What is memory? Encoding, storage, retrieval
Memory is keeping information over time and using it when needed.
- Encoding: turning what we sense into a form the brain can keep, and giving it meaning.
- Storage: holding it over time.
- Retrieval: bringing it back to use.
Memory can fail at any of the three steps.
The stage model
Atkinson and Shiffrin (1968) described three stores, one after another.
Sensory memory
- Very large capacity, lasts less than a second (sound about 2 seconds).
- Iconic memory for seeing and echoic memory for hearing. A sparkler traced in the dark looks like a line because of iconic memory.
Short-term memory (STM)
- Gets what we attend to. Holds about 7 items (plus or minus 2) for about 18–20 seconds.
- Mostly encoded by sound. Kept alive by maintenance rehearsal (repeating).
- Chunking groups items into bigger units so more fits.
Long-term memory (LTM)
- Unlimited capacity, lasts from minutes to a lifetime.
- Mostly encoded by meaning. Elaborative rehearsal (linking with what you know) moves information here.
Working memory
Baddeley and Hitch said STM is not just a box but a working memory, a workspace for thinking:
- Phonological loop: holds sounds and words for a short time.
- Visuo-spatial sketchpad: holds pictures and positions.
- Central executive: the boss that directs attention and links with long-term memory.
Levels of processing
Craik and Lockhart (1972) said memory depends on how deeply we process, not on which box it is in.
- Structural (shallow): how the word looks (capital letters?).
- Phonetic (intermediate): how it sounds (does it rhyme?).
- Semantic (deep): what it means and how it links to your life.
Deeper processing gives stronger, longer memories. This is why understanding beats cramming.
Types of long-term memory
- Declarative memory: facts, names, dates, events you can put into words.
- Episodic: your own experiences, with time, place and feelings (your first train trip). Strong emotional events can form very clear flashbulb memories.
- Semantic: general knowledge, word meanings, concepts (a triangle has three sides).
- Procedural (non-declarative) memory: how to do things, like swimming or typing. Hard to explain in words.
Knowledge in LTM is organised in categories, networks and schemas, which helps retrieval. Memory is also a constructive process: we rebuild memories using schemas, so they can change (Bartlett).
Key formulas and definitions
- Memory = encoding → storage → retrieval
- Sensory memory: huge, < 1 s (iconic, echoic)
- STM: 7 ± 2 items, ~20 s, kept by rehearsal
- LTM: unlimited, years, meaning-based
- Levels: structural < phonetic < semantic (deepest)
- LTM types: declarative (episodic, semantic) and procedural
Worked examples
1. You see lightning and for a split second still "see" its line after it is gone. Which memory store?
Sensory (iconic) memory. It holds a visual image for less than a second.
2. Rahul remembers a 10-digit number as 987-654-3210. Why does this help?
Chunking: 10 separate digits become 3 chunks, which fit easily within the 7 ± 2 limit of short-term memory.
3. Group A checks if words are in capital letters; Group B thinks what each word means. Who remembers more later and why?
Group B. Semantic processing is deeper than structural processing, so the memory lasts longer.
4. Classify: (a) how to tie shoelaces, (b) the capital of Japan, (c) your 10th birthday party.
(a) Procedural, (b) semantic (declarative), (c) episodic (declarative).
Common mistakes
- Thinking short-term memory means memories of the last few days. It lasts only about 20 seconds.
- Believing memory is an exact recording. Memories are rebuilt and can change.
- Confusing episodic and semantic: episodic has your own time and place; semantic is general fact.
- Thinking repeating alone is best. Linking meaning (elaborative rehearsal) works much better for LTM.