Psychology: Episodic and Semantic Memory

Episodic and Semantic Memory

Both explicit and implicit memories can be subdivided further. Most, in fact, has focused on just one type of explicit memory: episodic memory. This term refers to memory for specific events, including events outside the laboratory (e.g., the event of your 10th birthday) or inside (e.g., the event of memorizing a particular story). Just as important, though, is semantic memory. This is the memory that contains knowledge not tied to any time or place—your knowledge that London is the capital of England, that water is wet, that people become annoyed if you insult them. (Note that some information in semantic memory is concerned with semantics—including your memory for what the word special means, or what the opposite of hot is. Much of the information in this memory, however, is not specifically tied to semantics, and so some authors prefer to call it generic memory, or generic knowledge.)

Episodic and semantic memory can be distinguished on many grounds—including the specific brain areas that support each type of memory. This distinction is reflected in the fact that some forms of brain damage disrupt episodic memory but not seman-tic, and other forms do the reverse. For example, a patient known as Gene sustained a serious head injury in a motorcycle accident; the damage affected large areas of his frontal and temporal lobes, including his left hippocampus. As a result, he can recall no events at all from any time in his life. “Even when detailed descriptions of dramatic events in his life are given to him—such as the derailment, near his house, of a train carrying lethal chemicals that required 240,000 people to evacuate their homes for a week,” Gene remembers nothing of this or any other event. But he does remember some things. He remembers that he owned two motorcycles and a car, he knows that his fam-ily has a summer cottage where he spent many weekends, and he recalls the names of classmates in a school photograph (D. Schacter, 1996). In short, Gene’s episodic mem-ory is massively disrupted, but his memory for generic information is largely intact.

Other patients show the reverse pattern. One woman, for example, suffered damage to the front portion of her temporal lobes as a result of encephalitis. As a consequence, she has lost her memory of many common words, important historical events, famous people, and even the fundamental traits of animate and inanimate objects. “However, when asked about her wedding and honeymoon, her father’s illness and death, or other specific past episodes, she readily produced detailed and accurate recollections”.

Data like these make it clear that we need to distinguish between semantic and episodic memory. But these categories can themselves be subdivided. For example, peo-ple who have suffered brain damage sometimes lose the ability to name certain objects, or to answer simple questions about these objects (e.g., “Does a whale have legs?”). Often the problem is quite specific—and so some patients lose the ability to name liv-ing things but not nonliving things; other patients show the reverse pattern (Mahon & Caramazza, 2009). Indeed, sometimes the symptoms caused by brain damage are even more fine-grained: Some patients lose the ability to answer questions about fruits and vegetables, but they’re still able to answer questions about other objects (living or non-living). These data suggest that separate brain systems are responsible for different types of knowledge—and so damage to a particular brain area disrupts one type of knowledge but not others.