therefore, been "worked over" once at least before they can be modified by attention.1 This is one reason for the high degree of accuracy of mere "impressions," or of judgments with regard to sensations inattentively experienced.

To conclude our summary, we may quote the closing paragraphs of the chapter on attention:

"I must not omit to emphasize the fact that I do not assume the processes of attentional facilitation here described merely for cases where the attention is intensively directed upon its object. I believe, on the contrary, that no central function ever wholly disappears; that a certain degree of excitation (which I have repeatedly referred to, in contradistinction to intercellular tetanus, as the tonus of the cells) is always present; that the degrees of this tonus vary; that its magnitude is primarily dependent on excitations that run their courses along related paths; that in connection with these, phenomena of inhibition and facilitation may appear, etc. But the more intensively the attention is applied to one complex of paths, the more it is withdrawn from the rest."

We pass now to a consideration of the comparative validity of Exner's theory of attention. We recognize that in any attempt to evaluate theories representing the life work of men who are recognized as authorities, we are treading on dangerous ground. Any judgment must be a merely tentative one; indeed it can hardly be called a judgment, - it is rather an investigation of the ground of the differences in the theories and a statement of the alternatives offered in the acceptance of the one or the other.

It is evident that the fundamental concept in Exner's theory is that of coördinated facilitation and inhibition, and of these two processes we are concerned only with the member which other theories of the day reject-facilitation. Exner treats of facilitation first as a purely physiological process, and secondly as a process involved in attending. What he had to say under the first rubric we have quoted in our first chapter. We suspended comment there in order to review the theory as a whole before criticising any part of it. As we return to

it now, the account of the various experiments on animals seems to us to be an account of facts known before presented here under a new name. Certainly we knew that there was interaction between nuclei connected with groups of muscles assuming a single function, or closely related functions. But these nuclei are in close anatomical connection. If Bahnung means simply that nerve currents in the same organ, or in organs with close and definite anatomical connections, can reinforce each other, then it is no new concept. We think the whole subject would have been clearer if Exner had stated

this himself, and then given his reasons for emphasizing and further illustrating by experiments of his own facilitatory interaction of certain nuclei of the nervous system. It seems to us that he emphasizes the experimental proof of this interaction in the nervous system of animals because he wishes to extend the concept further to cases where there is no direct, intimate anatomical connection, and the facilitating process is accompanied by consciousness. To this extension of the concept he gives the name of "attentional facilitation," our second subordinate topic. Having accepted the first, the purely physiological concept of Bahnung, what have we to say to this extension of it to activities accompanied by consciousness?

In the first place we must recognize that facilitation in attention is as yet only an hypothesis. Exner would doubtless admit this, for he refers occasionally to the hypothetical nature of his explanations (e. g., p. 87). At the same time he maintains that the hypotheses advanced are those which are in closest correspondence with our knowledge of the physiology of the nervous system. From this standpoint there are many facts to render probable the hypothesis of attentional facilitation. (1) All nervous impulses are recognized from the outset to be both excitatory and inhibitory.1 (2) No more intimate connection of the cortex with other parts of the nervous system needs be supposed for combined facilitation and inhibition than for inhibition alone. (3) The brain centres certainly "work over" incoming currents in some fashion, and there is no reason apparently against the assumption that their energy may reinforce that of the incoming current, while Exner shows that there are many reasons for the supposition. (4) Moreover, in many cases where two organs function together, the limen of their common discharge is lower than the limen of either alone, when the two are separated. In these cases "facilitation" may mean either the lowering of the limen of discharge or the reinforcement of a nerve current. For these reasons among others, the concept of Bahnung is valid from the physiological standpoint.

The crucial point in the psychological application of Bahnung is found in Exner's assertion that attention increases the intensity of a sensation, but that increase of intensity due to attention is recognized as different from increase of intensity due to the stimulus. Wundt and Külpe also recognize, as indeed every one must, that the intensity of a sensation ordinarily increases in attention, but they ascribe the increase to "associative co-excitation." They deny that attention di

E. g., Wundt, "Phys. Psych.," I, pp. 252, 258.

rectly intensifies a sensation. Exner admits the existence of associative co-excitations, but ranks them as secondary phenomena, and finds them insufficient to account for the facts of attention. When psychology has obtained better experimental control of attention, test-experiments may be devised to decide between the theories of Wundt and Exner. At present, we can make no absolute decision. If we accept the theory of Wundt and Külpe that attention is purely inhibitory, we must explain the increased clearness and efficiency of an idea primarily by the law of the relativity of consciousness, and secondarily by associative co-excitation. At the same time we have no satisfactory schema for the process of inhibition itself.1 If we accept the theory of Exner that attention is both inhibitory and facilitatory, we explain the increased clearness and efficiency of an idea by correlating them with the facilitatory processes, while at the same time the absence of unrelated ideas is ascribed to coöperative inhibitions; we maintain that attention intensifies sensations, but that intensification due to attention is recognizably different from intensification due to increased stimulus. Both theories must acknowledge that attention does actually reinforce some ideas while it inhibits others. Any instance of close attention in daily life is a picture of the two processes combined. But Exner regards the reinforcement or facilitation as equally fundamental with the inhibition; or rather, throughout his discussion he refers to facilitation as the more fundamental process, preceding or occasioning an inhibition of unrelated regions. Wundt and Külpe reverse the order of the two processes, and, moreover, deny that there is any direct facilitation by central processes; all reinforcement must come by way of associative co-excitation. Neither side has final and completely satisfactory proof for its position; and until we know more of the physiology of the central nervous system, the question whether attention is primarily facilitation or inhibition must be left open.

