VI. Evidence for multiple memory systems
A. There are people who have damage to the hippocampal/
medial-temporal regions of the brain who show a pattern of anterograde
amnesia, an inability to form new, long-term declarative
memories.
1. These people often have a fully functioning working memory
and can demonstrate all forms of nondeclarative memory.2. Scientists and medical specialists have found no evidence to
suggest these people have the ability to form new episodic
memories, and yet they showed normal nondeclarative or implicit
memory. So, if shown a list such as the one described in
the episodic memory section above, they have very poor or
no conscious recollection of that list. Yet, they exhibit normal
implicit memory when tested for that (e.g., priming).
3. Famous people with amnesia include Henry Molaison (H.M.)
and Clive Wearing.
4. Other people show impairments in episodic, but not semantic
memory. Individuals with Alzheimer’s dementia show impairments
in both episodic and semantic memory.
B. Behavioral data: Dissociations across tasks
1. Dissociations are findings showing that a variable affects one
component of the memory system in a particular way but has
no effect on another component of the memory system.
a. The existence of dissociations suggests these memory
processes are mediated by different brain systems.
b. For example, there are factors that improve explicit memory
but do not improve implicit memory. In a study by
Jacoby (1983), individuals who generated words during
a study (e.g., provided an antonym for hot: _____) remembered
those words better on a later explicit recall
test than individuals who simply read those words. On an
implicit priming test, however, individuals who generated
words during study were not faster to read those words
in a later implicit naming test than individuals who read
those words. In fact, the opposite was true.
2. Factors that affect episodic tests do not always influence
semantic tests in the same way. Older adults generally show
significant impairment in episodic memory tests such as
recall, but often show no impairment (and sometimes better
performance) on semantic memory tests such as vocabulary
or world knowledge.