Three basic stages
Memory is the system that records and recalls experience. It works in three stages:
- Encoding: turning information into a form the brain can store.
- Storage: keeping it over time.
- Retrieval: getting it back out when needed.
A failure at any stage can look like "forgetting".
The three-store model
- Sensory memory holds a fleeting copy of what you see or hear for a second or two.
- Short-term (working) memory holds what you are thinking about now. Miller's classic estimate was about seven items, plus or minus two; newer work suggests roughly four chunks. Without rehearsal it fades in about twenty to thirty seconds.
- Long-term memory is the large and durable store.
Chunking groups items into meaningful units, so a phone number as 3-3-4 digits is easier than ten single digits.
Types of long-term memory
- Explicit (declarative): facts and events you can state. It has episodic memory (your last birthday dinner) and semantic memory (Paris is the capital of France).
- Implicit (non-declarative): shown through performance, such as riding a bicycle (procedural memory) or a conditioned reaction.
Encoding well
Shallow processing (noticing the font) leads to weaker memory than deep processing (thinking about meaning). Elaborative rehearsal, linking new material to what you know, beats simple repetition. The spacing effect says that studying in several spread-out sessions produces better long-term retention than one cramming session of the same total length.
Retrieval
Recall (producing information, as in an essay) is harder than recognition (picking it from options, as in multiple choice). Retrieval cues help: the encoding specificity idea says memory is best when conditions at recall match those at learning, as in the same room or mood. Testing yourself also strengthens memory (the testing effect).
Forgetting and distortion
- Decay: traces fade without use.
- Interference: old material disrupts new (proactive) or new disrupts old (retroactive).
- Retrieval failure: the memory is there but the cue is missing, as with the tip-of-the-tongue state.
Memory is reconstructive, not a recording. In studies of the misinformation effect, people who read a misleading description after seeing an event often report details that were never there.
Worked example
A student has a biology exam in two weeks. Plan A: read the chapter for six hours the night before. Plan B: study for one hour on six separate days, ending each time by quizzing herself without notes.
Plan B uses spacing, deep processing and the testing effect, so it should give stronger long-term retention, even though the total time is the same. On exam day, practising in a quiet room like the exam hall adds a small context match benefit.