is no line of demarcation between the two, one simply merges
into the other. That this 'memory' image is due to objective strain is
rendered evident by its recurrence.

In connection with this it is interesting to note that some of the
undoubted phenomena of memory are also recurrent. 'Certain sensations
for which there is no corresponding process outside the body are
generally grouped for convenience under this term [memory]. If the eyes
be closed and a picture be called to memory, it will be found that the
picture cannot be held, but will repeatedly disappear and appear.'[20]

The visual impressions and their recurrence often persist for a very
long time. It usually happens that owing to weariness the recurrent
images disappear; but in some instances, long after this disappearance,
they will spontaneously reappear at most unexpected moments. In one
instance the recurrence was observed in a dream, about three weeks after
the original impression was made. In connection with this, the revival
of images, on closing the eyes at night, that have been seen during the
day, is extremely interesting.

#Unconscious visual impression.#--While repeating certain experiments on
recurrent vision, the above phenomenon became prominent in an
unexpected manner. I had been intently looking at a particular window,
and obtaining the subsequent after-images by closing the eye; my
attention was concentrated on the window, and I saw nothing but the
window either as a direct or as an after effect. After this had been
repeated a number of times, I found on one occasion, after closing the
eye, that, owing to weariness of the particular portion of the retina, I
could no longer see the after-image of the window; instead of this I
however saw distinctly a circular opening closed with glass panes, and I
noticed even the jagged edges of a broken pane. I was not aware of the
existence of a circular opening higher up in the wall. The image of this
had impressed itself on the retina without my knowledge, and had
undoubtedly been producing the recurrent images which remained unnoticed
because my principal field of after-vision was filled up and my
attention directed towards the recurrent image of the window. When this
failed to appear, my field of after-vision was relatively free from
distraction, and I could not help seeing what was unnoticed before. It
thus appears that, in addition to the images impressed in the retina of
which we are conscious, th