The conclusions reached by Bianchi, in his recent study of "The

We notice a similar criticism of Külpe's treatment of inhibition is made by Meumann in L'Année Psychologique, 1894, p. 514. He says: "I cannot share the opinion of the author that inhibition may be regarded as an independent process. We can think of the inhibition of physical or psychical processes only as the negative side of another process. We can only suppose that the energy of one part of the brain is lessened because some other part is expending a surplus of energy. Inhibition, then, does not explain the clearness of a sensation, but just the reverse is true: we interpret the appearance of inhibition in one part of the nervous system as a consequence of the expenditure of too great energy in another part."

Functions of the Frontal Lobes," must be taken account of in any attempt to explain attention by means of inhibitory or facilitatory processes in the frontal lobes. Bianchi's experiments were performed upon twelve monkeys and six dogs. All the operations were successful except two, and the animals were kept under observation for months or even years. The skill and care with which the whole work was performed cannot be called in question. For his conclusions, Bianchi makes no greater claim than that they give "a plausible explanation of the phenomena observed. I feel, at any rate, certain of the accuracy of the observations themselves."2 On the basis of these observations he states very positively that "the frontal lobes are not centres of inhibition. Without attempting to go fully into the theories concerning inhibition and its centres, it will be granted that inhibition depends upon a general psycho-physiological process, and that every part of the nervous system becomes, under different circumstances, either an inhibitory or an inhibited centre. . Physiology and psychology swarm with facts showing the error of those who assume a special cortical centre for inhibition.'

193

One statement in this connection we must object to. "We may ask ourselves whether there exists really any centre the function of which is to inhibit, hence whether there exists a faculty of attention. I reply distinctly, No." The "hence" in this sentence is obviously a non sequitur.

Bianchi's own "hypothesis is that the frontal lobes are the seat of the coördination and fusion of the incoming and outgoing products of the several sensory and motor areas of the cortex. The frontal lobes would thus sum up into series the products of the sensori-motor regions as well as the emotive states which accompany all the perceptions, the fusion of which constitutes what has been called the psychical tone of the individual. With the

organ for the physiological fusion which forms the basis of association, disappear also the physical conditions underlying reminiscence, judgment and discrimination, as is well shown in mutilated animals."5

Bianchi's general description of the rank and influence of the frontal lobes agrees with that given by Wundt, but their characteristic physiological process is said to be one of coördination and fusion instead of a process of inhibition. This tallies with Exner's definition of Bahnung, and it seems at first sight to add much to the probability of Exner's theory. The inhibitory theorists, however, would doubtless maintain that Bianchi misinterprets their concept of inhibition. They could agree with him in regarding the frontal lobes as necessary for the fusion of impressions, and yet explain the relation between the two by assuming that the fusion of certain impressions is possible only when there is inhibition of all other impressions. It must also be remembered that Bianchi's experiments were made upon animals that had already had the use of their frontal lobes for some time. Many of the phenomena that persisted after their removal must have been at some earlier time dependent upon the functioning of the frontal lobes, so that conclusions must be drawn very carefully. Yet, after all due allowance

has been made for these two objections to Bianchi's summary disposal of the inhibitory function of the frontal lobes, it still seems to us that his observations tend to overthrow the theory of the purely inhibitory character of these functions. The animals operated upon performed all simple acts in a wholly normal way. With regard to higher functions, they were passive, and unresponsive to stimuli that formerly had excited their higher activities. It is hard to see how such results can be fully explained on the hypothesis that the sole function of the frontal lobes is inhibition.

In

Our restriction of the term "explanatory" to the three types of theory discussed in this chapter leaves us open to the criticism of those who maintain that attention is primarily the direct result of variations in peripheral organs. answer to the criticism we would say: (1) that the only completed theories of this order are those of Ribot (in so far as he considers attention as essentially motor) and Münsterberg. These have already been reviewed in the preceding chapter; and although each has made positive contributions to our knowledge of the phenomena of attention, it is evident that neither goes far enough to be called an explanation. A third attempt is being made by Dr. Heinrich of Zürich, but at the date of our writing only the first chapter of his work has been published. Moreover, references in an earlier work show that Dr. Heinrich admits the probability of the dependence of attention upon central factors. ("Die moderne physiologische Psychologie," pp. 129 and 232.)

CHAPTER IV.

Attention and Distraction: An experimental investigation of the effect of so-called distractions on sensible discrimination.

2

In the preceding review of the current theories of attention' frequent reference has been made to the relation between changes in attention and changes in the intensity of a sensation. At one time attention was frequently taken to be the same thing as an increased intensity. Later it was maintained that attention only indirectly heightened the intensity of sensations.3 Others, again, have regarded the intensification as an essential part of the process of attention, but not the whole process; and, moreover, the intensification due to attention is said to be recognizably different from that due to increase in the intensity of the stimulus. Still a fourth

1

' Ebbinghaus' Zeitschrift für Psychologie und Physiologie der Sinnesorgane, Bd. IX, Heft 5 u. 6, S. 342-389.

James Mill, etc.

3 Wundt, Külpe, etc. Exner.