SHADOW 
Shadow, particularly attached 
shadow, would seem to be the 
major determinant of perceived 
depth for distant objects.  If the 
shadow contrast were 
diminished, the faces would 
appear relatively flat and 
indistinct.

The pictorial cue based on 
shading and shadow is also a 
critical factor in depth 
perception, both in pictures 
and in everyday life. Consider a 
sculpture of uniform color, 
such as the one cut into Mt. 
Rushmore. The presidents’ 
faces appear three-dimensional 
even at distances at which all 
other cues would be 
ineffectual. Clearly it is the 
play of light and shadow that 
creates the veridical 
perception here. Primarily 
responsible is the shading that 
results from the depth within 
the object itself, referred to as 
attached shadows (or 
chiaroscuro) although cast 
shadows--the shadows that fall 
on surrounding surfaces--may 
also play a role.

    Of the two types of shadow, 
attached shadow is the more 
important in creating an 
impression of depth. Although 
we often notice cast shadows, 
there is not yet a great deal of 
experimental evidence of their 
effectiveness as a depth cue. 
Some evidence suggests that 
cast shadow is a cue to depth in 
that it helps us to construct 
mentally a plane that might not 
otherwise be perceived. In one 
recent study by Albert Yonas 
and his co-workers at the 
University of Minnesota, 
shadows from objects floating 
in the air were cast upon a 
ground plane. Without the 
shadow, the distance of the 
floating object would be more or 
less indeterminate, since it 
could be anywhere between the 
viewer and infinity, but, as a 
result of the shadow, the 
subjects were able to localize 
the object as directly above its 
shadow. Since the shadow’s 
distance was given by its 
location on the ground, the 
object’s distance was also 
thereby determined.