Categories and concepts- introduction

CS182/Ling109/CogSci110

Spring 2008

Lecture Outline

• Categories– Basic Level– Prototype Effects– Neural Evidence for Category Structure

• Aspects of a Neural Theory of concepts• Image Schemas

– Description and types– Behavioral Experiment on Image Schemas

• Event Structure and Motor Schemas

Concepts are not categorical

Mother

• The birth modelThe person who gives birth is the mother

• The genetic modelThe female who contributes the genetic material is the mother

• The nurturance modelThe female adult who nurtures and raises a child is the mother of the child

• The marital modelThe wife of the father is the mother

• The genealogical modelThe closest female ancestor is the mother

(WFDT Ch.4, p.74, p.83)

Radial Structure of Mother

The radial structure of this category is defined with respect to the different models

CentralCase

Stepmother

Adoptivemother

Birthmother

NaturalmotherFoster

mother

Biologicalmother

Surrogatemother

Unwedmother

Geneticmother

Marriage

• What is a marriage?

• What are the frames (or models) that go into defining a marriage?

• What are prototypes of marriage?

• What metaphors do we use to talk about marriages?

• Why is this a contested concept right now?

Concepts and radial categoriesConcepts can get to be the "prototype" of their category in

various ways. • Central subcategory (others relate to this)

• Amble and swagger relate to WALK• Shove relates to PUSH

• Essential (meets a folk definition: birds have feathers, beaks, lay eggs)

• Move involves change of location.

• Typical case (most are like this: "sparrow")• Going to a conference involves air travel.

• Ideal/anti-ideal case (positive social standard: "parent"); anti-ideal case (negative social standard: "terrorist")

• Stereotype (set of attributes assumed in a culture: "Arab")• Salient exemplar (individual chosen as example)

Category Structure• Classical Category:

– necessary and sufficient conditions

• Radial Category: – a central member branching out to less-central and non-central cases

– degrees of membership, with extendable boundary

• Family Resemblance: – every family member looks like some other family member(s)

– there is no one property common across all members (e.g. polysemy)

• Prototype-Based Category• Essentially-Contested Category (Gallie, 1956) (e.g. democracy)

• Ad-hoc Category (e.g. things you can fit inside a shopping bag)

Neural Evidence for category structure

• Are there specific regions in the brain to recognize/reason with specific categories?

Category Naming and Deficits

• People with brain injury have selective deficits in their knowledge of categories.

• Some patients are unable to identify or name man made objects and others may not be able to identify or name natural kinds (like animals)

A PET Study on categories (Nature 1996)

Study

• 16 adults (8M, 8F) participated in a PET (positron emission tomography) study.– Involves injecting subject with a positron emitting radioactive

substance (dye) – Regions with more metabolic activity will absorb more of the

substance and thus emit more positrons– Positron-electron collisions yield gamma rays, which are detected

• Increased rCBF (regional changes in cerebral blood flow) was measured– When subjects viewed line drawings of animals and tools.

The experiment

• Subjects looked at pictures of animals and tools and named them silently.

• They also looked at noise patterns (baseline 1)• And novel nonsense objects (baseline 2)• Each stimulus was presented for 180ms followed

by a fixation cross of 1820 ms.• Drawings were controlled for name frequency and

category typicality

medial

lateral

PremotorACC

Left middle temporal gyrus

Calcarine Sulcus

Conclusions

• Both animal and tool naming activate the ventral temporal lobe region.

• Tools differentially activate the ACC, pre-motor and left middle temporal region (known to be related to processing action words).

• Naming animals differentially activated left medial occipital lobe (early visual processing)

• The object categories appear to be in a distributed circuit that involves activating different salient aspects of the category.

What are schemas?

– Regularities in our perceptual, motor and cognitive systems

– Structure our experiences and interactions with the world.

