What did Perky Prove

C. W. Perky’s (1910) experiments on mental imagery are taken by many philosophers to prove that mental imagery and seeing can be introspectively indistinguishable. As a result, they are sometimes used in support of a view I call ‘perceptualism’ about mental imagery: the idea that seeing and mental imagery are fundamentally the same kind of mental state, differing only in degree or in terms of cause. Here, I argue that close attention to the details of Perky’s experiments, their deceptive nature in particular, undermines both claims. Philosophers have been relatively incautious when reporting on Perky’s experiments and what they ‘prove’, including when referring to updated variants. This paper is a corrective.