Chapter IV: Part 4

This leads to a classification of physical systems which is decisive for our problem. In all of them process is to be regarded as necessarily determined, but among the various cases we find enormous differences in the relative influence which limiting topographical conditions, on the one hand, and the play of actual forces, on the other, exert upon the course of events. Wherever we have given topographical conditions, preëstablished and not changeable by the process itself, their existence means the exclusion of some dynamical possibilities and the restriction of the process to only the possibilities compatible with those conditions. Electric charges may move through the conductor in various ways, but they are _prevented_ from leaving it, and so their final distribution depends upon its form. Again the electric current may have one direction or the other, its distribution may vary enormously; but, if the wires are surrounded by isolating material, the dynamics of the current itself will remain restricted to the interior of the wires. The most extreme case will consist in a system where preëstablished topographical arrangements exclude all processes except only one; and an example of this type is given by the piston’s motion strictly confined between the walls of the cylinder.

In this case the steam in the cylinder exerts its pressure in all directions, but, owing to the topographical conditions, it is not allowed to do work except in _one_ direction, in that, namely, in which the piston is free to move for a certain distance. Consequently, nothing but the motion as such is determined dynamically in such a system, whereas its direction is strictly enforced by topographical arrangement.

Now this is exactly the relation between dynamics and preëstablished topographical conditions which we find in typical industrial machines. The number and forms of special one-way functions which may be enforced in such systems are enormous and varied. Still the general principle is everywhere the same. Sometimes a little more than the minimum may be left to dynamical determination, but at present no one would construct mechanical systems for industrial purposes where the form and distribution of process would be to any considerable degree a matter of dynamics.

It is the same idea again which occurs to Aristotle when he views the remarkable order of celestial movement. His spheres are topographical conditions enforcing that order. And since Cartesius, neurologists have worked with the same concepts wherever they have dealt with orderly organic function in higher animals and in man. It is not the dynamics of nervous processes as such which they suppose tend toward coördinated function. Vitalists may have such a mystical idea! Rather, special anatomical topography is the only explanation for order; and by it the dynamics of process are compelled to produce orderly results.

Once more we return to point out that it is the same conception which forms the common basis of both introspectionism and behaviorism, so far as their physiological principles are concerned. Take vision, for example. How many things may be present simultaneously in one actual field! Still, excluding extreme peripheral regions, there does not seem to be any confusion for the most part. One object appears separated from all others, and the sharpness of its contours is evidence of a high accuracy of function. But the field is not only clear as such; it also corresponds admirably to the physical realities. Points which are neighbors in physical space are neighbors also in the visual field; the center of a circle in physical space appears as the middle of a symmetrical figure in vision, and so forth. All this order is as remarkable as it is necessary for our response to the objects which, in the form of bodily movement, must be adjusted properly to the physical world. The order of projected images upon the retina is easily explained by the properties of the pupil, the lens and so forth. But what about the processes which, streaming from here into the brain, will eventually determine experience and behavior? Since experience and behavior show a similar order, this order must have been enforced or preserved throughout the entire process. Only one kind of explanation seems, then, to be possible: In the nervous system we have a topographical arrangement, preventing confusion and mixture during conduction. Indeed, if from each point of the retina local processes are conducted on definite and isolated paths toward their final cortical termini, and if the totality of these termini somehow reproduces the geometry of local retinal processes, then the dynamics of the process are excluded completely from the determination of its own direction and distribution. In terms of such a construction of the facts we can feel secure that the most important property of vision, i.e., its accurate order, is guaranteed by so trustworthy a factor as preëstablished anatomical conditions.

Similar considerations would lead to similar results in the case of touch and hearing. But what about learning and habit formation?

At the present time most psychologists would answer this question by saying that in some parts of the nervous system, between its optical and acoustical sectors, for instance, paths of nervous activity are not fixed once for all in the youth of an individual. Either no paths will be ready for conduction at first, or else from one point of the tissue several paths will conduct processes equally well in several directions, so that disorderly diffusion will occur. In the adult, however, we observe a great many associations, let us say, again, between the optical and the acoustical centers, and very seldom is there any confusion in the play of reproductions. The thing we have before us now is called a book, its parts pages, and so forth. It is a serious symptom if some one does not call things by their right names. Normally, the connection between definite visual processes and definite acoustical and motor processes works astonishingly well. What other explanation can be offered? Where we had at first no conducting path or perhaps several indifferent paths, we might assume that with time one single path has become differentiated and so much more susceptible to excitation than all the others, that now processes must follow this one path. This would mean that, disregarding the _genesis_ of this dominant one-way function, the perfect order of association and reproduction is again explained altogether in terms of the properties of topographical conditions. Though these conditions are not supposed to exist in the same manner in infancy, and though the changes by which they are produced remain obscure at the present time, when once they are established the direction and order of processes is as rigidly enforced by them, and any influence of dynamics will be as utterly excluded, as is the case supposedly in simple sensory conduction. As the railroad train remains on its tracks because these determine one way of least resistance, and as the enormous power of the engine has no influence upon direction, so in reproduction as well as in sensory processes all order and direction is a result of prearrangement, independently of the actual properties and dynamical forces of the process itself.

