Page:Philosophical Review Volume 2.djvu/407

. 4.] the direction of the attention is the Nachklang of revived sensory associates.

This principle also goes far to explain the relation to each other of the two so-called laws which are usually stated independently in connection with reaction-times: (1) greater intensity of stimulus diminishes the reaction-time, and (2) motor reactions are shorter than sensory reactions. Both are ready deductions from the “law of sensori-motor association.” More intense stimulation gives a shorter reaction than less intense, because it arouses more and stronger motor associates; or, put physiologically, because it has greater dynamogenic effect, and so facilitates motor discharge. This is clearest, when the signal is foreknown and the attention is consequently not drawn to it. But this means, when a particular kind of motor association is emphasized by the direct act of earlier attention. Now this is the second case–motor reaction. The motor associates are pictured, dwelt upon, emphasized beforehand, the motor centers are put into a state of high potential, the stimulus is left to discriminate itself without attention–and thus the reaction time is shortened. It is evident that in the sensory reaction, part, at least, of the dynamogenic influence of the stimulus goes into the attention (discrimination of signal); while, in the motor reaction, it all goes into the reaction, which is already prepared for, besides, by motor attention.

Applying this thought to the rise of speech and its method, we find abundant reason for the variety of types found among adults. Visual, auditory, and motor memories of words date back to early childhood, and do not arise synchronously. Visual pictures of figure arise and get comparatively fixed in childhood some months before the child begins to speak or write, as is shown by its recognition of simple figures, animals, and later letters. Its auditory images, however, date back still farther: this is seen in the very early recognition of words heard. The motor (speech and writing) memories, on the