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, object, verb,
or movement.

Certain rules were observed in the composition of the series. Since
the test was for permanence, to avoid confusion no number was used in
more than one couplet. No two numbers of a given series were chosen
from the same decade or contained identical final figures. No word was
used in more than one couplet. Their vowels, and initial and final
consonants were so varied within a single series as to eliminate
phonetic aids, viz., alliteration, rhyme, and assonance. The kind of
assonance avoided was identity of final sounded consonants in
successive words, _e.g._, lane, vine.

The series were composed in the following manner: After the
twenty-eight numbers for four series had been chosen, the words which
entered a given series were selected one from each of a number of
lists of words. These lists were words of like-sounded vowels. After
one word had been chosen from each list, another was taken from the
first list, etc. As a consequence of observing the rules by which
alliteration, rhyme, and assonance were eliminated, the words of a
series usually represented unlike categories of thought, but where two
words naturally tended to suggest each other one of them was rejected
and the next eligible word in the same column was chosen. The
following is a typical series from the _A_ set.

_A_^{1}. Numbers and Nouns.

19 42 87 74 11 63 38
desk girl pond muff lane hoop vine

The apparatus used in the _A_ set and also in all the later sets may
be described as follows: Across the length of a table ran a large,
black cardboard screen in the center of which was an oblong aperture
14 cm. high and 12 cm. wide. The center of the aperture was on a level
with the eyes of the subject, who sat at the table. The aperture was
opened and closed by a pneumatic shutter fastened to the back of the
screen. This shutter consisted of two doors of black cardboard sliding
to either side. By means of a large bulb the length of exposure could
be regulated by the operator, who stood behind the table.

The series--consisting of cards 4x21/2 cm., each containing a printed
couplet--was carried on a car which moved on a track behind and
slightly below the aperture. The car was a horizontal board 150 cm.
long and 15 cm. wide, fixed on two four-wheeled trucks. It was divided
by vertical partitions of black cardboard into ten compartments, each
slightly wider than the aperture to correspond with the visual angle.
A curtain fastened to the back of the car afforded a black background
to the compartments. The couplets were supported by being inserted
into a groove running the length of the car, 3 cm. from the front. A
shutter 2 cm. high also running the length of the car in front of the
groove, fastened by hinges whose free arms were extensible, concealed
either the upper or the lower halves of the cards at the will of the
operator; _i.e._, either the foreign symbols or the words,
respectively. A screen 15 cm. high and the same length as the car,
sliding in vertical grooves just behind the cards and in front of the
vertical partitions, shut off the objects when desired, leaving only
the cards in view. Thus the apparatus could be used for all four types
of series.

The method of presentation and the time conditions of the _A_ set were
as follows:--A metronome beating seconds was used. It was kept in a
sound-proof box and its loudness was therefore under control. It was
just clearly audible to both operator and subject. In learning, each
couplet was exposed 3 secs., during about 2 secs. of which the shutter
was fully open and motionless. During this time the subject read the
couplet inaudibly as often as he wished, but usually in time with the
metronome. His object was to associate the terms of the couplet. There
was an interval of 2 secs. after the exposure of each couplet, and
this was required to be filled with repetition of only the
_immediately preceding couplet_. After the series had been presented
once there was an interval of 2 secs. additional, then a second
presentation of it commenced and after that a third. At the completion
of the third presentation there was an interval of 6 secs. additional
instead of the 2, at the expiration of which the test commenced.

_A_^{13-16} had five presentations instead of three. The test
consisted in showing the subject either the numbers or the words in
altered order and requiring him to write as many of the absent terms
as he could. In the object and movement series the objects were also
shown and the movements repeated by the subject if words were the
given terms. The time conditions in the test were,

Exposure of a term 3 secs.
Post-term interval in A^{1-12} 4 secs.
Post-term interval in A^{13-16} 6 secs.

This allowed the subject 7 secs. for recalling and writing each term
in A^{1-12} and 9 sec. in A^{13-16}. If a word was recalled after that
time it was inserted, but no further insertions were made after the
test of a series had been completed. An interval of 3 min. elapsed
between the end of the test of one series and the beginning of the
next series, during which the subject recorded the English word of any
couplet in which an indirect association had occurred, and also his
success in obtaining visual images if the series was a noun or a verb
series.

As already indicated, four series--a noun, an object, a verb, and a
movement series--given within a half hour, constituted a day's work
throughout the year. Thus variations due to changes in the
physiological condition of the subject had to affect all four types of
series.

Two days later these series were tested for permanence, and in the
same way as the tests for immediate recall, with this exception:

Post-term interval in A^{13-16} 8 secs.

