Chapter XIII: Section II: showed that the shorter filled distances are (9)

Seconds Seconds.
1 Figures alike: Left 30.8 Right 31.9
2 " unlike: Simple 27.10 Complex 34.62
3 " " Small 24.54 Large 33.30
4 " " Gray 25.61 White 29.53
5 " " Line 31.91 Angle 38.54
6 " " Plain 23.92 Marked 37.48
7 " " (colored) 5 seconds 27.75 10 seconds 29.15
8 " " (gray) 5 seconds 25.42 10 " 32.12
9 " " 1st exposure 12.64 2d exposure 36.45
10 " " Vertical line 34.94 Hor. line 34.49
11 " " Full-faced 28.10 Outline 41.08
12 " " Figure 29.26 Int. lines 39.32
13 " " Figure 34.03 Vert. lines 36.40
14 " " Stationary 28.88 Moved 37.39
15 " " Gray 30.90 Colored 37.81
16 (See Table XVI.)

If we put these results into the form of propositions, we find:

1. That when the objects are similar surfaces, seen under similar conditions, the chances of the recurrence and persistence of their images are, on the whole, practically equal.

2. That surfaces bounded by complicated outlines have an advantage in ideation, other things equal, over surfaces bounded by simple outlines.

3. That as between two objects of unequal area--color, form, and other conditions being the same--the larger object has the advantage in the ideational rivalry.

4. That the image of a white object has a like advantage over the image of a gray object.

5. That broken or complex lines have in ideation an advantage over straight or simple lines.

6. That an object with varied content, other conditions remaining the same, has an advantage over an object with homogeneous surface.

7 and 8. That an increase of the time during which the attention is given to an object increases the chances for the recurrence of its image or idea.

9. That of two objects to which attention is directed in succession, the object last seen has a distinct advantage in the course of ideation following close on the perception of the objects.

10. That lines of similar appearance and equal length, one of which is vertical and the other horizontal, have, like surfaces of similar appearance and form and equal dimensions, practically equal chances of recurrence and survival in ideation, the slight difference in their chances being in favor of the vertical line.

11. That as between two figures of similar form and equal dimensions, one of which has a filled homogeneous content and the other is a mere outline figure, the latter has a marked advantage in the course of ideation.

12. That of two linear and symmetrical figures, of which one is an outline figure with continuous boundary, and the other consists of the same linear elements, similarly disposed, as the first, but has its lines disconnected so that it has no continuous boundary, the latter figure has the advantage in ideation.

13. That if, with material similar to that described in paragraph 12, the disconnected lines are arranged so as to be vertical and equidistant, the advantage in ideation still remains with the disconnected lines, but is much reduced.

14. That if one of two figures, of similar appearance and form and of equal dimensions, is kept in motion while it is exposed to view, and the other is left at rest, the image of the moving object is the more persistent.

15. That, under like conditions, colored objects are more persistent in ideation than gray objects.

16. That lines and sharp angles, as compared with broad surfaces, have a strong directive force in the determination of the attention to their images or ideas; that this directive force is strongest in the case of very acute angles, the attention being carried forward in the direction indicated by the apex of the angle; but that uncompleted lines, especially when two such lines are directed towards each other, have a similar and not much inferior force in the control of the course of ideation.

If we should seek now to generalize these experimental results, they would take some such form as the following:

Abstraction made of all volitional aims and all æsthetic or affective bias, the tendency of an object to recur and persist in idea depends (within the limits imposed by the conditions of these experiments) upon the extent of its surface, the complexity of its form, the diversity of its contents, the length and recency of the time during which it occupies the attention, the definiteness of the direction which it imparts to the attention (as in the case of angles and lines), its state of motion or of rest, and, finally, its brightness and its color.

These conditions, however, are for the most part but conditions which determine the energy, diversity, complexity and definiteness of the active processes involved in the bestowal of attention upon its object, and the experiments show that such active processes are as essential in ideation as in perception. The stability of an image, or internal sensation, thus depends on the activity of its motor accompaniments or conditions. And as the presence of an image to the exclusion of a rival, which but for the effect of these motor advantages would have as strong a claim as itself to the occupation of consciousness (cf. Series I., X.), may be treated as a case of inhibition, the greater the relative persistence of an image or idea the greater we may say is the 'force' with which it inhibits its rival. Exclusive possession of the field involves, to the extent to which such possession is made good, actual exclusion of the rival; and exclusion is inhibition. Our generalization, accordingly, may take the following form:--

The inhibitory effect of an idea, apart from volitional or emotional bias, depends upon the energy, diversity, complexity and definiteness of the motor conditions of the idea.

* * * * *

CONTROL OF THE MEMORY IMAGE.

BY CHARLES S. MOORE.

Since Gallon's classic investigation in the field of mental imagery several similar investigations have been pursued in the same direction, chiefly, however, for the purpose of discovering and classifying types of imagination.

Little has been done in the line of developing and studying the problems of the memory image proper, and still less, in fact almost nothing, is to be found bearing on the control of the visual memory image. The general fact of this control has been presented, with greater or less detail, based upon returns from questionaries. Gallon himself, for example, having referred to instances in which the control was lacking, goes on to say[1]: "Others have complete mastery over their mental images. They can call up the figure of a friend and make it sit on a chair or stand up at will; they can make it turn round and attitudinize in any way, as by mounting it on a bicycle or compelling it to perform gymnastic feats on a trapeze. They are able to build up elaborate structures bit by bit in their mind's eye and add, substract or alter at will and at leisure."