If for the sake of order dynamics shall not take part in the distribution of processes, and if distribution shall be merely an effect of given topographical conditions, important consequences follow.

First of all, excluding only the somewhat obscure _genesis_ of associations and habit, what happens in the nervous system will depend either upon inherited machine arrangements or upon secondarily _acquired_ arrangements. Therefore, where an actual performance is not an instance of the learning process as such, it must be explained either by original topographical conditions, or by past learning, i.e., by acquired changes in those conditions.[17] Now, this alternative is nothing but the old dualism of nativistic and empiristic explanation. No reader of all the famous discussions between nativists and empirists can have a serious doubt that a nativistic explanation has always meant the assumption of a given anatomical basis for the actual fact in question. If such explanation did not seem to be acceptable, then only one other possibility was left open, that of learning. These authors never entertain the idea that some specific and orderly function might occur without being controlled either by special arrangements preëstablished _ad hoc_ or by arrangements acquired in learning. What may this third alternative be? Vitalism? We shall see.

In well-established one-way streets what happens at the end of them will mainly depend upon what has happened at the entrance. Sensory experience will therefore consist of purely local elements of experience, the genuine properties of which must depend upon local stimuli exclusively. If, for the maintenance of order, the isolation of processes in each pathway and in each final cell (of the brain) must be absolute, then no influence of processes in other parts of the nervous system will be able to alter sensory experience, and so it must remain the same whatever the changes of attitude. By enumerating the actual properties of all elements at a given time we give an exhaustive account of the presented field. This is what has been called the summative, or mosaic, character of sensory experience, as it is understood from this viewpoint. Evidently, in terms of it, the sensory field becomes “inflexible,” exactly as its physiological basis is mainly determined by rigid topography. It also becomes “poor,” because the variety of experiences is restricted to those indifferent patterns of elements which we may find by varying independently the properties of the local elements. Any organization of processes in the field is excluded because order must be explained by functional separation. Specific function, dynamically extended over an area of the field, is excluded for the same reason; we have to deal with a purely _geometrical_ pattern of _local_ processes.

How “empty” and “dead” does the organism appear in this theory! Dynamically, it has nothing to contribute to the monotonous elementary currents conducted compulsorily from a point of stimulation to a point of reaction. So it becomes an indifferent stage for actors indifferent to the stage as well as to each other. As an object of research in dynamics it is less interesting than a molecule or a soap-bubble which are both of them functional wholes.

If between the field of sensory processes and the effector organs conduction is determined in the same manner as, in this theory, it is between local stimuli and the elements of that field, a thoroughly adequate formula for research in psychology will be: to find out what stimuli produce what reactions in the effector organs. The statement that stimuli, on the one hand, and reactions, on the other, are the only points of interest in psychology, corresponds absolutely to the picture of the organism, and especially the nervous system, as lacking any characteristic process of its own as a whole. Since other schools do not pretend to have new positive ideas about the functioning of the nervous system, that seductive formula of behaviorism has found a rather general assent as expressing the viewpoint of natural science in psychology. Unfortunately, in its present usage, it is not only seductive, but also ambiguous and superficial.

From the fact that in this theory dynamics is excluded from the determination of order and distribution, one more consequence follows immediately. Everywhere in nature dynamical events depend upon the properties of those processes and materials which exert influences upon one another. In a solution, containing Na_{2}SO_{4} and BaCl_{2}, BaSO_{4} will be precipitated because of certain properties of Ba, SO_{4} and H_{2}O which, in their mutual relations, determine the dynamics of the process. Two electric currents will produce mutual attraction of their conductors if both have the same direction; repulsion, on the other hand, if the direction of one current is opposite to that of the other. The rule is general, that “relative properties” as exemplified in these cases are decisive for dynamical interaction. A theory, therefore, which excludes dynamics from the determination of distribution, allowing it the production only of elementary nervous current, will have to draw the inference that the properties of local processes have no influence whatever upon the total distribution in the field. A given local process will be altogether indifferent to its neighbors, running its course uninfluenced by their existence. All possible patterns may be produced by appropriate sets of peripheral stimuli; no mutual forces are admitted which, in the whole field, would produce certain definite distributions rather than others. A similar consideration in the case of association and reproduction will occupy us later on.

When confronted with such an unretouched picture of current assumptions about physiological functions, most psychologists will protest. They will declare that one should not take too literally what has been used rather as an analogy in a preliminary endeavor to develop ideas about the processes of the nervous system. Every one admits, moreover, that there are cases of “irradiation” in some parts of the tissue! To this criticism I must answer that if _all_ analogies chosen, in the first tentative picturing of orderly nervous function, are of the same type, using topographical arrangements as the basis of order, this may be taken as evidence that other analogies do not occur to these authors. Preliminary though it may be, it remains a machine-picture, and no other has been developed, which is different in principle. As to irradiation of current, this concept as such does not mean more than a lack of definiteness and accuracy in the machine; it presupposes order enforced by strict isolation as the normal case, a slight deviation from which is the whole content of the idea. I admit that it makes our ideas about nervous functioning a little more nebulous than they should be according to the extreme viewpoint of machine theory; but I deny that in this manner _order_ of distribution can be or has been explained by any one. Granted that all conductors may “leak” a little at certain points and that, therefore, local processes may become interfused mutually to a certain degree, I am unable to deduce orderly distribution or organization from such an indifferent “spreading” or interpenetration of essentially isolated units.

