Harvard Psychological Studies, Volume 2

by Unknown

B. REACTIONS TO SIMPLE AND COMPLEX OPTICAL IMPRESSIONS

Since the preceding experiments seem to show that reactions on optical impressions are different according as the figures are more or less complex, it would seem that we ought to be able to measure by graphic methods the reactions to visual fields of varying grades of complexity and in this way to demonstrate their different motor powers.

A Porter kymograph was used on which to register the reactions. Resting on the top of the drum, and revolving with it, was a circular band of white paper, upon which were pasted the different figures to be observed. A screen was placed in front of the kymograph, thus concealing the figures; but at their level was a little square window in the screen, which, when the eye was placed in the proper position, allowed the subject to see one of the figures but nothing more. A few inches in front of this window was an eye-rest which kept the eye properly placed. A tambour received the movement from the subject and communicated it to a straw which made a scratch on the smoked paper which covered the drum.

The figures used in this experiment form two series, one, composed of geometrical figures, varying in complexity from a circle to a very complex figure consisting of many overlapping squares, triangles, etc., and the other composed of colored figures varying in complexity from a simple square of one color to a very complex mixture of various colors. The area of the visual field is about the same in all cases,—an inch square. The geometrical figures were formed of black lines on a white background. The figures used are shown in the accompanying illustrations.

The subject would be seated in front of the screen, his eye at the eye-rest a few inches in front of the window in the screen, and the forefinger of the right hand on the tambour, which is to the right of and behind the screen, and thus not seen while the eye is at the rest. Then as the drum revolves and brings a figure in front of the window, the subject observes this figure carefully, and when it is all in the field of vision he presses down with his forefinger, thus producing a curve on the drum surface. He tries to make the same finger-movement every time, whatever the figure at the window may be. But his attention is not to be too much taken up with the making of the movement, for he must be closely observing the figure. If he looks at the figure until he observes its characteristics clearly and then turns his attention from this to the finger-movement, it is evident that the optical sensation would not have much effect upon the movement. The movement must be performed while his interest in the figure is highest. Now, after a little practice, any one can accustom himself to make a certain definite movement in about the same way every time, and he can then agree that he shall make this movement as a reaction to a given stimulation. Then when the stimulus comes he makes the movement without any longer thinking of the character of the movement. It has become, to a certain extent, automatic and can look out for itself.

This is the state into which I have tried to get my subjects. Their whole attention is to be taken up with the seeing of the figures in the window, and to these figures they are to react as automatically as possible. Thus, though finger-movements are usually voluntary, all the capricious character of voluntary action will be removed here, and if the stimulus is the same in all cases, the reaction tends to assume the form of a uniform movement. There is, then, a chance to see the influence of different optical stimuli upon this action.

FIG. 2

Six different geometrical figures were seen at each revolution of the drum and six reactions given by the subject. Between figures a white surface would occupy the field of vision. The simple and complex figures were distributed so that the subject never knew what kind of a figure would come next. The purpose of the experiment was kept as much as possible from the knowledge of the subjects; but some, knowing my general problem, surmised quite correctly my main object here.

Ten revolutions were made at each sitting, thus causing the subject to react ten times to each figure. Then a new drum paper was taken and the case with the colored figures placed upon it. This had five colored figures, and ten revolutions were made also in this case. Thus, in all, in any one day, the subject would make one hundred and ten of these finger-movements.

Since we have in all these experiments tried to find out in the different figures merely differences in the amount of the reaction, and not differences in the character of the reaction, we shall keep up this method here. Now a stronger reaction makes a higher curve, and since the drum is all the while revolving, and since the higher the curve, other things being equal, the longer it takes, the stronger reaction will also make a wider curve. So it would seem that if we wish to observe the differences in the amounts of reaction the most natural course to pursue would be to measure the heights and widths of the curves we have registered. This accordingly has been done.

In our discussion of these measurements let us, then, first, take up the curve heights, and of these, those of the geometrical figures which we call U, V, W, X, Y, Z. The height is measured from a base-line [drawn by revolving the drum after the subject has taken his finger from the tambour] to the highest point reached. These measurements are taken from two hundred reactions to each figure, divided among seven different subjects.

