What does a double dissociation demonstrate about cognitive modules?

• A. That separate brain modules can support different cognitive functions
• B. That a single brain region controls all cognitive functions
• C. That cognitive functions are not localized in the brain
• D. That impairments cannot reveal brain structure relationships

Answer: (A)

Double dissociation shows that different cognitive abilities rely on distinct neural substrates, meaning separate brain modules can support different functions. In the classic pattern, one person has trouble with function A but not function B, while another person has trouble with function B but not function A. This independence indicates that A and B depend on different brain areas, supporting the idea of modular, localized cognitive processes. It’s stronger evidence for distinct neural systems than a single dissociation, and it rules out the notion that a single region underlies all functions.