The most important of these modifications is the abbreviation of the speech process involved in thinking.  This has doubtless many forms, according to the structural or functional peculiarities of the individual mind.  The least modified form is that known as “talking to one’s self” or “thinking aloud.”  Here the speaker and the hearer are identified in a single person, who may be said to communicate with himself.  More significant is the still further abbreviated form in which the sounds of speech are not articulated at all.  To this belong all the varieties of silent speech and of normal thinking.  The auditory centers alone may be excited; or the impulse to linguistic expression may be communicated as well to the motor nerves that communicate with the organs of speech but be inhibited either in the muscles of these organs or at some point in the motor nerves themselves; or, possibly, the auditory centers may be only slightly, if at all, affected, the speech process manifesting itself directly in the motor sphere.  There must be still other types of abbreviation.  How common is the excitation of the motor nerves in silent speech, in which no audible or visible articulations result, is shown by the frequent experience of fatigue in the speech organs, particularly in the larynx, after unusually stimulating reading or intensive thinking.

All the modifications so far considered are directly patterned on the typical process of normal speech.  Of very great interest and importance is the possibility of transferring the whole system of speech symbolism into other terms than those that are involved in the typical process.  This process, as we have seen, is a matter of sounds and of movements intended to produce these sounds.  The sense of vision is not brought into play.  But let us suppose that one not only hears the articulated sounds but sees the articulations themselves as they are being executed by the speaker.  Clearly, if one can only gain a sufficiently high degree of adroitness in perceiving these movements of the speech organs, the way is opened for a new type of speech symbolism—­that in which the sound is replaced by the visual image of the articulations that correspond to the sound.  This sort of system has no great value for most of us because we are already possessed of the auditory-motor system of which it is at best but an imperfect translation, not all the articulations being visible to the eye.  However, it is well known what excellent use deaf-mutes can make of “reading from the lips” as a subsidiary method of apprehending speech.  The most important of all visual speech symbolisms is, of course, that of the written or printed word, to which, on the motor side, corresponds the system of delicately adjusted movements which result in the writing or typewriting or other graphic method of recording speech.  The significant feature for our recognition in these new types of symbolism, apart from the fact that they are no longer a by-product