Week 9 Basics of Memory - Learning & Forgetting Flashcards
Many findings from Ebbinghaus’s experiments
• Spacing effects: repetitions more effective if you space them out over time rather than mass them consecutively
• List length effects: Worse memory when you study longer lists versus shorter lists
• Forgetting curve: the shape of how memory declines over time
Ebbinghaus contribution on experimental tradition of memory
–Presenting randomized lists of “non-meaningful” stimuli to participants under controlled conditions
–Control for exposure duration, retention interval, etc.
-Various reasons why something is not remembered
Decay Theory
Stored memories fade over time
–Brown-Peterson paradigm: Subjects learn trigram, count backwards by seven for a period of time (to prevent rehersion)
• Almost no memory after ~20 seconds
Interference Theory
• Started with John McGeoch (1932) – claimed that decay theory is conceptually flawed
–With memory, forgetting occurs because over time there is more interfering mental activity
• Specifically, forgetting occurs because there is competition between things we are attempting to remember
–There is greater competition as we learn more
Interference Theory, why is there competition
–When we learn, we associate things together
–When presented with one of those things in isolation (the cue), we can recall the associate
=The more associations there are, the harder it is to remember thing
Interference theory and lockdown
• Interference theory can even explain why lockdowns impair memory
-We are associating what we learn to the same cues! E.g., our house, our surroundings
- This makes it harder to remember particular things
What is interference
More associations to a cue, the harder it is to retrieve the correct memory
– proactive interference Inability to retrieve new associates can be because of interference from older ones
-retroactive interference Inability to retrieve old associates can be because of interference from newer ones
Interference in Lab Studies
• AB-CD paradigm
–Two lists of items with no overlapping associations
–During the memory test, subjects presented with a cue (e.g., “dog” or “hope”) and asked to retrieve the associate
• AB-AC paradigm
–Second list shares the same cues as the first
–Worse performance on List 2 items compared to the AB-CD condition (this is proactive interference)
result of Interference in Lab Studies
Decay theory has difficulty explaining why performance in AB-CD lists is better than AB-AC lists
–Performance on AB-AC lists is worse due to response competition
–When the A cue is presented, both B and C compete to be retrieved in AB-AC lists
–No competition is present in AB-CD lists
What about decay from short-term
memory
• Re-analysis of all Brown-Peterson results by Underwood (1957)
–Huge variation in how much material was forgotten over time
–Big predictor of forgetting: Number of previous experimental trials
• More trials = poorer performance
• Underwood’s interpretation: Subjects suffer from proactive interference from previous trials
Release from Proactive Interference:
Wickens, Born, and Allen (1963)
• Switching the stimulus type causes big improvement in performance
–Digits to letters, or letters to digits
–New category hasn’t been learned, so it should suffer less interference
• Many manipulations cause release from PI
• No obvious decay explanation of these results
Consolidation Theory
• Learned memories are in one of two states:
–Perseveration period: Memories are vulnerable
–Consolidation phase: Memories that survive the perseverated phase are permanently stored and won’t be forgotten
• If consolidation does not occur, the memory will be forgotten
Three predictions of consolidation theory
- Protecting memories during perseveration should enhance consolidation and prevent forgetting
- Interrupted perseveration should prevent consolidation and prevent memory from being stored
- If consolidation is prevented, the memory is not stored and
remembering should be impossible
Proof for Protecting memories during perseveration should enhance consolidation and prevent forgetting
mental inactivity following learning leads to better memory (as it provides time for memories to be consolidated).
• Going to sleep after learning leads to better memory than being awake (Jenkins & Dallenbach, 1924). Mental activity whilst still awake prevents memory consolidation.
Proof of Interrupted perseveration should prevent consolidation and prevent memory from being stored
• This is confirmed by studies on retrograde amnesia – where most recent memories before the trauma were lost because they were not consolidated.
• Studies involving induced retrograde amnesia show similar effects – e.g. removal of the hippocampus, electroconvulsive shock.
• The longer the delay between learning and electroconvulsive shock (ECS), the better the memory (Duncan, 1949). When ECS was given one hour after learning, rats performed as well as the controls (same applies to removal of the hippocampus). This is because these memories are consolidated in that time, and no longer require the hippocampus. The longer the delay between learning and lesion, the better the memory.
Study of If consolidation is prevented, the memory is not stored and remembering should be impossible
If you re-test memories forgotten after ECS, they should not be remembered.
Quartermaine, McEwen & Azmitia, 1972: when tested soon after ECS, rats showed no memory of learned responses. However, when tested 72 hours after, the rats exhibited memory. This does NOT fit with the predictions of consolidation theory (is an example of spontaneous recovery)
Some memories never seem to be forgotten
–Bahrick and colleagues:
• Foreign language courses: Virtually no forgetting from 3 to 50 years
• 80-90% recognition of HS classmates 50 years later
Hybrid theories:
Consolidation + interference: the consolidation process protects older memories from interference
• Consolidation involves exporting memories from the hippocampus to the cerebral cortex
The shape of the forgetting function
• Mathematical form of forgetting contributes to the debate
–Forgetting is non-linear with respect to time A lot of forgetting happens quickly but Less forgetting happens as time continues
Exponential function of forgetting fuction
– Implies that loss is a fixed proportion for each unit of time
– Example: if 50% of items are forgotten in the first hour, we will expect 50% of the remaining items to be forgotten on the next hour
– Most decay functions in nature are exponential: radioactive decay, leak from a bucket, etc
Power functions shape of forgetting
– Forgetting described by the amount of time raised to a power
– Power functions imply that the proportional loss decreases with respect to time
– In other words, if 50% of items are forgotten on the first hour, we might expect 40% of the remaining items to be lost on the next hour, 30% on the hour after that, etc
The shape of the forgetting function conclusion
• The data overwhelmingly support a power function (Rubin & Wenzel, 1996)
–Wixted (2004) has argued that forgetting is driven by interference, but as time progresses, memories are more likely to be consolidated, which slows forgetting
Temporal context
® Ecker, Tay & Lewandowsky (2015) found that there is similarly better memory for a given list when there is greater rest BEFORE a list. This supports a modified interference theory based on temporal context.
® Temporal context suggests that interference between items depends on how closely the items were studied in time. There is more interference from items that are studied closer in time to each other.
® Pre-study and post-study rest produces greater separation between lists, and this leads to less interference between them
Inhibition Theory
• Inhibition theory emerged in the 1990’s, when most researchers subscribed to interference theory
• It began with the discovery of retrieval-induced forgetting (Anderson, Bjork, & Bjork, 1994)
–Remembering can cause forgetting!
