In cognitive neuropsychology, which pattern demonstrates that two cognitive functions rely on different neural substrates?

• A. Associations
• B. Dissociations
• C. Single Dissociation
• D. Double Dissociations

Answer: (D)

A double dissociation is demonstrated when one patient shows impairment in one cognitive function while another function remains intact, and a second patient shows the opposite pattern—impairment in the second function with preservation of the first. This opposite pattern across individuals indicates that the two functions rely on different neural substrates, because damage to one brain system disrupts only one function and damage to a different system disrupts only the other. It provides strong evidence that the processes are functionally and neurally separable, not dependent on a single shared resource. In contrast, a single dissociation (one function impaired, the other preserved) can be explained by various alternative factors and does not definitively prove separate substrates, and associations (co-occurring deficits) imply shared resources rather than independence.