Implicit memory - PowerPoint PPT Presentation

About This Presentation
Title:

Implicit memory

Description:

Implicit memory Schacter and many other researchers distinguish between implicit and explicit memory This lecture will begin by surveying some historical observations ... – PowerPoint PPT presentation

Number of Views:272
Avg rating:3.0/5.0
Slides: 69
Provided by: Baycre
Category:

less

Transcript and Presenter's Notes

Title: Implicit memory


1
Implicit memory
  • Schacter and many other researchers distinguish
    between implicit and explicit memory
  • This lecture will begin by surveying some
    historical observations regarding implicit memory
  • It will then focus on a particular type of
    implicit memory, habits or skills, that are
    mediated by the basal ganglia
  • Particular attention will be given to lesion
    studies and studies of patients with Parkinsons
    disease, which is associated with impaired basal
    ganglia functioning

2
Implicit memory
  • implicit memory
  • occurs when previous experiences facilitate
    performance on a task that does not require
    conscious recollection of those experiences
  • explicit memory
  • occurs when the task requires conscious
    recollection of past experiences

3
Implicit memory
  • Historical survey
  • Maine de Biran proposed that after sufficient
    repetition a habit can be executed automatically
    and unconsciously without awareness of the act
    itself or of the previous episodes in which the
    habit was learned
  • Maine de Biran also developed a form of multiple
    memory system

4
Implicit memory
  • Historical survey
  • Carpenter (1874) noted the importance of
    autobiographical recognition or awareness in
    normal memory
  • Neurology
  • Korsakoff noted that amnesic patients were
    affected by previously experienced events even
    though they were consciously unaware of these
    events
  • Claparede refusal of amnesic to shake hands after
    he had pricked her hand

5
Implicit memory
  • Historical survey
  • Neurology
  • Schneider 1912 showed that amnesics required less
    information across learning trials to identify
    fragmented pictures

6
Implicit memory
  • Historical survey
  • Psychiatry
  • Freud and Janet investigated patients suffering
    hysterical amnesia as a result of emotional
    trauma
  • these patients could not explicitly remember the
    traumatic event, but their memories of these
    events were expressed indirectly (implicitly)
  • Janet --hysterical amnesia consists of 1. the
    inability of a subject to evoke memories
    consciously and voluntarily and 2. Automatic,
    compelling, and untimely activation of these
    memories

7
Implicit memory
  • Modern research on implicit memory
  • effects of subliminally encoded stimuli
  • several studies have shown that stimuli that are
    not represented in subjective awareness
    (consciously) are nevertheless processed to high
    levels by the perceptual system

8
Implicit memory
  • e.g., Kunst-Wilson Zajonc (1980)
  • presented geometric shapes for 1 ms claimed it
    was too brief a period of time to permit its
    perception subsequently tested recognition
    (forced choice) and preference (forced choice)
  • Results recognition (RN) was at chance Subjects
    preferred the previously presented geometric shape

9
Implicit memory
  • e.g., Bargh Pietromonaco (1982)
  • presented hostile words and then later had
    participants rate a target person
  • results showed that explicit recognition memory
    of hostile words was at chance, although
    ratings of the target person were more negative
    than those who did not receive prior exposure
  • e.g., divided attention study of Eich (1984)

10
Implicit memory
  • e.g., divided attention study of Eich (1984)
  • auditory divided attention task
  • unattended channel -- presented homophones (e.g.,
    taxi fare)
  • subsequently participants showed no explicit RN
    memory in yes/no task, but tended to spell
    homophones in biased direction compared to
    baseline performance

11
Implicit memory
  • Learning and conditioning without awareness
  • participants learn rules or contingencies without
    explicit memory for them
  • this phenomenon was studied in multitrial
    learning experiments and in classical
    conditioning experiments

12
Implicit memory
  • Implicit learning studies of Reber
  • subjects were presented letter strings that were
    organized according to rules of an artificial
    grammar
  • Reber reported that subjects could categorize
    these strings correctly even though they were
    unable to consciously aware of the rules

13
Implicit memory
  • Repetition priming effects
  • facilitation in processing of a stimulus as a
    function of recent prior exposure to the same
    stimulus
  • note repetition priming has been observed under
    a wide variety of test conditions, none of which
    require explicit reference to a prior study
    episode
  • lexical decision (word/nonword) -- DV latency
  • word identification
  • word stem or fragment completion (e.g., __
    ss__ss__)