[1] Gallon, Francis: 'Inquiries into Human Faculty and its
Development,' London, 1883, p. 109.

More recent writers classify the students, or other persons examined, according to these persons' own statements with regard to the nature and degree of control over the mental images which they consider themselves to possess. An article by Bentley[2] is the only study of a specific problem of the memory image. After a glance at the literature with reference to methods pursued in the investigation of problems of memory in general, Bentley outlines 'a static and genetic account' of the memory image in particular, and presents details of experiments 'carried on for the special investigation of the visual memory image and its fidelity to an original presentation.'

[2] Bentley, I.M.: 'The Memory Image and its Qualitative
Fidelity,' _Am. Journ. of Psychol._, 1899, XI., pp. 1-48.

Of the many memory problems as yet unattacked, that of the control of the mental image is one of the most interesting. The visual image obviously offers itself as the most accessible and the experiments described in this report were undertaken with the purpose of finding out something about the processes by which control of this image is secured and maintained. The report naturally has two aspects, one numerical and the other subjective, presenting the statements of the subjects as to their inner experiences.

The term 'suppression' is used as a convenient one to cover the enforced disappearance of the designated image, whether it be directly forced out of consciousness (a true suppression) or indirectly caused to disappear through neglect, or limitation of the attention to the other image which is to be retained.

As this was an investigation of the control of memory images, the presence of these images under conditions most favorable to their vividness and distinctness was desirable. An immediate mental recall at the end of five seconds of visual stimulation, under favorable though not unusual conditions of light, position and distance, seemed most likely to secure this desideratum. Experimentation showed that five minutes was, on the whole, a suitable period in which to secure the information needed without developing a fatigue in the subject which would vitiate the results.

The experiments made in the visual field were restricted to visual memory images which were called up by the subject during the five minutes succeeding a five seconds' presentation of one or two objects. The subject sat, with his eyes closed, about four feet from a wall or screen, before which the object was placed. At a signal the eyes were opened, and at a second signal five seconds later they were closed. If an after-image appeared the subject reported its disappearance, and then called up the image of the object just presented, and reported as to its clearness, vividness, persistency and whatever phenomena arose; and when directed he sought to modify the image in various ways to be described later.

There were six subjects in experiments conducted during the winter of 1900-1901, and six (five being new ones) in experiments of the fall of 1901. They were all good visualizers, though they differed in the readiness with which they visualized respectively form or color.

The experiments of the first few weeks were designed to establish the fact of control by the subjects over a single visual memory image as to its position, size, outline, color, movement and presence. In general it was established that a considerable degree of control in these particulars existed in these subjects.

Later, two objects were presented at a time, and were such small articles as a glass ball, a book, a silk purse, an eye-glass case, an iron hook, and so forth. Still later, colored squares, triangles, or discs were used exclusively.

The investigation followed these lines: I. Movements of a single image; II. Changes of color of a single image; III. Movements of two images in the same and in different directions; IV. Suppression of one of two images; V. Movements of a single image, the object having been moved during the exposure.

I. MOVEMENTS OF A SINGLE IMAGE.

The first table gives the time in seconds taken to move voluntarily a single image (of a colored square or disc) to the right, left, up or down, and in each case to restore it to its original position. There were thirty movements of each kind for each of the six subjects, making one hundred and eighty for each direction and also for each return, the total of all movements being fourteen hundred and forty. The distance to which the subjects moved the images was not fixed, but was in most cases about twelve inches. The time was taken with a stop-watch, and includes the time between the word of command, 'right,' etc., of the director and the verbal report 'now' of the subject. It includes, therefore, for each movement two reaction times. The subject reported 'now' the instant the color reached, or appeared at, the designated place, not waiting for the completion of the shape which usually followed. Two of the subjects (H. and K.) took much longer than the other four, their combined average time being almost exactly four times the combined average time of the other four.

TABLE I.

MOVEMENTS OF A SINGLE IMAGE.

30 Movements of Each Kind for Each Subject Average Time in Seconds.

To To
Subjects Right Return Left Return Up Return Down Return Averages
B. 1.30 1.07 1.06 1.11 1.13
0.58 0.73 0.46 0.45 0.55

G. 1.44 1.15 0.99 0.82 1.10
0.92 0.89 0.76 0.57 0.78

H. 7.12 6.42 5.96 5.85 6.34
4.51 4.41 4.36 4.40 4.42

I. 1.28 1.34 1.62 1.47 1.43
0.67 0.62 0.86 0.72 0.72

J. 1.71 1.42 1.40 1.14 1.50
1.34 1.53 0.77 0.74 1.09

K. 4.81 4.64 3.29 3.28 4.01
2.40 2.71 1.91 1.56 2.14

Averages 2.95 2.67 2.39 2.23 2.59
1.72 1.82 1.52 1.41 1.62

NUMERICAL.

The general averages for the different movements show that movement to the right was hardest, to the left next; while movement downward was the easiest. A marked exception is seen in I., for whom the upward movement was the hardest and movement to the right was the easiest. J. found movement to the left hardest. For the return movements, the general averages show that the return from the left is the hardest, from the right next; while from below is the easiest. Here again I. found the return from above the hardest and from below the next hardest; while from the left was the easiest.