– May be grounded in a specific cognitive system, but are not situation-specific in their application (can apply to many domains of experience)

Basis of Image schemas

• Perceptual systems

• Motor routines

• Social Cognition

• Image Schema properties depend on– Neural circuits

– Interactions with the world

Image schemas

• Trajector / Landmark (asymmetric)– The bike is near the house – ? The house is near the bike

• Boundary / Bounded Region – a bounded region has a closed boundary

• Topological Relations– Separation, Contact, Overlap, Inclusion, Surround

• Orientation– Vertical (up/down), Horizontal (left/right, front/back)– Absolute (E, S, W, N)

LMTR

bounded region

boundary

Similarity:

• Perceptual and motor systems

• Basic functional interactions with the world

• Environment

Variation:

Cross-linguistic variation in how schemas are used.

Cross-linguistic Variations

English

Japanese

Tamil

English

ON

AROUND

OVER IN

Bowerman & Pederson

Dutch

Bowerman & Pederson

AAN

OM

BOVEN IN

OP

Chinese

Bowerman & Pederson

SHANG

ZHOU

LI

Spatial schemas

• TR/LM relation

• Boundaries, bounded region

• Topological relations

• Orientational Axes

• Proximal/Distal

schema Containerroles

interiorexteriorportalboundary

Representing image schemas

Interior

Exterior

Boundary

PortalSource

Path

GoalTrajector

These are abstractions over sensorimotor experiences.

schema Source-Path-Goalroles

sourcepathgoaltrajector

schema name

role name

Schema FormalismSCHEMA <name>

SUBCASE OF <schema>

EVOKES <schema> AS <local name>

ROLES < self role name>: <role restriction>

< self role name> <-> <role name>

CONSTRAINTS <role name> <- <value>

<role name> <-> <role name>

<setting name> :: <role name> <-> <role name>

<setting name> :: <predicate> | <predicate>

Trajector/Landmark Schema

• Roles:Trajector (TR) – object being located

Landmark (LM) – reference object

TR and LM may share a location (at)

TR/LM -- asymmetry

• The cup is on the table

• ?The table is under the cup.

• The skateboard is next to the post.

• ?The post is next to the skateboard.

Boundary Schema

Region ARegion B

Boundary

Roles:BoundaryRegion ARegion B

Bounded Region

Roles:Boundary: closed

Bounded Region

Background region

Topological Relations

• Separation

Topological Relations

• Separation

• Contact

Topological Relations

• Separation

• Contact

• Coincidence:

Topological Relations

• Separation

• Contact

• Coincidence:- Overlap

Topological Relations

• Separation

• Contact

• Coincidence:- Overlap- Inclusion

Topological Relations

• Separation

• Contact

• Coincidence:- Overlap- Inclusion

- Encircle/surround

Orientation

• Vertical axis -- up/down

up

down

above

belowupright

Orientation

Horizontal plane – Two axes:

Language and Frames of Reference

• There seem to be three prototypical frames of reference in language (Levinson)– Intrinsic– Relative– Absolute

Intrinsic frame of reference

frontback

right

left

Relative frame of reference

frontback

left??

right??

Absolute frame of reference

north

west

south

east

TR/LM and Verticality Schemas

• The book is under the table.up

down

under

Proximal/Distal Schema

.

Simple vs. Complex Schemas

Container Schema

• Roles:– Interior: bounded region– Exterior– Boundary

C

C C

TR

TR

out in

TR/LM + Container

Container Schema Elaborated

– Complexities –more roles/specifications:• Boundary properties

– Strength– Porosity

• Portals

Source-Path-Goal

Constraints:

initial = TR at Source

central = TR on Path

final = TR at Goal

Source Path Goal

SPG -- simple example

She drove from the store to the gas station.

TR = she

Source = the store

Goal = the gas station

Source Path Goal

SPG and Container

She ran into the room.