14
Implicit memory
  • Repetition priming effects
  • 1. used to study nature of lexical representation
  • e.g., studied the effects of auditory
    presentation on subsequent word identification
    and lexical decision tasks
  • results showed little or no priming
  • e.g., morphologically similar words (e.g., seen)
    facilitate priming of (sees), but visually
    similar words do not prime each other (e.g.,
    seen) versus (seed)

15
Implicit memory
  • Repetition priming effects
  • 2. used to study relation of implicit to explicit
    memory
  • stimulated by studies of Warrington and
    Weiskrantz on amnesics
  • this study showed that amnesics showed excellent
    retention when they were asked to complete
    three-letter stems of recently presented words
    even though their yes/no recognition memory was
    impaired

16
Implicit memory
  • Repetition priming effects
  • 2. used to study relation of implicit to explicit
    memory
  • several studies have shown that variations in
    level or type of study processing have
    differential effects on priming versus
    remembering
  • e.g., Jacoby Dallas (1981) showed that
    answering questions about the meaning of a target
    word improved yes/no recognition memory relative
    to answering questions about presence of a
    letter, but that word identification was
    unaffected

17
Implicit memory
  • Repetition priming effects
  • 2. used to study relation of implicit to explicit
    memory
  • modality shift
  • Jacoby Dallas (1981) showed that changing from
    auditory (at study) to visual (at test) severely
    attenuated priming effects as assessed by word
    identification, but had little effect on yes/no
    recognition performance

18
Implicit memory
  • Repetition priming effects
  • 2. used to study relation of implicit to explicit
    memory
  • other factors that have been manipulated
  • study-test delay--variable effects
  • manipulations that affect retroactive and
    proactive interference (and hence explicit
    memory) have little effect on word-stem or word
    fragment completion

19
Implicit memory
  • Repetition priming effects
  • 2. used to study relation of implicit to explicit
    memory
  • other factors that have been manipulated
  • study-test delay--variable effects
  • manipulations that affect retroactive and
    proactive interference (and hence explicit
    memory) have little effect on word-stem or word
    fragment completion

20
Implicit memory
  • Habit or skilled learning
  • Several lines of evidence suggest that the
    caudate nucleus mediates a particular type of
    implicit memory, habit memory or memory for
    skills, that are incrementally acquired
  • This type of memory can be dissociated from
    explicit memory
  • Caudate nucleus is part of the basal ganglia

21
Implicit Memory
Explicit Memory
Priming
Nonassociative Learning
Neocortex
Reflex Pathways
Facts (Semantic Memory)
Events (Episodic Memory)
Skills and Habits
Simple Classical Conditioning
Striatum
Medial Temporal Lobe
Emotional Response
Skeletal Musculature
Amygdala
Cerebellum
Squire and Knowlton (1994) Squire (1987)
Declarative vs. procedural memory
22
Habits and skills
  • Characteristics of habits and skills
  • Habits are learned (acquired via experience
    dependent plasticity)
  • Habits are performed repeatedly over time
  • Habits are performed almost automatically and
    nonconsciously
  • Habits tend to involve an ordered, structured,
    action sequence
  • Habits are elicited by a particular context or
    sequence (either internal or external)
  • Habits can be habits of thought and habits of
    motor expression

23
Habits and skills
  • Background
  • Anatomy
  • Basal ganglia (BG) plays an important role in
    normal voluntary movement
  • Input to BG received from cerebral cortex and
    output sent to brain stem and via the thalamus
    back to the prefrontal, premotor, and motor
    cortices

24
BG in relation to brain structures
  • Basal ganglia receives i/p from cerebral cortex
  • o/p from BG goes from thalamus back to cerebral
    cortex
  • o/p also goes to spinal cord

25
Habits and skills
  • Background
  • Basal ganglia
  • Consists of 4 major nuclei
  • Caudate nucleus
  • Putamen
  • Globus pallidus
  • Subthalamic nucleus
  • Striatum consists of caudate nucleus, putamen,
    and ventral striatum

26
BG
  • Coronal view of BG in relation to surrounding
    structures
  • Medial view of BG note left side is anterior
    right side is posterior

27
Habits and skills
  • Background (circuits in BG)
  • There are several circuits connected to
    prefrontal regions of the cortex these include
  • Dorsolateral prefrontal circuit
  • Involved in executive function
  • Lateral orbitofrontal circuit
  • Plays a major role in mediating empathic,
    socially appropriate responses
  • Anterior cingulate circuit
  • Appears to play an important role in motivated
    behavior