Arranging the subjects in the order of the average time, taken for all the movements, including the returns to the original position, we have

H. 5.35 average time out and back.
K. 3.07 " " " " "
J. 1.29 " " " " "
I. 1.07 " " " " "
G. .94 " " " " "
B. .84 " " " " "

SUBJECTIVE.

All the six subjects whose time records appear in Table I. and also four others whose time was not recorded reported eye movements, or a tendency to eye movement. A. and K. reported that when the image was dim there was accommodation as for long vision and when the image was vivid there was accommodation as for near vision. B. ideated the new position and the eye movement occurred automatically. G. reported a contraction of the scalp muscles and a tendency to cast the eyes up and locate the image at the back of the head inside; this was an inveterate habit. He reported also accommodation for the different distances of the image and an after-feeling of strain in the head. H. reported a strong tendency in the eyes to return to the center, _i.e._, the original position, and to carry the image back there. All the subjects frequently reported a sense of relief in the eye muscles when the command to return the image to the center was given--also, a tension in the forehead in the upward movement which was accentuated (with H.) when there was headache. J. reported, 'always eye strain,' and noticed that the eyes usually turned as far as the new position, but sometimes stopped short of it. K. reported first an eye movement, then an ideation of the image in the new position. E. and H. turned the head to right and left for movements of the image in those directions. A., B., E. and F. believed that they could inhibit the eye movement. Subjects were at times unconscious of eye movements. H. articulated the names of the colors of the image and found that it aided the movement of the image to say to himself, for example: "Don't you see that blue square there?"

All but J. reported a loss in vividness and also, though to a less degree, in distinctness whenever the image was moved away from the center. J. found no difference. H. reported that details of the object which were reproduced in the image when at the center were not discernible in the image in other positions, also that at the left the image was more vivid than at the right. B.'s memory image of a watch, three minutes after it was called up, was still so clear that he read from it the time. E., who was an experienced photographer, had no difficulty in recalling outline, light and shade, but had difficulty in reproducing color. I. frequently lost the form in making the required improvements.

Under manipulation the memory image usually retained its distinctness and vividness with no loss or with but slight loss when in its original position, to the end of the five minutes of the experiment. The image, also, seldom disappeared except for the momentary disappearances in passing from one position to another, which are referred to later. Under passive observation of the memory image disappearances, though of short duration, were frequent and there was a noticeable fading away of color and loss of outline.

The memory image almost without exception, when first recalled, was located in the direction and at the distance of the object presented.

In moving from the center to right and left the image remained in the same plane with a few exceptions; in moving up and down it moved on an arc whose center was at the eye. This was especially true of the downward motion, which was almost always to a greater distance than any of the other motions.

C., D., F. and H. felt the need of a support for the image in any except the central position. This was true especially of the position above the center, but was entirely overcome by practice by C., F. and H., and partially by D. In movements where time was to be recorded, the distance was from six to eighteen inches, but the image could be carried by all the eleven subjects to any part of the room or beyond the room. Usually the method followed was to fix the attention on the suggested position and then the image appeared there, sometimes complete at the outset, but usually in part at first, then developing instantly to completion. When the subject was requested to trace the image _in transitu_, this could usually be accomplished, but the time was much longer. Frequently, in such a case, the image was lost during the last third or fifth of its journey. J. "felt conscious of a something that went in the suggested direction but did not develop details out of this material; had to await development of the image at the new locality." "At times _forced_ this development out of the vague something that seemed to go over." G. had 'no feeling of transition in space.' K. did not perceive the image _in transitu_. I. perceived the image _in transitu_ when the movement was away from the center but when the image was to return to the center its passage was too quick to be followed; 'it came out at the center.'

J. noticed that in moving from the center the image took a curved path towards himself, and that the position _to_ which the image moved always seemed further away than the position _from_ which it came, but the new position seemed to be readjusted when the next movement occurred.

The return to the center seemed easier to all the subjects except G., who was conscious of no difference between the movements with respect to ease. Several described the return to the center as like the return of a small ball snapped back by a stretched elastic cord.

With D. a suggestion of weight in the perception of the object was a hindrance to moving its memory image. Also the image of a short piece of brass tubing persisted in rolling off the table and along the floor and could not be held stationary. Other objects rotated rapidly, and much effort was needed to 'slow down' the rotation and to bring the objects to rest and keep them at rest.

II. CHANGES OF COLOR OF A SINGLE IMAGE.

Tables II. and III. show the results of experiments in changing the color of a single image. This was usually a square, sometimes a disc. The time of optical perception was five seconds. After the disappearance of after-images, if there were any, eighteen to twenty-four changes were made in the color of the memory image, occupying from four and a half to six minutes.

The colors were saturated blue, green, yellow and red, and each one was changed into each of the other colors and then restored. The order of change was varied to avoid uniformity of succession. The four colors were shown to the subjects each day before the experiments began, to establish a standard. The time was taken with a stop-watch, and includes the time between the director's word of command, 'green,' etc., and the subject's report, 'now,' or 'green,' etc. It includes, therefore, two reaction times. The subject reported 'now' the instant he secured the desired color, not waiting for the completion of the shape that usually followed.

TABLE II.

CHANGES OF COLOR. SINGLE IMAGE. 72 CHANGES OF EACH COLOR.

[Label 1: Subject.]
[Label 2: To Green.]
[Label 3: Return to Blue.]
[Label 4: To Yellow.]
[Label 5: Return to Blue.]
[Label 6: To Red.]
[Label 7: Return to Blue.]
[Label 8: To Blue.]
[Label 9: Return to Green.]
[Label 10: To Yellow.]
[Label 11: Return to Green.]
[Label 12: To Red]
[Label 13: Return to Green.]

