According to ED. VON HARTMANN, Attention is either spontaneous or
reflex. The voluntary fixing our mind upon, or choosing an idea,
image, or subject, is _spontaneous attention_, but when the idea for
some reason impresses itself upon us then we have enforced, or _reflex
attention_. That is simply to say, there is active or passive
observation--the things which we seek or which come to us unsought.
And the "seeking for," or spontaneous action can be materially aided
and made persevering, if before we begin the search or set about
devoting Attention to anything, we pause, as it were, to determine or
resolve that we _will_ be thorough, and not leave off until we shall
have mastered it. For strange as it may seem, the doing this actually
has in most cases a positive, and very often a remarkable result, as
the reader may very easily verify for himself. This Forethought is far
more easily awakened, or exerted, than Attention itself, but it
prepares it, just as Attention prepares Interest.

Attention is closely allied to Memory; when we would give attention to
a subject for continued consideration, we must "memorize" it, or it
will vanish. Involuntary memory excited by different causes often
compels us to attend to many subjects whether we will or not. Everyone
has been haunted with images or ideas even unto being tormented by
them; there are many instances in which the Imagination has given them
objective form, and they have appeared visibly to the patient. These
haunting ideas, disagreeable repetitions or obstinate continuances,
assume an incredible variety of forms, and enter in many strange ways
into life. Monomania or the being possessed with one idea to the
exclusion of others, is a form of overstrained attention, sustained by
memory. It is _enforced_.