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Remembering and Forgetting

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									Remembering and Forgetting



  Cognitive Neuroscience
                Learning and Memory

Two kinds of knowledge:
     Hard-wired
     Learned (memories)


―Learning is the process of acquiring new information,
  while memory refers to the persistence of learning in a
  state that can be revealed at a later time‖ (Squire)

The study of how the brain remembers is largely a study of
  how the brain learns; memory systems reflect learning
  systems.
                  Distinctions in memory

   Time scale of storage:
       Sensory memory
       Short-term memory (STM) –working memory
       Long-term memory (LTM)
   Types of memory (knowledge:
       Procedural/declarative
       Implicit/explicit
   Stages of memory
       Encoding
       Storage-consolidation
       retrieval
                            functional

        structural   material       information

large




small
            Time-Scale: Sensory Memory

   Information available for brief periods, over-
    ridden by incoming info

       Visual:     iconic (500 ms)
       Auditory:   echoic (several seconds)


   Evidence: full/partial report
K   L   N   R   S

J   H   M   T   W

Q   X   P   B   V
P   H   V   K   S

T   J   M   R   V

Q   Z   B   L   W
                       H.M.
            Scoville & Milner (1957)-etc.
   Bilateral medial temporal lobectomy
    (hippocampi)
   Age 29 to alleviate chronic, severe epilepsy
   Normal IQ
                        H.M.
              Scoville & Milner (1957)
   Normal digit span (7 +/-2)-a test of STM
   Despite normal STM, if the examiner left the
    room he would not remember ever having met the
    person or performed the task
   Effects of learning persist temporarily, can create
    new short-term but not long-term memories
   Supports the distinction between STM/LTM
                           K.F.
               Shallice & Warrington (1970)
   28 years old
   Left parieto-occipital damage following a motorbike
    accident at age 17
   Normal IQ
   Normal memory ability otherwise
   Digit span=1

   HM and KF provide a double dissociation of STM/LTM
              Why is a double dissociation useful?
Courtney, et al., 1997
                           H.M.
                 Scoville & Milner (1957)
   H.M.’s recall of old memories is relatively intact
   His memory performance represents a distinction
    between types of learning or formation of new
    memories (new STM vs. new LTM)

   anterograde/ retrograde amnesia
       Anterograde: loss of ability to create new lasting
                     memories
       Retrograde:  loss of ability retrieve old memories
               Types of LTM memory:
               Procedural/Declarative
H.M.
    not all types of new, long-term memory creation were
     affected
    Motor procedures
                 Types of memory:
               Procedural/Declarative
H.M.
      cognitive procedures
                   Types of Knowledge:
                 Procedural vs. Declarative
   Procedural:       knowledge of processes (motor,
                      perceptual or cognitive)
   Declarative:      knowledge of facts and events
                      (knowledge ―that‖)
         Episodic:   knowledge of specific personal experiences,
                      their content, time place
         Semantic:   world, word knowledge
      Types of Memory or Memory Retrieval:
                Implicit/Explicit
   Implicit:        knowledge that can be retrieved
                     without conscious recollection
   Explicit:        knowledge that can be retrieved
                     only with conscious recollection
   Neurologically intact individuals (as well as
    amnesics) show many dissociations in terms of
    implicit/explicit memory abilities
       Types of Memory or Memory Retrieval:
                 Implicit/Explicit




Subjects report digits were presented in completely random sequences, altho RTs to
   repeating sequences become faster as compared to random sequences
                      Memory stages

   Encoding
   Consolidation/storage
   Retrieval

   HM—difficulties specifically in consolidation
       Although his amnesia was primarily anterograde, there
        was a retrograde component
                       Memory Stages:
                        Consolidation
   Retrograde amnesia:
       Focal retrograde amnesia: primary deficit is a loss of
        remote memory
       Graded retrograde amnesia: memory loss inversely
        related to time of learning  implies consolidation
                       Memory Stages:
                        Consolidation


   Korsokoff Syndrome:
           long-term alcohol abuse leads to vitamin deficiences that
           cause brain damage-diencephalic (dorso-medial thalamic
           nucleus, mamillary bodies, MTL, frontal)
          Shows similar profile as hippocampal lesions
                         Neural Bases

   Neocortex:
         creating new procedural memories
         Implicit memory retrieval
   MTL and diencephalon:
         Creating and consolidating declarative memories
         Explicit memory retrieval
   Frontal lobes:
         Encoding and Retrieval
    McClelland, McNaughton & O’Reilly (1995)

Two learning systems: Neocortical, hippocampal

   Neocortex:         -learns slowly, by making small
                       adjustments to connections among neurons
                       -allows integration into complex knowledge
                       structures
   Hippocampus:       -learns quickly
                       -supports rapid, one-trial learning
                       -during consolidation serves as
                       ―teacher‖ to the neocortex, until
                       neocortical connection changes are robust
                           Frontal Lobes

   Damage is associated with high false recognition
    rates (false memories)
       Work is ongoing to understand to what extent this is
        due to encoding or retrieval failures (or both)
           If encoding failure: expect improvement with instructions and
            strategies for more efficient encoding
           If retrieval failure: expect improvement with instructons for
            more stringent retrieval criteria
           False memories

Chair
Stapler
Basement
Button
Giraffe
Fork
Book
Train
Lettuce
Garage
Apricot
Glass
          False memories

button
door
cellar
train
shoe
spoon
soldier
                                 False Memories

   Lest you be overconfident:

    ―In a 1992 op-ed piece for the New York Times, Garry Trudeau recollected some of his experiences
    related to the draft for the Vietnam War. Trudeau remembered receiving calls of concern from
    friends and family on the night of the draft lottery, after they had heard about his low number. He
    then recalled a series of events involving his attempts to gain a draft deferment: requesting a
    national security deferment from the draft board for his work with a magazine; deciding not to apply
    for conscientious objector status because he could imagine circumstances in which he would take
    another’s life; preparing for his interview with the draft board by receiving a ―memorable haircut‖;
    and finally, gaining a medical deferment from the board after sending them, upon his physician
    father’s advice, X-rays revealing a past ulcer. This recollection, he reported, remained unchanged
    for 20 years.
            However, after talking to others and examining the records of his draft correspondence,
    Trudeau uncovered some notable discrepancies between his recollection and what actually
    happened. No family member or friend remembers making a call of concern. Trudeau now believes
    he imagined their concerns, because the act ov examining this recollection led him to remember that
    he was in fact out having a few beers that night. He discovered that he actually applied for an
    occupational deferment and, upon reflection, wonders how he could have believed that working for a
    ―glorified travel magazine‖ was justification for a national security deferment. He also neer received
    a ―memorable haircut‖, not did he apply for conscientious objector status in part because of the
    prohibitive paperwork‖ (Dodson & Schacter)
                False Memories

―To what extent is the life we remember the
  knowledge and expectations we have, and the self
  we seem to ourselves to be, a product of
  experience and to what extent a product of our
  imagination?‖ (Johnson, 1985)

								
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