The chicks seemed to 
perceive the photographs 
exactly as we would. Those 
trained to peck at mounds 
pecked at the photograph with 
the shadow at the bottom. Those 
trained to peck at depressions 
pecked at the photograph with 
the shadow at the top. Thus, at 
least one pictorial cue is 
effective in an animal. Rarely 
do animals lower than primates 
react to pictures, probably 
because they respond directly 
to the picture as a two-
dimensional surface rather 
than to what the contours on 
the surface represent 
symbolically. But what is most 
astounding about these results 
is that half of the chicks in 
each group were raised from the 
time of hatching in cages 
where the light always came 
from below. Thus, for these 
chicks, if any learning about 
the significance of shadow 
occurred, it would be the 
opposite of what would be 
learned under natural 
conditions. But whether the 
chicks were reared with light 
from above or from below, the 
result was the same. Shadow at 
the top cued depressions, and 
shadow at the bottom cued 
elevations. If there are no flaws 
to be found in this experiment 
and the findings can be 
confirmed, we must conclude 
that cast shadow as a cue to 
depth is innate, not learned.