Encoding and Retrieval from long-term memory (LTM)

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Encoding and Retrieval from long-term memory (LTM)

• Overview
• Memory is generally believed to rely upon three
  major processes
• Encoding
• Consolidation
• Retrieval
• This lecture will focus on LTM. By this I mean
  the retrieval of information from an experience
  long after that experience has passed

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LTM
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
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Encoding and Retrieval from long-term memory (LTM)

• Multiple memory systems perspective
• Long-term memory consists of all the different
  types of memory shown in the previous slide
• Explicit (declarative) memory refers to memory
  that can be declared or described to other people
• It includes episodic memory, memory for events in
  our personal past. Episodic memories are
  temporally dated, spatially located, and
  personally experience
• semantic memory, our general knowledge about
  things in the world

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Encoding and Retrieval from long-term memory (LTM)

• Multiple memory systems perspective
• Implicit (nondeclarative) memory refers to
  nonconscious forms of memory that are indirectly
  expressed as changes in behavior
• As shown in slide there are a variety of
  different types of implicit memory that are
  implemented in different brain regions

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Encoding and Retrieval from long-term memory (LTM)

• The story of HM
• HM had epileptic seizures that could not be
  controlled by medications
• At the age of 27 he had surgery to remove site
  thought to be source of seizures
• Surgery removed hippocampus, amygdala, and much
  of the surrounding medial temporal lobe
• HMs STM and working memory intact
• HM has relatively intact memory for information
  learned well before surgery language intact
  (semantic memory intact) and has memory for
  experiences that occurred prior to surgery

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Encoding and Retrieval from long-term memory
(LTM)

• HM
• HM has an anterograde amnesia. That is, HM cannot
  remember new events that he experienced after his
  surgery
• Anterograde amnesia is global that is he cannot
  remember new events regardless of their content
  or modality
• HM also has impaired semantic memory for new
  facts (e.g., flower child was thought by him to
  be a child who grows flowers)
• In other words HMs episodic and semantic memory
  is impaired
• Long-term memory consists of all the different
  types of memory shown in the previous slide
• Explicit (declarative) memory refers to memory
  that can be declared or described to other people
• It includes episodic memory, memory for events in
  our personal past. Episodic memories are
  temporally dated, spatially located, and
  personally experience
• semantic memory, our general knowledge about
  things in the world

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Encoding and Retrieval from long-term memory (LTM)

• Multiple memory systems perspective
• HM also has a retrograde amnesia that is, he
  forgets events that occurred prior to surgery
• His retrograde amnesia is temporally graded The
  closer the event to surgery the less likely he is
  able to recall it
• This finding suggests that the medial temporal
  lobes are not always required to retrieve
  memories (One possibility is that some process
  occurs that makes it possible to retrieve
  information that does not rely on medial temporal
  lobes)
• Long-term memory consists of all the different
  types of memory shown in the previous slide
• Explicit (declarative) memory refers to memory
  that can be declared or described to other people
• It includes episodic memory, memory for events in
  our personal past. Episodic memories are
  temporally dated, spatially located, and
  personally experience
• semantic memory, our general knowledge about
  things in the world

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Encoding and Retrieval from long-term memory (LTM)

• Multiple memory systems perspective
• In 1962 Milner and colleagues showed that HM
  improved on tasks requiring skilled movements
• HMs improvement was comparable to controls
• Skill was called mirror tracing because it
  requires participants to draw the outline of a
  star while looking at the reflection of his hand
  and the star on the mirror
• HM from had no conscious recollection of having
  done this task in the past
• This is now viewed as a form of non-declarative
  or implicit memory tasks

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Encoding and Retrieval from long-term memory (LTM)

• Multiple memory systems perspective
• Other forms of implicit memory include priming
  effects that were reported by Warrington
  Weiskrantz (1968)
• In this study amnesics shown list of words (e.g.,
  absent) at test participants were given word
  stem completion task (e.g., abs_____), and
  instructed to complete with first word that comes
  to mind
• Results showed that amnesics (and controls) were
  more likely to complete word stems with
  previously studied words

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Encoding and Retrieval from long-term memory (LTM)

• Multiple memory systems perspective
• How episodic memories are formed?
• Encoding refers to the processes by which
  information is transformed into a memory
  representation
• These processes are set into motion at the time
  of the experience. One way to investigate
  encoding processes is to identify ways in which
  those processes can be affected.

