The functional mechanisms and the neural correlates of visual mental imagery (the faculty whereby we can use our "mind's eye" to visualize objects in their absence) are at the centre of a lively debate in cognitive neuroscience. Neurocognitive models have proposed a functional equivalence between visual perception and visual mental imagery, which would be subserved by common neural substrates, such as the retinotopic areas in the occipital lobe. However, brain-damaged patients may demonstrate either impaired imagery and preserved perception, such as the classical Charcot and Bernard case and the patients described by Moro et al. (2008, this issue), or the opposite pattern of performance, consisting of preserved imagery and impaired perception. This double dissociation provides a strong challenge to models postulating a functional and anatomical equivalence of perception and imagery, and suggests that these functions have partly distinct neural correlates.