by Len Horridge

Short- and long-term memory

If you think of memory as the flow of information through the mind, three broad stages of information processing can be distinguished.

First, there is the sensory register – a very short-term sensory memory of the event. At the second level is a short-term, or working, memory. Then there is long-term memory.

Sensory memory

Roughly speaking, the sensory register concerns memories that last no more than about a second. If a line of print were flashed at you very rapidly, say, for one-tenth of a second, all the letters you can visualise for a brief moment after that presentation constitute the sensory register. This visualisation disappears after a second.

Sensory memory lasts such a short time (from a few hundred milliseconds to one or two seconds) that it is often considered part of the process of perception. Nevertheless, it represents an essential step for storing information in short-term memory.

Short-term memory

When you are trying to recall a telephone number that was heard a few seconds earlier, the name of a person who has just been introduced, or the substance of the remarks just made by a colleague, you are calling on short-term, or working, memory. This lasts from a few seconds to a minute; the exact amount of time may vary somewhat. You need this kind of memory to retain ideas and thoughts as you work on problems. In writing a letter, for example, you must be able to keep the last sentence in mind as you compose the next. To solve an arithmetic problem such as (3 x 3) + (4 x 2) in your head, you need to keep the intermediate results in mind (3 x 3 = 9) to be able to solve the entire problem.

Short-term working memory is an active process, where the goal is not so much to move the information into longer-term memory, but merely to keep it until it is put to use (think of how you repeat a phone number to yourself until you can dial it on the phone.)

In a classic study undertaken in 1956, George Miller found that the amount of information which can be remembered on one exposure is between five and nine items, depending on the information. Applying a range of + or -2, the number 7 became known as Miller’s Magic Number: the number of items which can be held in short-term memory at any one time. As a new item comes into our mind, we must let an existing item go, as there is only a finite amount of space in our short-term memory.

If we wish to retain a piece of information from our short-term memory for longer than a few dozen seconds, we need to make a conscious effort to do so. This then encodes the information in a more enduring way.

Long-term memory

Long-term memory lasts from a minute or so to weeks or years, and the limits of its capacity are not known. In fact, it seems limitless. From your long-term memory you can recall general information about the world, memories of specific past experiences, specific rules previously learned, significant events that have marked your life, the meanings of words and the physical skills that you have learned.

The palest ink is better than the best memory.

Chinese proverb

Most people have a good short-term memory; it is the long-term one that they would like to work on. The reason for this is that our ability to recall an event or experience fades with time.

When delivering training, trainers are painfully aware of the following statistics about recall after such events:

  • 38 per cent loss after 2 days
  • 65 per cent loss after 8 days
  • 75 per cent loss after 30 days.

You can see that there is a swift loss should you not back training up with either follow-on events or coaching and this is an indicator of how our memory needs help, too.

To make training more memorable, we need to do certain things, mostly ensuring that we tell, show and experience in the training, as the recall level rises from 70 per cent if only told to 85 per cent if also experienced over a period of three weeks. More importantly, after three months the difference is staggering: only 15 per cent will be recalled after that time if told, but if experienced this is around 65 per cent.

We have episodic memory (events, crises and so on) and factual memory. Most people are good at the first one (where were you when you heard about the London bombings on 7th July?), but less good at the second; this is only because the episodic memory has been replayed and replayed (and often refined) many times (in the case of September 11th, through the media as well as our own memory). In other words, we have practised and rehearsed this many times, often subconsciously.

Many strategies to improve the retention of what we really need and/or want to recall are based on the above.