178 RESPONSE IN THE LIVING AND NON-LIVING 
retina. The recurrent after-image is very distinct at 
the beginning and becomes fainter at each repetition ; 
a time comes when it is difficult to tell whether the 
image seen is the objective after-effect due to strain 
or merely an effect of ‘memory. In fact there 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 recur- 
rence. 
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 
erouped 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. ’! 
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 im- 
pression 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 
' E. W. Scripture, The New Psychology, p. 101. 