Let us compare the consequences of the theory with observation. Some relevant data have already been mentioned. Other and much more important data will occupy us in the next chapters.

That constancy of brightness and of size cannot be explained by the assumption of one-way conduction determining local sensory experience in terms of local stimulation does not need further discussion, since, because of their incompatibility with that assumption, those facts are commonly believed to exemplify the influence of meaning. But now that experimentation has shown that the meaning theory does not seem to explain them either, neither the empiristic nor the nativistic assumptions help us in these cases. So we must try to conceive a third kind of nervous function other than the types in which processes are strictly directed either by inherited or by acquired arrangements. If there is a third reasonable assumption, it will be necessary to apply it also in those other cases, such as constancy of form, speed, localization, and so forth, which are so similar to constancy of brightness and size, that the same explanation should obviously be given in all these instances. Quite generally then the alternative between empiristic and nativistic hypotheses must be misleading.

The introspective theorem that changes of attitude cannot influence “true” sensory experience does not agree better with the facts. It seems rather to be an arbitrary definition of “true” sensory experience. In observation, at least, if I transform the white in the shadow and the black in full light into two similar grays, _by “introspection_,” there can be no more radical influence of attitude upon sensory experience than this transformation which occurs under constant conditions of stimulation. And the same holds wherever introspection, destroying natural experience by an artificial technique, finds its “true” sensations instead. Fortunately in one part of our science at least, this seems to be the prevailing opinion. When we analyze a clang we hear several notes appear successively in the mass which previously we heard as a _unity_. If in this case we agree that under constant conditions of stimulation our attitude transforms one sensory reality into others, and that the clang heard as one is not less real than the partial tones apparent during analysis, we have no right to contradict similar observations in other cases.[18]

As to the statement that sensory experience is a purely local affair, each point of a sensory field depending upon “its” local stimulus exclusively, we must reiterate that no grounds have ever been given for such a radical assumption. Rather it seems to be an _a priori_ belief about what _ought_ to be the nature of things, experience to the contrary notwithstanding. As far as observation goes the properties of local retinal stimulation do not simply determine the size, the form, the localization and the brightness of local experience; neither does retinal speed determine seen speed, as it probably ought to according to the thesis that the geometry of retinal facts determines spatial experiences. As a matter of observation, all the well-known “illusions” may be cited as evidence of the fact that local processes depend upon _sets_ of stimuli. To some degree this controversy will be settled by pragmatic principles: the decision will go to that side whose principles prove most fruitful in the further development of psychology. In the meantime, however, we may carry on our analysis of the polemical situation at present.

Almost all psychologists agree, in the case of one experience, upon the fact that local sensory experience is determined by more than merely local stimulation. This case is that of color-contrast, which most psychologists suppose to be an effect of interaction in the nervous system. If here the point-to-point correlation between retinal stimuli and sensory experience is surrendered, because the determination of local experience by conditions in a larger area is too evident, how can we proceed hereafter as if this discovery and concession had not been made? It took science some time before it would accept simple observation even in this case. Helmholtz refused to do so and, of course, he applied the meaning theory in order to save its fundamental belief, i.e., the point-to-point determination of local sensory fact by local stimulation. But after the first step has been made, we should realize not only that one theory of contrast has taken the place of another, but also that instead of applying persistently one general principle to all sensory experience, we have begun to accept a new one. In the future, wherever experience does not correspond to local stimulation, we should, at least, consider the possibility that such an experience may depend upon the total set of conditions in a larger field, exactly as contrast does. _If_ it does, this may help us to understand why changes of attitude affect sensory experience in some cases. Sensory experience, which depends upon the constellation of stimuli in a larger area, and therefore does not correspond to merely local, inflexible units of process, may be influenced by “processes of attitude” as well. The most important point, however, seems to be that if we find a type of process depending upon _sets_ of stimuli instead of single ones, this process may be that “third possibility” we are seeking. Certainly, it would neither be like the elementary processes of nativistic machine theory, i.e., absolutely determined by _inherited_ arrangements, nor like the processes of empiristic theory, upon which a similar compulsion is exerted by _acquired_ arrangements.

In the next chapters I shall try to show that other facts, much more important than those we have considered hitherto, point exactly in the same direction. For the sake of order in nervous function the machine theory excludes _organization of process_ in the field. But we shall see that organization may be regarded as a typical fact in sensory experience. Again the theory excludes the assumption of any specific process dynamically extended over an area of the field. But it will not be difficult to show that there are experiences in great number the specific properties of which belong to _extended wholes_ and do not exist in local isolation. This means also that the real variety of processes occurring in the sensory field is simply enormous when compared with those essentially indifferent patterns of local elements which may occur according to the machine theory.