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Encoding and Retrieval from long-term memory (LTM)

• Multiple memory systems perspective
• Elaboration of the meaning of incoming
  information refers to interpreting that
  information and connecting it with other
  information (this process has been shown to
  involve frontal lobes)
• Thus, it appears that medial temporal lobes
  (amnesics) and frontal lobes appear to affect in
  episodic encoding of information

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Encoding and Retrieval from long-term memory (LTM)

• Role of attention
• Craik and many other investigators have shown
  that dividing attention at encoding plays an
  important role in subsequent memory performance
• Participants were presented 15 words auditorily
  presented under one of two conditions.
• Full attention. Words were presented by themselves

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Encoding and Retrieval from long-term memory (LTM)

• Role of attention
• Divided attention. As words were presented
  participants had to perform an attention-demanding
  secondary task (monitor position of asterisk on
  a computer screen
• Results. Participants remembered 15 words in the
  full attention condition and 9 words in the
  divided attention condition
• Shallice and colleagues (1994, Nature) have shown
  that left frontal lobe appears to play an
  important role in the encoding of episodic verbal
  information in a PET study

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Encoding and Retrieval from long-term memory (LTM)

• Levels of processing
• Craik and Lockhart (1975) proposed that memory
  for material will depend upon aspects of the
  stimulus that are attended to
• shallow aspects of the stimulus may be the
  structure of the word, somewhat deeper aspects
  of the stimulus may be the sound of the word, and
  deeper aspects the meaning of the word

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Encoding and Retrieval from long-term memory (LTM)

• Levels of processing
• Craik and Tulving (1975) performed an experiment
  in which participants made 1 of 3 decisions about
  a word structuralupper or lower case letters
  phonologicalword rhymed with target word
  meaningword a member of a category
• Participants were not told memory would be tested
  (called incidental learning)

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Craik Tulving, 1975
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Encoding and Retrieval from long-term memory (LTM)

• Levels of processing
• Conclusions
• Note memory performance appears to be a
  byproduct performing a task because participants
  were not directed to learn
• Memory performance is also strongly affected by
  task being performed
• Limitation no independent way of measuring depth
  of processing

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Encoding and Retrieval from long-term memory (LTM)

• Transfer appropriate processing
• Morris and colleagues (1977) performed a study in
  which participants studied words about which they
  had to make a semantic or rhyme judgment
• At test, in the standard condition, participants
  had to decide whether or not the word had been
  studied in the rhyme condition, participants had
  to decide whether a studied word rhymed with the
  presented word

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Morris et al. 1977
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Encoding and Retrieval from long-term memory (LTM)

• Transfer appropriate processing
• Conclusion
• The processing at encoding is effective to the
  extent that the processing at encoding overlaps
  with the processing at retrieval
• This is called transfer appropriate processing
• Tulving and Thomson (1973) formulated a similar
  idea that they called the encoding specificity
  principle the degree to which an item will be
  remembered depends upon the similarity between
  the way the stimulus was processed at encoding
  and at retrieval

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Encoding and Retrieval from long-term memory (LTM)

• Semantic elaboration and encoding
• Studies have measured brain activity of
  participants while encoding words under semantic
  or perceptual conditions (e.g., Gabrieli et. al.
  1996)
• These studies have shown that the left inferior
  frontal cortex and left medial temporal lobes are
  more activated under semantic than perceptual
  conditions

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Encoding and Retrieval from long-term memory (LTM)

• Semantic elaboration and encoding
• Wagner et al. (1998) performed an fMRI study in
  which participants were scanned as they made
  semantic judgments about words
• Memory for words was tested and then was
  correlated with fMRI encoding data
• Analyses showed greater activation of the left
  inferior frontal lobe cortex and left inferior
  medial temporal lobe for words that were recalled
  compared to words that were not recalled

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Encoding and Retrieval from long-term memory (LTM)

• Generation and spacing
• Generation effect. Demonstrated by Slamecka and
  Graf (1978)
• In this exp. Participants in the read condition
  read pairs of words and made a synonym (e.g.,
  unhappy sad) or a rhyme (e.g., pad sad)
  decision. In the generate condition, they
  generated a synonym (e.g., unhappy s___) or a
  rhyme (e.g., pad s__)

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Slamecka and Graf (1978)
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Encoding and Retrieval from long-term memory (LTM)

