Question

Explain what we mean by single and double dissociations and give an example of each.

Answer 1

In Single Dissociation localized damage affects one task but not another task or ability.  An example of "single dissociation" is a patient who cannot name an object when he or she can only see it, but can when he or she uses other senses like touching or smelling.

Double Dissociation is when two related mental processes are shown to function independently of each other. For example, Double Dissociation is speech and language comprehension. Although both processes pertain to use of language, the brain structures that control them work independently. When a part of the brain called the Broca's area is damaged, patients may still understand language but be unable to speak fluently. They know what they want to say, but are unable to express themselves.  On the other hand, when a part of the brain called Wernicke's area is damaged, patients may still speak fluently, but be unable to comprehend language. This results in properly constructed but nonsensical sentences.