28
Habits and skills
  • Background (diseases associated with BG deficits)
  • Movement disorders associated with basal ganglia
  • Parkinsons disease (described by Parkinson 1817)
  • Hypokinetic disorder
  • Impaired initiation of movement (akinesia)
  • Reduced amplitude and velocity of movement
    (bradykinesia)
  • Involuntary tremulous movement
  • Lessened muscular power
  • Increased muscle tone (rigidity)
  • Shuffling gait

29
Habits and skills
  • Parkinsons disease (described by Parkinson 1817)
  • Results from an insufficiency of a
    neurotransmitter (dopamine) in the substantia
    nigra
  • It has been shown that px with PD have a
    deficiency in dopamine in the striatum, most
    particularly in the putamen
  • in 1960s it was shown that injection of L-DOPA,
    the precursor of dopamine led to a reversal of
    symptoms temporarily (for about 5 years)
  • Huntingtons disease
  • Hyperkinetic disorder
  • Excessive movements
  • Heritable and results from a gene defect

30
Habits and skills
  • Role of BG in learning and memory
  • BG is involved in S-R association formation or
    the formation of habits or skills, and this form
    of memory is dissociable from declarative memory
  • Animal lesion study (see Eichenbaum, 2002 for
    further information)
  • This has been investigated in an 8-arm radial
    maze with different task requirements (e.g.,
    McDonald White, 1993)

31
Habits and skills
  • Animal lesion study
  • Win-shift maze
  • maze is put in a room and the rat is permitted to
    encode stimuli around the room to provide spatial
    cues
  • on every trial a food reward is placed at the end
    of the maze rat is released from centre of maze
    and is allowed to retrieve food
  • optimal performance occurs if the rat enters each
    arm only once. This means the rat must have
    memory for the mazes that were previously entered

32
Habits and skills
  • Role of BG in learning and memory
  • Win-stay maze
  • 8-arm radial maze used, but maze surrounded by a
    curtain, and lamps were used to illuminate 4
    randomly selected arms of the maze
  • food was baited in the illuminated mazes only
    when an arm was entered for first time, the maze
    was rebaited after second time the light was
    turned off and no more food was provided
  • task was to associate a particular stimulus
    (light) with food across all trials and it was
    expected that declarative memory was not
    required, but habit memory was required

33
radial arm mazes
  • Radial arm maze configurations to illustrate
    win-shift and win-stay procedures
  • rewarded arm

34
Habits and skills
  • Results
  • Win-shift
  • Rats with hippocampal damage made more errors
    than controls by visiting previously visited maze
    arms
  • Rats with striatal damage were unimpaired
    compared to normal animals (controls)
  • Win-stay
  • Normal control rats learned strategy over several
    sessions
  • Rats with hippocampal damage learned somewhat
    faster than controls
  • Rats with striatal damage were badly impaired and
    were at about chance levels of performance even
    after extended practice

35
Habits and skills
  • Conclusions
  • Selective damage to the hippocampus impairs
    performance on a task requiring declarative
    memory
  • Selective damage to the striatum interferes with
    habit learning

36
Sequence learning
  • Human research
  • Further support for the dissociation between
    habit memory and declarative memory
  • Sequence learning

37
Sequence learning
  • Human research
  • Evidence suggests that amnesics are unimpaired in
    manual sequence learning (Reber Squire (1998).
    Journal of Cognitive Neuroscience 10, 248-265
  • This perceptual-motor habit was investigated in a
    serial response time (SRT) task paradigm
  • SRT task. Participants are shown a visual cue in
    1 of 4 locations by pressing a key corresponding
    to the location of the cue
  • Cues follow a repeating sequence of locations (n
    12 124313214234)

38
Sequence learning
  • Amnesics and controls and controls were given SRT
    training. Other unimpaired control groups
    (Memory) memorized the sequence of responses (see
    Table for details). All groups had their implicit
    and explicit memory tested
  • The Memory control groups memorized the sequence
    of responses by watching the computer screen and
    attempting to memorize the sequence of responses

39
Sequence learning
40
Sequence learning
  • Results
  • Amnesics and controls had decreasing SRT RTs to
    practiced SRT across trial blocks
  • Next figure presents implicit memory performance
    by group
  • Note amnesics and controls were the only groups
    to show implicit memory

41
Sequence learning
  • Top panel. Open bars present RT for sequence S1
    (practiced by amn and con) open bars shaded bar
    presents RT for N1 (unpracticed)
  • Bottom paneldifference between S1 and N1
    (measure of implicit memory

