Chapter 11

Forgetting

Memory

• Internal record or representation of past experience

• Not necessarily the same as the original experience

Comparative Psychology View of Memory

• Not experiences stored or retrieved

• Experience’s ability to change an organism’s behaviour under certain conditions

• Stimulus control

Forgetting

• Deterioration in learned behaviour following a period without practice

• Defined behaviourally

• Note: extinction is not the same as forgetting

Measuring Forgetting

• Training

• Waiting for some period (“retention interval”)

• Testing

Free Recall Method

• Train, wait, test

• Performance deterioration?

• “All-or-nothing” test of behaviour

• May not be appropriate for complex tasks

• Some elements remembered, others not

Prompted (Cued) Recall

• Give prompts to increase likelihood of behaviour

• Number of prompts needed?

Relearning Method

• Reinstall original training procedure after retention period

• How many trials (or time) needed compared to original training to return to initial level of proficiency?

Recognition Method

• Subject only has to identify material previously learned

• E.g., distinguish between original stimulus and a number of distracter stimuli

Delayed Matching to Sample

• Show S+

• Wait

• Choose from S+ and S-

Sample

Delay

Matching

Extinction Method

• Train two subject groups

• Put both on extinction, but one has delay between training and extinction and the other doesn’t

• Compare rate of extinction

Gradient Degradation Method

• Establish stimulus control

• Measure generalization gradient over time

• If generalization gradients flatten: forgetting

Variables in Forgetting

Retention Interval

• Time between learning and testing

• Greater the interval, less retained (i.e., more forgetting)

• But, time is not an event (time doesn’t account for forgetting)

• Need causal factors

Degree of Learning

• Overlearning

• Learn to asymptote, then keep training

• Point of diminishing return

Prior Learning

• Meaningful material easier to retain than random material (e.g., learning katas)

• Prior experience important in determining what is meaningful (e.g., words in known or unknown language)

DeGroot (1966)

• Arranged chess pieces in legal patterns on board

• Chess masters and novices; 5 seconds to observe

• Masters reproduced arrangement 90% of time, novices only 40%

• Is this prior experience, or do chess masters forget less than other people?

Chase & Simon (1973)

• Chess pieces placed randomly on board

• Masters no better than novices at recall

• Past learning of “legal” arrangements is what increased masters’ performance in deGroot (1966) study

Proactive Interference

• Previous learning interferes with recall

• Paired Associate Learning (PAL) technique– Subjects learn paired lists, tested with 1 item and

must recall second– All learn A-C list, but some previously learned

A-B list– In testing, give A and ask to recall C– Those with A-B learning have more difficulty

recalling C when given A

Proactive PAL Design

Experimental Group

Phase 1 (A-B) Phase 2 (A-C) Phase 3 (C?)

apple-ball apple-comb apple-???

aardvark-birch aardvark-car aardvark-???

atom-banana atom-cod atom-???

ant-bomb ant-cream ant-???

Phase 1 (N/A) Phase 2 (A-C) Phase 3 (C?)

apple-comb apple-???

aardvark-car aardvark-???

atom-cod atom-???

ant-cream ant-???

Control Group

Levine & Murphy (1943)

• Proactive interference with attitudes

• Students read pro- and anti-communism passages

• Students who had prior pro-communist attitudes forgot anti-communist elements of passages but remembered pro-elements (and vice versa)

• Attitudes not innate; effect of prior learning

Subsequent Learning

• Inactivity during retention interval leads to less forgetting than activity

• Implies forgetting partly based on learning new material

Rec

all (

%)

100

50

Hours after learning tested

0 2 4 6 8

sleep

awake

Retroactive Interference

• New learning interferes with ability to recall earlier learning– PAL technique– Subjects learn A-C, but some then learn A-B– Test by giving A and recalling C– Subjects who learned A-B have worse recall

for C

Retroactive PAL Design

Experimental Group

Phase 1 (A-C) Phase 2 (A-B) Phase 3 (C?)

apple-comb apple-ball apple-???

aardvark-car aardvark-birch aardvark-???

atom-cod atom-banana atom-???

ant-cream ant-bomb ant-???

Phase 1 (A-C) Phase 2 (N/A) Phase 3 (C?)

apple-comb apple-???

aardvark-car aardvark-???

atom-cod atom-???

ant-cream ant-???

Control Group

Context

• Learning occurs in a context

• Various stimuli around the learner

• These stimuli serve as cues to evoke a behaviour

• If stimuli absent, may have cue-dependent forgetting

• Stimulus control

Perkins & Weyant (1958)

• Train two groups of rats in two mazes, one black, one white

• 1 minute retention interval

• Half of each group tested in original maze, half in maze of opposite colour

• Opposite colour rats did poorly compared to original maze tested rats

Kamin (1957)

• Gave rats avoidance learning, tested at various retention intervals.

Avo

idan

ce (

%)

Retention Interval (hr)

0 12 24 36 48 60 72 84

100

50

State-Dependent Learning

• Train under a particular physiological state (e.g., drug condition) and test under various states

• Recall best when in the same state as training

Application: Foraging

• Finding food

• Cache: food store

• Retrieval of food later

• Spatial memory

• Wide variety of species

• Accuracy can be quite high for very long times

Application: Eyewitness Testimony

• Notoriously poor

• Basic issue of retention interval and forgetting

• Also the nature of the question used to retrieve information

Loftus & Zanni (1975)• Subjects watched film of auto accident• Asked “Did you see <the>/<a> broken headlight?”• “the” subjects twice as likely as “a” subjects to say

“yes”• Actually, no broken headlight shown• Reinforcement history• Previous conditioning: “the” (definite article)

implies presence; “a” implies possible presence

Learning to Remember

• In essence, improving learning

• Practice increases retention

• Overlearning

• Mnemonics

• Context cues

• Prompts