Locke’s Representative Realism
 The 17th Century philosopher John Locke was the most prominent advocate of this theory.
 He asserted that there are primary qualities which are "explanatorily basic" in that they can be referred to as the explanation for other qualities or phenomena without requiring explanation themselves (similar to the concept of Foundationalism), and that these qualities are distinct in that our sensory experience of them resembles them in reality.
 Secondary qualities (including colour, smell and taste) are those which one's experience does not directly resemble.

Criticisms of Representationalism
 Skeptics object that, since we only have knowledge of the representations of our perceptions, how is it possible to know for sure that they resemble in any significant way the objects to which they are supposed to correspond?
 If perception involves "pictures in your head", then who is it that is viewing those pictures (a homunculus?), and would it not result in an infinite regress of observers within observers?
 How can this theory be consistent with neurophysiology which presents the brain as an assembly of billions of discrete quasi-independent local processors interconnected in a massively parallel network?
 Even if there is a spatial representation in the brain, why (and how) should it be conscious of itself?