42
Sequence learning
  • This Figure presents for each group explicit
    memory performance, assessed by recognition
    memory performance of 5 sequences (1 target and 5
    lures) on a scale from 0 to 100

43
Sequence learning
  • Results
  • Note amnesics showed little evidence of explicit
    memory, in comparison to other groups
  • Memory controls (esp. young) showed explicit
    memory performance

44
Sequence Learning
  • Filled squares amnesic
  • Open square combined performance of young
    subjects
  • Open triangle controls
  • Open circle Mem old participants
  • Note cross-over interaction

45
Sequence learning
  • Conclusions
  • Proposed that cross-over interaction shown in
    Figure 5 reflects encapsulation of implicit and
    explicit memory in different memory systems
  • Explicit memory mediated by hippocampal/diencephal
    ic brain structures
  • Implicit memory mediated by motor cortex,
    neostriatal, supplementary motor area

46
Sequence learning
  • Human research (PD)
  • Wilkinson 2009, Neuropsychologia, 47, 2564-2573
  • Investigated implicit explicit memory in SRT
    task in PDs and controls
  • Hypothesized that PDs would be impaired in their
    implicit memory for SRTs and would also be
    impaired in their explicit memory for explicitly
    presented SRTs

47
Sequence learning
  • Human research (PD)
  • Wilkinson 2009, Neuropsychologia, 47, 2564-2573
  • Exp. 1 implicit SRT
  • Sequence was presented probabilistically to
    introduce noise and decrease opportunities for
    explicit learning
  • E.g., one group of Ps were shown
    3-1-4-3-2-4-2-1-3-4-1-2, 85 of the time and
    4-3-1-2-4-1-3-2-1-4-2-3, 15 of the time
  • 10 blocks of trials each block with 120 trials of
    SRT task

48
Sequence learning
  • Human research (PD)
  • Implicit sequence learning assessed by comparing
    difference between probable and improbable
    sequence Reaction time

49
Sequence learning
  • PDs shown in back controls shown in white
  • designates blocks in which difference between
    probable and improbable sequence is significant
    (p lt .05)
  • Note evidence of implicit learning for controls
    stronger than for PDs

50
Sequence learning
  • Human research (PD)
  • Explicit sequence learning
  • After final implicit SRT block presented,
    explicit sequence learning was tested
  • Inclusion condition participants were presented
    a sequence of 5 cues from probable sequence and
    were instructed to recall the next correct
    response (Inclusion)
  • Exclusion condition participants were presented
    sequence of 5 cues from probable sequence and
    were instructed to respond with the next cue that
    was inconsistent with the training sequence

51
Sequence learning
  • Results show that for controls and PDs there was
    no significant difference between inclusion
    probable and baseline and between exclusion
    probable and baseline
  • Hence no evidence of explicit memory for sequence

52
Sequence learning
  • Human research (PD)
  • Conclusion Wilkinson data suggest that PDs are
    impaired in probabilistic sequence learning
    relative to controls
  • There is no evidence for explicit memory for
    either group
  • Findings suggest that BG plays a role in implicit
    sequence learning
  • Findings by Reber and Squire, which showed that
    amnesics were not impaired in sequence learning,
    suggest that a form of habit memory was not
    mediated by MTL

53
Implicit memory- cognitive habits
  • Human research Cognitive habits
  • Traditionally the impairment in the basal ganglia
    was known to result in motor deficits based on
    observations of patients with PD and Huntingtons
    disease
  • Aside PD affects dopaminergic input to the
    striatum Huntingtons disease affects cells in
    the striatum
  • It now appears that BG is involved in acquisition
    of cognitive habits that involve the gradual
    formation of S-R associations

54
Implicit memory- cognitive habits
  • Human research
  • Probabilistic classification learning
  • Knowlton and her colleagues have studied px and
    their performance on the probabilistic
    classification task
  • weather prediction task
  • Participants are presented 1 to 3 of 4 cards and
    task was to predict sunshine or rain based on
    cues presented cards had complex geometric
    shapes
  • Each card and card combination was
    probabilistically associated with 2 outcomes
  • after making prediction participant was given the
    actual outcome (see next figure)

55
Probabilistic classification learning
  • Panel A. Probability of sunshine for individual
    cards
  • Panel B. conjoint probabilities associated with
    various card combinations and example of trial
    series

