Cognitive Psychology Class Notes > Semantic Memory

Definition of Semantic Memory:

• relatively permanent memory store for general world knowledge

Models of Semantic Memory Organization

Feature Comparison Model:

Demo: Sentence Verification Task

True or false:

A robin is a bird.

A bulldozer is a bird.

A bat is a bird.

A chicken is a bird.

• 2 Types of Features:

1. characteristic features:

• features that are descriptive, common, and frequent, but not essential to the meaning of the item
• ROBIN: flies, perches in trees
• the robin does not have to fly or perch to be considered a robin

2. defining features:

• features absolutely essential to the meaning of the item
• ROBIN: animate, has feathers, has red breast

• 2 Stages of Processing:

1. Process all features of subject with predicate; comparison of characteristic features.

• if low similarity between features --> respond 'false'
• if high similarity between features --> respond 'true'
• if intermediate similarity, Stage 2 processing

2. Create comparison question; comparison of defining features.

• A bat is a bird --> a bat is a mammal; is a bird a mammal? A chicken is a bird. --> does not fly, does chicken have feathers?
• takes more time to respond

• Research FOR Feature Comparison Model:

• typicality effect:

A carrot is a vegetable.

A rutabaga is a vegetable.

• we make faster sentence verification decisions when an item is a typical member of a category, rather than an unusual member
• WHY? high similarity between features allows for Stage 1 processing only for 'A carrot is a vegetable'; Stage 1 and Stage 2 processing is necessary for 'A rutabaga is a vegetable'

• Research AGAINST Feature Comparison Model:

• category size effect:

A poodle is a dog.

A squirrel is an animal.

• we make faster sentence verification decisions when an item is a member of a small category
• small categories contain more defining features; therefore, FC model would predict that there should be more Stage 2 processing for small categories and thus longer RTs

Semantic Network Models:

• PDP approach
• Collins & Loftus (1975)
• ACT*, ACT-R

• Characteristics:
• concepts represented as nodes in network
• nodes are linked together by pathways
• proposition = node 1 --- pathway --- node 2
• spreading activation
• frequently used links have greater strengths
• intersection search
• priming

Prototype Approach:

• prototypes best represent categories
• prototypes need not really exist
• degrees of prototypicality (prototypical to nonprototypical)
• apple is a prototypical fruit
• tomato is a nonprototypical fruit

• Empirical Characteristics of Prototypes:
  1. Prototypes are often supplied as better examples of a category (Mervis, Catlin, & Rosch, 1976).
  2. Prototypes serve as reference points (Rosch, 1975a)
  3. Prototypes receive more priming from category names and are judged more quickly (Rosch, 1975b) 'fire engine red' vs. 'muddy red'
  4. Prototypes can substitute for a category name in a sentence (Rosch, 1977)
  5. Prototypes share common attributes in a family resemblance category (Rosch & Mervis, 1975)
• Levels of Categorization:
  1. superordinate level --> musical instruments
  2. basic level --> guitar
  3. subordinate level --> Fender Stratocaster
• Basic-level categories have special status (Rosch et al., 1976):
  1. share more attributes
  2. have shapes in common
  3. are used to identify objects
  4. produce priming effect
  5. are first learned by children
  6. experts use subordinate level as basic level