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Semantic memory is a form of long-term memory that stores general information about the world, as opposed to autobiographical memories or learning tied to a particular event. It is used both to retrieve and to apply knowledge in specific situations. People use semantic memory in a wide array of life contexts, from babies discovering that they can manipulate their surroundings, to students using a foundational knowledge of reading to acquire other knowledge, to adults figuring out driving directions based on the position of the setting sun.
Basic information such as the meaning of words as well as more complex reasoning skills fall into the category of semantic memory. The process starts early in life as young children add to their knowledge of the world constantly. For example, most two-year-old children can identify a cat. By the time a child is four or five, he or she likely knows that a cat has fur and that a lizard does not. Although the child may have no specific memory of learning this fact, he or she can identify from pictures which of the two animals is furry. This latter task involves not only retrieving information, but also applying it.
As is often the case in psychology, understanding the function of semantic memory can also be understood by looking at what happens when it fails to function properly. This happens most commonly with older adults, whose ability to access certain memories may lapse. In simple instances, this may involve briefly forgetting the name of the author who wrote Tom Sawyer. More complicated problems may arise from age-related problems such as Alzheimer's. Although Alzheimer's is most commonly associated with loss of personal or episodic memory, it also may effect semantic memories, especially concerning word meanings.
Furthermore, some mental health conditions may disrupt semantic memory. Disorganization in memory structures might be part of the thought-pattern difficulty experienced by some people with schizophrenia. Some researchers believe this particular type of memory disruption consists of not being unable to recall information, but of being unable to properly interpret and apply information. Mood disorders, especially bipolar disorder, may interfere with the process of forming new semantic memories or with retrieving existing memories.
Semantic memory may use information stored in several different areas of the brain, such as visual information stored in the temporal cortex and factual information stored in the frontal cortex. If everything works well, these various areas can communicate with each other. For example, a person looking at a domestic cat will be able to identify it and also recall that a domestic cat is a four-legged mammal falling into the category of felines. In the case of a stroke or traumatic brain injury, those lines of communication might break down, resulting in a failure in semantic memory. For instance, a person may then look at a domestic cat and not be able to associate what he or she sees with the other information he or she knows about cats.