Transcript Powerpoint

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Chapter 9
Incidental Forgetting
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Forgetting
Incidental Forgetting
 Occurs
without the
intention to forget.
Motivated Forgetting
 Occurs
when people
purposefully engage in
processes/behaviors
that intentionally
diminish a memory’s
accessibility.
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60 Minutes Show on Superior
Autobiographical Memory
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http://www.cbsnews.com/video/watch/?id=7166313n&tag=contentMain;contentBody
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Hyperthymestic Syndrome
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Hyperthymestic Syndrome:
 Uncontrollable remembering
 Like the person on the TV
show “Unforgettable”
Parker, Cahill, and McGaugh’s
(2006) case study of AJ:
 41 years old
 Remembers every day of her
life, in detail, since her teens.
 Feels as though she relives the
events she remembers.
 Remembering feels
“automatic” and not under
conscious control.
 Can verify events with the diary
she keeps.
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AJ’s superior memory has
costs:
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She cannot forget unpleasant
memories.
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Constant reminders are
distracting and sometimes
troubling.
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Ebbinghaus’s (1913)
Forgetting Curve
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Forgetting increases as time
progresses – the rate of forgetting
changes
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Ebbinghaus (1913) studied memory for
nonsense syllables and plotted:
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A retention curve
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A roughly linear relationship
between time and retention
A forgetting curve
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A logarithmic relationship between
time and forgetting
Data from Ebbinghaus (1913).
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A rapid rate of forgetting initially
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Less additional forgetting at longer
delays
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Forgetting Personal Memories
Meeter, Murre, and Janssen (2005)
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They aimed to determine the forgetting rate for people’s
memory of widely publicized events from headlines and TV
broadcasts, obtained from verifiable sources.
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Task:
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14,000 participants completed an internet questionnaire,
assessing recall and recognition for 1,000 dateable events.
Results:
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Like the Ebbinghaus results, recall for events shows a steep initial
drop, followed by a slower forgetting rate.
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Participants’ memory was worse for recall than for recognition of
the same events.

Recall for events dropped from 60% to 30% in a year, then stayed constant.
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After several years, 31% recall but 52% recognition.
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Forgetting Classmates
Bahrick, Bahrick, and Wittlinger (1975)
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Tested nearly 400 high-school graduates on their ability to
recognize and name classmates after delays of up to 30 years.
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Results were mixed:
 Relatively unimpaired :
 Ability to recognize their classmates’ faces/names.
 Ability to match up names to the appropriate portraits.
 Extensively impaired:
 Ability to recall a name, given a person’s portrait.
Conclusion:
 Recall, but not recognition, of well-learned personal material,
closely follows the forgetting curve first demonstrated by
Ebbinghaus (1913).
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Permastore
Bahrick (1984)
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Permastore:
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An analogy to permanently frozen
Polar regions.
Describes the leveling off of the
forgetting curve at long delays.
 Beyond this point, memories
appear impervious to further
forgetting.
PERMASTORE
Bahrick (1984)
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Forgetting of a foreign language
asymptotes (levels off) after about
2 years.
The overall level of retention is
determined by the level of initial
learning.
Data from Bahrick (1984).
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The Nature of Forgetting
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Generally, more is recognized than can be recalled; therefore, a
distinction should be drawn between a memory’s:
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It is difficult to prove definitively that a memory is truly unavailable.
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Availability:
 Whether or not an item is in the memory store.
Accessibility:
 Whether the memory can be retrieved, assuming that it is stored.
It could simply be temporarily inaccessible because it lacks an
appropriate cue.
Forgetting is not all or nothing but occurs gradually (in a graded
fashion).
Because we cannot differentiate between unavailable and
inaccessible memories they are both said to be forgotten.
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Factors that Discourage Forgetting
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Better initial learning leads to better retention.
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Repeated retrieval attempts (i.e. testing) builds up resistance to
forgetting (Linton, 1975).
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This works at least for those aspects of the memory that are practiced.
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Incomplete or inaccurate retrieval (e.g., containing reconstructive
inferences) may lead to memory distortions.
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Jost’s Law:
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All else equal, older memories are more durable and forgotten less
rapidly than newer memories.
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It is now widely believed that new traces are initially vulnerable to
disruption until they are consolidated into memory.
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Repeated Testing is Protective
The probability of
remembering
something
depends on the number
of times it has been
retrieved or called to
mind. Recalling an
event reduces the rate
of forgetting. Data from
Linton (1975).
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Types of Consolidation
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Consolidation: The time-dependent process by which new
memory traces are gradually cemented and interconnected in
memory.
Synaptic Consolidation
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Structural changes in the
synaptic connections between
neurons.
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The gradual shift of a memory’s
reliance away from the
hippocampus and to the cortex.
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Accomplished by repeatedly
“replaying” a memory’s various
components until they are
interlinked.
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May take years to complete in
humans.
Relies on biological processes
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Systemic Consolidation
May take hours to days to
complete.
Memories remain vulnerable
until these changes occur.
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Memories are vulnerable until
they become independent of the
hippocampus.
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Causes of Incidental Forgetting
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Trace decay – due to the passage of time.
