ATTENTION 183
the evidence is strong that the human brain is differentiated into a number of areas which are specialized centres of various forms of mental activity; and there is no question that attention involves nervous tension, nor that overtaxed brain cells respond to stimuli more slowly, with less ac curacy and with less intensity or vigour than fresh ones. We have good ground to believe that when a tract of the brain involved in any form of mental activity becomes fatigued, the intensity of the activity must be lowered, or in case of complete exhaustion, altogether stopped, until recuperation takes place. But when one centre or group of centres becomes fatigued, a flow of energy from sur rounding areas sets in to restore the equilibrium. Now, it is very probable that variations in the intensity or clear ness of the attention are only the conscious side of this process of exhaustion and recuperation. The shorter fluc tuations correspond to the rise and fall of the supply of energy in the smaller areas, and the longer fluctuation to this process in the larger areas. 1
Skillful public speaking must take cognizance of these conditions of the mental life. It is manifest that voluntary attention imposes a very heavy tax upon the nervous energy ; spontaneous attention makes a much lighter draft. This is an additional reason for seeking, whenever practicable, attention of the latter type. But in any case, and especially when the speaker can only avail himself of the voluntary attention of the hearer, the discourse should certainly adapt itself to the inevitable fluctuations of this function. Speak ing generally, the sentence should correspond to a single pulse of the attention. This is particularly true of the spoken sentence; for in reading a written sentence the reader may expend upon it two or more pulses of attention, but with the spoken sentence this is hardly practicable. Likewise we may say that the paragraph, or in spoken dis course, the development of a single point or brief phase of
1 For an interesting discussion of this whole subject, see "The Fluctuation of the Attention," by Hylan, Psychological Review series of Monograph Supplements, Vol. II, No. 2.
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