The study of brain processing of mental images is a very active area of research in both cognitive psychology and neuroscience (for a good review, see Kosslyn, 1988). In this chapter we will confine our attention to a particular hypothesis dealing with the linking of perceived mental rotations of a threedimensional object (as exemplified in the pioneering work of Shepard & Metzler, 1971; Shepard & Cooper, 1982) with the sequence of internal activities in the visual cortex (brain state-space). This hypothesis was first put forth by Carlton (1988). Carlton's formalism links a path in geometrical space to a path in brain state-space. This mathematical construct bridges complex mental percepts with neurophysiological states which presumably can be measured using SQUID (superconducting quantum interference devices; Williamson, Kaufman , & Brenner, 1979), neuromagnetic imaging (Aine, George, Supek , & Maclin, 1991; Marg, 1991) or other electrophysiological (e.g., neurocognitive pattern analysis; Gevins et aI. , 1987) technologies .