Double dissociations have been used to support specificity of mental functions (Coltheart, 1985; Crowder, 1972; Shallice, 1988; Tulving, 1983; Vallar, 1999). Simple dissociations arise when a brain-damaged patient is impaired on one of two tasks hypothesised to rely on separate functions. Simple dissociations do not necessarily imply functional independence as the result may be due to a difference in task difficulty. A double dissociation is formed if a second patient shows a selective deficit in the second task, thereby controlling for task difficulty. Double dissociations are commonly interpreted as signifying a partition of systems (Gabrieli, Fleischman, Keane, Reminger, & Morell, 1995; Nyberg & Tulving, 1996), modules (Coltheart, 2001; Coltheart & Davies, 2003; Peretz & Morais, 1989), or processes (Roediger, Weldon, & Challis, 1989).