SPG. Source ↔ Container.Exterior

SPG.Path ↔ Container.Portal

SPG. Goal ↔ Container.Interior

PATH landmarks

past across along

LM

LM

LM

Part-Whole Schema

Part

Whole

semantic schema Containerroles:

interiorexteriorportalboundary

Representing image schemas

Interior

Exterior

Boundary

PortalSource

Path

GoalTrajector

These are abstractions over sensorimotor experiences.

semantic schema Source-Path-Goalroles:

sourcepathgoaltrajector

Language and Spatial Schemas

• People say that they look up to some people, but look down on others because those we deem worthy of respect are somehow “above” us, and those we deem unworthy are somehow “beneath” us.

• But why does respect run along a vertical axis (or any spatial axis, for that matter)? Much of our language is rich with such spatial talk.

• Concrete actions such as a push or a lift clearly imply a vertical or horizontal motion, but so too can more abstract concepts.

• Metaphors: Arguments can go “back and forth,” and hopes can get “too high.”

Simulation-based language understanding

Analysis Process

SemanticSpecification

“Harry walked into the cafe.” Utterance

CAFE Simulation

Belief State

General Knowledge

Constructions

construction WALKEDform

selff.phon [wakt]meaning : Walk-Action constraints

selfm.time before Context.speech-time selfm..aspect encapsulated

The INTO construction construction INTO subcase of spatial-prep

form selff .phon [Inthuw]

meaningevokes Trajector-Landmark as tlevokes Container as contevokes Source-Path-Goal as spgtl.trajectorspg.trajectortl.landmarkcontcont.interiorspg.goalcont.exteriorspg.source

Simulation specification

A simulation specification consists of:- schemas evoked by constructions- bindings between schemas

Language and Thought• We know thought (our

cognitive processes) constrains the way we learn and use language

• Does language also influence thought?

• Benjamin Whorf argues yes• Psycholinguistics

experiments have shown that linguistics categories influence thinking even in non-linguistics task

Language

Thought

cognitive processes

Universal Schemas and Cultural Frames

• Image Schemas appear to be universal– Colors– Spatial schemas – container, support– Action Schemas – grasp, general controller

• Frames are specific to a culture– Commercial Transaction (CT), stock market– Baseball, Cricket– Linguistics, Philosophy

• Frames have roles and constraints like schemas. – “shortstop” evokes the baseball frame– framing has a major role in politics

Frames

• Frames are conceptual structures that may be culture specific• Words evoke frames

– The word “talk” evokes the Communication frame– The word buy (sell, pay) evoke the Commercial Transaction (CT) frame.– The words journey, set out, schedule, reach etc. evoke the Journey frame.

• Frames have roles and constraints like schemas. – CT has roles vendor, goods, money, customer.

• Words bind to frames by specifying binding patterns – Buyer binds to Customer, Vendor binds to Seller.

Event Frames

Event frames have temporal structure, and generally have constraints on what precedes them, what happens during them, and what state the world is in once the event has been completed.

Sample Event Frame:Commercial Transaction

Initial state:Vendor has Goods, wants MoneyCustomer wants Goods, has Money

Transition:Vendor transmits Goods to CustomerCustomer transmits Money to Vendor

Final state:Vendor has Money

Customer has Goods

Sample Event Frame:Commercial Transaction

Initial state:Vendor has Goods, wants MoneyCustomer wants Goods, has Money

Transition:Vendor transmits Goods to CustomerCustomer transmits Money to Vendor

Final state:Vendor has Money

Customer has Goods

(It’s a bit more complicated than that.)

Partial Wordlist for Commercial Transactions

Verbs: pay, spend, cost, buy, sell, charge

Nouns: cost, price, payment

Adjectives: expensive, cheap

Meaning and Syntax

The various words that evoke this frame introduce the elements of the frame in different ways. , goods and money

Information expressed in sentences containing these words occurs in different places in the sentence depending on the word.

An experiment on Image Schemas

• Richardson and Spivey (2003) operationalized this question by presenting participants with sentences and testing for spatial effects on concurrent perceptual tasks.

• An interaction between linguistic and perceptual processing would support the idea that spatial representations are inherent to the conceptual representations derived from language comprehension (Barsalou, 1999).

Example verbs

The servant argued with the master.

The storeowner increases the price.