If dynamics are excluded from the determination of distribution, local process will correspond everywhere with its stimulus; the actual properties of stimulation in their mutual relationships will play no rôle in the whole affair, as they would undoubtedly in the case of dynamical interaction. Reviewing our observations, however, we find that everywhere the aspect of sensory experience depends upon the properties of stimuli in their mutual interrelationship. This is well known in the case of contrast and tonal fusion, but we may cite as well all those observations which were discussed at length in the last chapter. Constancy of brightness, for instance, depends upon the relation of the illumination and brightness of the neighborhood to the brightness of the field in question. That _organization_ in the field depends upon the definite “relative properties” of local conditions, will be shown in the next chapter.

All these facts make it probable that something is wrong with the machine theory; they look as though they might be better understood by dynamical theory. Sometimes the observer finds dynamical events quite obviously occurring directly within the field. This is particularly the case, when sudden stimulation or change of stimulation is followed by a _development_ of process. If we cause a bright figure suddenly to appear in the dark, this figure will have at once neither its full size nor its “right” place. Instead it will appear with an energetic movement of extension as well as of approach. At the moment of abrupt disappearance, it will appear to have a movement of contraction and recession. Obviously, such observations would be exceedingly strange if considered in terms of machine theory. Or again, take the surprising fact that in touch, as well as in vision and hearing, the distance of objects and events may vary considerably if the stimuli are given in a certain manner. In some beautiful experiments of von Frey two distant points of the arm touched at the same time will appear to be one-half the distance apart which they appear to be when touched in slow succession. Scholz and Kester have both measured the mutual “attraction” which lights as well as sounds show when presented under adequate conditions. If the machine theory did not have its inordinate historical prestige, no one would hesitate to take these observations as evidence of dynamical interaction within the field. The stroboscopic movement, which belongs to the same class of observations, has acquired a unique importance by the fact that experimentation in this field led Wertheimer explicitly to discard the purely summative theory of sensory experience, not only for the problem in question but generally.[19] If at some distance from each other two stimuli are successively projected upon the retina of a subject, a movement will be seen, starting from the locus of the first and ending in the region of the second. Under favorable conditions there will not even be two “impressions.” One “thing” will move from one place to the other--certainly a case of dynamics which it would be difficult to understand by the theory of isolated local processes. After the more important properties of stroboscopic movement were investigated by Wertheimer, Koffka and others, there was much discussion, mostly about minor points, which almost tended to obscure the main facts. As was to be expected also, meaning was rather liberally offered as an explanation. Nevertheless, if conditions and the attitude of the observer are not too inadequate, we undoubtedly _have_ movement in the visual field. Those who do not believe direct experience, where it contradicts the supposed properties of “true” sensation, may deduce the “reality” of that movement from the fact that, when repeated, it produces an after-image of movement in the opposite direction, exactly as “real” movement does. Though, historically, Wertheimer’s investigation was the beginning of _gestalt_ theory, in the proper meaning of that phrase, the following considerations of sensory process will take another slant, because to me another way seems more advisable as an introduction.[20]

There are several well-known arguments which favor the machine
theory. I have sometimes heard that it gives us a picture of
nervous function which, clear and simple in itself, is the more
easy to understand since in practical life we enforce order
everywhere in the same manner, i.e., by arrangements _ad hoc_. I
must confess that such a policy of the least scientific effort
seems to me unacceptable. The comfort and the habits of the
scientist do not count where he must deal with the properties of
his subject-matter. Furthermore, only the psychologist, neurologist
and physiologist will save time and effort by an assumption
which explains order by arrangement. They simply hand their
problem down to somebody else; wherever, in theory, a problem of
function is reduced to one of special arrangements, the science
of “morphogenesis” in its ontogenetic and phylogenetic branches
is amicably asked to solve it, i.e., to explain the origin of the
arrangements. So the avoidance of difficulties in our science
means that others have proportionally more difficulties. And,
by the way, at some point functional problems must be treated
as truly functional. If it is barely possible to understand the
ontogenesis of anatomical structure by the working of “special
arrangements” in the egg and germ, it would be ridiculous to
explain _phylogenesis_ by arrangements which bring it about.

Yet it will be said that we do have special arrangements
guaranteeing definite function in a great many organs of the body.
Nobody can deny it, and I shall admit at once that the existence
of the optic nerves as a conducting system between the eyes and
the brain may be regarded as an example. Still, in our body, there
is another conducting system in which a great many substances are
transported along with the _blood_. And here, though the conduits
are a general arrangement “for transportation,” we do _not_ have
special arrangements for carrying each part of the fluid to its
right place. What a definite part of the tissue pours into the
blood or takes away from it at a given time is not determined
by isolating conductors; everywhere it depends upon the actual
relationship between the state of the tissue in question and the
chemical properties of the blood, and yet normally we have order in
the whole affair. The example shows that the existence of “organs”
does not allow us to draw any inference about elementary processes
being kept in order entirely by machine-arrangements.

