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

• 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

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

-> 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

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

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

• 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?

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

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 word-stem completion task (after incidental encoding in auditory modality)

-> priming not limited to visual modality

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)

• 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?

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)

• 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)

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

• 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

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 = automaticityexplicit 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) -> formula allow to get Exclusion = i (1- e) purified estimates for implicit (i) and explicite = Inclusion – Exclusion (e) memory contributions

i = Exclusion/(1-R)

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

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

• 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

• 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

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 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

Amnesia / Amnesic Syndrome:selective LTM impairments caused by

neurological condition

time

anterogradeamnesia

retrogradeamnesia

recentpast

remotepast

onsetof neurologicalcondition

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 non- verbal info (scenes, houses etc.)

• 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?

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?

• 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.

-> 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

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)