familiarity build them up. Qualities which to a little child demand
separate acts of attention are with the adult merged into his perception
of the object. Just as simple words, although composed of separate
letters, are perceived as units, so with training, more complex units
may be found which can be attended to as wholes. So (to the ignorant or
the uninstructed) what is apparently attending to more than one thing at
a time may be explained by the complexity of the unit which is receiving
the attention.

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