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Implicit versus explicit memory: Definitions
• implicit memory: past experiences influence perceptions, thoughts and actions without awareness of person that any info from past is accessed
• explicit memory:conscious access to info from past (“I remember that..” )
-> involves conscious recollection -> term generally used synonymously with episodic memory
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• concept evolved out of neuropsychological research in patients suffering from amnesia; later studied in cognitive psychology, social psychology, developmental psychology etc.
• first systematic study in densely amnesic patient H.M. (Brenda Milner, 1960s, in Montreal)
• H.M.:
in 1953, bilateral surgical removal of medial temporal-lobes to stop his epileptic seizures, which couldn’t be treated with medication
Implicit memory:What studies in amnesia have told us
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Is normal implicit memory limited to motor learning in amnesia? No!
• Warrington & Weiskrantz (1970) demonstrate that amnesic patients show preserved implicit memory on list learning with word stem completion task
• Study: table, garden, telephone, lamp, umbrella etc.
Test: - Free Recall- Yes/No recognition- Word stem completion: tab____?
gar____?(Instructions: think of any word that fits stem)
• Finding: amnesic patients show memory deficits on first 2 tests but normal performance on word stem completion
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-> normal performance of patients on completion task but impaired cued recall and free recall -> type of access (implicit vs explicit) to stored info critical
Repetition priming in amnesia: Lack of retrieval intentionality is
important
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Can repetition priming also be shown to be different from explicit memory in normal
subjects? • Tulving, Schacter, & Stark (1982):
fragment completion task
study: incidental learning with semantic decisions; judge words in terms of animacy
(e.g. twilight, assassin, dinosaur, mystery)
test: complete fragments with first word that comes to mindch_ _nko_t__us
_ssa__in
repetition priming: more completions of studied than non-studied words
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Repetition priming in normal subjects
• Tulving, Schacter, & Stark (1982):
+ repetition priming effects long-lasting (no ‘forgetting’ over a week or more)
+ by contrast, recognition memory for previously studied words shows some forgetting
->> even in normals implicit memory can be distinguished from
explicit/episodic memory
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• informal (unethical!) observation with ‘mock crisis’ in 1960s:faked crisis during surgery causes subsequent agitation in patients recovering from surgery, without their knowing why
• systematic (ethical!) studies show that encoding under anesthesia produces repetition priming when patients are tested after surgery on word-fragment completion task
-> no allocation of attention required at encoding
Does repetition priming require attention at time of encoding?
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Is repetition priming linked to semantic memory?
Does it benefit from semantic encoding ?(LoP study; Graf & Mandler)
study:- semantic decisions (animate /inanimate)- physical decisions(# of capital letters)
test:- cued recall- fragment completionFinding: no LoP effect on completion task -> not likely that semantic memory involved
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Is repetition priming a perceptual type of memory?
two important findings:
• reductions in repetition priming effects with
+ changes in modality between study and test(e.g. encoding of words in auditory modality
word-fragment completion test in visual modality)
+ changes in perceptual characteristics of words between study and test (e.g. font, uppercase/lowercase)…
-> suggests that priming reflects a perceptual type of memory; fits with finding of no LoP effect
best term to capture phenomenon: perceptual priming
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If it is perceptual, can priming be observed in other sensory modalities?
• yes; evidence for perceptual priming on auditory word-stem completion task (after incidental encoding in auditory modality)
-> priming not limited to visual modality
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Can perceptual priming be observed with non-verbal stimuli?
• experiments with possible and impossible objects by Schacter & Cooper (early 90s)
Study: judge whether object faces left or right
Test: object decision task with 100 ms exposurewith studied and non-studied objects
Finding: more accurate performance with previously studied objects (priming)
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• Schacter & Cooper (early 90s)
comparison of encoding effects for recognition memory (explicit) and perceptual priming on object decision task (implicit)
+ physical vs semantic judgements at encoding (left-right facing vs what real object does it remind
you of)
-> semantic encoding only improves recognition
-> finding suggests that priming perceptual in nature
Is perceptual priming on object decision task an expression of semantic memory?
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Interpretation of perceptual priming: Perceptual representation systems (PRS)
• theory proposed by Schacter & Tulving:
+ perceptual representation systems: not dedicated memory systems but
perceptual systems that keep memory as by-product of perceptual analysis
analogy: hot-tube effect with stove
+ memory representations in PRS operate implicitly
(no conscious recollection possible)
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• Schacter & Tulving:
visual representation system for words -> representation: visual word forms
visual representation system for objects-> representation: structural descriptions of
objects
auditory representation for words-> representation: auditory word forms
(phonology)
perceptual representation systems rely on brain structures that perform perceptual analyses
e.g. visual representation systems localized in visual cortex
Interpretation of perceptual priming: Perceptual representation systems (PRS)
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Functional neuroimaging evidence for perceptual priming in PRS: reductions in brain
activation
C: unprimed objectsD: primed objects
activity reductions in visual cortex for primed objects
effect at behavioural level:
priming = facilitated performance
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• typical set-up of priming study
study: incidental encoding of word list (table, garden, telephone,
umbrella etc.)
priming test: word stem completion complete word stem with first
word that comes to mindrea___??gar___??net___??
