Page:Mind (New Series) Volume 12.djvu/311

 PHYSIOLOGICAL FACTORS OF THE ATTENTION-PROCESS. 297 the sensory stimulus falls upon the auditory neurones and sets free a further quantity of neurin in paths of levels i. and ii., this overflows in part into these higher-level paths and the mental system of the idea of self -in-house apperceives the sound, converting the undiscriminated sensation of sound into the percept, a-noise-in-my-house-at-night. This is a percept that has a large affective value, for it leads directly to the excitement of the mental system that sub- serves the instinctive tendency to defence of self and belong- ings and which physiologically consists of numerous paths leading to widespread activity of both visceral and skeletal muscles. The contractions of these numerous groups of muscles determine a great influx of neurin to the afferent side of the nervous system, which influx brings about that general condition of raised tonus and widespread nervous activity which we feel as a state of emotional ex- citement. Then at last the whole nervous system is thoroughly awake ; the neurones of all levels and all parts are fully charged so that any slight stimulus will cause their discharge ; the excitation-process spreads freely from one system of upper-level paths to another, ideas as to what action must be taken flow rapidly and action follows ; cona- tion and attention are at a maximum. The conjunction and interaction of the two systems of excitement, that of the mental system of the idea of self-in- house and that directly set up by the recurring sensory stimulus is the essential condition of the culmination of the process. On the one hand, if the stimulus does not recur at this stage the whole excitement will die down, the accumu- lated charges of neurin will drain slowly away, the high degree of tonus of neurones and of muscles subsides, the viscera resume their gentle regular activity and sleep is restored. On the other hand, in the absence of the conditions that bring up the idea of self-in-my-own-house, if for example I am lying at an hotel, this idea will not arise or, if it arises, is quickly suppressed and replaced by the idea self-in-hotel, and the sound is then perceived as noise-in-hotel. This perception has no such emotional value as the other, it does not lead to any instinctive excitement of visceral and skeletal muscular systems ; hence there results no such free liberation of neurin in large groups of afferent neurones as occurs in the other case. And in the absence of this the nervous system adapts itself to the recurrent sound, i.e., the excitation-process initi- ated by it fails to propagate itself through any wide system of upper-level paths, but becomes confined to a comparatively narrow set of lower-level paths.