Do working memory tests secretly rely on long-term memory?
Memory for word order, locations and colors showed no sign of leaning on long-term memory, but memory for object-word pairs did, so some popular working memory tasks are contaminated and others are not.
Source
When Does Episodic Memory Contribute to Performance in Tests of Working Memory?
Study at a glance
- Design
- Human experiment — Seven within-subject experiments alternating two memory tasks in mini-blocks with fresh materials each block; accuracy across trials within a block indexes proactive interference; Bayesian mixed models
- N
- Separate samples per experiment: 50 each in 1a, 1b and 3, 49 in 2a, 60 in 2b (online, English speakers); 33 in Exp 4 and 29 in Exp 5 (in-lab German-speaking students)
- Population
- Young adults aged 18-35: English native speakers via Prolific and University of Zurich students
- Outcome
- Change in recall accuracy (or reproduction error) across trials within a mini-block for serial recall, probed recall, object-word pairs, spatial and color reproduction; protrusion errors in Exp 4
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What they did
The researchers used proactive interference, the tendency for older memories to disrupt newer ones, as a fingerprint of episodic long-term memory, since working memory is thought to be protected from it. Participants did mini-blocks of four (or eight) trials of one task with the same small set of words or objects, then switched to a different task and fresh materials, which should release any interference. Across seven experiments they compared serial recall and probed recall of word lists with an object-word pairing task, a spatial location task, and a color reproduction task, including a version with slow five-second-per-word presentation.
What they found
Accuracy on the object-word pairs task reliably declined across trials within a mini-block in every experiment that used it, showing proactive interference. Serial recall, spatial location memory and color reproduction showed evidence against such a decline, and probed recall showed interference only in one experiment (2a) that the authors judge a false positive after three later experiments found evidence against it. In Experiment 4, words from earlier trials were not chosen increasingly often as a block went on.
The limits
What it doesn't show
The conclusion rests on the assumption that working memory contents are immune to proactive interference, which some researchers dispute. Absence of interference does not prove that no long-term trace was formed; the authors note the Hebb repetition effect shows traces exist, so their account (a 'flexible gate' that decides when to use long-term memory) is an interpretation rather than something directly tested. Samples were young adults, mostly tested online, and results for some tasks were inconsistent across experiments, which the authors attribute to sampling error.
Key terms
- Proactive interference
- When earlier learned information makes it harder to retrieve newer, similar information.
- Release from proactive interference
- The recovery of performance when the type of material changes, showing that interference built up from similar earlier trials.
- Episodic long-term memory
- Memory for specific experienced events, which has no fixed capacity limit but is vulnerable to interference.
- Task impurity
- The problem that a test meant to measure one process (like working memory) may also draw on other processes.
- Flexible-gate hypothesis
- The proposal that working memory only admits long-term memory information when a monitoring process judges it will give a better answer.
- Protrusion error
- Recalling an item from a previous trial's list, often in the same list position it originally held.
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Quiz yourself
What did the researchers treat as the signature of episodic long-term memory use?
Common questions
Why would long-term memory contamination matter for working memory research?
If people use long-term memory on supposed working memory tests, researchers may overestimate working memory capacity and misattribute effects to working memory mechanisms.
How does proactive interference reveal long-term memory use?
Working memory is thought to be shielded from interference from earlier trials, so if performance drops as similar trials accumulate, the task must be drawing on episodic long-term memory.
Why might object cues, but not list positions, invite long-term memory use?
The authors suggest objects are rich, distinctive cues that make episodic retrieval effective, whereas positions and locations vary on only one or two dimensions and make weaker episodic cues.
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