OUTLINE

1. SEMANTIC VERSUS EPISODIC MEMORY

2. HOW IS KNOWLEDGE STORED

3. AN EARLY MODEL: THE T.L.C.

4. A MORE RECENT MODEL; THE A C T *

5. SYMBOLIC VERSUS CONNECTIONIST ARCHITECTURES

6. EXAMPLE OF A CONNECTIONIST SYSTEM

Semantic versus Episodic memory
TWO TYPES OF PERMANENT MEMORY

Episodic memory: memory for "episodes"
    -spatial temporal factors important (eg., the context of where, when, who with etc); usually measured by accuracy measures, has autobiographical reference

Semantic: Memory for knowledge of the world, facts, meaning of words etc
-example : knowing that the first month of the year is April (alphabetically) but January (chronologically); usually measured by latency (RT) measures

Note that in both cases: inferences can occur

example from semantic memory

Q: what was Napoleon's telephone number?

Q: During the Franco-Prussian war was any city bombed from the air?


THE TLC

Test: (sentence verification task) present items such as;

robin has a red-breast

robin has wings

robin can breathe

prediction???
 

but what if we looked at false items

robin is an animal

robin is a type of vehicle
 

predict ????


THE ACT MODEL

-attempts to integrate recent advances in the study of episodic and semantic memory studies

-a system that learns

-note the overall structure

show

declarative versus procedural knowledge

in Declarative memory: information is represented as propositions
-propositions "grow" as additional information is learned


examples

-in Procedural memory: information is represented as production rules (and systems); that is as IF-THEN contingency pairs

TABLE 6-11 Assumptions of Anderson's ACT Theory.

Declarative Knowledge

1. Strength Assumption: Each link has a specified strength, and the strength of a newly formed link is low, but is incremented every time the link is used.

2. Activation Assumption: At any instant a small portion of the nodes in long-term memory are in an active state; all other nodes are not.

3. Spread of Activation Assumption: Activation spreads out from an active node to the passive nodes to which it is linked. The stronger the link between two nodes, the more likely it is that the activation will spread along that link. The spread of activation has a limited capacity, in that the more links that are being activated at once, the less activation will spread to any one.

4. Dampening Assumption: Periodically activation is dampened throughout the network. i.e., all nodes and links are deactivated.

5. Active List Assumption: A maximum of 10 nodes can be kept on the Active List (ACT's working memory). Nodes on this Active List are not dampened, so they remain active as long as they are kept on the list.

Procedural Knowledge

6. Strength Assumption: Each production has some strength associated with it, and the strength of a production is incremented everytime the production is executed.

7. Choice Assumption: The conditions of all productions are compared with active memory to see if their conditions are met. The stronger productions are compared with active memory more quickly than the weaker productions. If the condition of a production is met, then it is carried out.


Note: Some of the implications for the ACT* Model

-propositional networks build up with experience

-some "nodes" have more connections to them than do some other nodes

-activation spreads through these connections proportional to the number involved, and to the strength of any one link
        -that is the more connections there are, on average, activation to any one link is weaker relative to a node with fewer connections

TASK:
PHASE 1: LEARN A SET OF SENTENCES OF THE FORM "PERSON X IS IN LOCATION Y"

can manipulate the number of propositions associated with each person and with each location ("PROPOSITIONAL FAN")

PHASE 2: PRESENT A SENTENCE, ASK Ss TO DECIDE WHETHER OR NOT THE SENTENCE HAD BEEN PRESENTED IN THE LEARNING PHASE I (NOTE A RECOGNITION MEMORY TASK)
MEASURE RT TO MAKE THE DECISION!!


PREDICTION: RT TO RESPOND TO A TRUE RESPONSE WILL INCREASE AS A FUNCTION OF PROPOSITIONAL "FAN" (THE NUMBER OF LINKS)

HOW DOES THIS OCCUR?
-MUST FIND AN INTERSECTION BETWEEN THE CONCEPTS NAMED IN THE TEST SENTENCE
-UPON ACTIVATION OF A NODE, ACTIVATION SPREADS IN ALL DIRECTIONS TO CONNECTED NODES
-THE MORE LINKS, THE LESS ACTIVATION WILL SPREAD IN A GIVEN INSTANCE OF TIME. THEREFORE LONGER IT SHOULD TAKE TO FIND AN INTERSECTION

FINDING AN INTERSECTION MEETS THE "IF" PART OF A PRODUCTION, WHICH TRIGGERS THE "THEN" PART.. .THAT IS INITIATES A RESPONSE "YES"
BUT WHAT ABOUT FALSE SENTENCES (THOSE NOT PRESENTED IN PHASE 1)?


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