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Varieties of Secondary Memory

Atkinson and Shiffrin depicted long-term memory as one box in the mid-1960s. Since then, psychologists have found several different systems that contribute to secondary or long-term memory. The relevant distinctions are often conveyed in pairs of opposites:

—episodic vs. semantic memory (memory for single events vs. information extracted from repeated events)

—declarative vs. procedural memory (memory for facts vs. processes)

—implicit vs. explicit (memory which is automatically retrieved vs. memory which requires a a conscious act of retrieval)

These are distinct forms of memory. In some cases they are based in distinct biological systems within the brain. For example, procedural memory seems to require the cerebellum, the "small brain" at the back of the skull. Episodic memory seems to require the hippocampus and temporal lobes. Implicit memory is embedded in many brain systems and acts semi-independently, while explicit memory requires some coordination by the executive processes of the frontal lobes.

What are different names for episodic memory?

Consider the first distinction: between single events and repeated events. Memory researcher Endel Tulving (1972) coined the term episodic memory for memory of single episodes of your life. Episodic memory is sometimes called single-event memory because it is a memory for a distinct experience at a particular time and place. It can also be called autobiographical memory. It seems to have a tag on it that says, "This was an event in my life."

Episodic memory can be entirely wiped out by brain damage to the hippocampal/temporal lobe area. Clive Wearing is a famous patient who lost his event memory after an infection of the brain. He does not remember a moment of his life, before or after the encephalitis. As soon as information leaves his working memory, it is forgotten, and he always feels like he is "just waking up" or "just becoming conscious for the first time."

What happens in cases of dissociative amnesia?

Episodic memory can also be lost independently of other forms of memory in certain cases of dissociative amnesia. Dissociative amnesia is the classic amnesia syndrome seen in old-time movies. Some people who experience a psychological trauma react by forgetting who they are. They forget personal information—memory linked to their identity. In other words, they lose episodic memory. However, they retain memory for factual knowledge. Such a person could tell you that 2+2 equals 4. The same is true of Clive Waring, who has disattached knowledge like the fact that England returned Hong Kong to the Chinese (something that happened after his brain damage). Clive's problem, being due to brain damage, is irreversible. Most episodes of dissociative amnesia caused by psychological trauma are reversible.

Why has the name "semantic memory" gone out of favor with some psychologists?

Knowledge like "2 + 2 = 4" or "Hong Kong is part of China" is encountered repeatedly. This distinguishes such knowledge from personal event knowledge, which represents a unique and one-time event. Tulving's term for non-episodic memory, semantic memory, has gone out of favor with some psychologists, because "semantic" means "related to word meanings" and this type of memory involves more than words. Therefore researchers now distinguish between memory for single events (episodic memory, which requires the brain area called the hippocampus) and memory for general knowledge abstracted from repeated events (declarative and procedural memory, which require other brain areas).

What problem did N.T. have?

Tulving studied a patient known as N.T. who, like Clive Waring, lost all his episodic memory. In N.T.'s case, the damage was caused by a stroke. N.T. was capable of learning new word meanings, skills, and facts. He lost only his memory for the individual events of his life. Note that non-episodic memory in this case involved both skills (procedural memory) and facts (declarative memory).

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