However, I may be forgetting that in physiology and pathology we
have much evidence for assuming a “projection” of retinal points
upon definite points of the _area striata_ in the brain! I am
not certain whether the facts in question prove that between
the retina and the _area striata_ conduction is completely a
point-to-point affair. But that does not matter, since at the
present time neurologists no longer believe that the _area striata_
is the terminus of optic processes and that visual experience is
concomitant with processes in _this_ area. If up to this region
conduction should be a matter of strictly isolated paths, the
functional problem we are occupied with would have to be solved in
parts beyond the _area striata_.

I shall be told that the nervous system consists of cells the
fibers of which _are_ isolated from each other. I answer that in
its gray ganglionic and nuclear fields conditions are different.
Here mutual influence is not only possible; it is necessary.

But what of the all-or-none law? Does it not prove that elementary
conduction is a matter of each single nerve fiber, occurring in
one definite manner as long as the properties of the conductor
remain the same? Experimental investigation of the all-or-none law
is not yet complete and, so far as I know, we have no evidence as
yet of its application to central fields. Supposing, however, that
it holds in brain tissue as it seems to hold in peripheral nerves,
the alternative between a strict machine theory of distribution
and dynamical conceptions would remain as open as before, because,
then, in each part of the nervous system the number of elementary
organs taking part in any actual process, i.e., the density of the
process, would have to be determined somehow, as would also the
frequency of current in each single organ. Both properties of the
process may either depend upon given local arrangements or upon
dynamical intercourse in the ganglionic tissue. As distribution
of energy is a dynamical problem in physics notwithstanding the
quantum theory, so the all-or-none law, as a sort of quantum theory
in nerve physiology, does not exclude dynamical distribution of
process.

A final argument which maintains that distribution of process by
preëstablished and isolating conductors is the only way to explain
the order of the field in its relation to the external physical
world, seems to have two parts. _First_, it presupposes that
dynamical interaction, not controlled by special arrangements
at each step, must produce chaos and confusion. We have here the
old human prejudice which, in a great many cases of dynamical
interaction, is absolutely unwarranted. _Secondly_, as to the
relation between the external physical world and the sensory field,
the theory of isolated conductors enforcing order would explain a
strict correspondence of sensory facts to _retinal stimulation_.
But in the last chapter we saw that much experience is exiled “into
the dust-cloud” of psychology by introspectionism just because it
does _not_ agree at all with the properties of stimulation. To
be sure, the constancy of size, form, brightness, localization
and speed in the sensory field corresponds fairly well with the
constant properties of _physical objects_; but this agreement is
_not_ explained by the machine theory of vision which refers to
constant relations between local _retinal stimulation_ and local
experience.

If we are not satisfied by the alternative between order enforced by preëstablished arrangements and order determined by acquired arrangements, what else can produce order? For the moment we restrict our discussion to sensory processes and return to our statement (cf. p. 111) that, in physical systems, the relative influence of topographical conditions, on the one hand, and of the play of actual forces, on the other, may vary enormously. In typical man-made machines the rôle of topographical conditions prevails to such an extent that the only rôle of dynamics is to drive processes along a path laid down by those conditions. This means that typical machines are essentially a _special_ type of physical system and that outside the little world of man-made machines there exists an immense world of other physical systems, in which the direction of processes is not completely determined by topographical arrangements.

Let us consider a drop in a current of water which moves through a narrow pipe. Why does it move? Because, aside from inertia, pressure is higher on one side of it than on the other. But this difference of pressure works in one direction only, the walls of the pipe excluding all its other effects. Now let us suppose that the pipe disappears and that the drop (and the whole column of water in the pipe) becomes a part of a larger volume of water. The drop will probably also move in its new environment. But now it is exposed to forces on all sides, and its movement will be in the direction of the _resultant_ vector of force. Obviously this movement is no less necessary than was the movement in the pipe, but here there is no local arrangement which can determine a single direction as the only one possible. Therefore the path of the drop will be determined _dynamically_ in the new case, i.e., by resultant force at each moment. It follows that in this situation the path which our drop takes will depend upon the dynamical situation it encounters at each stage, and that it will change when this situation changes. This is one simple example out of millions. _In all of them not only movement, or process as such, but also the direction and distribution of process is determined_ _dynamically by interaction_. It is events of this type which are excluded almost completely from machines, and the same type of process is practically excluded by standard neurological and psychological theory. _Gestalt_ psychology sees no ground for its exclusion and rather proposes to give this type of process a fundamental rôle in psychological theory.

