Short-Term Memory

Short-term Memory: Definition

Short-term memory is exactly as it sounds, quick and short. Our short-term memory refers to the memory systems in our brain that are involved in remembering bits of information for a short period.

This short time usually lasts about thirty seconds. Our short-term memory works as a visuospatial sketchpad for information that the brain has recently soaked up so that those sketches can be processed into memories later.

How information is encoded in the short- and long-term memory stores differ in terms of encoding, duration and capacity. Let’s take a look at the short-term memory store in detail.

Short-term Memory Encoding

Memories stored in short-term memory are usually encoded acoustically, i.e., when spoken aloud repeatedly, the memory is likely to be stored in short-term memory.

Conrad (1964) presented participants (visually) with letter sequences for a short duration, and they had to recall the stimuli immediately. In this way, the researchers ensured that short-term memory was measured.

The study found that participants had more difficulty recalling acoustically similar stimuli than acoustically dissimilar ones (they were better at remembering ‘B’ and ‘R’ than ‘E’ and ‘G’, even though B and R looked visually similar).

This finding shows that short-term memory encodes information acoustically, as similar-sounding words have similar encoding and are easier to confuse and recall less accurately.

Short-Term Memory Capacity

George Miller, through his research, said that we could hold (normally) around seven items in our short-term memory (plus or minus two items). In 1956, Miller even published his theory of short-term memory in his article ‘The Magical Number Seven, Plus or Minus Two’.

Miller also suggested that our short-term memory works by chunking information rather than remembering individual numbers or letters. Chunking can explain why we can recall items. Can you remember an old phone number? Chances are that you can! This is because of chunking!

More recent research suggests that people can store approximately four chunks or pieces of information in short-term memory.

Finally, Miller’s (1956) research into short-term memory did not consider other factors that affect capacity. For example, age could also affect short-term memory, and Jacob’s (1887) research acknowledged that short-term memory gradually improved with age.

Jacobs (1887) conducted an experiment using a digit span test. He wanted to examine the capacity of short-term memory for numbers and letters. How did he do this? Jacobs used a sample of 443 female students aged eight to nineteen from one particular school. Participants had to repeat back a string of numbers or letters in the same order and the number of digits/letters. As the experiment continued, the number of items gradually increased until the participants could no longer recall the sequences.

What were the results? Jacobs found that the student could recall 7.3 letters and 9.3 words on average. This research supports Miller’s theory of 7+/-2 numbers and letters that could be remembered.

Fig. 1 - Jacobs (1887) used letters and number sequences to test short-term memory.

Duration of Short-term Memory

We know how many items we can remember, but how long does it last? Most of the information that is kept within our short-term memory can be stored for around 20-30 seconds or sometimes less.

Some information within our short-term memory can live for around a full minute but, for the most part, will decay or be forgotten quickly.

So how can the information last longer? Rehearsal strategies are what allow the information to last longer. Rehearsal strategies such as repeating the information mentally or aloud are the most effective.

But there can be problems with rehearsal! The information in short-term memory is highly susceptible to interference. New information that enters short-term memory will quickly remove old information.

Peterson and Peterson (1959) presented participants with trigrams (nonsensical/meaningless three-consonant syllables, e.g., BDF). They gave them a distractor/interference task to prevent rehearsal of the stimuli (counting backwards in groups of three). This procedure prevents the information from being shifted to long-term memory. The results showed that accuracy was 80% after 3 seconds, 50% after 6 seconds, and 10% after 18 seconds, indicating the duration of storage in short-term memory of 18 seconds. In addition, recall accuracy decreases the longer the information is stored in short-term memory.

Improve Short-term Memory

Is it possible to improve our short-term memory? Absolutely! -- Through chucking and mnemonics.

Chunking is so natural for humans that we don’t often realise that we are doing it! We can remember information well when we can organise the information into arrangements on a personally meaningful arrangement.

Short-term Memory Examples

Short-term memory examples include where you parked your car, what you had for lunch yesterday, and details from a journal you read yesterday.

There are three different types of short-term memory, and it is dependent upon the type of information that is being processed for storage.

Acoustic short-term memory -- This type of short-term memory describes our ability to store the sounds we are bombarded with. Think of a tune or song that gets stuck in your head!

Iconic short-term memory -- Image storage is the purpose of our innate short-term memory. Can you think about where you left your textbook? When you think of it, can you picture it in your mind?

Working short-term memory -- Our memory is working hard for us! Our working short-term memory is our ability to store information until we need it later, like an important date or telephone number.