Heights of Curves
		U	V	W	X	Y	Z
Subject	A	6.83	6.68	6.59	6.55	6.63	6.79
	B	8.64	7.26	6.41	7.79	6.39	9.75
	C	6.67	6.55	6.73	6.85	5.87	8.53
	D	21.35	21.26	21.46	21.90	21.33	21.31
	E	16.13	15.77	15.17	15.85	15.29	16.08
	F	16.90	16.97	16.14	16.52	15.81	17.91
	G	11.42	11.32	11.39	11.48	11.06	11.10
		87.94	85.51	83.89	86.94	82.38	91.48
Average		12.56	12.26	11.98	12.42	11.77	13.07
Arranged in order of height of curve
		Z	U	X	V	W	Y
		13.07	12.56	12.42	12.26	11.98	11.77

If we put the figures in the order of strongest reaction for the different subjects we get the following table:

Subject	A	U	Z	V	Y	W	X
	B	Z	U	X	V	W	Y
	C	Z	X	W	U	V	Y
	D	X	W	U	Y	Z	V
	E	U	Z	X	V	Y	W
	F	Z	V	U	X	W	Y
	G	X	U	W	V	Z	Y

It is seen from these results that, although the subjects differ, the height of the curve varies directly with the complexity of the figure. The order of the figures, which we get by measuring the height of the curves and then putting that figure with the highest curve first, with the next highest second, and so on, is exactly the same order in which we should put them if we were asked to put the most complex first, the next second, and so on. Though the individual subjects may vary somewhat from this rule, when they are all grouped together there are no exceptions.

The variations of the reactions with the different subjects may be shown very clearly in the following way, where the different figures are in the left-hand side arranged in order of descending complexity. "1st place," etc., refer to the order of arrangement of the figures by the different subjects as shown in preceding tables. Thus, Z, 3 times, 1st place, means that three subjects have in the average a higher curve for Z than for any other figure.

	1st place	2d place	3d place	4th place	5th place	6th place
Z	3 times	2 times	0 times	0 times	2 times	0 times
U	2 times	2 times	2 times	1 time	0 times	0 times
X	2 times	1 time	2 times	1 time	0 times	1 time
V	0 times	1 time	1 time	3 times	1 time	1 time
W	0 times	1 time	2 times	0 times	3 times	1 time
Y	0 times	0 times	0 times	2 times	1 time	4 times

One can see at a glance from this, how, as the figures decrease in complexity, they take their position further on in the series. If a diagonal is drawn from the upper left-hand corner to the lower right, it will pass through or near the larger numbers in the table, thus showing that the figures belong in the ordered series in the places already shown.

Next in order let us take up the measurements of the widths of curves for the same geometrical figures which we have been considering.

Widths of Curves in mm.
		U	V	W	X	Y	Z
Subject	A	20.83	20.59	20.93	21.22	20.21	21.89
	B	11.18	10.77	10.46	10.31	9.92	10.79
	C	4.28	4.43	4.10	3.78	4.95	4.70
	D	21.08	19.36	18.33	18.75	18.17	21.09
	E	14.22	13.85	13.40	13.56	11.96	14.13
	F	17.00	15.26	15.92	16.52	14.52	16.47
	G	5.25	5.19	5.30	5.08	5.11	5.37
		93.84	89.45	88.44	89.22	84.84	94.44
Average		13.40	12.78	12.63	12.75	12.12	13.49
Order		Z	U	V	X	W	Y
		13.49	13.40	12.78	12.75	12.63	12.12

If as before we take the orders for the different subjects, we get the following table:

Subject	A	Z	X	W	U	V	Y
	B	U	Z	V	W	X	Y
	C	Y	Z	V	U	W	X
	D	Z	U	V	X	W	Y
	E	U	Z	V	X	W	Y
	F	U	X	Z	W	V	Y
	G	Z	W	U	V	Y	X

Here, as before, in the case of the heights, it is seen that though the order is different with the different subjects, yet the general tendency is to place the most complex figures first and the simplest last. The most simple figure Y never comes in front of the fifth place except with subject C, who places it first. This exception may be ascribed to the fact that this subject, on account of his going away, did not have so many tests. In fact only one day's work of 10 reactions for each figure is recorded, and it is but natural that some variations from the standard should occur in his case.