From Blue. From Green.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

B. 1.72 0.50 1.66 0.38 1.81 0.50 1.23 0.56 1.10 0.65 1.33 0.56
G. 1.15 0.60 1.10 0.79 0.89 0.65 1.75 0.87 1.04 0.75 1.35 0.71
H. 4.67 4.25 4.87 4.06 4.81 3.83 5.27 4.50 5.81 4.89 5.37 4.94
I. 2.27 1.25 1.77 1.19 1.83 1.25 2.15 0.93 1.71 1.04 1.92 1.15
J. 1.38 0.81 1.29 0.94 1.29 0.95 1.65 1.08 1.15 0.77 1.60 0.81
K. 2.35 1.71 1.96 1.66 2.10 1.19 2.25 1.25 2.17 1.73 2.44 1.27

Av. 2.26 1.52 2.11 1.50 2.15 1.39 2.41 1.53 2.15 1.65 2.34 1.57

[Label 1: Subject.]
[Label 2: To Blue.]
[Label 3: Return to Yellow.]
[Label 4: To Green.]
[Label 5: Return to Yellow.]
[Label 6: To Red.]
[Label 7: Return to Yellow.]
[Label 8: To Blue.]
[Label 9: Return to Red.]
[Label 10: To Green.]
[Label 11: Return to Red.]
[Label 12: To Yellow.]
[Label 13: Return to Red.]

From Yellow. From Red.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

B. 1.79 1.06 1.35 0.87 1.89 1.10 1.54 0.58 1.71 0.62 1.31 0.71
G. 1.50 1.10 1.48 0.87 1.31 0.88 1.33 0.92 1.35 0.91 0.77 0.58
H. 5.02 4.54 5.73 3.91 6.15 4.17 6.35 3.91 5.89 4.69 5.54 4.37
I. 2.29 1.31 2.54 1.19 2.29 1.27 2.85 1.10 2.50 1.21 1.65 1.31
J. 1.35 0.98 1.35 0.65 1.27 0.88 1.42 1.04 1.31 1.02 1.25 0.85
K. 3.02 1.52 3.21 2.04 2.23 1.79 2.54 1.56 2.66 1.60 2.88 1.81

Av. 2.49 1.76 2.61 1.59 2.52 1.68 2.67 1.51 2.57 1.68 2.23 1.62

TABLE III.

CHANGES TO THE FOUR COLORS.

Average time in seconds. 72 changes from and 72 changes to each color.

[Label 1: To Blue.]
[Label 2: Return from Blue.]
[Label 3: To Green.]
[Label 4: Return from Green.]
[Label 5: To Yellow.]
[Label 6: Return from Yellow.]
[Label 7: To Red.]
[Label 8: Return from Red.]

[1] [2] [3] [4] [5] [6] [7] [8]
From blue, 2.26 1.52 2.11 1.50 2.12 1.39
" green, 2.38 1.53 2.16 1.64 2.33 1.57
" yellow, 2.49 1.75 2.61 1.59 2.52 1.68
" red, 2.67 1.52 2.58 1.68 2.27 1.62

Average, 2.52 1.60 2.48 1.59 2.17 1.58 2.33 1.55

_Changes from_ a presented color. _Returns to_ a presented color.
216 movements. 216 movements.

_From_ presented yellow, 2.52 _To_ presented yellow, 1.67
" " red, 2.49 " " red, 1.61
" " green, 2.29 " " green, 1.58
" " blue, 2.16 " " blue, 1.47

Average, 2.37 Average, 1.58

_Changes to_ a color _from_ _Returns from_ a color _to_
a presented color. a presented color.
216 movements. 216 movements.

_To_ blue, 2.52 _From_ blue, 1.60
" green, 2.48 " green, 1.59
" red, 2.33 " yellow, 1.58
" yellow, 2.17 " red, 1.55

Average, 2.37 Average, 1.58

The six subjects fall into two groups--three, H., I., and K., taking longer than the other three. As in the previous experiment H. was markedly longer than any of the others.

There were seventeen hundred and twenty-eight changes in all, including returns to the original color. There were two hundred and sixteen changes from each of the four colors as presented, to each of the other three and, of course, the same number of returns to the presented color.

The change to blue from the other presented colors was the most difficult and the change to yellow was the easiest.

The averages (216 exp. each) are,

Sec.
To blue, 2.55
" green, 2.48
" red, 2.33
" yellow, 2.17

The returns to the presented colors did not differ greatly from each other, the averages (216 exp. each) being:

Sec.
From blue, 1.603
" green, 1.597
" yellow, 1.589
" red, 1.549

From red appears to be the easiest change, and from blue the hardest.

The getting away from a presented blue was the easiest and from a presented yellow the most difficult, as seen by these averages (216 exp. each):

Sec.
From yellow, 2.54
" red, 2.49
" green, 2.29
" blue, 2.16

The returns to the presented colors show that it was hardest to get back to the presented yellow, easiest to get back to the presented blue, the averages (216 exp. each), being:

Sec.
To yellow, 1.67
" red, 1.61
" green, 1.58
" blue, 1.47

The facts as to blue and yellow shown by these four tables of averages may be expressed also in this way:

If a blue square was shown, it was easier to change the blue memory image into the other colors, and also easier to get back the blue memory image after such changes, than if any other of the three colors was presented.

