 One of the main motivations for experience-content internalism is the idea that only internally individuated states can figure in psychological explanations. This mirrors one of the main motivations for internalism about the contents of other mental states. The general issue is reviewed in the entry on  externalism.  In the case of experience, philosophers have pursued this debate with respect to Marr’s computational theory of vision, one of the leading empirical theories of visual processing. The debate is over whether Marr’s theory itself posits any externally-individuated contents, or whether the contents it posits are all individuated internalistically. If Marr’s theory is correct and explanatory, and if the representational contents it posits are externally individuated, then it provides a counter-example to individualists’ claims that only internally-determined contents figure in psychological explanation. The debate thus focuses on exactly what commitments Marr’s theory makes about the individuation of perceptual content.