Chapter 9 Pt. 2 Flashcards
Spreading activation
Semantic networks
- When a node is activated, activity spreads out along all connected links
- concepts that receive activation are primed and more easily accessed from memory (distance important)
Lexical decision task
Participants read stimuli and are asked to say as quickly as possible whether the item is a word or not
Coglab:Lexical decision task
Independent variable is association between first and second word (if associated, second word RT faster)
Called priming effect
Dependent variable: reaction time
Coglab results
Word then non word had fastest reaction time then:
- nonword then word
- associated words
- unassociated words
- two non words
Myer and Schvaneveldt-lexical decision task
- “yes” if both strings are words, “no” if not
- some pairs were closely associated
- reaction time was faster for those pairs (spreading activation)
Criticism of Collins and Quillians semantic network
- Can’t explain typicality effect (canary is a bird is quicker to identify than an ostrich is a bird even though they are same distance from bird node)
- Cognitive economy (hand example)
- Some sentence verification results are problematic for the model (e.g. pig as animal instead of mammal)
The connectionist approach
- creating computer models for representing cognitive processes
- parallel distributed processing
- knowledge is represented in the distributed activity of many units
- weights determine at each connection how strongly an incoming signal will activate the next unit
“Units” in the connectionist approach
Input units: activated by stimulation from enviro
Hidden units: receive input from input units
Output units: receive input from hidden units
How learning occurs in the connectionist approach
- network responds to stimulus (might be random at beginning)
- provided with correct response (from feedback etc)
- modifies responding to match correct response
Error signal in connectionist approach
-difference between actual activity of each output unit and the correct activity
Back propagation (in connectionist approach)
- error signal transmitted back through the circuit
- indicates how weight should be changed to allow the output signal to match the correct signal
- process repeats until the error signal is zero
Graceful degradation (connectionist approach)
Disruption of performance occurs gradually as parts of the system are damaged
In semantic network: 1 concept is at one node and if it’s broken it’s gone
In connectionist approach: concept represented at multiple units and if one is damaged, concept may still be there
What type of learning process is the connectionist approach
A slow learning process that creates a network capable of handling a wide range of inputs
Learning can be generalized (if for e.g. new concepts share a lot of features with old concepts)
Categories in the brain
Different areas of the brain may be specialized to process information about different categories
- double dissociation for categories “living things” and “non living things”
- category specific memory impairment (patient K.C and E.W could name non living objects but not living)
Sensory-functional (S-F) hypothesis
- distinguishing living things depends on perceiving their sensory features
- artifacts are more likely to be distinguished by their function
