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| The stage theory of memory states that human memory consists of three stages: (1) the sensory register, which holds an exact image of each sensory experience for a very brief interval until it can be fully processed; (2) short-term memory, which holds information for approximately 30 seconds (information will fade from short-term memory unless the material is rehearsed; the capacity of short-term memory is 7 ± 2 items, but this can be increased by organizing the material into larger chunks); and (3) long-term memory, which indexes information and stores it primarily in terms of its meaning. Three kinds of long-term memory are procedural, episodic, and semantic. Procedural memory is memory for skills and other procedures. Episodic memory refers to memory for specific experiences that can be defined in terms of time and space, while semantic memory refers to memory for meaning. The organization of memory in long-term memory has been characterized as an associative network. One network model is called the spreading activation model. Three ways that psychologists measure memory retrieval are the recall method, the recognition method, and the relearning method. An alternative to the stage model is the levels of processing model, which views the differences between short-term and long-term memory in terms of degree rather than separate stages. Psychologists have identified four ways in which forgetting occurs: (1) decay theory, which states that forgetting occurs simply because time passes; (2) interference theory, which states that forgetting occurs because other memories interfere with retrieval (interference may occur from memories that were formed by prior learning, called proactive interference, or from memories that were formed by later learning, called retroactive interference); (3) schema theory, which holds that memory changes over time to become more consistent with our beliefs, knowledge and expectations; and (4) repression, the process by which memories that are upsetting or threatening may be forgotten. The biological basis of memory is called the memory trace or engram. A theory that has been proposed to explain the biological nature of memory is synaptic facilitation, which views learning as a change in the synapses. Amnesia is a major memory disorder. Anterograde amnesia, caused by damage in the hippocampus, is an inability to store and/or retrieve new information. Retrograde amnesia is the inability to retrieve old, long-term memories. Research suggests that eyewitness testimony and recall may be inaccurate because of biased questioning or the characteristics of the eyewitnesses. A controversial use of hypnosis to recall past memories is called hypnotic age regression. Much research has been conducted trying to improve the accuracy of eyewitness testimony. |