If another color than blue was shown it was harder to change the memory image of that color to blue than to any of the other colors, and also harder to get back to the memory image of that color from blue than from any of the other three colors.

If a yellow square was shown, it was harder to change the yellow memory image into the other colors, and also harder to get back the yellow memory image after such changes than if any other of the three colors was presented.

If another color than yellow was shown, it was easier to change the memory image of that color to yellow than to any of the three other colors, and also easier to get back to the memory image of that color from the yellow than from any of the other three colors except red.

If we combine _all_ the changes into a color (both changes from another presented color and returns to this color previously presented) we find that changes to green are hardest, to yellow easiest. The averages (for 432 exp. each) are,

Sec.
To green, 2.03
" blue, 1.99
" red, 1.97
" yellow, 1.92

The changes away from a color (both from this color previously presented and from this color to the other previously presented colors) show that it was hardest to get away from yellow, easiest to get away from blue, the averages (for 432 exp. each) being:

Sec.
From yellow, 2.06
" red, 2.02
" green, 1.94
" blue, 1.88

As for the subjects, all six found yellow the easiest to change into, one finding red equally easy.

SUBJECTIVE.

For seven of the subjects, mental repetition of the name of the color (usually accompanied by articulatory movements) tended to bring up the color, and one other subject occasionally used this method of bringing about a change that was difficult. With D. the color did not come at repetition of the name. G. was assisted by auditory recall of the name. Nine subjects reported a feeling of strain, usually in the eyes as of focusing, occurring especially when there seemed a difficulty in producing the desired change. The tension attended almost exclusively changes of the presented color, not restorations of that color. For D. this strain was considerable, for G. there was also an after-feeling of strain in the head. For G. the image was clearest when the feeling of strain was least, and J. secured the promptest and clearest results when he could most nearly rid himself of anxiety as to the result. K. in one instance (a change from green to yellow) became conscious of the setting of his jaws and motions of feet and body in aid of his attempt. H. frequently had the feeling of physical fatigue.

In most cases the restoration of the presented color was as a complete square, triangle, etc. In changes from the presented color the new color appeared at a corner, or edge, or as a patch at the center. With E. the "color flashed over the whole field and then had to be restricted to the figure." B. "held the outline, emptied of the old color, while it was filled in with the new." D. "had a clear outline, and the new color came in small blotches inside, and effort spread them out to cover the whole figure." For I. the "new color came sliding in from the right side over the old, which, however, disappeared as if it were moving out of focus." With A. the new color usually came from either the lower left-hand or the upper right-hand corner. F. kept a clear outline and the new color came in from the right.

When E. found it difficult to create at the center the desired color, he thought of some object (garment, grass, sky, etc.) of that color and then transferred it to fill in the outline preserved at the center. B. moved the colored figure aside and in its place put one of the desired color, moved the new figure up to the old and there superposed it. With G. the new colors seemed of new material and there was felt to be an accumulation about the center, of old color-material. Then he located the square outside of this imaginary debris and began again. H. found that the colors of his own experiments, in which he used color squares framed in black, came to his mind at the names of the desired colors, and the association soon gave him the figure also. I. located the new colors around the presented one, first all at the right; then green at the left, red at the right, yellow above, when presented blue was at the center; then yellow and green were at the upper left-hand corner, while red came from behind. The new color 'slid in over the old.' It was found easier to secure the desired color when its position was known beforehand. J. also used a similar device. He 'turned towards the places and brought out the required color and filled the central outline with it.' He tried to break up this scheme and got red without going after it but found himself 'at a loss to find the colors.' Later he succeeded so that the required color simply appeared in the outline of the old color at the center. K. turned his eyes to corners of the central outline, then to the center, and found that this aided in developing the desired color from the corners inward. When difficulty arose, he experienced muscular tension in body and legs and jaws.

Five of the subjects considered the change from a presented color to blue the hardest and one found the change to red hardest. Green was placed second in difficulty by one, and blue second by the one who found red the hardest. Three reported the change to yellow the easiest and two the change to red.

The change from red to yellow caused 'an unpleasant sensation' in C. and the new figure 'had a maroon halo.'

A. in returning from green or blue to yellow passed through a gray; so, once, in changing from yellow to green, and once, green to red. With A. blue retinal clouds, which often came, aided changes to blue and hindered at times changes to other colors. B. had a fusion of yellow and red in changing from yellow to red. G. had a tendency to leave uncolored the lower left-hand corner and it 'was wood-colored'; G. had a gray image as the result of fusion of retinal clouds with red memory image. With H. blue always came in as robin's-egg blue, which then had to be changed to the standard blue. In one instant the green memory image seemed to shift into a purple and change to a positive retinal image which interfered with changes to other colors. J. found whistling and humming an aid in relaxing an unnatural state of tension which would hinder the best results. To increase the vividness of the image he would recall the black background on which the colored squares had hung. In one experiment K. became 'desperately tired of yellow,' which was the presented color, so that his 'mind was ready to jump to any color rather than yellow.' The returns to yellow were, in this experiment, slower than the changes from yellow.

The images sometimes changed sizes, being at times smaller, but usually larger than the object. In one experiment of C. the image was four times the size of the object, which was a green square with sides of one inch.

