Transcript A pioneer of the scientific study of memory: Hermann

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
Implicit memory:
What studies in amnesia have told us
• 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 temporallobes to stop his epileptic seizures, which couldn’t be
treated with medication
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
Repetition priming in amnesia:
Lack of retrieval intentionality is important
-> normal performance of patients on completion task but
impaired cued recall and free recall
-> type of access (implicit vs explicit) to stored info critical
Can repetition priming also be shown to be
different from explicit memory in normal subjects?
• Tulving, Schacter, & Stark (1982):
fragment completion task
study:
test:
incidental learning with semantic decisions;
judge words in terms of animacy
(e.g. twilight, assassin, dinosaur, mystery)
complete fragments with first word that
comes to mind
ch_ _nk
o_t__us
_ssa__in
repetition priming: more completions of studied
than non-studied words
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
Does repetition priming require attention at
time of encoding?
• 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
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 completion
Finding:
no LoP effect on completion task
-> not likely that semantic memory involved
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
If it is perceptual, can priming be observed in
other sensory modalities?
• yes; evidence for perceptual priming on auditory wordstem completion task (after incidental encoding in
auditory modality)
-> priming not limited to visual modality
Can perceptual priming be observed with nonverbal 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 exposure
with studied and non-studied
objects
Finding: more accurate
performance with previously
studied objects (priming)
Is perceptual priming on object decision task an
expression of semantic memory?
• 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
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)
Interpretation of perceptual priming:
Perceptual representation systems (PRS)
• 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
Functional neuroimaging evidence for perceptual
priming in PRS: reductions in brain activation
C: unprimed objects
D: primed objects
activity reductions in
visual cortex for
primed objects
effect at behavioural
level:
priming = facilitated
performance
Problems for studying perceptual priming as
type of implicit memory
• 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 mind
rea___??
gar___??
net___??
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)
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 = automaticity
explicit memory = recollection
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)
Exclusion = i (1- e)
e = Inclusion – Exclusion
i = Exclusion/(1-R)
-> formula allow to get
purified estimates for
implicit (i) and explicit
(e) memory contributions
Process dissociation procedure
finding:
attention only
affects estimates
of explicit not of
implicit memory
-> procedure
offers powerful
way to study
implicit and
explicit memory
processes
separately
explicit
implicit
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
Types of implicit memory other than perceptual
priming: Conceptual priming
• 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 - ??
priming effect:
(note: no perceptual cue from
study phase)
previously studied category members
more likely generated than others
• conceptual priming typically normal in amnesic patients
Types of implicit memory other than perceptual
priming
• 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
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!!
Does implicit memory occur in everyday life?
• yes, most certainly
BUT 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
Amnesia / Amnesic Syndrome:
selective LTM impairments caused by neurological
condition
retrograde
amnesia
remote
past
anterograde
amnesia
recent
past
time
onset
of neurological
condition
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
Neuroanatomical basis of anterograde amnesia:
Where is brain damage typically localized?
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 nonverbal info (scenes, houses etc.)
How can anterograde amnesia be explained?
What is the nature of the memory impairment?
•
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
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)
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?
Motor-skill learning: a type of implicit memory
that is normal in H.M.
• 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
Normal perceptual priming on word-stem
completion task in anterograde amnesia
-> normal performance of patients on completion task but
impaired cued recall and free recall
-> type of access (implicit vs explicit) to stored info critical
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)