centers. It is probable, therefore, that a given degree of intensity of each particular sense-quality involves as an element in its conscious value a motor ingredient–be it in part an element of consciousness from the potential condition of the motor centers themselves, or in whole from the kinaesthetic centers. The distinction between sensory and motor consciousness is largely logical: all consciousness is both. Every sensation reverberates outwards in the muscles and this muscular resonance reacts upon the sensory factor. It is clear that the largest amount of the motor ‘ingredient’ attaches to the most intense sensation. Now we also know that the exercise of attention involves a large amount of motor innervation; its constant and necessary accompaniments are motor. Consequently the rising tide of motor incitation due to the rising intensity of sensation is at once an increasing relative stimulus to the attention.
On the other hand, the ordinary opinion is true, that the idea of a movement is already the beginning of that movement. In the light of this principle it is easy to see that, when I turn my attention to a sensation, I in so far start into more vigorous existence the motor ingredients of that sensation. This in turn brings out more intensely the sensory ingredients–and the second aspect of this ‘reasoning in a circle’ is made clear.
To put the matter in a nutshell–just in as far as the motor ingredient is large, that is, in as far as the sensory ingredient is intense, just to this degree will the direction of the attention be secured, on the one hand, and both the ingredients intensified by this act of attention on the other hand. The two facts, therefore, that intensity draws attention and attention increases intensity may be stated in terms of a single principle which I venture to call the “law of sensori-motor association,” i. e., every sensational state is a complex of sensor and motor elements, and any influence which strengthens the one, tends to strengthen the other also.
The reflex attention which follows upon increased intensity of sensory excitation is, therefore, the Nachklang of revived motor associates; and the increased intensity which follows
