Here is an entry on the Psychology of Interest (basically, about attention). It is a treatment of Herbart's doctrine on apperception; we know that Charlotte Mason, like the Catholic Encyclopedia authors, was critical of some of Herbart's thinking. See the CE Herbart and Herbartianism.
There is also an article about the Will which includes some discussion of attention. I'm bolding the parts that especially seem to relate to this discussion about habits and the role attention plays in them.
an act of will is the usual condition of attention and of all sustained application of the cognitive faculties.
St. Thomas teaches that will acts on the organism only through the medium of feeling, just as in cognition, the rational faculty acts upon the material of experience. .... Just as the most abstract intellectual idea has always its "outer clothing" of sense-imagery so volition, itself a spiritual act, is always embodied in a mass of feeling: on such embodiment depends its motive-value.
Thus if we analyze an act of self-control we shall find that it consists in the "checking" or "policing" of one tendency by another, and in the act of selective attention by which an idea or ideal is made dynamic, becomes an idée-force, and triumphs over its neglected rivals. Hence control of attention is the vital point in the education of the will, for will is simply reason in act,
As we have said, control of attention is the vital point in the education of will. In the beginning, the child is entirely the creature of impulse. It is completely engrossed for the time by each successive impression. It exhibits plenty of spontaneity and random action but the direction of these is determined by the liveliest attraction of the moment.Finally, a bit on Habit and its relation to attention.
As experience extends, rival tendencies and conflicting motives come more and more into play, and the reflective power of the rational faculty begins to waken into existence. The recollection of the results of past experience rises up to check present impulses.
As reason develops, the faculty of reflective comparison grows in clearness and strength, and instead of there being a mere struggle between two or more motives or impulses, there gradually emerges a judicial power of valuing or weighing those motives, with the ability of detaining one or other for a longer or shorter period, in the focus of intellectual consciousness. Here we have the beginning of selective attention.
Each exertion of reflection strengthens voluntary, as distinguished from merely spontaneous, attention. The child becomes more and more able to attend to the abstract or intellectual representation, in preference to urgent present feeling which seeks to express itself in immediate action. This is furthered by human intercourse, injunctions from parents and others in regard to conduct, and the like. The power of resistance to impulse grows.
Each passing inclination, inhibited for the sake of a more durable good or more abstract motive, involves an increase in the power of self-control. The child becomes able to withstand temptation in obedience to precepts or in accordance with general principles. The power of steady adhesion to fixed purposes grows and, by repeated voluntary acts, habits are formed which in the aggregate constitute formed character.
Daily experience shows that the repetition of actions or reactions produces, if not always an inclination, at least an aptitude to act or react in the same manner. To say that a man is accustomed to a certain diet, climate, or exercise, that he is an habitual smoker or early-riser, that he can dance, fence, or play the piano, that he is used to certain points of view, modes of thinking, feeling, and willing, etc., signifies that owing to past experience he can do now that which formerly was impossible, do easily that which was difficult, or dispense with the effort and attention which were at first necessary.
Psychologically habit signifies the acquired facility of conscious processes. The education of the senses, association of ideas, memory, mental attitudes derived from experience and from studies general or special, the powers of attention, reflection, reasoning, insight, etc., and all these complex factors which formman's frame of mind and character, such as strength of will, weakness or obstinacy, irascibility or calmness, likes and dislikes, prejudices, and so on, are due largely to habits intentionally or unintentionally contracted. ...
Compared to the quality of the sounds to be produced, the special activity of the pianist's fingers or the singer's vocal organs is but a means to an end. Hence the musician becomes less conscious of this activity but more conscious of its result. In any case, since the energy flows naturally in the wonted direction, effort and attention are in inverse ratio to habit.
At the same time that habits grow, attention has to be paid to their dangers, and the child must not be allowed to become a mere automaton. Habits of reflection and attention, together with determination and strength of will, will enable the child to control, direct, and govern other habits