Matlin, Chapter 8

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Matlin, Chapter 8
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Semantic Memory

• Semantic memory our organized knowledge base
• Example of importance of large knowledge base in
  artificial intelligence expert systems

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Semantic memory theories

• Feature comparison theory
• What is stored in memory? A feature list for
  concepts
• Two types of features characteristic features,
  that usually occur, and defining features, that
  must occur for the concept
• Examples what are defining and characteristic
  features of dog? Chair?

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Semantic memory theories

• Testing feature comparison theory sentence
  verification task
• Example a canary is an animal
• Dependent variable reaction time

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Semantic memory theories

• Prediction if two nouns have few or no features
  in common, quick RT and say no
• If two nouns have many features in common, quick
  RT and say yes
• If intermediate number of features in common,
  slower reaction time more variable response
  among subjects

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Semantic memory theories

• Typicality effect highly typical members of a
  categoryfaster reaction times on sentence
  verification task due to greater number of
  features in common with the category

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Semantic memory theories

• Weaknesses of feature comparison theory
• Many categories not captured by a mere list of
  features
• Problems determining defining features for many
  categories
• Does not deal with relationships within categories

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Semantic memory theories

• Prototype theory idealized representation of a
  category probably represents average of
  exemplars in category
• Typicalitysome exemplars more prototypical than
  others graded structure within category

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Semantic memory theories

• Levels of categories superordinate, basic
  level, and subordinate
• Example motorized vehicle car Camry XLE
• Much communication occurs at basic level useful
  levelnot too general, but not overly specific
• Experts talk more in subordinates (specifics)

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Semantic memory theories

• Weaknesses of prototype theory
• Does not deal with specific memories for
  exemplars
• Does not describe how categories change over time
• Not all category boundaries are as fuzzy as
  theory assumes

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Semantic memory theories

• Exemplar theory first item learned in a
  category becomes exemplar new items are compared
  to it (and, if similar enough, are added to
  category)
• Additional items can be stored specifically, so
  category can have several exemplars (instead of
  just one main prototype)

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Semantic memory theories

• Compromise possibilities
• Maybe small categories use exemplars and large
  categories use prototypes
• Maybe we use both, but with different brain
  hemispheres (left for prototypes, right for
  exemplars, according to some research)

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Semantic memory theories

• Network theoryCollins Loftus
• Links among nodes

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Edible
Nutritious
Red
Fruit
Seed bearing
Crisp
Apple
Sphere-shaped
Granny Smith
Golden Delicious
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Semantic memory theories

• Frequency of use (how often nodes activated
  together) determines strength of link
• Strength of link represented in network by length
  of line between nodes
• Typicality more typical concepts used in
  connection with category more often than less
  typical concepts

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Semantic memory theories

• Spreading activation an activated node causes
  other nodes to which it is linked to become
  activated
• Activation gets weaker as links are more distant
• Can conceptualize stream of consciousness as
  spreading activation

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Semantic memory theories

• Andersons ACT network theory similar to one by
  Collins Loftus, but node represents a
  proposition instead of just a concept, and
  nature of relationship between nodes is specified
• His theory actually is much more complicated, but
  beyond the scope of this book or course

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Semantic memory theories

• PDP (parallel distributed processing) theory
• Neural network weighted connections similar to
  what other network theories are saying can be
  used to create simulations of knowledge networks,
  as well as useful organized knowledge bases

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PDP example
Marti
Joe
Sam
Liberal
Engineering
Conservative
Art
Senior
Junior
Soph
Psych
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Characteristics of PDP

• Parallel searchinfo flows through network in
  parallel
• Partial info still allows computation to occur
• Spontaneous generalizations conclusion about a
  general category based on specific info in
  network (if one example of psychology major is
  liberal, might generalize that most or all psych
  majors are liberal
• Default assignment conclusion about member of
  category due to category knowledge

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Schemas and scripts

• Schema any organized set of knowledge
• Script familiar activity that usually occurs in
  a fixed sequence, involves certain actors in
  certain settings
• Examples restaurant, going to doctor, grocery
  shopping
• Knowing schema or script in advance aids
  comprehension

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• The procedure is actually quite simple. First
  you arrange
• items into different groups. Of course one pile
  may be
• sufficient depending on how much there is to do.
  If you have
• to go somewhere else due to lack of facilities
  that is the next
• step otherwise, you are pretty well set. It is
  important not
• to overdo things. That is, it is better to do
  too few things at
• once than too many. In the short run this may
  not seem important
• but complications can easily arise. A mistake
  can be expensive
• as well. At first, the whole procedure will seem
  complicated.
• Soon, however, it will become just another facet
  of life. It is
• difficult to foresee any end to the necessity for
  this task in
• the immediate future, but then, one never can
  tell. After the
• procedure is completed one arranges the materials
  into
• different groups again. Then they can be put
  into their
• appropriate places. Eventually they will be used
  once more
• and the whole cycle will then have to be
  repeated. However,
• that is part of life.

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Schemas and scripts

• Memory and scripts memory often is better for
  script-relevant events (could be using script to
  reconstruct memory)
• Certain exceptions to the usual script can be
  remembered even better than script actions
  e.g., things that interrupt the usual script, are
  unexpected, emotional
• Example the class when lightning struck the
  building just out the window

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Schemas and scripts

• False memory and scripts recall or recognition
  based on script can cause memory for
  script-relevant actions, props, etc. that were
  not part of a specific experience
• Example even if article didnt mention paying
  cashier at restaurant, will later tend to
  remember having read it

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Schemas and scripts

• Bransford Franks study (The old car pulled the
  trailer up the steep hill.) shows how schemas
  were created (4 scenarios) that then shaped
  memorywe remember the schema (general
  representation) not the specific sentences
• Inferencesschemas and scripts guide us in making
  inferences (I assume he paid the cashier thats
  the usual procedure)

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Schemas and scripts

• Inferences later can be remembered as having
  happened (source error)
• Schema-related memory errors increase over time
  since the event