Transcript Chapter 5

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
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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
aardvark-birch
Control Group
Phase 1 (N/A)
Phase 2 (A-C)
Phase 3 (C?)
apple-???
apple-comb
apple-???
aardvark-car
aardvark-???
aardvark-car
aardvark-???
atom-banana
atom-cod
atom-???
atom-cod
atom-???
ant-bomb
ant-cream
ant-???
ant-cream
ant-???
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
100
Recall (%)
• Inactivity during
retention interval
leads to less
forgetting than
activity
• Implies forgetting
partly based on
learning new material
sleep
50
awake
0
2
4
6
8
Hours after learning tested
Retroactive Interference
• New learning interferes with ability to
recall earlier learning
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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
Control Group
Phase 1 (A-C)
Phase 2 (A-B)
Phase 3 (C?)
Phase 1 (A-C)
Phase 2 (N/A)
Phase 3 (C?)
apple-comb
apple-ball
apple-???
apple-comb
apple-???
aardvark-car
aardvark-birch
aardvark-???
aardvark-car
aardvark-???
atom-cod
atom-banana
atom-???
atom-cod
atom-???
ant-cream
ant-bomb
ant-???
ant-cream
ant-???
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
• Gave rats avoidance
learning, tested at
various retention
intervals.
Avoidance (%)
Kamin (1957)
100
50
0
12
24
36
48
60
72
Retention Interval (hr)
84
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
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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
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In essence, improving learning
Practice increases retention
Overlearning
Mnemonics
Context cues
Prompts