Problems for studying perceptual priming as type of implicit memory
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Problems for studying perceptual priming as type of implicit memory
• does performance on priming task always reflect implicit memory?
no! -> problem of ‘explicit contamination’
e.g. subjects may rely on conscious recollection to perform stem completion task even when no explicit memory instructions are given
-> presumed implicit memory task may not always measure concept of implicit memory
• L. Jacoby’s approach to purify measures of implicit memory:
process dissociation procedure (method of opposition)
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Process dissociation procedure to purify measures of implicit memory
• experiment by Jacoby et al. with word-stem completion task
Study: incidental encoding of words under full or divided attention
Test: word-stem completion task under Inclusion or Exclusion instructions
Jacoby’s terminology: implicit memory = automaticityexplicit memory = recollection
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Process dissociation procedure• inclusion condition:
try to generate a word that begins with stem; simply take first word that comes to mind; you can take one presented earlier-> implicit and explicit memory work in same direction
• exclusion condition:
try to complete stem but avoid completions of words presented earlier-> implicit and explicit memory work in opposite direction
Inclusion = e + i (1 - e) -> formula allow to get Exclusion = i (1- e) purified estimates for implicit (i) and explicite = Inclusion – Exclusion (e) memory contributions
i = Exclusion/(1-R)
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finding:
attention only affects estimates of explicit not of implicit memory
-> procedure offers powerful way to study implicit and explicit memory processes separately
Process dissociation procedure
explicit implicit
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Types of implicit memory other than perceptual priming
• motor skill learning (e.g. mirror drawing task)
+ normal in amnesic patient H.M.
-> does not rely on medial temporal lobe structure
+ patients with Huntington’s disease (neurological disease of motor system; brain damage in basal ganglia) show impaired motor skill learning but normal perceptual priming
-> does not rely on PRS either-> type of implicit memory that is different
from perceptual priming
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• can be shown with category instance generation task
study: incidental encoding of words (e.g., cycle, tree, mail, elephant, tulip etc.)
test: name as many members of the following category in 1 min
e.g., flowers - ?? (note: no perceptual cue from study phase)
priming effect: previously studied category members more likely generated than others
• conceptual priming typically normal in amnesic patients
Types of implicit memory other than perceptual priming: Conceptual priming
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• is conceptual priming different from perceptual priming?
yes!!
+ it benefits from semantic encoding (LoP effect)
+ not affected by switch in perceptual modality between study and test
+ dissociation in patients with Alzheimer’s disease:
normal perceptual priming but impaired conceptual priming
-> suggests that they rely on different brain structures
-> conceptual priming not based on PRS; instead builds on semantic memory
Types of implicit memory other than perceptual priming
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Are they really different types of implicit memory?
• perceptual priming
• conceptual priming
• motor skill learning
-> research suggests that each of them relies on different brain structures and has different
functional characteristics (e.g. modality, LoP effect, forgetting curve)
BUT commonality:implicit access to information from past -> unconscious form of memory!!
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Does implicit memory occur in everyday life?
• yes, most certainlyBUT difficult to grasp given its unconscious
nature
• applied research shows:+mere exposure to advertisements influences
subsequent affective judgments of these ads (attitudes), although subjects don’t
remember seeing them (Perfect & Askew, 1994)
• Schacter’s examples:
+ unintentional plagiarism (conceptual priming?)
e.g. George Harrison’s ‘My sweet lord’
+ motor skills, e.g. in sports and music
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Amnesia / Amnesic Syndrome:selective LTM impairments caused by
neurological condition
time
anterogradeamnesia
retrogradeamnesia
recentpast
remotepast
onsetof neurologicalcondition
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Neurological conditions that can produce amnesia
• temporal lobe resection (neurosurgery)• traumatic closed head injury (massive blow to head)• herpes simplex encephalitis (viral infection)• ischemia (vascular problem; interruption of blood flow to
brain)• stroke, ruptured aneurysm (bleeding from blood vessel)• Korsakoff’s syndrome (Vitamin B1 deficiency)• Alzheimer’s disease (type of dementia)
Milder, more limited memory impairments also with:• epilepsy (brain seizures)• brain tumors• chronic alcoholism
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Neuroanatomical basis of anterograde amnesia: Where is brain damage typically
localized?
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Selective memory impairments of H.M. and other patients suffering from
anterograde amnesia
• in neuropsychological testing:
+ normal IQ+ normal perceptual and language functions+ severe deficits on episodic memory tasks; not specific to particular info / material:
e.g. problems with- learning of word lists
- recognition of faces and other non- verbal info (scenes, houses etc.)
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• general findings in amnesic patients:
+ normal STM capacity on digit-span task + normal forgetting curve on Brown-Peterson task
+ normal recency effect in serial position curve
How can anterograde amnesia be explained?
What is the nature of the memory impairment?
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Additional evidence showing that memory deficit is specific to LTM in amnesic patients:
lists larger than STM span extremely difficult to learn for patients (Drachman & Arbit, 1966)
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How can anterograde amnesia be explained?
What is the nature of the memory impairment?
• STM / WM intact-> problem in long-term memory (LTM)
but does it affect all aspects of LTM?
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• mirror tracing task: builds on procedural memory for skills
• improvement in tracing performance with practice but no recollection of previous training sessions (i.e. episodes)
-> suggests that H.M. retains some info over long-term and can access it implicitly
Motor-skill learning: a type of implicit memory that is normal in H.M.
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-> normal performance of patients on completion task but impaired cued recall and free recall -> type of access (implicit vs explicit) to stored info critical
Normal perceptual priming on word-stem completion task in anterograde amnesia
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How can anterograde amnesia be explained?
What is the nature of the memory impairment?
• STM / WM intact-> problem in long-term memory (LTM)
• implicit memory intact+ perceptual priming + conceptual priming+ motor-skill learning procedural memory
(learning how to)
-> problem in explicit memory (consciously processed info in LTM)