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How can we measure forgetting

recall test

recognition test


What is a recall test

recall of events, story recall (hard to score)

free recall of lists of nameable items (% recalled),

cued recall e.g. paired associates (% recalled)

serial recall (% in correct position)


What is a recognition test

ability to discriminate “old” from “new” items (% correct)


Who was Ebbinghaus (1885) and what did he do?

learned many lists of 13 nonsense syllables to criterion (2 correct serial recalls), and then relearned each after a variable interval


Forgetting is orderly, explain

forgetting, measured appropriately, can often be described by a simple mathematical function of the retention interval (here a power function)


What causes forgetting?

orderliness of forgetting might suggest some inevitable decay process: loss from storage.

but this can’t be the whole story:
- information not recalled now may be recalled later
- further prompts or cues may succeed in eliciting recall

so some cases of “forgetting” due to retrieval failure not loss

moreover, some memories show essentially no loss over time


Why does a longer retention interval not necessarily increase forgetting?

no forgetting of school class-mates over 30 years (assessed using yearbooks (Bahrick et al., 1975, J.Exp.Psy:Gen)

“flashbulb” memories (e.g. JFK assassination, 9/11 attack)

but forgetting of former students by teachers does increase with interval —>

teachers subsequently encounter many more students
so, forgetting attributable to interference from other similar memories?


How can we test 'interference' v decay theories?

under normal circumstances, retention interval — time in storage — is confounded with the number of other experiences accumulated during the interval.

so, control the interval, vary intervening experiences

if forgetting due to interference, then p(recall) should decrease with more exposure to similar stuff, with time held constant


How is some forgetting clearly attributable to interference?

'paired associate” learning (1940s,1950s): participant must learn (say) 10 arbitrary pairings between “stimulus” and“response” words.

P learns List 1 to criterion

then learns List 2 to criterion

test on either List 1 or List 2

later recall of List 1 worse when List 2 was learned afterwards - retroactive interference

later recall of List 2 worse when List 1 has been learned before - proactive interference

implication: retrieval difficulty increases when other similar material has been learned, holding retention interval constant.


How are time v intervening (similar) experiences predictors of event forgetting?

at end of season, two rugby teams recalled games played: clear forgetting over a season (though some games are more memorable)

each player missed some games:
- if control for time, the number of games played during the interval is a significant predictor of forgetting
- but not vice versa.

in general, there is ample evidence that retrieval failure is increased by interference from similar material


What factors influence p(retrieval)?

processing at encoding/acquisition

consolidation after encoding

(more on) Interference from other memory traces at retrieval

similarity of encoding and retrieval contexts

[underlying theme: memory is an associative system, not a container]


What is organisation at acquisition

deliberate rote rehearsal does increase later recall

hence the primacy effect in free recall – first few items get more rehearsals

but mere rote rehearsal is a relatively ineffective learning strategy


What do incidental memory exps show?

processing the meaning of, and actively organising, the material are effective learning strategies


Mandler (1967) study

groups 1 and 2 sorted words on cards into 2-7 categories of their own devising

group 1 were also told to try to learn the words. Group 2 were not

no difference in a later recall test (if control for N of categories).

group 3, who just placed the cards into columns while trying to learn the list, remembered less than Groups 1 and 2.


Moral of organisation at acquisition

organising the material is what produces effective acquisition, not effort to learn (by itself)


What is depth of processing at acquisition?

Craik and Tulving (1975) study


Craik and Tulving (1975) study

showed a series of unrelated words, and gave one of three orienting tasks:

is it written in upper/lower case?

does it rhyme with X?

does it fit into a sentence(e.g. “The man broke his ____”)

later unexpected recognition test


Moral of depth of processing at acquisition

processing the meaning is better than processing surface form

(unless: details of surface form are what you are required to remember – “transfer-appropriate processing”)


What do mnemonics demo?

the power of appropriate elaboration at acquisition

one-is-a-bun mnemonic for sequence learning

first, learn the rhyme

to learn a sequence: form a vivid image representing the rhyme item for position X in interaction with what you want to remember at position X

remembering: Just go through the rhyme


Method of loci

first, memorise a route around a familiar building or garden, so that you can walk around it in your “mind’s eye”

learning the speech: At each point in the route, form a striking image representing the idea you want to mention at that point

remembering: Traverse the route, reading and interpreting the images.


What does learning form?



What does retrieval do to associations?

activates them


Why do mnemonics work?

they bind ideas to a pre-established framework which organises them (e.g. serial order, in the case of the method of loci and ‘one-is-a-bun’)

imagery encourages formation of rich nexus of associations between the frame “hook” and the concept attached to that hook.

forces exhaustive retrieval attempts


General moral of associations, retrieval and mnemonics

effectiveness of learning involves forming associations among representations that already exist in the mind, including representations of

elements of the new experience/fact

elements of the context

elements of prior knowledge


Retrograde memory loss after concussion

John Terry (at that time at Chelsea) "I remember walking out for the second half and nothing else until waking up in the ambulance on the way to the hospital”.


What is phase 1 of consolidation?

after traumatic brain injury (e.g. concussion) or ECT, there is often retrograde memory loss spanning many minutes, even hours (way beyond duration of “working memory”),

disruption of process of consolidation of memory trace in hippocampal/medial temporal cortex system


What does consolidation of novel traces suffer from?

interference from consolidation of further novel traces

sleep improves memory for material learned in last few hours (Jenkins & Dallenbach, 1924)

alcohol and barbiturates impair learning (disrupt consolidation)

but improve memory for material learned just before! (“retrograde facilitation”)


What is phase 2 of consolidation?

over a longer timescale (months, years), recent LTM traces are more vulnerable to hippocampal damage than older traces

amnesic patients with damage to hippocampus/ medial temporal cortex typically show gradient of retrograde amnesia over years -- older memories better preserved, more robust [“Ribot’s law”, 1882] -- e.g. HM

over time, re-activation of distributed representations in cortex from hippocampal trace reinforces direct links between elements of those representations, creates robust traces no longer dependent on hippocampus.


What is associative interference at retrieval?

E.g. In paired-associate experiments, can vary similarity of stimulus terms, response terms, etc.

interference maximal when the same (or similar) stimulus terms are used for each list: competition between two associative links from the same retrieval cue


What is the 'fan effect"

in fact retrieval as e.g. of associative interference

S learns 0-4 new “facts” about each of set of famous people, e.g.

Napoleon had a wart on his nose

later, true/false RT measured for test statements, e.g.:

Napoleon was Emperor of France (actual true)

Napoleon had a wart on his nose (experimental true)

Napoleon was six feet tall (false)