Transcript Spreading Activation 1

Spreading Activation 1
Long-Term Memory Store
• Unlimited capacity
• Duration - thought by some to be
permanent
Maintenance Rehearsal
Sensory
Input
Encoding
Sensory
Memory
Attention
Long-term
Working or
memory
Short-term
Memory Retrieval
Encodings
• Different formats
• Implicit Memory  Production rules
– Neural locus of production rules is cerebellum
• Explicit Memory  Network of connected
nodes
– Distributed most likely throughout entire
cortex and other areas.
Serial Search Models
• Forster 1989
– Serially search to match word
• Frequency ordered phonological list
– Explains more frequent words are accessed first
• Semantically associate list
– Priming & Context plays a role and makes less
frequent words be accessed faster
Serial Search Models
Forster’s Model
Serial Search Models
Evaluation
• Physiological unrealistic
– Neuron transmission slow
• 100 time steps can be computed in ½ second
(Feldman & Ballard, 1982)
– But retrieval of a word is FAST
– If we know ~75K words, searching serially is
time consuming.
Parallel Search Models
• Morton’s Logogen model (1964, 1979).
– (father of other models to come)
Parallel Search Model
Morton’s Logogen Model
• The lexical entry for each word comes with a
INPUT [k]
logogen unit
cat
skip
camp
cot
• Input such as [k] of “cat” activate the relevant units in
parallel.
• The lexical entry becomes available once the logogen ‘fires’
– (i.e., reaches threshold)
Parallel Search Model
Morton’s Logogen Model
Threshold
Analogy of logogen unit ‘firing’.
INPUT /kaet/
cat
skip
camp
cot
Parallel Search Model
Morton’s Logogen Model
‘cat’
[kæt]
High frequency words
have a lower
threshold for firing,
so it takes less to
activate.
lower threshold =
shorter RT
‘cot’
[kot]
Network connection of Logogens
cradle
baby
bed
hospital nurse
dentist
doctor
heat
delirium
sun
green
grass
mammal
bird
canary
rain
fever
animal
yellow
ostrich
Spreading Activation
cradle
baby
bed
“doctor” spread activation to “nurse”
so “nurse” becomes semi-activated.
NURSE now requires less to fire.
hospital nurse
dentist
doctor
heat
delirium
sun
green
grass
mammal
bird
canary
rain
fever
animal
yellow
ostrich
Parallel Search Models
Evaluation
Accounting for Data
– High frequency words have lower threshold
– Multiple Networks: Words related by…
• meaning are linked in a semantic network
• sound are linked in a phonological network
– How to deal with ability to judge something as a
non-word?
• Impose a timer. After a certain time period, decide not a
word
Appeal - Efficiency
• Lexical access is in parallel