In the pipe the drop of water moves because movement, under differential pressure, is an approach toward equilibrium. Such is the effect of forces at all points of all systems. When surrounded by water, the movement of the drop will still be an illustration of the same rule.[21] The only difference is that now the direction of movement, according to the rule, will depend upon the actual _dynamical_ situation. If we consider all the drops in the given volume of water, we will find the distribution of water gradually changing from one moment to the next. But whereas in pipes the distribution of the movement in space depends upon the form and the spatial position of the pipes, in the “dynamical case” it depends mainly upon the play of actual forces. In pipes, order is produced by _exclusion_ of dynamical interaction; whatever distribution may result in the “dynamical case” is _produced_ by dynamics itself.

At this point our interest concentrates upon this question, whether Aristotelians and modern theorists are right in assuming that _anything_ may happen in dynamical interaction and that, therefore, dynamics is to be regarded almost as a synonym for disorder. What we see around us in inorganic nature seems to corroborate that opinion, since the blind meeting of forces and processes usually leads to chaos and destruction. What we have before us in these cases, however, may be described as follows: There is a thing at rest or a process going on uniformly; suddenly a new factor impinges upon the first thing or process from without, and after a short while, another new influence, again independent, is exerted from without, and so forth. Anything indeed may happen under these circumstances, and in most cases the end result of such fortuitous concurrence is disorder and destruction. This, I think, is the picture most men have in mind when they refer to dynamics, as though accidental impact were its only form!

There are, however, other cases, much more interesting for our present discussion. If in a basin, for instance, water is somehow distributed, perhaps in full movement, at a given moment there is a definite pressure at each point, and everywhere differences of pressure will tend to alter the distribution and the direction of local drops of water. Supposing now that the basin itself does not change and that no outer influences accidentally impinge upon the system during its redistribution, what will the result of continual internal interaction be? If we try to find the answer by imagining an indefinite number of drops, each moving under the resultant force in its immediate proximity, and each again influencing its proximate neighbors by that movement,--if we notice that this picture changes continually, as the distribution, and, therefore, the actually resultant force at each point changes in the smallest fraction of a second,--then we are inclined to dismiss the task as beyond our efforts, and to treat the events of this field in terms of the confusion or destruction that is attributed to nature in the case of accidental impacts.

But in this we are wrong. We are projecting our own confusion into the course of objective events. We become guilty of anthropomorphism. The physicist has quite a different attitude toward the problem. By observation, as well as by theoretical calculation, he is led to the conclusion that, generally, undisturbed dynamical interaction will produce a definite orderly distribution.

Let us review an example we entertained at the beginning of this chapter. To Aristotelian theorists the striking order of astronomical movements appeared inexplicable without the assumption of special arrangements controlling them. Now in modern times no one believes in those crystal spheres. But the order is there! And since the stars did not “_learn_” to move so orderly, some factors other than preëstablished and acquired topographical arrangements must be able to produce and to maintain order in distribution and movement. And in the prevalent conception of the solar system, it is continuous dynamical interaction, without any topographical arrangements, which produced and still maintains the order.

Other examples may be found in all parts of physics and chemistry: when two atoms come into their sphere of mutual influence, the play of dynamic interaction immediately begins, and, as the case may be, depending upon their “relative properties,” they either separate again or they form an orderly molecule,--an architectonic structure,--without the aid of any arrangements _ad hoc_.

If we suspend a number of straight wires so that they form different angles with each other, the whole distribution being irregular, electric current entering the wires turns them into parallel lines. This is an orderly result of electrodynamic interaction.

Or again, we pour oil into a liquid with which it does not mix. In spite of the violent interaction of molecules at their common surface, this surface remains sharply determined, not by any arrangement enforcing this orderly distribution, but just by the play of surface dynamics between the oil and the other liquid. If specific density is the same for both liquids, these surface forces will change the distribution until the oil forms a regular sphere swimming in the other liquid.

I might go on to describe hundreds of examples. In all of them the situation would be the same in principle. Dynamical interaction, undisturbed by accidental impacts from without, leads to orderly distribution, though there are no special preëstablished arrangements.

And what is the explanation of this general tendency in undisturbed dynamics? It is simple enough. In all these systems we have one resulting force at each point at each instant of time. All the resultant forces together form one texture of stresses. From the principles of physics one can deduce, therefore, that, _for the system as a whole_, the immediate effect of all those forces will have one definite direction. At each point the forces will produce changes of movement or process which, when considered in their totality, bring the system nearer to the balance of the forces themselves. The factor of inertia may cause the real course of events to deviate from the ideal exemplification of this principle. But where, as in most organic systems, inert velocities not corresponding to actual forces are destroyed by friction, the real distribution of processes will exhibit the principle perfectly, and will finally reach a state of stability, of rest or of stationary process. The fact that this state will be an _orderly_ distribution has been explained by Ernst Mach as follows: In orderly and regular distributions the totality of internal stresses will be more balanced than in a state of disorder. Therefore, by undisturbed interaction a system approaches order. For all details I must refer the reader to the literature quoted at the end of this chapter.[22]

_Dynamical self-distribution_ is the third kind of functional concept which I propose to add to psychological theory, in addition to distribution enforced by inherited arrangements and order determined by acquired arrangements. More concretely and for the visual field, my assumption is that the order and distribution in this field is in each case the result of dynamical interaction. From this viewpoint the processes underlying the visual field in a state of _rest_ represent the equilibrated distribution of sensory dynamics under actually given conditions. When not at rest, sensory dynamics will be in a state of _developing dynamical distribution_.