III. MOVEMENTS OF TWO IMAGES IN THE SAME AND IN DIFFERENT DIRECTIONS.

Table IV. gives the results of experiments in the movements of two images, the objects presented being colored squares or discs. Time of perception was five seconds. After the disappearance of after-images, if there were any, eighteen to twenty-four movements with returns to original positions were made, occupying five or six minutes. The colors were saturated blue, green, yellow and red. Four of the movements were such as separated the two images, and in four the two moved uniformly. The first four movements were right and left, left and right, up and down, down and up; the left-hand object followed the first direction indicated. The right-and-left movements involved the crossing of the images. The last four were _both_ to right, to left, up, down. The time was taken with a stop-watch and includes the time between the director's word of command and the subject's report, 'now.' It includes, therefore, two reaction times. The subject reported the instant the colors reached, or appeared at, the suggested positions.

It is to be noticed that H. was very much slower than any of the others in making the movements, both out and back; and that K., while also slower (though much less so than H.) in making the movements outward, was no slower in making the return movements.

TABLE IV.

MOVEMENTS OF TWO IMAGES.

Twenty movements of each kind for each subject. Averages in seconds.

In Opposite Directions.

Subj. L.-R. Ret. R.-L. Ret. U.-D. Ret. D.-U. Ret.

B. 1.82 2.90 2.10 2.27
0.86 0.87 0.73 0.86

G. 3.02 2.86 2.68 2.63
1.98 2.25 1.63 2.01

H. 9.18 10.30 7.50 7.15
5.16 6.90 5.36 5.21

I. 4.17 3.52 3.40 3.37
1.26 1.47 1.23 1.31

J. 2.17 2.90 2.87 2.27
1.05 1.63 1.02 1.13

K. 5.51 6.43 5.16 4.81
1.43 1.48 1.20 1.23

Ave. 4.32 4.82 3.82 3.75
1.96 2.43 1.87 1.96

Average of all movements involving separation (480), 4.18. Returns, 2.06.

In Same Direction.

Subj. R. Ret. L. Ret. U. Ret. D. Ret.

B. 1.31 1.22 1.30 1.11
0.72 0.67 0.72 0.85

G. 2.66 2.35 3.01 2.53
2.00 1.86 2.22 1.86

H. 8.45 7.91 5.66 7.66
6.53 5.95 5.96 6.11

I. 2.57 2.27 2.13 2.05
0.97 1.26 1.00 1.13

J. 1.11 1.16 1.08 11.5
0.68 0.90 0.73 0.71

K. 3.97 3.91 3.60 4.07
1.35 1.50 1.75 1.71

Ave. 3.33 3.14 2.79 3.10
2.04 2.02 2.04 2.06

Average of all movements together (480), 3.09. Returns, 2.04.

NUMERICAL.

There were nineteen hundred and twenty movements in all, including the returns to the original positions.

In the order of difficulty as shown by the time taken, the movements stand as follows, the numbers being the averages in seconds for one hundred and twenty movements of each kind:

1. Right and left (_i.e._, crossing), 4.82 sec.
2. Left and right, 4.32 "
3. Up and down, 3.82 "
4. Down and up, 3.75 "
5. Both right, 3.33 "
6. Both left, 3.14 "
7. Both down, 3.10 "
8. Both up, 3.04 "

SUBJECTIVE.

In the experiments in which the time was recorded, there was no disappearance of either image except where movements were made successively. In these cases frequently the image which was awaiting its turn vanished until the first image was placed, a time varying from a quarter of a second to three or four seconds. Occasionally the image already placed would vanish, while the other was _en route_; the subject's attention in both these cases being centered exclusively on the image he desired to move. This was especially the case when the distances to which the images were moved were great, as to the ends of the room or to ceiling and floor. In other experiments, where, after the movements took place, the images were held for a short time, there were disappearances of one image or the other ranging from one quarter of a second to fifteen seconds, most of the absences, however, being under five seconds. The absences were more numerous in the latter half of the five minutes covered by the experiment. Occasionally a noise in the adjoining room or in the street made the images disappear.

The greater ease of vertical as compared with horizontal movements recalls an observation of Ladd,[3] in which the idioretinal light was willed into the shape of a cross. Ladd says: "The vertical bar of the cross seems much easier to produce and to hold steadily in the field." This present observation is also in accord with that described above in the case of movements of a single image.

[3] Ladd, G.T.: 'Direct Control of the Retinal Field,' PSYCH.
REV., 1894, L, pp. 351-355.

On several occasions G. reported that the crossing movement was the easiest, and that the return to the original places was not easier than the other movements. In one experiment he reported the field at the center cloudy, so that it was a relief to get away from it. G.'s time records on these occasions did not support his feeling with regard to the return to the original places, but they show that the crossing movements were, in two or three instances, quicker than the 'left-and-right' movement, and the impression of promptness thus made persisted to the end of the experiment. The four movements in which both images moved uniformly were easier than the four in which movements in different directions were involved.

All the subjects were frequently conscious of eye movements, and more frequently conscious of a tendency to eye movement, which was, however, inhibited. That the strain in the eyes was practically constant during all the movements away from the original places, seems evident from the unanimous reports of a sense of relaxing and relief in the eyes, attending the movement of returning to the original places. The distance to which the images were moved was a powerful factor in producing this sense of strain. When the two images were moved and held but a few inches apart there was no sense of strain and no conscious alternation of attention. Practice increased greatly the distance at which the images could be held apart without conscious alternation of attention, but the strain of holding them apart and of inhibiting eye movement increased with the distance.