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Applies to working memory and priming effects (activation levels).
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Hard to demonstrate empirically.
Context shifts – this results in different cues being available
and the ones present during encoding being absent.
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This is especially likely as an explanation for infantile amnesia
(forgetting of early childhood).
Interference – storing similar memories impedes retrieval.
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Over time, many similar experiences occur, especially since people are
creatures of habit.
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Factors that Encourage Incidental
Forgetting
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Trace Decay:
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The gradual weakening of memories resulting from the mere
passage of time.
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Commonly thought to partially determine the rate of forgetting for
verbal and visual working memory.
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Repetition priming and familiarity are considered especially
vulnerable to trace decay.
Either:
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A memory’s activation may fade, but the underlying memory is left
intact (i.e. stored/available).
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The memory’s structural elements (i.e. its associations) degrade
along with its activity level.
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Factors that Encourage Incidental
Forgetting
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A biological basis of decay:
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Neurons die and synaptic connections degrade over time, along
with the associated learned behavior.
Trace decay is difficult to prove behaviorally because:
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It is necessary to rule out alternative sources of forgetting, including:
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Rehearsal
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Interference from any new experiences/memories.
It is typically impossible to show whether the memories are
unavailable or just inaccessible.
Factors that Encourage Incidental
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Forgetting
Correlates of Time
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Even if the passage of time (decay) isn’t the direct cause of
forgetting, a correlate of time may, instead, be responsible.
Contextual Fluctuation
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Mismatches between the retrieval
and encoding contexts
encourage forgetting.
 Incidental context (internal and
external) shifts over time.
 Thus, the current incidental
context is most similar to
recent events.
May explain infantile amnesia
 Infant perspective and
linguistic abilities differ
considerably from an adult’s.
Interference
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It is difficult to discriminate
between similar memories.
 The number of similar
experiences/memory traces
accumulates over time.
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Interference arises whenever the
cue that is used to access a
target becomes associated with
other memories.
 e.g. it is difficult generating the
verb meaning of “DUCK”
because the noun meaning is
so dominant.
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Factors that Encourage Incidental
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Forgetting
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Interference
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Competition Assumption (Anderson, Bjork, &
Bjork, 1994):
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A cue activates all of its associates to some degree.
The activated associates compete for access to
awareness.
 Competitors are any associates other than the
target memory.
Interference:
 Any negative effect on memory arising from having
competitors.
 Increases with the number of competitors a target
has, supported by the cue-overload principle:
 The tendency for recall to decrease with the
number of to-be-remembered items paired with
the same cue.
Adapted from Anderson and Neely (1996).
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An Example of Interference
Imagine you are trying to recall where you parked in a shopping center you visit
frequently. Previous parking experiences (e.g. episode #2) interfere with recall
because of shared cues.
From Anderson and Neely (1996). Copyright © Academic Press. Reproduced with permission from Elsevier.
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Retroactive Interference
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Forgetting caused by encoding new traces into memory in between
the initial encoding of the target and when it is tested.
 Introducing a related second list of items impairs recall of the first list
compared to a control condition.
 Especially strong interference if the two lists share cues.
 More training on the second list results in more first list impairment.
Data from Barnes and Underwood (1959).
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Retroactive Interference in
Everyday Life
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Baddeley and Hitch (1977):
 Task:
 Rugby players were asked to
recall the names of teams they
played earlier in the season
 Control:
 Some players missed certain
games, leaving a measure of
forgetting due to decay as
opposed to interference from
intervening games
 Results:
 Time wasn’t a good predictor of
forgetting
 Forgetting increased with the
number of intervening games
Data from Baddeley and Hitch (1977).
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Conclusion:
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Forgetting was due to interference,
rather than trace decay
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Proactive Interference
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The tendency for older memories to interfere with the retrieval of more
recent experiences and knowledge.
 The number of previous learning experiences (e.g. lists) largely
determines the rate of forgetting at long delays.
 Especially strong interference if the learning experiences are similar
(e.g. share a cue).
 Proactive interference effects are worse for recall than for recognition.
Adapted from Underwood (1957).
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Part-Set Cuing Impairment
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Part-Set Cuing Impairment:
 The tendency for target recall
to be impaired by the provision
of retrieval cues drawn from
the same set (e.g. category) of
items in memory.
 The impairment worsens
with the number of cues
provided from the set.
 If items in a set share a
common cue (category):
 Presenting some items
strengthens their
associations to the cue.
 Competition for noncues
increases.
 Memory for noncues
worsens.
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Slamecka (1968):
 Task:
 Study lists of words from
several semantic
categories (e.g. TREES;
BIRDS)
 In the final test, some
people were given some
of the members of each
category as cues to help
recall the rest.
 Results:
 Ironically, providing the
cues (i.e. competitor
items) reduced recall for
the noncue items (i.e.
targets).
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Trees
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Elm
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Oak
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Maple
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Pine
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Aspen
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Beech
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Palm
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Cues provided:
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Elm
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Maple
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Aspen
Noncue items (targets):
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Oak
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Pine
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Beech
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Palm
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Part-Set Cuing in Everyday Life
 Collaborative
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Inhibition:
The tendency for a group of individuals to remember
significantly less material collectively, compared to the
combined performance of group members individually recalling
alone.
