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

I. Report of experiments. Tabulated results for visual distances, light stimuli, weights and sounds. Distraction discontinuous; effect on memory; on duration of attention; on degree of attention. Disturbing factors: two methods of judging weights; experimental investigation by Prof. C. E. Parrish; different methods of addition; use of memorial images. Report of experiments by Mr. F. E. Moyer: effect of different modes of addition as distraction; effect of memorial images on overestimation of stimulus. II. Comparison of results with Prof. Münsterberg's: restriction of comparison. Results of comparing all four series; only two series. Faulty treatment of numerical results. Explanation by expectant attention. Analysis of expectancy in both experiments. Distinction between attention and intensity of stimulus. III. Sources of error observed and precautions suggested. Pre-adjustment of the attention. Continuity of the distraction; kinds of distraction and individual treatment of them. Methods for remembering stimuli. Results tested by other experimental methods; Patrizi's experiments. Experiments by Bertels.

Summary of the four chapters.


On Certain Physiological Concepts Involved in Theories of Attention.

In our later examination of various theories of attention, we shall find certain physiological concepts introduced. The validity of their use in the maintenance of different positions will be considered in connection with the discussion of the

theories in whose favor they are adduced. But the concepts themselves are neither so generally accepted nor so well established by physiological experiments as to admit of our introducing them without a preliminary definition of their significance and value in physiology itself. The two topics requiring brief notices of this sort are cerebral localization on the one hand, and Bahnung and Hemmung-neural reinforcement or facilitation and inhibition on the other hand.

Cerebral Localization. The physiological controversies over localization in the cortex, carried on by Hitzig, Munk, Ferrier, Goltz, Flourens, Horsley and many others, have resulted in the establishment of a few definite principles of cerebral functioning. These are summed up by Wundt as the principles of the Indifference of Function; the Substitution of Function; and the Localization of Function same three principles are stated less formally by W

'Physiologische Psychologie," IV ed., Vol. I, pp. 235, 236.

the following words: "The clinical history of a dog or of a monkey having suffered a removal of some portion of the Rolandic area altogether negatives a strict localization of function, and at most suggests its local concentration.

We thus picture the cortical organ in a semi-fluid state of differentiation, still variable by new instruction, rather than as a petrified and invariable collection of specialist organs tied down to particular functions and exclusively performing these functions."'1 In the same article Waller shows very clearly that the differences in theories of localization have been mainly due to a widely differing and even contradictory use of words for phenomena that were identical, and to the inferences drawn from these words.2

Neural Reinforcement (Facilitation) and Inhibition: "Bahnung" and "Hemmung."

We do not need to take any special notice of the physiological character and basis of inhibition. While there is still discussion in regard to its mechanism, the fact of inhibition, as tested, for instance, in the action of the vagus nerve on the heart, is well known and has frequently been demonstrated.

It is only mentioned here in connection with the opposite and more hypothetical process of neural reinforcement or facilitation. This latter idea plays a most prominent part in the theories of attention put forth by Exner and von Kries. They both refer to it as "a physiologically well established fact." I have searched the recent physiological journals and archives for confirmation of this statement, and have been unable to find mention of it. Exner, however, in his "Entwurf zu einer physiologischen Erklärung der psychischen Erscheinungen" gives his own physiological proof of the existence of Bahnung, and I quote rather fully from his report of the observations on which he bases this concept.

Exner uses Bahnung to mean just what we expect the word to mean-" the opening of a path." It is a facilita- tion of the course of the nerve current, due either to its reinforcement by charges from the centre, or to the lowering of the limen of discharge.* Exner states that he first reached his conclusion that there must be Bahnung in connection with his experiments on reaction time. But he maintains also

"On the Functional Attributes of the Cerebral Cortex," Brain, Parts LIX and LX, 1892.

2 Op. cit., p. 346 seq.

"Entwurf zu einer physiologischen Erklärung der psychischen Erscheinungen" (1894), p. 7 4 Op. cit., p. 82.

that he has succeeded in proving its existence experimentally by the following experiments with animals.1

(1) Pass an electric shock through the paw of a rabbit. Since the reflex contraction follows in an animal whose brain has been severed from the spinal cord, this reflex must be controlled by a cord centre. Now lessen the electric shock until it is too weak to produce any contraction. Apply this feeble shock to the paw, and apply to the cortex a shock also too feeble to produce any result alone. If the two are given in rapid succession, one reinforces the other, and the paw is flexed. Exner states that this is not a "summation," since in summation the reinforcing stimuli follow the same path as the reinforced. Summation, however, is one particular form of Bahnung.

(2) A passing reference is made to the fact that the reflex contraction following a needle prick is much stronger if we give close attention to the prick. Assuming that the cortex is in a state of excitation in attention, Exner uses the phenomenon as an instance of cortical Bahnung of a spinal cord centre.

