A pioneer of the scientific study of memory Hermann Ebbinghaus epilepsy by mikeholy


									   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
                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 temporal-
  lobes 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____?
             (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:     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 mind
                     ch_ _nk

      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)

- semantic decisions
(animate /inanimate)
- physical decisions
(# of capital letters)

- cued recall
- fragment completion
Finding:      no LoP effect on completion task
              -> not likely that semantic memory involved
       Is repetition priming a perceptual type of
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
Study: judge whether object
faces left or right

Test: object decision task
with 100 ms exposure
with studied and non-studied
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

  + 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

priming = facilitated
    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
   Problems for studying perceptual priming as
             type of implicit memory
• does performance on priming task always reflect implicit
  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
  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

  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
  -> 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 explicit
  e = Inclusion – Exclusion         (e) memory contributions
  i = Exclusion/(1-R)
           Process dissociation procedure

attention only
affects estimates
of explicit not of
implicit memory

-> procedure
offers powerful
way to study
implicit and
explicit memory
separately                  explicit   implicit
 Types of implicit memory other than perceptual

• 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

    -> 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 - ??   (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
• is conceptual priming different from perceptual priming?

       + 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

       -> conceptual priming not based on PRS;
          instead builds on semantic memory
      Are they really different types of implicit
• 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

       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
              retrograde       anterograde
              amnesia          amnesia

remote              recent                     time
past                past

                             of neurological
    Neurological conditions that can produce
• 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
• 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

• 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.)
     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
  (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)

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