Short-Term Memory Duration and Capacity
Short-term memory, also known as primary or active memory, is the information we are currently aware of or thinking about. The information found in short-term memory comes from paying attention to sensory memories.
A quick overview:
- Short-term memory is very brief. When short-term memories are not rehearsed or actively maintained, they last mere seconds.
- Short-term memory is limited. It is commonly suggested that short-term memory can hold seven plus or minus two items.
Duration of Short-Term Memory
Most of the information kept in short-term memory will be stored for approximately 20 to 30 seconds, but it can be just seconds if rehearsal or active maintenance of the information is prevented. Some information can last in short-term memory for up to a minute, but most information spontaneously decays quite quickly.
For example, imagine that you are trying to remember a phone number. The other person rattles off the phone number, and you make a quick mental note. Moments later you realize that you have already forgotten the number. Without rehearsing or continuing to repeat the number until it is committed to memory, the information is quickly lost from short-term memory.
You can increase the duration of short-term memories to an extent by using rehearsal strategies such as saying the information aloud or mentally repeating it. However, the information in short-term memory is also highly susceptible to interference. Any new information that enters short-term memory will quickly displace any old information. Similar items in the environment can also interfere with short-term memories.
While many of our short-term memories are quickly forgotten, attending to this information allows it to continue the next stage — long-term memory.
Capacity of Short-Term Memory
The amount of information that can be stored in short-term memory can vary. An often-cited figure is a plus or minus seven items, based on the results of a famous experiment on short-term memory.
In an influential paper titled "The Magical Number Seven, Plus or Minus Two," psychologist George Miller suggested that people can store between five and nine items in short-term memory. More recent research suggests that people are capable of storing approximately four chunks or pieces of information in short-term memory.
Distinction Between Short-Term Memory and Working Memory
Short-term memory is often used interchangeably with working memory, but the two should be utilized separately. Working memory refers to the processes that are used to temporarily store, organize, and manipulate information. Short-term memory, on the other hand, refers only to the temporary storage of information in memory.
Distinguishing Short-Term From Long-Term Memory
Memory researchers often use what is referred to as the three-store model to conceptualize human memory. This model suggests that memory consists of three basic stores: sensory, short-term, and long-term and that each of these can be distinguished based on storage capacity and duration.
While long-term memory has a seemingly unlimited capacity that last years, short-term memory is relatively brief and limited. Chunking information into small groups makes it easier to remember more items for a short period.
The information-processing view of memory suggests that human memory works much like a computer. In this model, information first enters short-term memory (a temporary holding store for recent events) and then some of this information is transferred into long-term memory (a relatively permanent store), much like information on a computer being placed on a hard disk.
How Can Short-Term Memories Become Long-Term Memories?
Since short-term memory is limited in both capacity and duration, the retention of memories requires transferring the information from short-term stores into long-term memory. How exactly does this take place? There are a few different ways that information can be committed to long-term memory.
As mentioned earlier, chunking is one memorization technique that can facilitate the transfer of information into long-term memory. This approach involves breaking up information into smaller segments. If you were trying to memorize a string of numbers, for example, you would segment them off into three or four item blocks.
Rehearsal can also help information make it into long-term memory. You might use this approach when studying materials for an exam. Instead of just reviewing the information once or twice, you might go over your notes over and over again until the critical information is committed to memory.
The exact mechanisms for how memories are transferred from short-term to long-term stores remain controversial and not well understood. The classic model, known as the Atkinson-Shiffrin model or multi-modal model, suggested that all short-term memories were automatically placed in long-term memory after a certain amount of time.
More recently, other researchers have proposed that some mental editing takes place and that only particular memories are selected for long-term retention. Still, other researchers dispute the idea that there are separate stores for short-term and long-term memories.
Recent research has shown that exercise may also help increase short-term memory. One experiment found that treadmill exercise in rats with Alzheimer's led to improvements in short-term memory by increasing neurogenesis, offering hope for new approaches that alleviate some of the symptoms associated with Alzheimer's disease.
A Word From Verywell
Short-term memory plays a vital role in shaping our ability to function in the world around us, but it is limited in terms of both capacity and duration. Disease and injury can also have an influence on the ability to store short-term memories as well as convert them into long-term memories.
As researchers continue to learn more about factors that influence memory, new ways of enhancing and protecting short-term memory may continue to emerge.
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