If now, as before, we investigate where each figure occurs in the series for the different subjects we get the following table:

Times in
	1st place	2d place	3d place	4th place	5th place	6th place
Z	3	3	1	0	0	0
U	3	1	1	2	0	0
V	0	0	4	1	2	0
X	0	2	0	2	1	2
W	0	1	1	2	3	0
Y	1	0	0	0	1	5

Here we again see the large numbers on a line from the upper left-hand to the lower right-hand corner.

Thus we get the following order from the geometrical figures as measured by the height and width of the curves:

Height	Z	U	X	V	W	Y
Width	Z	U	V	X	W	Y

The only difference, it is seen, is that the positions of V and X are reversed in the two series. Such a change would on our principle be fairly likely to occur, since V and X are figures near to each other in complexity and the motor effects are very similar.

FIG. 3

In the same manner, the following tables show the reactions to the colored figures of different grades of complexity. And first, as before, is the table of the heights of the curves for the different subjects, given in millimetres. The numbers given represent the averages of all reactions made. We will call the figures, for the sake of reference, L, M, N, O, P.

		L	M	N	O	P
Subject	A	5.75	6.01	5.90	5.82	5.74
	B	6.72	5.56	6.35	7.53	4.94
	C	10.92	10.90	10.76	10.52	10.99
	D	25.49	25.42	26.23	25.89	25.52
	E	20.63	20.82	20.37	20.55	20.30
	F	15.67	15.23	15.15	15.98	14.51
		85.18	83.94	85.26	86.29	82.00
Average		14.20	13.99	14.21	14.38	13.67

Order arranged as before in a descending series according to height of curve:

O	N	L	M	P
14.38	14.21	14.20	13.99	13.67

This is exactly, as I should judge, the order of the complexity of the figures reacted to.

The arrangement by the individual subjects is as follows:

Subject	A	M	N	O	L	P
	B	O	N	L	M	P
	C	P	L	M	N	O
	D	N	O	P	L	M
	E	M	L	M	N	P
	F	O	L	M	N	P

We see that individual differences are stronger here than in the geometrical figures, but that the same tendency to react more strongly to the complex is present in nearly every case. This can be brought to the eye more clearly if we observe the table in which is shown the position of the different figures in the series of the different subjects.

Times in
	1st place	2d place	3d place	4th place	5th place
O	2	1	2	0	1
N	1	2	0	3	0
L	0	3	1	2	0
M	2	0	2	1	1
P	1	0	1	0	4

M here presents the principal exception, coming too often in the first place.

Finally we give the tables for the widths of the curves for the colored figures; and first the table of the averages of all the subjects for all the figures:

		L	M	N	O	P
Subject	A	25.76	24.27	25.06	24.77	23.14
	B	9.42	9.49	9.06	9.84	8.11
	C	5.85	5.35	5.62	5.80	5.24
	D	13.68	13.53	13.18	13.26	13.38
	E	22.06	21.37	22.50	22.17	20.44
	F	16.30	15.08	16.65	16.76	15.13
		93.07	89.09	92.07	92.60	85.44
Average		15.51	14.85	15.35	15.43	14.24

Order, arranged in a descending series according to width of curve:

L	O	N	M	P
15.51	15.43	15.35	14.85	14.24

Here the order is not just the same as we got from a measurement of the heights. The three complex figures have changed places somewhat, but there is no exchange of a simple and a complex.

The arrangements by the individual subjects are as follows:

Subject	A	L	N	O	M	P
	B	O	M	L	N	P
	C	L	O	N	M	P
	D	L	M	P	O	N
	E	N	O	L	M	P
	F	O	N	L	P	M

The three complex figures have different places with different subjects, but very seldom is a simple figure found among the complex, or vice versa.

