In the second place doing more than one thing at a time does not imply attending to more than one thing at a time.  An activity which is habitual or mechanical does not need attention, but can be carried on by the control exercised by the fringe of consciousness.  Attention may be needed to start the activity or if a difficulty of any kind should arise, but that is all.  For the rest of the time it can be devoted to anything else.  The great speed with which attention can flash from one thing to another and back again must be taken into consideration in all this discussion.  So far as attention goes, one can do as many things at a time as he can make mechanical plus one unfamiliar one.  Thus a woman can rock the baby’s cradle, croon a lullaby, knit, and at the same time be thinking of illustrations for her paper at the Woman’s Club, because only one of these activities needs attention.  When no one of the activities is automatic and the individual must depend on the rapid change of attention from one to the other to keep them going, the results obtained are likely to be poor and the fatigue is great.  The attempt to take notes while listening to a lecture is of this order, and hence the unsatisfactoriness of the results.

The third fact which helps to explain the apparent contradiction under discussion is closely related to this one.  It is possible when engaged with one object to have several questions or topics close by in the fringe of consciousness so that one or the other may flash to the focal point as the development of the train of thought demands.  The individual is apparently considering many questions at the same time, when in reality it is the readiness of these associations plus the oscillations of attention that account for the activity.  The ability to do this sort of thing depends partly on the individual,—­some people will always be “people of one idea,”—­but training and experience increase the power.  The child who in the primary can be given only one thing to look for when he goes on his excursion may grow into the youth who can carry half a dozen different questions in his mind to which he is looking for answers.

By concentration of attention is meant the depth of the attention, and this is measured by the ease with which a person’s attention can be called off the topic with which he is concerned.  The concentration may be so great that the individual is oblivious to all that goes on about him.  He may forget engagements and meals because of his absorption.  Sometimes even physical pain is not strong enough to distract attention.  On the other hand, the concentration may be so slight that every passing sense impression, every irrelevant association called up by the topic, takes the attention away from the subject.  The depth of concentration depends upon four factors.  Certain mental and physical conditions have a great deal to do with the concentration of attention, and these will be discussed later.  Individual differences