Note 55 — Chapter XVIII

The differences noted by Fechner between after-images and images of imagination proper are as follows:

After Images.Imagination-images.

Feel coercive;Feel subject to our spontaneity;

Seem unsubstantial, vaporous;Have, as it were, more body;

Are sharp in outline;Are blurred;

Are bright;Are darker than even the darkest

black of the after-images;

Are almost colorless;Have lively coloration;

Are continuously enduring;Incessantly disappear, and have to

be renewed by an effort of will.

At last even this fails to revive them.

Cannot be voluntarily changed.Can be exchanged at will for others.

Are exact copies of originals.Cannot violate the necessary laws of

appearance of their originals—e.g.,

a man cannot be imagined from

in front and behind at once. The

imagination must walk round him,

so to speak;

Are more easily got with shut thanAre more easily had with open than

with open eyes;with shut eyes;

Seem to move when the head or eyesNeed not follow movements of head

move;or eyes.

The field within which they appearThe field is extensive in three

(with closed eyes) is dark, contracted,dimensions, and objects can be

flat, close to the eyes, inimagined in it above or behind

front, and the images have noalmost as easily as in front.

perspective;

The attention seems directed forwards In imagining, the attention feels as

towards the sense-organ, inif drawn backwards towards the

observing after-images.brain.

Finally, Fechner speaks of the impossibility of attending to both after-images and imagination-images at once, even when they are of the same object and might be expected to combine. All these differences are true of Fechner; but many of them would be untrue of other persons. I quote them as a type of observation which any reader with sufficient patience may repeat. To them may be added, as a universal proposition, that after-images seem larger if we project them on a distant screen, and smaller if we project them on a near one, whilst no such change takes place in mental pictures.