Measuring Duration (Peterson & Peterson Technique): To determine how long STM lasts without rehearsal, researchers use interference tasks (like counting backward) to prevent the subject from repeating the information, revealing a rapid decay after 18-30 seconds.
Measuring Capacity (Digit Span): Capacity is often tested by asking individuals to recall increasingly long sequences of numbers. This led to the discovery of 'chunking,' where grouping small units into larger, meaningful strings increases the effective capacity of STM.
Serial Position Analysis: By observing which items in a list are remembered best, the model identifies the 'Primacy Effect' (LTM transfer of early items) and the 'Recency Effect' (STM retention of late items), supporting the existence of separate stores.
| Feature | Sensory Register | Short-Term Memory | Long-Term Memory |
|---|---|---|---|
| Coding | Raw/Sensory | Acoustic | Semantic |
| Capacity | Very High | items | Potentially Infinite |
| Duration | < 2 seconds | 18-30 seconds | Up to a Lifetime |
| Forgetting | Decay | Displacement/Decay | Interference/Retrieval Failure |
Identify the Evidence: When discussing the MSM, always reference the Serial Position Effect. The primacy effect supports LTM, while the recency effect supports STM, providing strong evidence that they are separate systems.
Case Study Application: Use the case of patient HM to illustrate the distinction between stores. HM could form no new long-term memories but had a functional STM, proving that the transfer process (rehearsal/encoding) can be damaged while the stores remain intact.
Critical Evaluation: Be prepared to argue against the 'unitary' nature of the stores. Modern theories suggest STM is actually a complex 'Working Memory' and LTM has different types (episodic, semantic, procedural), which the original MSM oversimplifies.
The Rehearsal Fallacy: Students often assume that any repetition leads to LTM. However, simple maintenance rehearsal is often insufficient for complex learning; without semantic processing (meaning), information is easily forgotten once the repetition stops.
Confusing Capacity and Duration: Capacity refers to how much can be held (e.g., 7 items), while duration refers to how long it stays there (e.g., 20 seconds). Ensure these metrics are not swapped when describing STM.
Overlooking the Sensory Register: Many focus only on STM and LTM, but the Sensory Register is the vital first 'filter.' Without attention, environmental data never enters the cognitive system at all.
