A very important principle is 
implicit in the foregoing 
discussion. When experience 
affects perception, it does not 
do so by molding the stimulus to 
conform to how things were 
seen in the past. It is not 
entirely a top-down process. 
Rather, in the cases we 
considered, such as the 
perception of fragmented 
figures, something was first 
perceived bottom-up, on the 
basis of certain principles of 
organization and without 
recourse to experience. Once 
that initial perception 
occurred, if what was seen was 
similar in some respect to 
objects seen in the past, those 
memories were accessed and 
they played a role in the 
further processing of the 
stimulus input. A useful term to 
characterize effects of this 
kind is enrichment. The 
perception is enriched by, 
though not entirely determined 
by, memories of earlier 
perceptual experience. Another 
way of describing these effects 
is to divide up the processing of 
the stimulus into stages. In the 
first stage, the stimulus is 
organized in accordance with 
various principles such as the 
Gestalt psychologists uncovered 
and the principles of uniform 
connectedness described 
earlier. In a further stage, the 
shape of units that are 
segregated and organized as the 
figure is described. In many 
cases, the process ends there, 
because the observer does not 
know that an alternative exists 
and is not searching for one. 
But if a search does take place, 
or if the organized stimulus is 
sufficiently similar to certain 
stored memories, then a final 
stage occurs. In this stage, the 
memory content is accessed 
and is woven into the final 
percept so as to enrich it.