Thus 11 secs. were allowed for the deferred recall of each term in
A^{13-16}.

In the movement series of this set, to avoid hesitation and confusion,
the operator demonstrated to the subject immediately before the series
began, once for each word, how the movements were to be made.

The _A_ set was given to three subjects. The results of each subject
are arranged separately in the following table. In the tests the words
were required in A^{1-4}, in A^{5-16} the numbers. The figures show
the number of terms correctly recalled out of seven couplets in
A^{1-12} and out of five couplets in A^{13-16}, _exclusive_ of
indirect association couplets. The figures in brackets indicate the
number of correctly recalled couplets per series in which indirect
associations occurred. The total number correctly recalled in any
series is their sum. The figures in the per cent. row give the
percentage of correctly recalled couplets left after discarding both
from the number recalled and from the total number of couplets given
those in which indirect associations occurred. This simply diminished
the subject's number of chances. A discussion of the propriety of this
elimination will be found later. In _A_^{1-12} the absent terms had to
be recalled exactly in order, to be correct, but in _A_^{13-16}, on
account of the greater difficulty of the three-place numbers, any were
considered correct when two of the three figures were recalled, or
when all three figures were correct but two were reversed in position,
_e.g._, 532 instead of 523. _N_ means noun series, _O_ object, _V_
verb, and _M_ movement series. Series _A_^{1}, _A_^{5}, _A_^{9},
_A_^{13} are to be found in the first and third columns, _A_^{2},
_A_^{6}, _A_^{10}, _A_^{14} in the second and fourth, _A_^{3},
_A_^{7}, _A_^{11}, _A_^{15}, in the fifth and seventh, and _A_^{4},
_A_^{8}, _A_^{12}, _A_^{16} in the sixth and eighth columns.

TABLE I.

SHOWING IMMEDIATE RECALL AND RECALL AFTER TWO DAYS.

_M_.
Series. Im. Rec. Two Days. Im. Rec. Two Days.
N. O. N. O. V. M. V. M.
A^{1-4} 6 7 3 1 6 7 2 1
A^{5-8} 5(1) 6 3(1) 6 6(1) 7 5(1) 6
A^{9-12} 7 7 4 6 7 6(1) 7 6(1)
A^{13-16} 4 5 2 2 5 3 2 2
Total. 22(1) 25 12(1) 15 24(1) 23(1) 16(1) 15(1)
Per cent. 88 96 48 58 96 92 64 66

_S_.
Series. Im. Rec. Two Days. Im. Rec. Two Days.
N. O. N. O. V. M. V. M.
A^{1-4} 6(1) 6 0 0 7 7 0 0
A^{5-8} 6 7 1 3 6 7 0 3
A^{9-12} 7 6 2 2 5 7 0 0
A^{13-16} 5 5 0 0 5 5 3 0
Total. 24(1) 24 3 5 23 26 3 3
Per cent. 96 92 12 19 88 100 12 12

_Hu_.
Series. Im. Rec. Two Days. Im. Rec. Two Days.
N. O. N. O. V. M. V. M.
A^{1-4} 6 7 0 1 5 6(1) 0 2
A^{5-8} 5(2) 7 1(2) 1 7 7 1 0
A^{9-12} 6(1) 7 2 2 6 7 0 5
A^{13-16} 4(1) 4(1) 0 2 5 5 0 1
Total. 21(4) 25(1) 3(2) 6 23 25(1) 1 8
Per cent. 95 100 14 24 88 100 4 32

These results will be included in the discussion of the results of the
_B_ set.

THE _B_ SET.

A new material was needed for foreign symbols. After considerable
experimentation nonsense words were found to be the best adapted for
our purpose. The reasons for this are their regularly varying length
and their comparative freedom from indirect associations. An objection
to using nonsense syllables in any work dealing with the permanence of
memory is their sameness. On this account they are not remembered
long. To secure a longer retention of the material, nonsense words
were devised in substantially the same manner as that in which Mueller
and Schumann made nonsense syllables, except that these varied
regularly in length from four to six letters. Thus the number of
letters, not the number of syllables was the criterion of variation,
though of course irregular variation in the number of syllables was a
necessary consequence.

When the nonsense words were used it was found that far fewer indirect
associations occurred than with nonsense syllables. By indirect
association I mean the association of a foreign symbol and its word by
means of a third term suggested to the subject by either of the others
and connected at least in _his_ experience with both. Usually this
third term is a word phonetically similar to the foreign symbol and
ideationally suggestive of the word to be associated. It is a very
common form of mnemonic in language material. The following are
examples:

cax, stone (Caxton);
teg, bib (get bib);
laj, girl (large girl);
xug, pond (noise heard from a pond);
gan, mud (gander mud).

