The notion of representation figures centrally both in Descartes’ scientific theorizing about sense in humans and in his conceptual speculations about the nature of human cognition.
Descartes’ philosophical innovation in the Dioptrics is the claim that sensing in humans is a kind of representing rather than a kind of resembling. This provides the cornerstone for his attack on traditional theories of sense, and it underwrites his own position that sensing (in humans) is a kind of thinking, ascribable to the rational soul rather than to any Aristotelean sensitive soul.