Commonsense reasoning

Cognitive Science Week 10

Which information is relevant to drawing a conclusion?

Which facts are affected by an event?

• Yale shooting problem

• Property inheritance

Tweety is a bird. So Tweety can fly?

Frame problem

Draw finger over a wall. What changes?

Wet paint?

Pour juice from one beaker to another.

- What changes? What remains the same?

• Qualification problem - boats, cars & chickens

Monotonic v. non-monotonic inference

monotonic inference

holds even if new information is added

non-monotonic inference

new information can invalidate

Ways to formalise non-monotonic inference

Frame axiom

painting one object (2) doesn't affect the location of another object (1)

Location [obj-1, loc-x, sit-a] Location [obj-1, loc-x, paint (obj-2, colour, sit-a)]

obj-1 stays in loc-x

Closed World Assumption

If it isn't in the database, it isn't - all relevant information is to hand.Cov Euston0805 09150835 09500845 10000910 1030

Is there a train at 9am?

Possible Worlds

Take three propositions, P, Q & RThere are several possible interpretations, or models:

P Dad is gardening; Q mum is reading; R wee Johnny is playing

P Q RT T TT F TT T FF T Tetc.

Possible: there's at least one possible world in which the proposition is satisfied

P R "possibly Johnny is playing"

N P "necessarily Dad is gardening“

P Q not N not Q

Modal operatorsMcDermott & Doyle (1980); Moore (1985)

Operator M - 'maybe‘; if consistent with all else known

Bird (x) & M Fly (x) Fly (x)

Formalise M in terms of modal operators

Bird (x) & not N not Fly (x) Fly (x)

If x is a bird and it is consistent that it can fly, then it can fly. Or 'typically birds can fly'.

Exceptions indicated by sentences:Penguin (x) not Fly (x)

Car(x) & M Got_petrol(x) Got_petrol(x)

This is a default rule

… believe that cars have petrol unless you have a reason to doubt it

Siphoned(x) not Got_petrol(x)

Extensions of the database

When checking whether something is consistent, you extend the database of facts:

all facts already known

+ all facts you can deduce from regular inference rules

+ anything you can deduce using default rules

Multiple extensions problem

Quaker(x) & M Pacifist(x)

Pacifist (x)

Republican(x) & M not-Pacifist(x)

not-Pacifist(x)

Quaker (Nixon), Republican (Nixon)

Pacifist (Nixon) & not Pacifist (Nixon)

How choose?

1. prioritise rules

a ‘fix’

2. world knowledge

Natural reasoning

Non-monotonic reasoning in the lab (Byrne, 1989)

Inference "suppressed" by adding information

If John hasn't finished his essay, then he will go to the library tonight.

John hasn't finished his essay.

+ If the library is open, John will go to the

library tonight.

Stevenson & Over (1995)

Can vary this effect by qualifying certainty

If John goes fishing, he will have fish for tea.

John goes fishing.

If John goes fishing, and if he catches a fish, he will have fish for tea.

John goes fishing.

If John goes fishing, he will have fish for tea. John is always / usually / never lucky as a fisherman.

John goes fishing.

Beliefs (world knowledge) affect reasoning

Oakhill, Johnson-Laird, & Garnham (1989)

All the Frenchmen are gourmets.

Some of the gourmets are wine drinkers.Some of the Frenchmen are wine drinkers 72 %

All the Frenchmen are gourmets.Some of the gourmets are Italians.

Some of the Frenchmen are Italians. 8 %

Belief biasEvans, Barston & Pollard (1983)

No nutritional things are cheap

Some vitamin tablets are cheap

Some vitamin tablets not nutritional

Believable Unbelievable

Valid 89% 56%

Not

Valid71% 10%

Illusion of explanatory depthRozenblit & Keil (2002)

students rate how well they understand (48) devices and phenomena

How a snare catches small animalsHow a computer mouse controls the cursor

… then write detailed explanations for 4Re-rate self-understanding (ratings drop)Rate explanations independently (closer to

the re-rating)

Core reading:Eysenck & Keane (2000). Cognitive psychology: A student handbook,

4th Edition. Chapters 16 (up to page 460) and 17.

Rozenblit & Keil (2002). The misunderstood limits of folk science: an illusion of explanatory depth. Cognitive Science, 92, 1-42.

Wilson & Keil (Eds.) (1999). The MIT Encyclopedia of Cognitive Science. (On the Science reference shelves in the Library.) Entries and essays on: BOUNDED RATIONALITY; FRAME PROBLEM; NONMONOTONIC REASONING.

And see other links on the module web page.

The Enclyclopedia is available from the Library as an electronic book