All these adjustments are executed as one concrete and individual act in response to the volitional impulse contained in the mental conception of the tone. The tone is conceived as a concrete whole. It is not normally broken up mentally into its four aspects of pitch, quality, vowel, and power. True, each one of these four characteristics of the tone may be separately considered by the singer. So also, to a certain extent, may the adjustments of the vocal organs be performed with special reference to one or the other characteristic of the tone. But in every case the muscular contractions are performed without direct conscious guidance. Whatever be the character of the tone mentally demanded, the vocal organs instantly adjust themselves to produce the tone. What is meant by saying that the muscular contractions are performed without conscious guidance? Does this mean that the singer is unconscious of the muscular contractions? Not at all. Muscular sense informs the singer, more or less distinctly, of the state of contraction or relaxation of the various muscles of the vocal organs. The singer always knows fairly well the condition of the various parts of the vocal mechanism. What is meant is this: The singer does not consciously direct the vocal organs to assume certain positions and conditions, and does not instruct the various muscles to contract in certain ways. The singer does not need to know, and in fact cannot know, what muscular contractions are required to produce any desired tone. Some connection exists between the organs of hearing and the vocal mechanism. That this connection has a physical basis in the nervous structure is fairly well established. "The centers for sight and for arm movements, for instance, or those of hearing and of vocal movements, have connecting pathways between them." (_Feeling and Will_, Jas. M. Baldwin, 1894.) The psychological law of tone-production is that the vocal organs adjust themselves, without conscious guidance, to produce the tones mentally conceived. In actual singing the practical application of this law is that the voice is guided by the ear.