• Generation effect
• Results showed better memory for generated
  material than read material, and better memory
  for more semantically processed material
• Why should this effect be obtained? Generation
  requires elaboration, and it requires attention
• Support for this finding comes from a study,
  which showed that the left frontal region is more
  activated when material is generated versus read

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Encoding and Retrieval from long-term memory (LTM)

• Spacing effect
• A great many studies have shown that learning and
  remembering occurs more efficiently if the
  learning trials are distributed (or spaced)
  compared to being massed (i.e., presented one
  after another)
• Why is distributed practice better?
• Several possible reasons less attention context
  changed when presentation spaced, and hence
  probably a more elaborated memory trace

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Encoding and Retrieval from long-term memory (LTM)

• Episodic encoding and binding and temporal lobes
• It is generally believed that episodic encoding
  is the binding together of various features of a
  stimulus into an integrated memory representation
  
• For example, if are shown an object, you will
  remember its shape, size, color, weight, tactile
  characteristics, etc. to a varying degree

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Encoding and Retrieval from long-term memory (LTM)

• Episodic encoding and binding and temporal lobes
• It is hypothesized the medial temporal lobe is
  responsible for binding these features into an
  integrated memory trace
• That is, the medial temporal lobe receives highly
  processed input from many brain areas when an
  event is encoded
• The medial temporal lobe is then responsible for
  binding together this input at encoding

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Encoding and Retrieval from long-term memory (LTM)

• Episodic encoding and binding and temporal lobes
• At retrieval, a retrieval cue is encoded. This
  retrieval cue typically consists of some of the
  input that was processed during encoding
• The processed retrieval cue converges on the
  medial temporal lobe, it triggers pattern
  completion in the hippocampus, and this in turn
  reactivates information in the lateral cortex

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Encoding and Retrieval from long-term memory (LTM)

• Episodic retrieval
• Episodic retrieval refers to the processes by
  which stored memory traces are retrieved
• It is generally assumed that retrieval produces
  the subjective experience of consciously
  remembering the past
• Episodic retrieval is assumed to depend on medial
  temporal lobe that support pattern completion and
  the frontal lobes that support strategic
  retrieval

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Encoding and Retrieval from long-term memory (LTM)

• Episodic retrieval
• Implications of the retrieval model just
  presented
• The process here means that there are multiple
  routes or ways in which a retrieval cue can
  access memory trace, and partial information may
  be enough to access memory trace
• Episodic retrieval is assumed to depend on medial
  temporal lobe that support pattern completion and
  the frontal lobes that support strategic
  retrieval

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Encoding and Retrieval from long-term memory (LTM)

• Episodic retrieval
• Importance of hippocampus during retrieval of
  episodes supported by finding that hippocampus
  was activated during successful retrieval but not
  during unsuccessful retrieval (Eldridge, 2000,
  Nature Neuroscience)

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Encoding and Retrieval from long-term memory (LTM)

• Episodic retrieval
• Although encoding and retrieval are similar in
  many respects in this model, it has been proposed
  that one difference is that during encoding
  processed information from lateral cortex
  converges to hippocampus, whereas during
  retrieval the partial cue connects with stored
  memory trace, and this then projects back to
  lateral cortex

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Encoding and Retrieval from long-term memory (LTM)

• Episodic retrieval
• There is also evidence for the hypothesis that
  retrieval of episodes from memory will
  re-activate those regions of the cortex that were
  activated during encoding of the event
• In an fMRI experiment participants were presented
  words paired with sounds or with pictures at
  retrieval participants were presented words and
  were required to remember whether sound or
  picture paired with words (Wheeler and Buckner,
  2001)

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Encoding and Retrieval from long-term memory (LTM)

• Role of recollection and familiarity in retrieval
• Behavioral data strongly suggest that recognition
  memory can proceed through recollection and
  through familiarity
• Recollectionyou remember contextual details
• Familiarity sense of having encountered stimulus
  in past in absence of recollection
• Dual-process theories of recognition assert that
  both types of recognition normally occur

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Encoding and Retrieval from long-term memory (LTM)

• Role of recollection and familiarity in retrieval
• For example, it has been shown that recollection
  is a slower process than familiarity (e.g.,
  Yonelinas, 2002)
• Dividing attention seems to affect more strongly
  recollection than familiarity