Forgetting and enhancing memory

The nature of forgetting. Ebbinghaus found that forgetting is fastest at first: the rate is greatest in the first nine hours, especially the first hour. After that it slows down, and not much more is lost even after many days. Reviewing new material soon after learning it is therefore very useful.

Why do we forget? Sometimes the information was never properly encoded: if you were distracted while reading, there is nothing to remember. Beyond that, three explanations:

• Trace decay (disuse) theory: learning leaves physical memory traces in the brain, which fade if not used. This is the earliest theory, but it failed a key test: people who sleep after learning forget less than those who stay awake for the same time. If time alone erased traces, both should forget equally.
• Interference theory: memories get in each other's way. In proactive interference, earlier learning hampers recall of later learning: after moving house you keep writing your old address. In retroactive interference, later learning hampers recall of earlier learning: after learning a new dance routine you can no longer remember the old one.
• Retrieval failure: the memory is stored, but the right cues are missing, so it cannot be brought back. The 'tip of the tongue' feeling, knowing you know an answer but being unable to say it, is retrieval failure.

Mnemonics are techniques for improving memory. Some use images:

• Keyword method: to learn a word in a new language, find a similar-sounding word in a language you know and link them with a picture. To remember that the Spanish 'gato' means cat, picture a cat sitting on a gate.
• Method of loci: imagine the items placed at different familiar locations along a route, such as rooms in your home, and 'walk' through them to recall them in order.

Others use organisation:

• Chunking: grouping items into meaningful units.
• First-letter technique: making a word or sentence from the first letters of items. The order of the planets can be recalled from 'My Very Eager Mother Just Served Us Noodles' (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune).

Other ways to improve memory:

• Process deeply: ask questions about the material and link it to what you know.
• Reduce interference: study similar subjects at different times; space out your study.
• Give yourself retrieval cues: organise material into categories while learning, so a category name later brings back its members.
• PQRST method (Thomas and Robinson): Preview the chapter, Question its main points, Read to answer your questions, Self-recite what you read, and Test yourself.