Double dissociation typically requires what condition?

• A. Two patients with opposite impairment patterns across two tasks
• B. A single patient with three impaired tasks
• C. No patients with dissociations are needed
• D. Only theoretical evidence without patients

Answer: (A)

Double dissociation is shown when two cognitive processes are supported by distinct neural systems, revealed by two patients with opposite impairment patterns across two tasks. In one case, the patient is impaired on Task A but can perform Task B, and in another case, the patient is impaired on Task B but can perform Task A. This opposite pattern demonstrates that the two tasks rely on separate mechanisms and brain areas, because damage to one system disrupts one task but not the other, and vice versa. Without two such opposing patterns, the independence of the two processes cannot be established. The other options don’t meet this criterion: a single case with multiple impairments doesn’t show independent systems, having no patients offers no empirical evidence, and relying only on theory lacks demonstration of dissociation.