Page:The New International Encyclopædia 1st ed. v. 02.djvu/259

steadily in consciousness. If, on the other hand, the attention fluctuates, there will be moments when the gray and the hiss undergo a loss of clearness; and since they are, at the best, only just visible and just audible, the loss of clearness will mean a loss of existence: the gray will merge into the white and the hiss will cease to he heard. The second alternative is realized. The gray appears, and is washed out, and ap- pears again, at intervals of a few seconds; and the sound of the flame is heard, ceases, and then is heard again, in precisely the same way. The average length of the single 'pulse' of attention — the time counted from appearance to reappear- ance, or from disappearance to the next follow- ing disappearance of the stimulus — is five or six seconds. (b) The range of attention is most easily determined by the aid of visual stimuli. A number of letters, e.g. chosen at haphazard and set in a space that falls well within the ob- server's range of vision, are shown upon a screen for so short a time that wandering or roving of the attention from letter to letter is prevented. Under such conditions it is possible to grasp, by a single 'act' of attention, some five or six sepa- rate impressions. If short and familiar words are exhibited, in place of the mixed letters, some four or five of these will be grasped by the atten- tive consciousness. The number of discriminable ideas present at the same time with the four or nve focal ideas in the background of conscious- ness cannot, in the nature of things, be accurate- ly ascertained. (See Consciousness.)

The physical basis ot the intermittence of attention may be sought in the mode of functioning of the nerve-cell. The cell is said by physiologists to 'discharge.' We may interpret the term literally, for the nerve-cell is a storehouse or reservoir of nervous energy, and gives off this energy when the appropriate stimulus arrives, not continuously or piecemeal, but all at once, by way of explosion. Now an exploded cell must be recharged before it can function again, and the period of recharging apparently corresponds to the periods of disappearance of the pale gray and the faint hiss of which we have spoken. In explanation of the limited range of attention, we can say no more than that the small group of ideas comprised within it represent the available energy of the total cortex, as directed upon the given stimuli; the fact of limitation must be considered as an ultimate fact of the psycho-physical organization.

a represents an inattentive, and b, an attentive consciousness. In a are five ideas, all proceeding at equal levels. In b, the third idea is being attended to, and its wave length is increased, while the wave lengths of the others are depressed.

(2) We pass to the question of the various forms or kinds of attention. It may be said at once that there is but one attention. The essential features of the attentive state are, always and everywhere, as we have just described them. The differences between one bit of attentive experience and another are differences, first, in the determination or motivation of attention; and secondly, in the sense-processes which are set up by the attentive attitude. We deal now with the determinants of attention. (a) There are certain stimuli and forms of stimuli which command our full and immediate attention. Thus, very intensive stimuli compel us to pay regard to them. However interesting our novel may be, we shall start up, automatically and unhesitatingly, if a gun is fired outside of the window of our room. We have no choice but to attend to the sudden, loud sound. Intensity, suddenness, novelty, movement — all these properties of stimuli are attention-compelling. The moving bird that flits across the landscape; the moving voice that rises and falls to the more stationary orchestral accompaniment; the moving stimulus in the field of touch — these things hold our attention whether we will or no. There is good physiological reason for the power of such stimuli, inasmuch as all alike are fitted by their attention-compelling properties to exert a marked influence upon nervous substance. There is also good biological reason for their efficacy. An animal so constituted as to leave unnoticed the sudden and novel and moving features of its surroundings would soon pay the forfeit of its neglect with life. This 'primary passive attention,' or 'involuntary attention,' is, then, a heritage from earlier and less secure conditions of living. Our ancestors could not have survived without it, and it persists, ingrained in our nervous constitution, even though in civilized communities the reason for its continuance has largely disappeared. (b) This single and masterful determination of attention, however, cannot persist unchanged. The organism grows in complexity: its sense-organs multiply. And this means that there may be rival claimants, so to speak, for the favor of attention. Suppose that eye and ear are simultaneously called upon — the eye by a moving object in one direction, the ear by an intensive sound proceeding from a different quarter. There will, evidently, be doubt and conflict, of a piece with the doubt and conflict that are set up by the occurrence of a number of potential motives to selective action. (See Action.) Furthermore, as the retrospective functions develop, and the mind is stocked with memories, each of the would-be determinants of attention will form a centre of association; ideas will cluster round it, some to help and some to hinder. So we reach the stage of 'active' or 'voluntary attention' — the sort of attention that we give to a new game of skill that we are learning or a new problem that we are seeking to solve. Here the attention is divided; no single set of ideas receives a full measure of it: there is effort and struggle and misdirection of energy. Again, however, attention cannot persist, unchanged, at this devel-