Perception, Knowledge, and 
Past Experience
The dark gray rock of the moon 
will always look highly 
luminous to us when seen in 
the dark night sky, whether or 
not we are conscious of its true 
reflectance.

Beginning students of 
perception soon learn that 
what we perceive is 
independent of what we know 
about the objects and events in 
the scene. Illusions do not 
disappear or diminish simply 
because we know they are 
illusions. Conversely, 
achieving veridicality is not 
based on knowing what is there 
in the world. An airplane high 
in the sky looks small despite 
our knowledge of its large size, 
whereas an unfamiliar object 
on the distant ground will 
generally be seen in its true 
size despite our lack of 
knowledge of what it is. A 
single black surface will never 
look black when only it is 
illuminated in a dark surround,
no matter how often we are
allowed to see that it is black by 
turning on the room lights. The 
dark gray rock of the moon will 
always look highly luminous to 
us when seen in the dark night 
sky, whether or not we are 
conscious of its true 
reflectance.

    Virtually every phenomenon 
discussed in this text 
illustrates the autonomy of 
perception from cognitive 
processing on a conceptual or 
linguistic level. We can only 
speculate about the reasons for 
this independence. But one of 
them surely is that perception 
is stimulus bound. By its very 
definition, perception is based 
upon—–even if not entirely 
determined by—–the stimulus. 
Therefore, if a particular 
stimulus pattern falls upon the 
retina—–a triangle, for 
example—–it stands to reason 
that the perception will in 
some sense conform to it—–in 
this case, to a triangular 
configuration—–even if we find 
out that the three contours 
derive from object contours 
that are in entirely different 
planes in the world or from 
contours that are curvilinear 
but happen to be viewed head-
on. Or, to give another example, 
if a stimulus cue informs us 
that one object is behind 
another, knowing it is actually 
in front will have no effect.