the
eyes, you turn from one object to another, the object left behind
simply retires to the background, without disappearing altogether;
and, {256} in the same way, when attention shifts from one noise to
another, the first noise does not lapse altogether but remains vaguely
heard. Or when, in thinking of a number of people, one after another
comes to mind, the first one does not go out of mind altogether when
attention moves to the next, but remains still vaguely present for a
few moments.

Laws of Attention and Laws of Reaction in General

Shifting occurs also in reflex action. Let two stimuli be acting at
once, the one calling for one reflex and the other for the opposed
reflex (as flexion and extension of the same limb), and the result is
that only one of these reactions will occur at the same time, the
other being completely inhibited; but the inhibited reflex gets its
turn shortly, provided the two stimuli continue to act, and, in fact,
the two reactions may alternate in a way that reminds us of binocular
rivalry or ambiguous figures. Three fundamental laws of reaction here
come to light.

(1) The _law of selection_: of two or more inconsistent responses to
the same situation (or complex of stimuli), only one is made at the
same time.

(2) The _law of advantage_: one of the alternative responses has an
initial advantage over the others, due to such factors as intensity
and change in the stimulus, or to habits of reaction.

(3) The _law of shifting_: the response that has the initial advantage
loses its advantage shortly, and an alternative response is made,
provided the situation remains the same.

These three laws hold good of reactions at all levels, from reflex
action to rational thinking.

The mobility of attention obeys these same laws; only, attention is
livelier and freer in its movements than reflex action or than the
shifting in rivalry. Attention is more mobile and less bound to rigid
rules.

{257}

Sustained Attention

The mobility of attention is only half the story. When we speak, for
instance, of a student as having good powers of attention, we are not
thinking of mobility but rather of the opposite.

Eye movement, which we employed before as a picture of the movement of
attention, affords also a picture of sustained attention. Remember how
the eye moves in reading. Every second it shifts, but still it keeps
to the line of print. Just so, attention keeps moving forward in the
st