suggestions of other and related impressions.

It follows from all that has been just said that our minds are never in
exactly the same state of readiness with respect to a particular process
of perceptional interpretation. Sometimes the meaning of an impression
flashes on us at once, and the stage of preperception becomes
evanescent. At other times the same impression will fail for an
appreciable interval to divulge its meaning. These differences are, no
doubt, due in part to variations in the state of attention at the
moment; but they depend as well on fluctuations in the degree of the
mind's readiness to look at the impression in the required way.

In order to complete this slight analysis of perception, we must look
for a moment at its physical side, that is to say, at the nervous
actions which are known or supposed with some degree of probability to
accompany it.

The production of the sensation is known to depend on a certain external
process, namely, the action of some stimulus, as light, on the
sense-organ, which stimulus has its point of departure in the object,
such as it is conceived by physical science. The sensation arises when
the nervous process is transmitted through the nerves to the conscious
centre, often spoken of as the sensorium, the exact seat of which is
still a matter of some debate.

The intensification of the sensation by the reaction of attention is
supposed to depend on some reinforcement of the nervous excitation in
the sensory centre proceeding from the motor regions, which are
hypothetically regarded as the centre of attention.[11] The
classification of the impression, again, is pretty certainly correlated