Short-Term Memory

Characteristics

Short-term memory has some important characteristics. First, short-term memory is limited in duration. Information in short-term memory is kept for only a short amount of time before it is transferred to long-term memory or it decays. Generally, short-term memory retains information for only 15–30 seconds. In order to keep information longer, information must be rehearsed frequently. With rehearsal, the information will reenter the short-term memory and be held for a further period. The longer information is stored in short-term memory, the easier it is to manipulate information to perform complex cognitive tasks.

Second, short-term memory has a limited storage capacity. Basically, the capacity of short-term memory is approximately seven items, plus or minus two. The total amount of information that can be stored in short-term memory might depend on the particular [Page 906]rules used to manage the information. Research has demonstrated that the chunking of information can increase the capacity of short-term memory. The process of chunking can reduce the loading of short-term memory by decreasing the number of items and increasing the size of each item. This chunking strategy allows the brain to automatically cluster certain items together and thus to remember the items much longer. This is why a hyphenated phone number is easier to remember than seven individual digits. Chunking is an important strategy for transferring short-term memory into long-term memory.

The third important feature of short-term memory is that it is subject to forgetting. Information in short-term memory is forgotten easily and quickly in the absence of further processing. Forgetting is mainly caused by decay, displacement, and interference. Decay is the primary mechanism of memory loss. Information in short-term memory decays over time. Short-term memory fades away after a few seconds without rehearsal. In addition, forgetting may occur through displacement: New information pushes out old information from short-term memory and replaces it. Moreover, interference seems to play a role in forgetting. Short-term memory is sensitive to disruption. Memory from earlier trials can interfere with recall of later ones. Information in long-term memory may also interfere with information in short-term memory.

Finally, short-term memory is regarded as a gateway to long-term memory. Attention plays an important role in selecting information to be held. Research has suggested that the perception of the importance of information determines to a great degree what information is subjected to further processing. Forgetting may begin with the information that has the least importance. Thus, the meaningfulness of an item is critical for its retention. Retention in short-term memory allows the opportunity for information to be transferred into long-term memory. Encoding and rehearsal are two main processes by which transfers occur from short-term memory to long-term memory. Encoding strategies may include substitution, which involves replacement of the incoming information by another symbol, or elaboration, which refers to developing a newly formed memory trace. Other factors, such as the intention to learn, the presence of incentives, interest in the information, and the level of arousal, also can affect encoding. Rehearsal allows more opportunity to encode into long-term memory. Activities such as using verbal rehearsal, forming mental images, and actively organizing information in short-term memory may enhance long-term retention. Adoption of rehearsal or encoding may depend on the existing knowledge in long-term memory. Information is remembered better if it can be linked to other known facts. With more existing knowledge about incoming information, there would be less effort to engage in rehearsal. However, passive residence in short-term memory may not be sufficient to transfer information into long-term memory.

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