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 also account for the presence or
absence of power of concentration--some people concentrate naturally,
others never get very deeply into any topic. Maturity is another factor
that is influential. A little child cannot have great concentration,
simply because he has not had experience enough to give him many
associations with which to work. His attention is easily distracted.