Why don’t they? Because we 
continue to perceive the 
orientation of these figures in 
the same way with the head 
(and eyes) tilted as with the 
head upright. Orientation 
constancy is achieved. Thus, 
the sides of the square appear to 
be horizontal and vertical no 
matter what the orientation of 
their retinal images. Similarly, 
the sides of the diamond appear 
to be oblique even with the 
head tilted. Only a change in 
perceived orientation affects 
perceived shape. In the case of 
the map of Europe, because the 
naive observer does not know it 
is disoriented, entirely 
different regions appear to be at 
the top, bottom, and sides than 
those that constitute the 
north, south, east, and west of 
the continent. Of course, once 
we know about disorientation, 
as with the map or the square 
and diamond, we can rotate a 
figure in imagination and thus 
overcome any effect of 
disorientation. For that reason, 
it is generally important in 
experiments on this issue to be 
sure that the observer does not 
know about the change of 
orientation.