8 Memory · 8.1 Memory
8.1.1 Memory: processes, physiological basis, stores and types
Memory is the system that encodes, stores and retrieves information; it leaves a physical memory trace in the brain that is fixed by consolidation (the hippocampus is key), it flows through sensory, short-term and long-term stores (Atkinson–Shiffrin, 1968), and long-term memory holds declarative (episodic, semantic) and non-declarative (procedural, priming) knowledge. Learning curves, Ebbinghaus and study habits are in EDU-LR-01; measuring memory, forgetting and mnemonics are in PSY-MM-02.
- APPSC Paper I
- Standard level
- 14 min read
- Free
Core facts
- Memory: retention of learning or experience over time; it has a neural, chemical and biological basis.
- Three processes (stages):
- Encoding: information is taken in and turned into a form the system can use (a code: visual, acoustic or semantic).
- Storage: the encoded information is held over time.
- Retrieval: stored information is brought back into awareness for use (recall is the common name for it).
- Failure at any of the three stages leads to "forgetting".
- Memory trace (engram): the physical and chemical change in the brain that stands for an encoded memory. Karl Lashley searched for the engram in rats and concluded it is spread across the cortex, not in one spot (law of mass action).
- Consolidation: the process by which a fresh, fragile trace becomes stable and lasting in long-term memory. A head blow can wipe out the minutes before it (retrograde amnesia), because those traces were not yet consolidated.
- Brain parts:
- Hippocampus (medial temporal lobe): forms new declarative memories and consolidates them; it is not the final store.
- Cerebral cortex: the long-term store of facts and events.
- Amygdala: emotional memories (fear).
- Cerebellum and basal ganglia: procedural (skill) memory and conditioned responses.
- Prefrontal cortex: working memory.
- Patient H.M. (Henry Molaison): most of both hippocampi and nearby medial temporal lobe tissue removed (1953) for epilepsy; afterwards he could not form new long-term declarative memories (anterograde amnesia) but could still learn new motor skills (mirror drawing). Studied by Brenda Milner.
- Neural basis of learning: Donald Hebb (1949): when one neuron repeatedly helps fire another, the connection between them grows stronger (Hebb's rule, popularly "cells that fire together wire together"); long-term potentiation (LTP): lasting strengthening of synapses after repeated stimulation, seen first in the hippocampus.
- Multi-store (modal / information-processing) model: Atkinson and Shiffrin, 1968. Three stores in sequence:
| Store | Capacity | Duration | Code |
|---|---|---|---|
| Sensory memory (register) | large | under 1 s (visual) to 2–4 s (sound) | raw sensory copy |
| Short-term memory (STM) | 7 ± 2 items (Miller, 1956) | about 18–30 s without rehearsal | mainly acoustic |
| Long-term memory (LTM) | practically unlimited | minutes to a lifetime | mainly semantic |
- Sensory memory: iconic (visual, under a second; George Sperling, 1960, partial-report method) and echoic (auditory, a few seconds).
- Attention moves information from sensory memory into STM; rehearsal keeps it in STM and helps move it to LTM.
- STM: brief memory for a small amount of information (a phone number dialled once). Peterson and Peterson (1959): with rehearsal blocked, recall fell to about 10% within 18 seconds.
- Chunking (Miller): grouping items into meaningful units raises how much STM holds.
- Working memory: Baddeley and Hitch, 1974; STM seen as an active workspace with parts: central executive, phonological loop, visuospatial sketchpad, and (added by Baddeley, 2000) the episodic buffer.
- Levels of processing: Craik and Lockhart, 1972; memory depends on how deeply information is processed, not on separate stores. Shallow → deep: structural (how it looks) → phonetic (how it sounds) → semantic (what it means). Deeper = better remembered.
- Types of long-term memory:
- Declarative (explicit): facts and events you can state ("knowing that"):
- Episodic: personal events tied to a time and place (my first day in college). Endel Tulving, 1972 split episodic from semantic.
- Semantic: general knowledge, word meanings, concepts and rules of logic (Hyderabad is in Telangana; 2 + 2 = 4).
- Non-declarative (implicit): shown in performance, not stated ("knowing how"):
- Procedural: skills and habits (cycling, typing, swimming).
- Priming: an earlier exposure makes a later response easier without awareness.
- Classical conditioning effects and simple non-associative learning (habituation).
- Declarative (explicit): facts and events you can state ("knowing that"):
- Autobiographical memory: memory of one's own life story (mostly episodic). Flashbulb memory: a vivid, detailed memory of where one was when an emotional event happened (Brown and Kulik, 1977).
Explained
1. The three processes with one example. You meet a new hostel warden named "Ravi Kumar". Encoding: you notice the name and link it to a friend called Ravi. Storage: the name stays in memory overnight. Retrieval: next morning you see him and the name comes to mind. If you never paid attention, the failure was at encoding; if you knew it yesterday and lost it, storage; if it is "on the tip of the tongue", retrieval.
2. Memory trace and consolidation
| Term | Meaning | Clue in a question |
|---|---|---|
| Memory trace / engram | physical-chemical change that represents the memory | "change in the brain representing an encoded memory" |
| Consolidation | trace becomes stable over time | "fixing", "stabilising", sleep helps it |
| Retrograde amnesia | loss of memories from before an injury | old memories lost |
| Anterograde amnesia | cannot form new memories after an injury | H.M. after surgery |
Consolidation takes time (from minutes to years for full storage in the cortex). Sleep, especially deep sleep, supports it. Electroconvulsive shock given right after learning in animal studies disrupts it, which is the classic evidence that consolidation exists.
3. Atkinson–Shiffrin step by step
- A stimulus enters the sensory register, which holds an exact copy for a moment.
- Only what we attend to passes to STM; the rest fades.
- In STM, items are lost in about 20–30 seconds by decay or pushed out by new items (displacement) unless rehearsed.
- Maintenance rehearsal (repeating) keeps items in STM; elaborative rehearsal (linking to meaning) moves them into LTM.
- From LTM, information is retrieved back into STM when needed.
4. Evidence for separate STM and LTM
- Serial position curve: in free recall of a list, the first items are recalled well (primacy: rehearsed into LTM) and the last items too (recency: still in STM). A 30-second delay with counting removes the recency effect but not primacy.
- Different codes: STM errors are often sound-alike (B for V); LTM errors are often meaning-alike.
- Amnesia cases: H.M. had normal STM but could not form new LTM.
5. Working memory: why it replaced the simple STM box
| Part | Job | Example |
|---|---|---|
| Central executive | directs attention, controls the other parts | planning steps of a sum |
| Phonological loop | holds speech-based sounds (inner voice) | repeating a phone number |
| Visuospatial sketchpad | holds images and spatial layout | picturing the route to the bus stop |
| Episodic buffer (2000) | joins information into one episode, links to LTM | recalling a scene with sound and sight |
STM is a store; working memory is a workspace that both stores and processes.
6. Levels of processing. In Craik and Tulving's (1975) tests, people judged words in three ways: "Is it in capitals?" (structural), "Does it rhyme with train?" (phonetic), "Does it fit the sentence He met a ___ in the street?" (semantic). Later, recognition was best for the semantic group. The idea challenged the store model: depth, not time in STM, decides retention.
7. Kinds of long-term memory at a glance
| Kind | Also called | Content | Example |
|---|---|---|---|
| Episodic | autobiographical events | what happened to me, when, where | my 10th class result day |
| Semantic | general knowledge | facts, meanings, concepts, rules | the capital of India |
| Procedural | skill memory | how to do things | riding a bicycle |
| Priming | implicit memory | easier processing after exposure | completing "ele___" as elephant after seeing it |
Episodic and semantic together are declarative / explicit; procedural and priming are non-declarative / implicit. Procedural memory survives amnesia better than declarative memory.
8. Where the memory types live in the brain
| Memory | Main brain parts |
|---|---|
| New declarative memories | hippocampus, medial temporal lobe |
| Stored facts and events | cerebral cortex |
| Emotional memory | amygdala |
| Skills, habits, conditioned responses | cerebellum, basal ganglia |
| Working memory | prefrontal cortex |
9. Neurotransmitters and hormones. Acetylcholine is important for forming memories; its loss is linked with Alzheimer's disease. Glutamate (NMDA receptors) is involved in LTP. Stress hormones (adrenaline, cortisol) in moderate amounts make emotional events memorable, which explains flashbulb memories.
Common traps
- ✗ "Retrieval means storing information." ✓ Storage is holding; retrieval is getting it back (recall).
- ✗ "The memory trace is a mental image." ✓ It is a physical and chemical change in the brain (engram).
- ✗ "The hippocampus is where long-term memories are permanently kept." ✓ It forms and consolidates new declarative memories; long-term storage is in the cortex.
- ✗ "H.M. lost all his old memories." ✓ He mainly could not form new declarative memories (anterograde amnesia); old memories and new motor skills largely remained.
- ✗ "Multi-store model: Baddeley and Hitch." ✓ Multi-store = Atkinson and Shiffrin (1968); working memory = Baddeley and Hitch (1974).
- ✗ "Levels of processing: Atkinson and Shiffrin." ✓ Craik and Lockhart (1972).
- ✗ "STM lasts several minutes." ✓ About 18–30 seconds without rehearsal; capacity 7 ± 2.
- ✗ "Iconic memory is auditory." ✓ Iconic = visual; echoic = auditory.
- ✗ "Rules of logic and concepts are stored in episodic memory." ✓ They are in semantic memory.
- ✗ "Procedural memory is declarative." ✓ Procedural is non-declarative (implicit); declarative = episodic + semantic.
- ✗ "Phonetic processing is the deepest level." ✓ Semantic (meaning) is the deepest; structural is the shallowest.
Quick revision
- Three processes: encoding → storage → retrieval.
- Memory trace (engram) = physical-chemical change; Lashley: spread across the cortex.
- Consolidation stabilises traces; hippocampus forms new declarative memories; H.M. = anterograde amnesia.
- Multi-store: Atkinson and Shiffrin 1968: sensory → STM → LTM.
- Iconic (visual, < 1 s, Sperling 1960); echoic (auditory, 2–4 s).
- STM: 7 ± 2 (Miller 1956), about 18–30 s (Peterson and Peterson 1959); chunking extends it.
- Working memory: Baddeley and Hitch 1974: central executive, phonological loop, visuospatial sketchpad, episodic buffer (2000).
- Levels of processing: Craik and Lockhart 1972: structural < phonetic < semantic.
- Declarative = episodic + semantic (Tulving 1972); non-declarative = procedural, priming, conditioning.
- Skills: cerebellum and basal ganglia; emotion: amygdala; working memory: prefrontal cortex.
Go deeper: Deeper (beyond what APPSC Paper I usually asks)
Deeper Advanced
1. Sperling's partial-report experiment (1960). Subjects saw a 3 × 4 grid of letters for 50 ms. Asked for the whole grid (whole report) they gave about 4 letters. When a tone right after the flash told them which row to report (partial report), they gave about 3 of the 4 letters in that row, so almost all 12 letters had been available for a moment. When the tone was delayed by about one second, this advantage vanished: iconic memory is large but very brief.
2. Miller's number and later limits. Miller (1956) called 7 ± 2 "the magical number seven". Later work (Cowan, 2001) suggests that, when chunking and rehearsal are prevented, STM holds about 4 chunks. Exams still use 7 ± 2.
3. Limits of each model
- Multi-store: too simple; STM is not one store, and rehearsal alone does not explain transfer to LTM (we remember many things we never rehearsed).
- Levels of processing: "depth" is hard to measure independently (circular reasoning), and it describes rather than explains.
- Working memory: the central executive is the least clearly defined part.
4. Reconsolidation. When a stored memory is recalled, it can become unstable again and must be re-stored. This is one reason memories change with each retelling and are open to distortion (see reconstruction in PSY-MM-02).
5. Flashbulb memories are confident, not always accurate. People are very sure of where they were during a shocking event, but follow-up studies show details change over time even while confidence stays high.
Practise this topic. Questions on Nature and physiological basis of memory; memory stores and types, with answers explained.
All Memory notes · APPSC Paper I syllabus · APPSC Paper I Mock 1 with answers · Start free
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