Memory is stored by means of three memory systems: sensory memory, short‐term memory, and long‐term memory.
Sensory memory. Sensory memory preserves incoming sensory information (in its original sensory form) for only a fraction of a second. (A visual memory trace is called an icon; an auditory memory trace is called an echo.) Sensory memory extends the duration of the perception of stimuli long enough that they can be recognized, transformed (encoded), and relayed to conscious awareness.
Short‐term memory. Short‐term memory (STM) has a limited duration (15 to 30 seconds) and a limited capacity, believed to be about seven pieces of information. (In his 1956 study, George Miller spoke of the magical number of seven, plus or minus two.) It is thought that STM can be increased by using a tactic called maintenance rehearsal (rote recital of stored information).
Long‐term memory. Long‐term memory (LTM) has an unlimited capacity and a very long duration; it is virtually limitless. Repetition and elaborative rehearsal (manipulation of information by giving it meaning) are helpful techniques in storing information in LTM.
Endel Tulving divided LTM into
procedural memory: retention of stimulus‐response associations and patterns of procedural responses (such as skipping rope and riding a bicycle)
episodic memory: memories of life events or experiences
semantic memory: knowledge of words, symbols, or concepts and the rules for their manipulation or usage, such as in a language
Researchers have also identified another type of LTM, metamemory, which is knowledge of how memory systems work and how to use them in retrieving stored information.
The permanence of LTM is supported by such phenomena as flashbulb memory, the consistent and detailed recollection of a significant occurrence. For example, many Americans still remember what they were doing when Pearl Harbor was attacked in World War II.
Primacy and recency effects are phenomena also associated with LTM.
Recall of information is enhanced when individuals have no information stored in STM and their attention to new stimuli is at its peak (a situation known as the primacy effect), as happens, for example, in more easily recalling words presented at the beginning of a list
Recall of the most recently presented information is also enhanced (a situation known as the recency effect), as happens, for example, in more easily recalling the words presented at the end of a list.
The plot of the likelihood of recalling items from a list is illustrated in the U‐shaped curve (known as the serial position curve) in Figure .