In the movements for which the time was recorded the distances varied, according to the subject, from six to eighteen inches, and varied at times with each subject. In the experiments without time record, A., B., C., E., F. and H. reported that they were able to move the images apart to ceiling and to floor, or to the opposite ends of the room, and to hold them there both in consciousness at the same time without either alternation of attention or eye movement, a tendency to which was felt but was inhibited. I. held them two feet apart without fluctuation of attention. A. reported: "I tend to turn my body to left or to right when I move the images in either of these directions." C., H. and I. said: "The eyes diverge when one image moves slowly to the right and one to the left." D. found a slight movement of the eyes which could be detected by the fingers placed lightly on the lids, when the attention was alternating between the images. K. had convergence and divergence of the eyes for crossing and separation respectively and he was accustomed to run his eye over the outline of the image. Strain in the scalp muscles was reported by A., B., E., F. and G. The up-and-down movements were universally characterized by a feeling as if one eye tended to move up and the other down. C. unconsciously inclined his head to the left in such movements as if to make the line of the two eyes parallel with the direction of the movement.

E., when holding the images two feet apart, had a strong feeling of difference of accommodation when alternating in observation and so judged the two to be in different planes.

When the movement seemed difficult the strain was greater, and when an image became dim the effort to restore its brightness or its distinctness of outline was accompanied by a feeling of bringing it nearer by accommodation and near focusing. J. found that the two images approached each other when he attempted to secure greater vividness. An analogous instance is that of A.G.C., a subject quoted in 'Mental Imagery of Students,' by French.[4] In calling up the image of a die this subject held up his hand as if it held the die. When there was no sense of strain the hand was fourteen inches from his face, but when effort was made to image all the sides of the die at once he unconsciously moved his hand to within four inches of his eyes. French says in this connection: "Situation depends on the attention involved and the inference is near that this phenomenon may be connected with feelings of convergence and accommodation which so often accompany concentrated visual attention."

[4] French, F.C.: PSYCH. REVIEW, 1902, IX., p. 40.

The movements were assisted by mentally saying, 'this image is here, that image is there,' in the case of D., G., H., I. and K.; or, at times, by articulating the names of the image, or of the color when the image was of a colored object. I. found it easy to hold outlines, but in order to retain colors in the movements of separation, he had to speak the names continually. H. also repeated the names continually, as, for example, 'violet here, orange there.'

A. represented the line of vision as going to each of the two images, which seemed connected by a line, thus making a triangle, and then pictured himself as standing off and seeing himself looking at the images. When the two objects were solid and the images were to be crossed, B. carried one image above or below the other, but when the objects were colored surfaces he conceived them as pure colors so that there was no sense of impenetrability to interfere with their crossing and they glided by each other. In the up-and-down movements he moved one at a time. C. and D. had to construct some support for the images. In most of the experiments H. first moved the images to a greater distance away, somewhat higher up and a little farther apart. In this new position the images appeared smaller and the suggested movements were made more easily. Sometimes in crossing two colored images he observed a partial mixture of the colors. J. found that a sharp movement of the head in the required direction aided materially in moving the images, and when the objects were colored surfaces fastened to the same card he found it necessary either to conceive the card as of rubber or to picture it as cut in two before he could make the movements of the images.

With A., B., C. and D. there were instances of unwilled movements of the images, in the experiments where the movements were not timed. These were much more frequent with D. than with the others, and to check them required prolonged effort. The more common movements of this sort were rotation of the image, change of its position, separation of its parts (if detachable in the object) and change of shape. E. had a return of the two images of a preceding experiment which persisted in staying a few seconds and which were as vivid as the two legitimate occupants of the mental field.

The images were duplicated five times on different days with A., and once each with C., F. and K.

A.'s cases were these. The 'wraith' of a small box whose image was out at the right, appeared above the other image off at the left and it was turned with a corner to the front. Again, at the central position each image was duplicated, the true pair being of full size, bright and distinct, the false pair small, dim and on a more distant plane, _i.e._, behind the others. One of the extra images persisted against all effort to banish it, for fifty-five seconds. Again, when twelve inches apart each image was similarly duplicated. In the fourth instance the images were at the center of the field. In the fifth, the right image, eight inches from the center, was duplicated, the extra image being still farther away and above. This second image was very dark, dim and vague in outline, and came and went slowly. The right image of C., when seven feet from the center, had a dim double above it. F. had moved the right-hand image (a violet disc) close to the left when a blue disc also appeared above it. Though repeating the word 'violet' he had imaged the violet disc as blue. K. was holding the two images a foot and a half apart when an extra pair appeared at the center. Both pairs persisted for sixty seconds and then the outer pair vanished, and the inner, the false pair, grew brighter.

As was said in the case of a single image, so with double images, the motion could be traced and often was traced when the movements were away from the original positions, but on the return to the original positions the images were not usually seen _in transitu_. For ten of the subjects, the image moved downward uniformly on an arc whose center was at the eye; and often the right and left movements were likewise on an arc. With E. the ends of the arc for motion right and left were higher also. H., I. and J. reported that all the movements were in the same plane. The upward movement was always to a less distance and the downward movement to a greater distance than the horizontal movements.

