What happened
Symbol sequences grew one item at a time. Each correct recall lengthened the next sequence; each error shortened it. The staircase converged on your span, the point where storage demand met capacity.
Why it happened
Items in working memory are maintained by active rehearsal and decay or interfere within seconds. Each additional item raises interference between traces, so recall probability falls steeply past capacity. Chunking works because it stores structure, not raw items.
Experimental design
Research protocol
Adaptive staircase (within-subjects); memory span procedure
- Independent variable (IV)
- Sequence length (number of items to recall)
- Dependent variable(s) (DV)
- Proportion correct per sequence length
- Maximum span reached (last length with criterion performance)
- Measured constructs
- Working memoryPhonological storageRehearsal
- Operational definitions
Digit span
Longest sequence of items recalled in correct order on a majority of trials
Working memory capacity
Limit on items held in an active, manipulable store (often ~4 chunks when rehearsal is controlled; Cowan, 2001)
Chunking
Recoding individual items into larger meaningful units to expand effective capacity
- Key terms
Magical number seven
Miller's (1956) synthesis that immediate memory span clusters near 7 ± 2 items before chunking.
Phonological loop
Baddeley's subsystem for maintaining verbal sequences via subvocal rehearsal.
Articulatory suppression
Interfering with rehearsal (e.g., repeating an irrelevant word) to isolate storage capacity.
The original experiment
Year
1956
Researchers
George A. Miller
Sample
Synthesis of psychophysical and memory-span experiments
Key finding
Immediate memory span clusters near 7 ± 2 items; recoding into chunks raises the information ceiling.
Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63(2), 81–97.
Where this shows up in the world
Phone numbers, postal codes and license plates are sized to span limits
Checklist design in medicine and aviation keeps steps within capacity
Instructional design sequences new material to avoid overload
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