56
Implicit memory- cognitive habits
  • Human research
  • Probabilistic classification learning
  • Note task has been designed so that specific
    memory for outcomes associated with card
    combinations is not as useful, first because
    there are several card combinations, and second,
    because any given card combination may have an
    outcome of sunshine or rain associated with
    it
  • More useful is a general sense of the
    relationship between cues and outcomes across
    trials

57
Implicit memory- cognitive habits
  • Human research
  • Probabilistic classification learning
  • Results
  • Controls
  • Over 50 trials normal controls improved from pure
    guessing (50) correct to about 70 correct
    (highest performance possible)
  • PD px did not show significant learning and
    performance was worse in px with more severe
    Parkinsonian symptoms (Knowlton, 1994, Science,
    273, 1399-1402)
  • After training PD px and controls were given
    questions about the task and nature of the
    stimuli (declarative tasks) performance of the
    two groups did not differ
  • Results from amnesics show an opposite
    dissociation unimpaired performance on the
    weather prediction task and impaired performance
    on the declarative memory task (Knowlton, 1994,
    Learning and Memory 1, 106-120 Reber, 1996,
    Behavioral Neuroscience, 110, 859-869)

58
Implicit memory- cognitive habits
  • Human research
  • Interactions between implicit and declarative
    memory
  • When task conditions favor implicit learning
    medial temporal activity decreases as striatal
    activity increases (Foerde, 2006 Foerde, 2007)

59
Implicit memory- cognitive habits
  • Human research
  • Foerde et al. (2006) PNAS, 103, 11778-11783
  • This experiment investigated the hypothesis that
    the declarative and habit memory systems compete
    with each other in tasks in which both systems
    are involved
  • This raises the possibility that it might be
    possible to modulate the operation of these
    systems by introducing a secondary task
  • Previous research has shown that performing a
    secondary task that requires working memory
    should decrease declarative memory and thereby
    bias (increase) the operation of the habit memory
    system

60
Implicit memory- cognitive habits
  • Human research
  • Prediction then is that dividing attention should
    affect the way in which a task is performed
  • Overview of procedure and design (see also next
    figure). Participants were given weather
    prediction training (PCT task) for two different
    cities based on presentation of two sets of cues
    half the cues for a given city were trained under
    single task conditions (ST) and half the cues for
    that city were trained under dual task conditions
    (DT)
  • Secondary task was tone counting task in which
    participants counted the number of high tones

61
Implicit memory- cognitive habits
  • Human research
  • After training participants were given a probe
    run in which participants were shown cues that
    had been trained under ST or DT conditions and
    were required to predict sun or rain (done in
    fMRI) no tone task administered here
  • After scanner, participants were given test of
    declarative memory which required flexible
    knowledge about task (e.g., participants shown
    all 4 single cues and asked to select cue most
    likely to be associated with sun task repeated
    for two-cue combinations, and 3-cue combinations)

62
Foerde procedure
  • Tone counting
  • Train on weather prediction (single, dual)
  • In DT condition report number of high tones
  • Baseline button push condition
  • Probe run predict weather

63
Implicit memory- cognitive habits
  • Results
  • Behavioral results shown in next figure showed
    that PCT performance during training was higher
    after run 2 than run 1 and marginally higher in
    ST than DT (See a)
  • Probe task (see b) no difference between ST and
    DT in weather prediction performance in probe
    task
  • Cue selection (test of declarative memory, see c)
    participants were significantly better in the ST
    than DT condition suggesting that a more flexible
    memory representation was obtained

64
  • Fig a. PCT performance during training
  • Fig b. PCT performance during probe task
  • Fig c. declarative memory performance

65
Implicit memory- cognitive habits
  • Results
  • fMRI results in next figure (see b) showed that
    probe accuracy was correlated with right
    hippocampus activity in ST but not DT condition
  • Figure d showed that probe accuracy was
    correlated with left putamen activity in DT but
    not in ST condition
  • Recall hippocampus associated with declarative
    memory
  • Putamen is part of BG, which is implicated in
    habit memory

66
fMRI results
67
Implicit memory
  • Conclusions
  • Memory for PCT can be either MTL or striatal
  • Declarative memory depends on executive
    functions, but habit learning does not appear to
    depend upon it (recall secondary task effects)
  • Although PCT performance can be supported by MTL
    or striatal systems, the type of memory system
    mediating performance affects flexibility of
    memory (recall declarative memory test)

68
Implicit memory
  • Conclusions
  • In disease states involving dysfunction of the BG
    medial temporal lobe may be present when normally
    striatum activity would dominate (Moody, 2004)
Write a Comment
User Comments (0)
About PowerShow.com