This can be seen easily from the following table:

Times in
	1st place	2d place	3d place	4th place	5th place
L	3	0	3	0	0
O	2	2	1	1	0
N	1	2	1	1	1
M	0	2	0	3	1
P	0	0	1	1	4

A theoretical word may close our report.

The growth of biology and physiology has tended to show that there is no break in the nervous mechanism. The stimulus goes to the brain and out through motor channels to muscles, glands, etc. The nervous current does not wait in the brain for the permission of the mind to leave on its journey to a muscle nor does it need mental reënforcement. The nervous current as a whole is a unity. The nervous system is a physiological instrument for producing the appropriate reaction to a certain stimulus. In the unicellular organism there is no nervous system, but the protoplasm receives the stimulus and produces the reaction. As we go up in the animal series a differentiation is seen to be present in the organism. Some parts are more concerned with the receiving of stimuli and others with the approach toward or withdrawal from the stimulating object. There is a division of labor. The nervous system is developed as a means of rapid communication between the different parts, but this communication is a physiological one. The stimulus sets up a chemical action in the sensory organ which is transmitted along the nervous path to the motor organ which is caused to react. As we ascend the animal series the differentiation becomes greater and greater, and consequently the means of communication must become more and more complex. So trunk lines are formed which lead to a centre, and from this centre again go out main lines which divide and subdivide until the muscles are reached. The centre acts as a kind of automatic switch-board.

Accepting such a view of the nervous system it must be granted that different stimulations would produce different reactions. It was my aim in the experimental work which has been described to show that this is true. And while much work has already been done in showing that different kinds, or different amounts of stimulation produce differences in reactions, it seemed important to demonstrate also that mere differences in the complexity of the stimulus bring about differences in the reaction. So the experiment of counting figures of different complexity was entered upon, and we found that it took longer to count figures the more complex they were in spite of the fact that the act of counting seems always the same. The question is how must the fact that counting becomes slower and slower, as the figures become more complex, be interpreted?

When we count a row of figures, the eyes do not move along at a regular uniform rate, but make a quick jump from one figure to the next, halt a moment, make another jump, and so on. Now, I think the principal difference comes in with the figures of different complexity in the time the eye halts at each figure. The halt is longer the more complex the figure is. It is well known that any visual object which stimulates the retina is brought by a reflex movement of the eye to the place of clearest vision. Of two objects stimulating the eye at the same time, the more pronounced one will produce the reflex and will hold the eye longer than a weaker stimulus. Similarly here, the more complex figure produces a stronger reflex and holds the eye longer than the simple figure. This is repeated at every figure in the series.

The complex figures have more features about them, all of which by way of the retina and optic nerve are represented in the cortex and thus more cortical cells are involved, which in turn produce a stronger stimulation of the muscles which move the eye in the proper way to see the figure, and thus the eye is held more strongly by the complex than by the simple figure.

Again in the second experiment, the subject reacts more strongly to the complex as shown already in explaining the first experiment and for the same reasons. It might be said that in looking at the colored figures, e. g., that since the same amount of retina is stimulated, the reaction ought to be the same. But we may presume that the complex figure, on account of the different shapes and contrasts on its surface, will more variously affect the same amount of retina and that the nervous currents sent to the cortex will, many of them, be stronger than those from the simple figure and will thus cause the cortical cells to be more strongly excited, or by a process of irradiation the stimulation will spread to adjoining cells and thus finally more cells be stimulated. However this may be, the amount of discharge into motor cells is certainly greater and the muscular reaction, therefore, also greater.

The interesting side of our results is thus given in the fact that we have here two activities—counting with highest speed and making hand-movements of certain length—which are performed every time with exactly the same intention and with the subjective impression of equal result, and which yet show marked differences according to the complexity of the psycho-physical stimuli. It is a new contribution to our knowledge of the independent motor power of ideas.

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ANIMAL PSYCHOLOGY

THE MUTUAL RELATIONS OF STIMULI IN THE FROG RANA CLAMATA DAUDIN[139]

BY ROBERT M. YERKES