The fact of attention or selection must of necessity involve also inhibition or neglect.  The very fact of the selection of certain objects and qualities means the neglect of others.  This fact of neglect is at first just as mechanical as that of attention, but experiences teach us to neglect some situations which by original nature attracted attention.  From the standpoint of education what we neglect is quite as important as what is selected for attention.

The breadth of a person’s attention, i.e., the number of lines along which attention is possible, must vary with age and experience.  The younger or the more immature an individual is, the greater the number of different lines to which attention is given.  It is the little child whose attention seems omnivorous, and it is the old person for whom situations worthy of attention have narrowed down to a few lines.  This must of necessity be so, due to the interrelation of attention and neglect.  The very fact of continuing to give attention along one line means less and less ability and desire to attend along other lines.

The question as to how many things, whether objects or ideas, can be attended to at the same time, has aroused considerable discussion.  Most people think that they are attending to several things, if not to many, at the same second of consciousness.  Experiments show that if four or five unrelated objects, words, or letters be shown to adults for less than one quarter of a second, they can be apprehended, but the probability is that they are photographed, so to speak, on the eye and counted afterwards.  It is the general belief of psychologists at present that the mind attends to only one thing at a time, that only one idea or object can occupy the focal point in consciousness.

The apparent contradiction between ordinary experience and psychological experience along this line is due to three facts which are often overlooked.  In the first place, the complexity of the idea or thing that can be attended to as a unit varies tremendously.  Differences in people account for part of this variation, but training and experience account for still more.  Our ideas become more and more complex as experience and 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.