PHYSIOLOGICAL FACTORS OF THE ATTENTION-PROCESS. 291 further effects. With the dawning self-consciousness comes a sense of my surroundings and the ' There is a noise ' passes into 'What is that noise?' with the stronger dis- agreeable affective tone, 'That ought not to be'. This implies a distinctly more attentive state than that of the preceding stage, and this is expressed by the greater tension of the muscles generally, perhaps also a raising of the head from the pillow and a setting of the muscles of ear, head and neck. Again the noise is repeated, and now comes like a flash, ' There's some one in the house '. The coming of this idea results in an immediate increase of Attention, clearly expressed in motor terms by my sitting up in bed with all the body set to an intense listening, while visual ideas of the spatial relations of the house become vivid as I try to refer the sound to this or that part, and at the same time my more rapid breathing and pulse indicate a considerable in- crease in the degree of emotional excitement. Once more I hear the noise and, listening intently, with all my muscles tense, with deep and hurried respirations and thumping heart, I rise to open the door as softly as possible and take measures for the defence of my property. Attention has reached the highest degree that this stimulus, in this particular set of circumstances, is capable of arousing. In this experience, which with slight variations must be more or less familar to almost all householders, we have a good illustration of the fact that the degree of Attention, that can be aroused by any object or stimulus, is to a large extent dependent upon the degree of awakeness at the moment of the incidence of the stimulus. For we have a series of states of successively higher degrees of Attention brought about by the repetition of one simple sensory stimulus, each incidence of the stimulus arousing a higher degree of Attention than its predecessor, because that predecessor has brought the mind to a more fully waking state. We see further that the increase of attentive activity is brought about by the co-operation of the four factors that are the chief, if not the sole factors, in all such cases of rising Attention, namely : 1. Sensory stimuli, which in the above case, although not violent, are nevertheless potent in arousing Attention in virtue of their relative novelty and of the contrast between them and the intervening periods of silence. 2. Muscular adjustment, beginning in this case with vague aimless movements and culminating in complex strenuous activity of pretty well the whole muscular system, directed .and co-ordinated to a particular end.
