Bisiach & Luzzatti 1978: People with hemispherical neglect in perception also have it in imagery.
There are exceptions to the perception/imagery similarity:
Servos & Goodale 1995: an Agnosic patient that could not even distinguish squares and circles in perception did well on mental imagery tasks.
Farah & Peronnet 1989: "...people differ in how fully they engage their early visual representations when generating mental images" and some people are more able to "efferently activate their visual systems than others, and that such people experience especially vivid mental imagery." [p970]
[p972] "Beginning at the retina, this processing passes through various intermediate representations in the LGN and occipital cortex that roughly preserve the spatial mapping of the retina, then culminates with relatively abstract representations of object appearance and location in temporal and parietal cortices."
Activating visual representations top down is image generation.
One can think about familiar objects without visualizing them. This suggests that imagery requires the intervention of "a seperate, attention-demanding process..."