May arise from the same mechanisms that produce part-set
cueing impairment:
 When members present some items to the group, it causes
interference, disrupting the rest of the group’s ability to
retrieve additional items.
+ Retrieval-Induced Forgetting (RIF)
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Retrieval-Induced Forgetting:
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Selective retrieval can harm
recall of other memories
related to the retrieved item
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Retrieval Practice Paradigm
(Anderson et al., 1994)
Compared to baseline items,
for which no related items
had been retrieved
Occurs in a variety of situations
in school:
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When reviewing facts
(Macrae & MacLeod, 1999)
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On short answer and essay
tests (Carroll et al., 2007)
Thus, retrieving what we
already know can
contribute to forgetting!
Recall Difference =
Retrieval-Induced
Forgetting
Practiced Category
Adapted from Anderson (2003).
Baseline Items
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Retrieval-Induced Forgetting (RIF)
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RIF in crime scene interrogations
(Shaw, Bjork, & Handal, 1995)
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Task:
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Study Phase:
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Retrieval Practice Phase:
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Watch a slideshow of a
crime scene (a party
where objects were
stolen)
Interrogate subjects about
some of the objects in the
slideshow
Results:
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Interrogating people about
some stolen items impaired
memory for related items
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Socially-Shared RIF
(Cuc, Koppel, & Hirst, 2007)
 Task:
 Study Phase:
 Two people, side-by-side,
studying together
 Retrieval Practice Phase:
 Only one of the two performed
retrieval practice, with second
person observing silently
 Results:
 Both participants showed RIF on
the final test
 Conclusion:
 People spontaneously recall events
along with the person actually
recalling aloud
 Thus, RIF may help shape a
society’s collective memory and
encourage uniformity of memory.
Interference Mechanisms
Mechanism
Associative
Blocking
Description
When a cue fails to elicit a
target trace because it
repeatedly elicits a stronger
competitor, leading people
to abandon efforts to
retrieve the target
Predictions
• StrengthDependence:
Interference should
increase with the
strength of the cuecompetitor association
• Cue-Dependence:
Forgetting is related to
the dominance of the
cue-item association,
not the activation of
memory itself
Associative
Unlearning
Melton and
Irwin’s (1940)
Unlearning
Hypothesis
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When the associative bond
linking a stimulus to a
memory trace is punished
by weakening it after being
retrieved inappropriately
• Cue-Dependence: The
damage is done to the
association between
the cue and the item,
not the memory itself
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Examples
• Tip of the Tongue: We
keep coming up with an
incorrect response
• Part-Set Cueing: Exemplar
cues keep intruding
• Cue-Overload: The more
associates, the more likely
a wrong answer will intrude
• RIF and Retroactive
Interference: Competitors
intrude during retrieval
practice and are punished
Difficult to demonstrate
empirically
Melton et al.’s (1940) Two-Factor Model of Retroactive Interference:
 Both unlearning and blocking are responsible for forgetting
An
Alternative
Interference
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Mechanism: Inhibition
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Inhibition:
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A reduction in the activity level of a contextually inappropriate response
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Allows:
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An unwanted response to be stopped
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An alternative response to be executed
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Results in a long-term difficulty in producing the inhibited response
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Occurs in both the motor and memory domains
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Inhibition in RIF
Prediction
Cue-Independence
Description
Forgetting caused by inhibition should generalize to
novel test cues (independent probes)
Both blocking and unlearning specifically tie forgetting
to the associations to the cues
Retrieval-Specificity
Active retrieval from long-term memory is necessary to
induce RIF for related information
The blocking hypothesis predicts that any method of
strengthening (retrieval or otherwise) is sufficient
InterferenceDependence
Interference from competitors during target retrieval is
necessary for RIF of related information
The blocking hypothesis predicts that any method of
strengthening (retrieval or otherwise) is sufficient
StrengthIndependence
The degree to which competitors are strengthened by
retrieval practice is unrelated to the size of the retrievalinduced forgetting deficit
Blocking predicts forgetting on the sole basis of
strengthening of the competitor
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Example
Learn:
FRUIT–BANANA
Original test:
FRUIT–B_____
• Produces RIF
Independent probe test:
MONKEY–B_____
• Produces RIF
Retrieval practice:
FRUIT–O_____
• Produces RIF
Extra study exposures:
FRUIT–ORANGE
• Does not produce RIF
High-frequency competitor:
FRUIT–BANANA
• Vulnerable to RIF
Low-frequency competitor:
FRUIT–GUAVA
• Resistant to RIF
Impossible retrieval practice:
FRUIT–LU_____
• Still produces RIF on
competitors
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A Functional View of Incidental
Forgetting
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In contrast to other proposed mechanisms of forgetting, which
occur passively, inhibition is an active mechanism that can
serve a useful purpose:
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Facilitates future retrieval attempts of the practiced memories by:
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Inhibiting competitors, thereby reducing interference
Therefore, forgetting can be useful!