Though the direction of local process in a system is not altogether determined by local arrangement, the result of dynamical self-distribution as a whole may still depend upon topographical conditions (cf. pp. 112-113). Thus the electric current in a network of wires is distributed dynamically; yet the actual distribution as a whole depends upon the position of the electrodes and upon the conductivities in all the conductors. Similarly, the totality of processes in the optical part of the nervous system will depend upon given conditions in each case. For the moment, though this will prove to be an inexact assumption when it is examined more closely, I shall suppose that in the interior of the optical network the general conditions of conduction remain constant. But, then, as a set of peripheral conditions, we have the patterns of different chemical reactions on the retina, as they are produced in each case by actual stimulation. Upon these varying conditions the self-distribution of process will depend primarily. If neurologists are correct when they assert that between the retina and the _area striata_ of both hemispheres, conduction is a matter of isolated pathways, then the _area striata_ will be a sort of “central retina,” in which the pattern of retinal stimulation is copied by a pattern of central processes. In this case _dynamical_ distribution will begin here, depending upon the actual pattern of processes in the occipital lobes.

It will be evident that the task such a theory must face is enormously more difficult than that of machine theory. Where arrangements are altogether responsible for distribution, the concrete dynamical properties of process are of little concern. If we do not know about them, it does not matter very much. In dynamical theory, on the contrary, the whole development of the theory requires that we know those properties of the process. And since as yet physiology is not very instructive concerning them, the extension of the theory depends instead upon the assumptions which we make. Experimentation on visual experiences will have to give us the necessary hints for making our hypotheses, and the consequences of our hypotheses will then have to be tested by experiments of the same sort. At the present time only the first steps have been made in this direction, and it will take us a long time before we feel firm ground under our feet. Let us remember, however, that all the perplexities we may find on our way, and all the mistakes we make in its course, are not to be referred to the fundamental concept of self-distribution by interaction; they should be referred to the particular assumptions concerning process, force and interaction, which we have made.

As an example which will make our analysis more concrete, I shall introduce one special problem. If from a given pattern, either on the retina or on the “central retina,” processes start into the conducting network beyond, and if their distribution is determined dynamically, why should differences among the processes, corresponding to differences in color, be preserved on the way? This is generally the case: to the accurate retinal contour of the image of a letter on a white page corresponds the sharp outline of the letter in my visual field. If the totality of processes issuing from the area of the letter remains detached somehow from the processes surrounding it, we may understand, perhaps, how even in dynamical distribution the most essential and crude geometrical properties of retinal pattern may be sustained. But how can one set of processes remain detached from the rest in dynamical theory? This embarrassing question certainly could not occur for the assumption of isolated pathways. My answer is based on the fundamental principle of the theory. If under these circumstances one set of processes remains detached from the rest there must be dynamical factors at work. Generally, processes corresponding to a definitely colored area will have definite properties as a class of processes, different from the properties of a class of surrounding processes which corresponds to another color. They will remain segregated in the nervous network if we suppose that in the ganglionic fields, where they “touch” each other, their differential properties provide _separating forces of contact_, so that they mutually exclude each other. Take as an example the contact of oil and water. Here interaction is so strong that the form of the surface is determined by it; but this surface as such remains a sharp boundary and the drop of oil remains detached from the water by those same molecular forces which, at the time, mold the form of the drop. I shall assume, then, that, in optical processes, contours are preserved by similar forces of antagonistic contact, depending upon differences in the properties on the two sides of the contour. From this viewpoint, interaction will thus determine general distribution; it will also have an influence upon size and form, and so forth, but it will not generally “dissolve” processes, corresponding to a homogeneous area of color, in the surrounding processes. This may seem a bold hypothesis. But recent experiments have shown that this assumption is in the right direction. It would be surprising if _all_ process differences should act as separating surface forces of the kind just described in the case of color, for in physics such forces exist between oil and water, for instance, but not between water and alcohol, or a great many other pairs of different materials. Indeed, when reëxamining the results of older experimental investigations, Liebmann[23] proved that, whereas very slight differences of brightness gave sharp contours, neighboring areas of different color, even with maximal differences of chroma _alone_, will show mutual diffusion.[24] We may conclude, then, that mainly differences of brightness provide effective forces of separation. Under normal conditions neighboring areas of different chroma will almost always be different in brightness. Therefore, sharp contours on the retina will in most cases give accurate contours in the visual field.

