Lecture 3: Theories of Long Term Memory LTM

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Lecture 3 Theories of Long Term Memory (LTM)

• Outline
• Knowing How vs Knowing That
• Memory Systems or Memory Processes?
• Tulvings Episodic / Semantic / Procedural
  distinction
• By the end of the lecture you should have
  learned
• Evidence for and against the episodic / semantic
  distinction
• The relevance of neuropsychological studies of
  amnesia and semantic dementia to theoretical
  accounts of long term memory.

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Knowing How vs Knowing That

• Philosophers as well as psychologists have tried
  to account for how our permanent memories might
  be organised
• Ryle (1949) A fundamental distinction exists
  between remembering based on knowing that and
  remembering arising from knowing how
• We know that
• we went to Spain last summer
• we parked our car in the science car park this
  morning
• the highest mountain in the world is Everest
• We know how
• to drive a car
• to touch type

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Background
1. When did you last ride a bicycle? 2. What is a
bicycle? 3. How do you ride a bicycle? These
questions reveal the different types of long
term memories we are capable of accessing.
1. Requires conscious recollection of unique
temporally distinct past experience 2. Requires
conscious recollection of knowledge, but no
unique experience 3. Unanswerable - unconscious
learning Researchers have developed a number of
different ways to conceptualise these differences.
The critical question is whether these types of
memories reflect the operation of different
memory systems, or whether they reflect different
way of accessing a unitary LTS
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Systems vs Processes
E.g. Are there different LTM systems OR differen
t types of information stored within a unitary
LTM?
Question reflects an important debate concerning
the cognitive architecture of memory Systems
vs Processes Is memory best characterised as
comprising multiple independent systems
(structures with individual properties) OR as a
unitary system, on which a variety of different
processes operate on information stored in a
variety of different codes Despite several
attempts (see Sherry Schacter, 1987) it has
proven very difficult to define a set of criteria
for what constitutes a memory system. There is
even less consensus as to what the systems are...
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Tulvings Model
The relationship between types of LT memory and
varieties of consciousness (Tulving, 1985).
Degree of conscious awareness
Memory System
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Tulvings Model

• The episodic / semantic / procedural distinction
  
• makes intuitive sense
• Subjects do not forget words - they forget
  information regarding the fact that the word was
  presented to them during the expt.
• Episodic, semantic and procedural memories are
  interactive Learning the meaning of a new word
  originally requires an episodic memory.
• Over time the meaning becomes assimilated into
  semantic memory and the original learning episode
  may be forgotten
• Learning to type initially requires episodic
  memory for the layout of the keys. Over time this
  becomes redundant
• The ability to disconnect information from the
  context in which it was learned is a useful
  property for a memory system - it saves on
  storage.

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Tulvings Model
Memory Systems and Memory Tasks Tulving argues
it is important to make the distinction between
memory systems and memory tests Until recently
considered equivalent e.g. Episodic memory test
(recognition of words) requires Episodic memory
system In fact, things are much more complicated
- people can do certain episodic memory tests by
using non-episodic memory systems e.g. you can
know that you have seen a word on a recognition
test before - without consciously recollecting
the event of studying it. It is the conscious
recollection of the original learning episode
that defines the episodic system.
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Procedural Memory
Neuropsychological data - Clive Wearing - still
able to play piano and conduct a choir. BUT can
new procedural memories be created in
amnesia? Claparade, 1911 Procedural learning in
Korsakoff patient. Patients with amnesia are able
to learn a number of tasks, despite having no
episodic memory for learning them.
Other research using larger groups of patients
with amnesic syndrome demonstrate that they can
learn this task as well as controls.
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Procedural Memory
Amnesics also demonstrate normal or near normal
learning on a wide variety of other tasks.
Dress making Finger mazes Jigsaw
puzzles Mirror-reading Mirror drawing /
writing Tower of Hanoi Closure pictures Repetition
priming
However, it is not clear what (if anything) these
tasks have in common.
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Procedural Memory
So what is procedural memory?
Danger of circularity - learning which is
preserved in amnesia is termed procedural...
Moscovitch (1984) Amnesics will do well if
1. It is obvious what is required 2. Responses
already exist in patients repertoire 3. Does not
require specific past events to be recalled
However, amnesics are very slow to learn many
things (e.g. programming a personal organiser)
Baddeley There are a number of different types
of learning, some of which do not rely on
episodic memory
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Episodic / Semantic Distinction
Evidence for episodic - semantic
distinction Obvious interdependence of two
memory systems makes finding evidence for
distinction difficult
Characteristics of episodic and semantic memory
Episodic Memory Reference is to
oneself Organised temporally Events remembered
consciously Susceptible to forgetting Context
dependent
Semantic Memory Reference is with respect
to general knowledge Not organised
temporally Events are known Relatively
permanent Context independent
But what about important autobiographical
events? The first time I - semantic or
episodic?
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Forgetting
Episodic - Semantic Distinction Forgetting
Episodic memory is more prone to forgetting
Some semantic memory has been described
asPermastore
40 of Spanish vocab learned at school is
retained 50 years later (Bahrick, 1984)
However, certain episodic events also appear very
resistant to forgetting -

• Autobiographical first-time events
• Dramatic, emotionally arousing events which
  lead to flash-bulb memories