In most cases the images were the size of the percepts, in a number of cases smaller, and in a few cases larger. This was determined by comparison between the image and the percept immediately on opening the eyes and seeing the object at the end of the five minutes occupied by the experiment. A similar mode of comparison showed that, in about half of the experiments, the images were at the end of five minutes approximately equal to the percept in clearness and distinctness of outline. A comparison of these results with those obtained in a series of experiments involving passive observation of the image seems to indicate that active manipulation of the image tends to maintain the qualitative fidelity of the image when at its original position. During the progress of the experiments the reports were almost unanimous and constant that at its original position the image was vivid and distinct, but lost in both respects when away from that position, the loss being greater the greater the distance to which it was moved. Frequently there was fluctuation,--a loss of vividness and then a restoration,--which A. frequently found to be rhythmical, while in general it was evident that an increase of effort or of attention was successful in restoring lost vividness and distinctness.

D., after three minutes, read the time in the image of a watch. In superposing green on yellow, in two instances, the yellow shone through, making a mixed color, and again, in moving a green disc and a yellow disc, the green became suffused with yellow, so that the two discs were one yellow and the other greenish-yellow. For C., similarity in the two objects presented tended to make both images less vivid and distinct and to render more difficult their retention and manipulation. When one of the two objects partially overlapped the other it was difficult to separate the two images, and the area of contact was very vague in the image of the under one, and when the scrutiny reached that portion the other image returned to its original overlapping position.

IV. SUPPRESSION OF ONE OF TWO IMAGES.

The next tables (V. and VI.) give the results of experiments in suppressing one of two images, the objects presented being saturated color squares, discs, triangles, etc., placed side by side, one above the other, or a smaller one superposed on a larger. The time of perception was five seconds. After the disappearance of after-images, if there were any, the subject was directed to suppress one of the two memory images, the one to be suppressed being indicated by the director. The subject reported as soon as the indicated image disappeared, and reported any return of the suppressed image and its later disappearance in consequence of his efforts. Also he reported any disappearance and reappearance of the retained image. Five minutes was the limit of the time for the experiments with a few exceptions. The times were recorded, and those given for the first suppression include the time between the director's command and the subject's report 'now' or 'gone,' and include, therefore, two reaction times. The later suppressions include but one reaction time.

TABLE V.

SUMMARY OF ALL SUPPRESSIONS. AVERAGE TIME IN SECONDS.

[Label 1: Image Suppressed]
[Label 2: No of Exper.]
[Label 3: Time of First Supp.]
[Label 4: Time of Ab. of Supp. Im.]
[Label 5: No. of Later Supp.]
[Label 6: Time of Later Supp.]
[Label 7: No. of Ab. of Supp. Im.]
[Label 8: Time of Ab. of Supp. Im.]
[Label 9: Time of All Supp.]
[Label 10: Time of All Absence of Supp. Im.]

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Right. 46 11.59 82.39 221 8.43 216 35.74 8.94 43.93
Left. 43 11.89 79.34 175 7.79 173 44.86 8.60 51.26
Upper. 22 11.67 49.77 150 6.26 147 29.75 6.95 32.35
Lower. 17 14.23 64 71 7.88 70 46.68 9.11 50.04
Central. 42 18.24 96.93 357 3.90 352 18.13 5.41 26.54
Marginal. 20 14.25 181.57 24 8.93 24 78.08 11.35 125.12
Sundry. 7 8.71 127.21 19 13.34 19 47.27 12.09 68.78
Averages. 13.48 91.25 6.46 32.14 7.60 41.86

TABLE VI

SUPPRESSIONS GROUPED BY SUBJECTS. AVERAGE TIME IN SECONDS.

[Label 1: Subject]
[Label 2: No. of Exp.]
[Label 3: Time of First Supp.]
[Label 4: Time of Ab. of Supp. Im.]
[Label 5: No. of Later Supp.]
[Label 6: Time of Later Supp.]
[Label 7: No. of Ab. of Supp. Im.]
[Label 8: Time of Ab. of Supp. Im.]
[Label 9: Time of All Supp.]
[Label 10: Time of All Ab. of Supp. Im.]

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
A. 11 28.32 11.29 117 14.90 114 10.35 16.05 10.44
B. 29 5.79 270.44 5 0.25 5 138.80 4.98 251.08
C. 18 7.88 43.08 64 3.94 63 67.49 4.81 62.07
D. 14 23.28 190.07 6 31.66 5 204.60 25.80 193.89
F. 10 12.67 86.07 230 1.95 230 67.92 2.40 10.09
G. 21 21.88 20.39 190 9.97 184 19.37 11.15 19.47
H. 21 15.27 73.27 47 10.30 47 84.48 11.84 81.02
I. 26 9.77 53.83 96 5.06 94 61.34 6.06 59.72
J. 26 3.59 32.18 209 1.40 208 31.69 1.64 31.75
K. 21 21.63 71.90 53 14.75 51 70.04 16.70 31.83
Averages. 13.48 91.25 6.46 32.14 7.60 41.86

There were ten subjects in most of the experiments, and the marked differences in the individual records which were evident in the previous experiments did not exist here except in the case of A., for whom alone the time required to obtain the suppression exceeded the time of absence of the suppressed image.

In several experiments the subjects were unable to suppress the indicated image, which in five cases was the image at the center of a disc and in two cases the outer portion of the disc. Further, five failures were by one subject, D., and one each by A. and F. The statistical report here given includes only the results of the successful experiments. Forty-four of the one hundred and ninety-seven were completely successful, as the suppressed image did not return throughout the entire period. The following table shows the grouping of the experiments according to the recurrence of the suppressed image: