Memory: Encoding & Storage

You’ll be able to

Describe the three-stage information-processing model of memory
Distinguish the ways information is encoded and the systems where it is stored
Explain the serial-position effect and levels of processing

The three-stage model

The classic Atkinson–Shiffrin model treats memory like an information-processing system with three stages. Sensory memory is a fleeting, high-capacity record of raw sensation — iconic (visual, about a quarter-second, demonstrated by Sperling) and echoic (auditory, a few seconds). Attended information passes into short-term memory, which holds about 7 ± 2 items (Miller’s "magic number") for around 20 seconds unless rehearsed. Working memory is the modern upgrade: an active workspace that manipulates information, not just stores it. Deeply processed information moves into long-term memory, whose capacity is essentially unlimited.

Encoding: getting information in

Information can be encoded in several ways: acoustic (by sound), visual (by image), and — most durably — semantic (by meaning). Craik and Lockhart’s levels-of-processing research shows that deep processing (thinking about meaning) produces far better recall than shallow processing (noticing appearance or sound). We can also boost encoding with chunking (grouping items, so "1-4-9-2" becomes a date), mnemonics (memory aids), and the spacing effect (distributed practice beats cramming). Effortful strategies almost always outperform mindless repetition.

Memory systems and the serial position effect

Long-term memory splits into explicit (declarative) memories we can state — semantic (facts) and episodic (personal events) — and implicit (nondeclarative) memories we cannot easily verbalize, such as procedural skills (riding a bike) and conditioned associations. Ordering matters too: the serial-position effect is our tendency to best recall the first items (the primacy effect, rehearsed into long-term memory) and the last items (the recency effect, still in short-term memory), while the middle is lost.

Worked example

A student is handed a 15-item grocery list, reads it once, and is quizzed a few minutes later. She remembers the first three items and the last two, but forgets most of the middle. Explain this pattern and name the effect.

1.Identify the phenomenon: recall depends on an item’s position in the list — this is the serial-position effect.
2.Explain the first items: the primacy effect — early items got the most rehearsal and were encoded into long-term memory.
3.Explain the last items: the recency effect — the final items are still active in short-term memory at the time of the quiz.
4.Explain the middle: middle items received neither enough rehearsal for long-term storage nor recency in short-term memory, so they are forgotten.

Answer: This is the serial-position effect. The first items are recalled via the primacy effect (rehearsed into long-term memory) and the last items via the recency effect (still held in short-term memory), while the middle items, lacking both advantages, are lost.

Checkpoint

A phone number is read aloud once, and moments later a listener can repeat it back but has forgotten it a minute later without rehearsing. Which memory system held the number?

Tip

Remember Miller’s capacity as 7 ± 2 and the short-term duration as about 20 seconds without rehearsal. Chunking raises effective capacity by grouping items, which is why phone numbers are broken into blocks.

Checkpoint

One student studies vocabulary by writing each word’s meaning and using it in a sentence; another just repeats each word aloud. The first student remembers far more. Which principle best explains this?

On the exam

Sort long-term memory quickly on the exam: explicit = "can declare it" (facts = semantic, events = episodic); implicit = "can’t easily state it" (skills = procedural, conditioned responses). A skill like typing is always implicit/procedural.

Answer the 2 checkpoints as you read.