A satisfactory definition of the various modes of vocal action can now be given. The correct vocal action is the natural operation of the vocal organs; the voice normally obeys the commands of the ear. An incorrect vocal action occurs when the throat is stiffened by the involuntary contraction of the muscles of the vocal mechanism. This definition of the vocal action does not solve the problem of tone-production. It is still to be determined how the involuntary contraction of the throat muscles is caused. CHAPTER II THE CAUSES OF THROAT STIFFNESS AND OF INCORRECT VOCAL ACTION Involuntary contractions of the voluntary muscles can occur only as reflex actions. If the muscles of the vocal organs are subject to involuntary contractions, the causes of these contractions must be sought through an investigation of the subject of reflex actions. Reflex actions are of several kinds; of these the simplest type, and the one most easily studied, is the muscular contraction due to the excitation of the sensory nerve endings located in the skin. Thus when the sole of the foot of a sleeping person is tickled, the leg is at first drawn up and then violently kicked out. An exhaustive discussion of the physiological and psychological features of reflex action is not called for here; a sufficient understanding of the subject may safely be assumed to be possessed by the reader. Involuntary muscular contractions often occur as reflex actions without any direct or tactual irritation of the sensory nerve endings. Several examples of this form of reflex action are now to be considered. These actions will be seen to be matters of such common experience as to call for no special proof. They are the following: (_a_) Reflex actions performed under the influence of sensory impressions other than those of touch or muscular sense. (_b_) Involuntary muscular contractions due to nervousness. (_c_) Contractions of the muscles of certain members, caused by the turning of the attention specially to the members. (_d_) Involuntary contractions of muscles, accompanying the exertion of other associated and antagonist muscles, and due to the radiation of nerve impulse. (_a_) _Reflex Actions due to Sensory Impressions other than those of Touch or Muscular Sense_ A wide range of movements is included under this heading. Of these it is necessary to mention only a few, such as the sudden start on the hearing of an unexpected noise, the instinctive movement of dodging to escape an approaching missile, and the raising of the arm to ward off an expected blow. Actions of a somewhat similar character normally occur in which it is not easy to point to the excitation of any sense or senses. These include the instinctive cowering attitude of fear, the play of facial expression caused by sentiment and emotion, etc. (_b_) _Involuntary Actions due to Nervousness_