COGS001Fall 2002

Module 6: Memory & Knowledge RepresentationLecture 2

An addition game

1 2 3 4 5 6 7 8 9

Two players, alternating turns

Nine cards, numbered from 1 to 9, are face up on the table

On each turn, pick one of the remaining cards

The winner: First player to hold cards adding up to 15

Another game

X 6 7 2

1 5 9

8 3 4

Two players, alternating turns

Board divided into 3 x 3 squares

On each turn, choose an unmarked square& mark it with ‘X’ (first player) or ‘O’ (second player)

The winner: first player to mark a row, column or diagonal

Variant: board is marked with numbers from 1 to 9

The winner: first player to mark squares adding up to 15

The Chicken Challenge

Tropicana (Atlantic City, Las Vegas)Beat the chicken, win $10,000

(formerly side shows, NYC Chinatown. . .)

MENACE:a set of boxes & beads learns tic-tac-toe...

Matchbox Educable Noughts and Crosses EngineDonald Mitchie, Edinburgh, 1964One matchbox for every possible game positionNine colors of beads, corresponding to nine movesInitial state: each box holds one bead of each (legal) color“Engine” : choose random bead from current box

(and set it aside next to its box)At the end of the game:

If MENACE loses, discard all the beadsIf MENACE wins, put back three copies of each bead

Early example of “reinforcement learning” algorithm

Tic-tac-toe lessons

• The same problem can be viewed in different ways– addition game: finding numbers to sum to 15– tic-tac-toe 1: “owning” a row/column/diagonal– tic-tac-toe 2: learned response to any of 300 positions

• Ginger the chicken• MENACE

• Different views lead to– different kinds of solutions– different degrees of difficulty

• for different skill sets• in different dimensions

• A motivation for specialized formsof information representation & processing

– biological– individual– cultural

Types of human memory

• Faces/places/words/...• Semantic/episodic/motor

= facts/events/skills• Short term/long term• Different

– behavioral characteristics– brain localization– clinical syndromes

How many kinds?

• Proliferation of hypotheses about memory subsystems – Different semantic memory areas for

animals/tools/etc. ?• clinical dissociations

• “priming” by associative connections

– Or unified semantic memory systemwith differing cross-modal connections? (Farah 1994)

– Different short- and long-term memory stores?– Or various mechanisms for modulation of attention? (Cowan 2000)

One idea about STM

• Representational basis: – activated part of LTM– not a separate “memory buffer”

• Neurobiological network– Frontal attention control systems maintaining posterior LTM

meaning representations in an activated state– LTM is “weight based”; STM is “activation based”

Semantic Short-term Memory

• Maintains small set of word meanings in heightened state of activation

• Distinct from “phonological loop”• Distinct from “syntactic working memory”

Haarmann et al. 2002

Neural network model of (semantic) STMHaarmann & Usher, 2001

HippocampusMedial temporal(episodic LTM)

Posterior system(semantic LTM)

Capacity-limitations on recency effects in semantic STM

• Task

– Category cued recall task

– Word pool: 6 semantic categories, 4 words each

– Example of trial: fan, car, lime, rat FRUIT? “Lime”

• Design

– List length (4, 6 words) X Serial position of probed word

Individual differences in Semantic STM spanpredict memory load effects

in on-line semantic anomaly judgment:

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0.6

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1

short long

Distance

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A')High span

Mid span

Low span

(Haarmann, Davelaar, & Usher, 2002)

Long: He was concerned about the heavy long steep narrow footpath strewn with rocks

Short: The boys admired the curly, new car of the secretary in the office.