(3) Sternberg has observed the Bahnung of other reflexes in the course of his studies on Hemmung, Ermüdung, und Bahnung der Sehnenreflexe im Rückenmarke.2

(4) Bahnung of the other sort, where the limen for discharge is lowered, is present in the action of the vagus nuclei. They lie in the medulla oblongata, and are connected by commissural fibres. If a section is made through these fibres, each half of the body breathes independently. If the two lungs move at the same time when the nuclei are connected, this must be because an increasing charge in either affects the other, so that it is more ready to discharge; and the actual discharge of the two must be simultaneous.

(5) The fifth case is taken from von Grossman's investigations of the three nuclei concerned in the breathing of the rabbit, one controlling the facial muscles, one the vagus muscles, and one the thoracic muscles. If one of the three is separated from its connection with the other two, these will continue to do their work; but the limen for their release of the inspiratory impulse is raised, and the animal makes movements which we call "gasping for breath." So that in this case we find the stimulation of one aiding the function of each of the others, and all three together reaching their exci

1 Op. cit., pp. 76-82.

2Wiener Akadem. Sitzber., Bd. C, Abth. III, Juni, 1891.

3Ueber die Athembewegungen des Kehlkopfes," I Theil. Wiener Akadem. Sitzber., Bd. XCVIII, Abth. III, Juli, 1889.

tation lir

for one a not as a allows ct as a facil

er point than is possible for any two, or ee that here we plainly have Bahnung, nt of a current, but as an influence which Tess off, or to discharge, more easily; i. e.,

Other 1 concepts will frequently recur in the subsequent chapters; but they are either so generally recognized as to need no special notice, or so intimately associated with the psychological theories we shall discuss later that we may advantageously consider them in their psychological connection rather than in this introductory chapter.


The Descriptive Theories of Attention.

Before attempting to give any account of our experimental investigation of the effect upon sensible discrimination of "free" and "distracted" attention, we shall pass in review some of the most important and typical theories of attention. The whole subject is still in a somewhat chaotic state. A summary of certain representative theories will tend to bring order out of the chaos and provide a basis for a more definite and intelligible treatment of isolated experiments. The old phrase, "Quot homines tot sententia," may well be taken to represent the number and variety of theories of attention advanced by the psychologists of this century. To indicate the importance of the problem and the incompleteness of its solution, I may quote from one of the most recent investigators of the subject, Dr. Heinrich of Zurich.

In the series of questions which concern psychology, attention takes the first and most important place. It is regarded as the fundamental condition of every human activity. In scientific investigation and thought, in practical action, in learning and teaching, attention is always a prerequisite if anything is to be accomplished. No wonder, then, that every psychology seeks to answer the question how those phenomena arise to which we give the name of Attention. Yet even now psychology has no theory, only many theories. Even now, as in the “good old times," each psychologist seeks to develop a theory of his own; and very few of these can be characterized as scientific.1


Yet in the general confusion two tendencies are discernible, according to which the theories may be roughly divided into two classes. One class includes the more purely "descriptive" theories, with more emphasis on the physiological aspect of attention, and less distinction between psychological

"Die Aufmerksamkeit und die Funktion der Sinnesorgane," Ebbinghaus' Zeitschr., IX, 5 and 6, Jan., 1896, pp. 342, 343.


and physiological, primary and secondary pheno ja. The other class includes the explanatory" theories, with stronger emphasis on the psychological aspect of attention. Naturally, these two principles of classification intersect, and no theory is merely descriptive or explanatory, physiological or psychological. But the distinction is a matter of convenience in the present discussion, and it also expresses a real difference in the general tendency of the theorists that largely accounts for the great dissimilarity in their treatment of the question.

The present chapter takes up the more exclusively descriptive and physiological theories of attention, recognizing as its three important types the sensory, motor, and sensori-motor theories. Any ambiguity in the meaning of these terms will be cleared away as we take up in detail the several types. I. Theories of attention as motor. We turn first to the motor theory, a theory which holds that attention is primarily a term covering a group or series of motor changes; processes preceding or following these changes are not an essential part of attention itself.


As the most complete presentation of a motor theory, Ribot's volume on "The Psychology of Attention" demands careful consideration. This work, however, is so well known that we need attempt no review of the discussion as a whole. We shall merely refer briefly to passages that state Ribot's position on certain contested points. After a detailed description of the "motor mechanism" and "muscular accompaniments" of attention, he definitely affirms that "these motor manifestations, with the state of consciousness which is their subjective side, are attention." They are its constitutive elements." And again, in speaking of voluntary attention, and of the nature of will, he maintains that “our only positive conception of will" is our idea of the action of the voluntary muscles. 2 He recognizes the intimate association between the power of attention and the frontal lobes3; but the correlation offers no obstacle to his theory, since he also regards the frontal lobes as the physiological organ for the regulation of the motor centres. He calls attention to three large groups of muscular concomitants1 : (1) Vaso-motor phenomena, including both peripheral and central hyperæmia; (2) Respiratory movements; (3) "Expressive" movements of other muscles of the body. Under

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