There is still controversy surrounding whether
there is anything special about flash-bulb
memories.
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Neuropsychological Data
Episodic - Semantic Distinction
Neuropsychological data
Amnesic patients have intact conversational
skills and perform normally on intelligence tests
(which assess knowledge). But - cannot remember
doing either five minutes later. So episodic,
not semantic memory is impaired in amnesia? Not
necessarily - IQ tests and language acquired
before onset of amnesia - not comparing like with
like. So amnesia impairment to acquire new
information (both episodic and semantic?) Gabrieli
et al, 1983 Trained HM with meanings of new
popular words. Showed very little learning More
recently, when provided with extensive
phonological cues (e.g Margaret Tha. - HM was
able to produce names for 18 / 36 famous faces.
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Reterograde Amnesia
Episodic - Semantic Distinction Reterograde
Amnesia (RA)
Comparing like with like Most amnesics also
demonstrate some degree of RA - difficulty in
recalling information acquired prior to the onset
of amnesia. Determining the extent of
reterograde amnesia difficult Has patient
forgotten or simply did not know in first
place? Butters Brandt, (1985) - PZ Alcoholic
science professor - developed WKS at
65 Autobiography (episodic) and publishing
career (semantic) provide reasonable indication
of what he knew when. PZ demonstrates poor
recall of both the names of scientists in his
discipline, and his major life events. E.g
Episodic and Semantic Memory equally impaired
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Reterograde Amnesia
Amnesics also have deficits on famous faces test
Controls
Amnesic patients
Although intuitively plausible, episodic /
semantic distinction not well supported by
evidence.
Episodic and semantic memories clearly differ in
content but may be different expression of same
underlying LTM system.
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Semantic Dementia
Synonyms Progressive fluent aphasia,
Fronto-Temporal Demantia (tvFTD) Neuropathology
Non-alzheimer type degenerative pathology of the
polar and inferolateral temporal cortex (relative
sparing of hippocampus in early stages).
Symptoms Progessive, selective deterioration
in semantic memory, affecting verbal and
nonverbal aspects of knowledge about objects,
people, facts, concepts and word meanings. E.g.
Patients response when shown a picture of a
giraffe Time 1 A giraffe Time 2 A tall African
animal Time 3 A horse Time 4 An animal Time 5
Dont know. Episodic memory is relatively
preserved (at least early in the course of the
illness)
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Update
Episodic - Semantic Distinction Update
Wheeler, Stuss Tulving (1997) - reformulated
the episodic / semantic distinction. Placed a
greater emphasis on distinction in terms of
conscious experience. Also argued that episodic
memory (and the conscious act of remembering) is
particularly dependent on cortical networks
involving PFC. Two lines of supporting
evidence 1. neuropsychological evidence from
patients with frontal lobe lesions. 2.
Functional imaging data from PET / fMRI studies.
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PFC Lesions
Episodic - Semantic Distinction PFC lesions
PFC lesions usually result from Head injury,
Neurosurgery Aneurysm
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PFC Lesions
Episodic - Semantic Distinction PFC lesions
PFC lesions do not result in a full blown amnesic
syndrome In fact, until recently, memory was
thought to be essentially intact in these
patients However, careful testing reveals
interesting pattern of impairment. In a
meta-analysis of studies assessing free recall,
cued recall and recognition in patient with
frontal lobe lesions, 2 findings emerged 1.
Recall is more impaired than recognition
(particularly when strategies can be used at
encoding and/or retrieval 2. Numerically, even
recognition memory is poor, relative to controls
.
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PFC Lesions
Episodic - Semantic Distinction PFC lesions
Wheeler, Stuss Tulving (1995) argued that this
pattern of results occurred because successful
recall is more reliant on conscious recollection
than successful recognition. BUT Both can be
influenced by non-conscious memory. Frontal lobe
patients also have other interesting memory
impairments- Source Amnesia Patients can often
remember the item / fact that was learned, but
cannot remember where or how the information was
acquired.
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PFC and Source Amnesia
Janowsky et al (1989) Asked FL patients and
controls to remember a list of previously
unrecallable facts (e.g. The name of the dog on
the crackerjacks box is Bingo) 7 days later
recall tested. Subjects asked about 20 old facts
and 20 new facts. When Ss answered correctly,
they were asked to recollect the source of the
info How did you learn this fact? When was the
last time you heard this fact? Source Error
1. Correctly recalling learned fact, but falsely
reporting that it was last encountered before the
learning trial 2. Correctly recall a new fact,
but falsely reporting that it was learned during
the learning trial.
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PFC and Source Amnesia
Result could be taken as evidence for
dissociation between semantic (fact) and episodic
(source) memory.
However, current theories ascribe this result to
a specific impairment in the ability to encode /
retrieve contextual information
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Functional Neuroimaging
In 25/26 studies the right prefrontal cortex
(PFC) was more active during retrieval of
episodic information compared to retrieval of
semantic information (Nyberg et al,
1996). Hemispheric Encoding and Retrieval
Asymmetry model (HERA) In general, Left PFC
involved in encoding, right PFC involved in
retrieval. BUT - it would appear that task
difficulty and nature of encoded / retrieved
material (e.g. verbal vs visual) might be more
important. ALSO - PET studies using subtraction
methodology rely on several key assumptions that
are particularly difficult to justify with
respect to memory research
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Summary

• Episodic / Semantic distinction is intuitively
  plausible
• There is something phenomonologically different
  about remembering what you had for breakfast and
  the name of the worlds highest mountain
• However, there is little compelling evidence
  that the distinction reflects the operation of
  two completely distinct memory systems.
• The debate is still active, and the terms are
  widely used, just not necessarily in the way in
  which Tulving proposes
• Baddeley speculates that semantic memories
  result from an accumulation of similar episodic
  memories. They become knowledge when we are no
  longer able to retrieve individual learning
  episodes