Without further discussion we can draw a rather important conclusion. We are accustomed to regard order enforced by rigid arrangements as exceptionally secure. If, however, the order of sensory experience be conceived as the result of sensory dynamics, this will seem to most people like explaining the quiet life of an orderly citizen as the outcome of many moral struggles and catastrophes. But, in this connection, the chief point is that in those cases in which the machine theory of visual order seems to be most convincing, dynamical theory gives exactly the same results. As an example we may take the symmetry of a seen circle, corresponding to the symmetry of its retinal image. Is it necessary to explain this correspondence by insulated conductors which maintain the geometrical properties of the retinal image all along the line of those processes underlying visual experience? By no means. Assuming that surface forces of separation keep the processes of the circle distinct from the surrounding processes, the dynamical influences exerted upon the processes of the circle will be the same in all directions,[25] if, in the immediate neighborhood of the circle, surrounding processes are homogeneous. Therefore, if the network has the same conducting properties throughout that part of the nervous system, i.e., if it is functionally “homogeneous,” there will be not the slightest reason why the symmetry of the process should be disturbed. In this case, dynamical theory gives the same result, then, which until now has been rather clumsily explained by preëstablished arrangements _ad hoc_.

Since the rôle dynamics plays is so slight in contemporary theory, it may seem very strange to some psychologists. Hence I wish to make the following statement expressly: _these concepts do not contain a single thought in the direction of vitalism_. It is true that a number of difficulties may be removed by them, difficulties which vitalism can still raise quite properly against the claims of unqualified “mechanistic” ideas. But, in our field of research, “mechanistic” ideas have almost always been explanations by topographical arrangements, and “dynamical” ideas, the type of idea prevalent in general physics, occurred no more to the mechanist than to the vitalist.

I shall not try to develop more detailed theorems about sensory dynamics until we become further acquainted with the main facts and their significance. Some consequences of dynamical theory will be obvious at once. From this viewpoint, sensory experience is allowed to be as _fluid_ and _manifold_ as, to observation, it reveals itself. Furthermore, as local processes are not isolated,--their existence and their actual properties depending upon the dynamical context in a larger area,--the visual field may prove to be _organized_. In this case, as everywhere in physics, organization will be found to depend upon what I have called the “relative properties” of stimulation. We may eventually find specific properties in experience characteristic of extended areas and not analyzable into local sensations, just as existence exclusively as _functional wholes_ is a property of many dynamical states in physics. The next chapters will be concerned with the development of these matters.

BIBLIOGRAPHY

K. Koffka: _The Growth of the Mind_. 1924.

W. Köhler: _Die physischen Gestalten in Ruhe und im stationären
Zustand_. 1920.

W. Köhler: _Gestaltprobleme und Anfänge einer Gestalttheorie_. 1924.

W. Köhler: _Komplextheorie und Gestalttheorie_. Psychol. Forsch. 6.
1925.

W. Köhler: _Zur Theorie der Regulation_. Arch. f. Entwicklungsmech.
1927.

M. Wertheimer: _Untersuchungen zur Lehre von der Gestalt, I_.
Psychol. Forsch. 1. 1921.

M. Wertheimer: _Drei Abhandlungen zur Gestalttheorie_. 1925.

V

_Sensory Organization_

A DYNAMICAL distribution will be rightly regarded as a functional whole. Take, for example, a simple electric circuit: the differences of potential and the densities of current distribute themselves along the conductors in such a manner that a stable or stationary state is produced and maintained. No part of this distribution is self-sufficient; local processes depend throughout upon the totality of the distribution.

If a similar conception is to be applied to the processes underlying sensory experience, we must avoid a mistake. Protesting against the atomism which had been introduced into the treatment of sensory experience, William James once said that, in the sensory field, local experiences are interwoven with their neighbors in a manner which is beyond the grasp of purely intellectual theory. He seems to think that, in original sensory experience, there is uniform continuity and that all cuts and boundaries are introduced later on for pragmatic reasons.

From the viewpoint of _gestalt_ psychology such a statement does not correspond to the facts. In the last chapter we saw that, notwithstanding the general dynamical interdependence throughout the field, there may be boundaries in it where forces of “segregation” and “separation” take the place of those of “coherence” operating elsewhere.

Indeed, in the visual field, for instance, we have two kinds of order. One of them is the order with which we found the machine theory occupied in its effort to explain how a given local process is properly placed between its neighbors, and not confused therewith. However, there is another order in the field which has escaped the attention of many psychologists, though it is not less important than the first. In most visual fields the contents of certain areas “belong together,” so that we have circumscribed, or bounded, units before us, from which their surroundings are excluded. If James did not admit this organization of the field as a sensory fact, the reason for it was the enormous power of the theory of meaning, which has been an obdurate obstacle to our seeing important problems, more in this connection than elsewhere. For the same reason there may be only a few readers who will not quarrel with the next paragraphs as long as they see any possibility of so doing.

When I look at the desk before me I find quite a number of circumscribed units which appear detached and segregated in the field: a piece of paper as against the surface of the desk, a pencil, an eraser, a cigarette, and so forth. In all these cases there are two mutually dependent conditions. The existence of a unit involves its segregation from its surroundings. In order to satisfy myself that I am here talking about realities, I may try to form other units consisting of parts of those objects and parts of their environment taken together. In some cases my attempt will be a complete failure. In others, where, for some reason, there is greater success, the result is so strange that it indicates by contrast what a specific reality the original organization was.