For both of these reasons nonsense words were the material used as
foreign symbols in the _B_ set.

The nonsense words were composed in the following manner. From a box
containing four of each of the vowels and two of each of the
consonants the letters were chosen by chance for a four-letter, a
five-letter, and a six-letter word in turn. The letters were then
returned to the box, mixed, and three more words were composed. At the
completion of a set of twelve any which were not readily pronounceable
or were words or noticeably suggested words were rejected and others
composed in their places.

The series of the _B_ set were four couplets long. Each series
contained one three-letter, one four-letter, one five-letter, and one
six-letter nonsense word. The position in the series occupied by each
kind was constantly varied. In all other respects the same principles
were followed in constructing the _B_ set as were observed in the _A_
set with the following substitutions:

No two foreign symbols of a series and no two terms of a couplet
contained the same sounded vowel in accented syllables.

The rule for the avoidance of alliteration, rhyme, and assonance was
extended to the foreign symbols, and to the two terms of a couplet.

The English pronounciation was used in the nonsense words. The
subjects were not informed what the nonsense words were. They were
called foreign words.

Free body movements were used in the movement series as in the _A_
set. Rarely an object was involved, _e.g._, the table on which the
subject wrote. The movements were demonstrated to the subject in
advance of learning, as in the _A_ set.

The following are typical _B_ series:

B2. Nonsense words and objects.

quaro rudv xem lihkez
lid cent starch thorn

B3. Nonsense words and verbs.

dalbva fomso bloi kyvi
poke limp hug eat

B4. Nonsense words and movements.

ohv wecolu uxpa haymj
gnash cross frown twist

The time conditions for presenting a series remained practically the
same. In learning, the series was shown three times as before. The
interval between learning and testing was shortened to 4 seconds, and
in the test the post-term interval of _A^{13-16}_ retained (6 secs.).
This allowed the subject 9 secs. for recalling and writing each term.
The only important change was an extension of the number of tests from
two to four. The third test was one week after the second, and the
fourth one week after the third. In these tests the familiar word was
always the term required, as in _A^{1-4}_, on account of the
difficulty of dealing statistically with the nonsense words. The
intervals for testing permanence in the _B_ set may be most easily
understood by giving the time record of one subject.

TIME RECORD OF _Hu_.

Series. Im. Rec. Two Days. Nine Days. Sixteen Days.
B^{1-4} Feb. 12 Feb. 14 Feb. 21 Feb. 28
B^{5-8} Feb. 19 Feb. 21 Feb. 28 Mch. 7
B^{9-12} Feb. 26 Feb. 28 Mch. 7 Mch. 14
B^{13-16} Mch. 5 Mch. 7 Mch. 14 Mch. 21

The two half-hours in a week during which all the work of one subject
was done fell on approximately the same part of the day. When a number
of groups of 4 series each were to be tested on a given day they were
taken in the order of their recency of learning. Thus on March 7 the
order for _Hu_ was B^{13-16}, B^{9-12}, B^{5-8}.

Henceforth there was also rotation within a given four series. As
there were always sixteen series in a set, the effects of practice and
fatigue within a given half-hour were thus eliminated.

In the following table the results of the _B_ set are given. Its
arrangement is the same as in Table 1., except that the figures
indicate the number of absent terms correctly recalled out of four
couplets instead of seven or five. Where blanks occur, the series was
discontinued on account of lack of recall. As in Table 1., the tables
in the first, third and fifth columns show successive stages of the
same series. Immediate recall is omitted because with rare exceptions
it was perfect, the test being given merely as an aid in learning.

TABLE II.

SHOWING RECALL AFTER TWO, NINE, AND SIXTEEN DAYS.

Days. Two. Nine. Sixteen. Two. Nine. Sixteen.
N. O. N. O. N. O. V. M. V. M. V. M.
Series. _M._
B^{1-4} 2(1) 4 1(1) 2 1(1) 2 4 4 4 2 4 2
B^{5-8} 3 1 2 1 1 1 2 2 2 1 1 1
B^{9-12} 2 3 0 3 0 2 3 2 2 0 2 2
B^{13-16} 2(1) 3 2(1) 0 2(1) 0 1 2 1 0 1 0
Total 9(2) 11 5(2) 6 4(2) 5 10 10 9 3 8 5
Per cent. 64 69 36 38 29 31 63 63 56 19 50 31