All the facts that you know, all the things you can do, many of the events of your life to date, plus all the surprising things that you are not even aware of knowing – this huge store of knowledge is what makes up your long-term memory.
You can think of your memory as a bit like a library. Close to the entrance is the working memory notice, where transitory items come and go. Inside the labyrinths of the main building is the vast archive of everything you know: your long-term memory collection.
Long-term memory is usually described as having two main divisions: episodic memory and semantic memory. Episodic memories are events and experiences clothed in personal detail – the stories from your life so far. Semantic memories are your store of knowledge and facts.
Psychologists also make a distinction between ‘knowing that’ and’ knowing how to.’Your episodic and semantic memories fall into the category of ‘knowing that. For example, with a moment’s thought, you can recount what you did last Sunday (episodic) and can also say with some certainty whether you know the answer to a factual question such as ‘What is the capital of Portugal?’ (semantic).
‘Knowing how to’ refers to procedural skills – physical and mental skills acquired over time that include anything from riding a bike or using a keyboard to mental processes such as interpreting other people’s behavior or learning by association. While episodic and semantic memories are explicit in that they can be consciously brought to mind, most of our proce dural knowledge is used automatically without conscious recollection of how to apply it. For this reason, procedural memories are also known as implicit memories.
Laying down long-term memories
Although we tend to think of long-term memory as our ability to store things that we learned or that happened to us some time ago, the term also applies to items from the last week, day, or even hour. Whether these more recent memories become fixed permanently into the long-term term store depends on a complex interaction between the world and the brain. Storage in long-term memory is thus a long way removed from a camera recording scenes or a tape recorder laying down sounds. The first part of the process is attention – the myriad fleeting experiences that pass us by unnoticed are not going to make it into long-term memory. Once our attention is focused, information still needs to be ‘encoded’ as it arrives – that is, processed so that it can be stored in long-term memory.
The most effective way to process information for long-term storage is to add meaning. The more we elaborate on meaning, the more established the memory is likely to become. For example, suppose you are told the following information about eels: ‘Eels live most of their lives in rivers. Before they breed, eels in North America and Europe migrate to the warm waters of the Sargasso Sea. The young eels, called elvers, remain there until they are 30 months old, when they migrate back to the river feeding grounds. There they stay until up to 19 years later when they finally return to the Sargasso Sea to breed and die.’ After one hearing, you might hold on to the gist of this story, but some of the details would almost certainly evade you after a while. However, if you made efforts to elaborate on the key details, you would be much more likely to retrieve them later on. For example, think about geographical locations: picture an eel in a river that you know well and then imagine the journey it would have to make to reach the Sargasso Sea – a region of the Atlantic, southeast of Bermuda. Now think about Bermuda – you may have taken a holiday there or know someone who has, or you may have heard of or read Wide Sargasso Sea, a novel by Jean Rhys. The young eels migrate back at 30 months – think of a child you know starting nursery school at two and a half. This is an exaggerated example, but it demonstrates how processes like these help to incorporate new information into a network of personal experiences and knowledge and create many routes back to it when you need it.
Memory retrieval
The final stage in long-term memory is retrieval. This is when we remember something (or find we have forgotten it). When memory cannot be accessed, it may be because it was never formed in the first place, or it may be that it cannot be accessed at that moment, often because other information in memory is interfering with retrieval.
Most events that lodge in long-term memory are encoded without conscious effort. Episodes that seize our attention and affect us significantly a re-laid down with a wealth of sensory and emotional details. Yet, at other times, this unconscious laying down of memories seems to be infuriatingly random. For example, it is hard to explain why the memory of seeing two strangers having a quarrel on a bus suddenly resurfaces from 25 years ago or why most of us have to keep looking up how to program the video recorder but have no problem remembering the names of the characters in a sitcom from years ago.
The answer to such questions may lie in attention and practice. If you never bothered to read the instructions for the video recorder properly and then used it infrequently, programming it is unlikely to have become part of your repertoire of procedural skills. On the other hand, the names of the sitcom characters had your full attention and were given effortless revisions once a week, month after month. In summary, it is not the case that everything we ever knew has shelf space in the memory library. Little used memories usually fade away over time through lack of use.
SEMANTIC MEMORY CAPACITY
- Most people are familiar with between 20,000 and 100,000 words, while a standard dictionary has around 70,000 entries.
- Chess experts store more than 100,000 different chess patterns and their associated game strategies in long-term memory.
- A qualified London taxi driver knows some 500 different routes by heart.