The girl hopes for a pony.

The athlete succeeds at the tournament.

The miner pushes the cart.

Aspect angles

• Vertical was 90 and horizontal 0.– Mean aspect angles were – (12=H, 42=Neutral, 69=V)

Example verbs

The servant argued with the master. 20 11 H

The storeowner increases the price. 85 75 V

The girl hopes for a pony. 55 36 V

The athlete succeeds at the tournament. 68 44V

The miner pushes the cart. 10 12 H

Free formForced choice

AVERAGE ASPECT ANGLE

The experiment

• Each trial began with a central fixation cross presented for 1000 ms. A sentence was presented binaurally through headphones. There was then a pause of 50, 100, 150 or 200 ms. – This randomized “jitter” was introduced, so that participants could not

anticipate the onset of the target visual stimulus. • The target, a black circle or square, then appeared in either the top,

bottom, left or right position, and remained on screen for 200 ms. • Participants were instructed to identify the stimulus as quickly as

possible, pressing one key to indicate a circle and another to indicate a square.

• Reaction times and accuracy rates were recorded. • The questions were interrogative forms of the filler sentences with an

object substitution in half of the cases (e.g., “Did the dog fetch the ball/stick?”). Participants responded “yes” or “no” by pressing designated keys.

Summary of Result

• There is an interference effect when the verb category is vertical (from norming study) and the visual stimulus object is vertical.

• Issues with the experiment?

Action Words- an fMRI study

• Somatotopic Representation of Action Words in Human Motor and Premotor Cortex– Olaf Hauk, Ingrid Johnsrude,and Friedemann

Pulvermuller*– Medical Research Council, Cognition and Brain

Sciences Unit Cambridge, United Kingdom– Neuron, Vol. 41, 1–20, January 22,

2004, Copyright 2004 by Cell Press

Traditional theory

• Unified meaning center in the left temporal lobe.– Connected to Wernicke’s area– Experiments on highly imageable words/nouns.

• Vocalization and grammar associated with frontal lobe– Connected to Broca’s area

Do action words activate the motor cortex

• Given: Cortical representations of the face, arm, and leg are discrete and somatotopically organized in the motor and premotor cortex

• Hypothesis: Words referring to actions performed with the face, arm, or leg would activate premotor networks.– neurons processing the word form and those processing the

referent action should frequently fire together and thus become more strongly linked, resulting in word-related networks overlapping with motor and premotor cortex in a somatotopic fashion.

• Experiment: An fMRI study with word stimuli from different effectors (face, arm, or leg). ROI based on movements (face, arm, leg)

Somatotopy in STS and MC

The Experiment• In order to find appropriate stimulus words, a rating study was first

performed. – Subjects were asked to rate words according to their action and visual

associations and to make explicit whether the words referred to and reminded them of leg, arm, and face movements that they could perform themselves

• From the rated material, 50 words from each of the three semantic subcategories were selected and presented in a passive reading task to 14 right-handed volunteers, while hemodynamic activity was monitored using event-related fMRI.

• The word groups were matched for important variables, including word length, imageability, and standardized lexical frequency, in order to minimize physical or psycholinguistic differences that could influence the hemodynamic response.

• To identify the motor cortex in each volunteer individually, localizer scans were also performed, during which subjects had to move their left or right foot, left or right index finger, or tongue.

Norming

(B) Mean ratings for the word stimuli obtained from study participants. Subjects were asked to give ratings on a 7 point scale whether thewords reminded them of face, arm, and leg actions. The word groups are clearly dissociated semantically (face-, arm-, and leg-related words).

All Actions

(C) Activation produced by all action words pooled together. Results are rendered on a standard brain surface (left) and on axial slices of the same brain (right).

Correlation with BOLD Signal

Neural Evidence for category structure

• Are there specific regions in the brain to recognize/reason with specific categories?

• No, but there are specific circuits distributed over relevant regions of the brain.

• What might the general characteristics of such circuits look like?

Schemas and Frames in Language

• Language Understanding Model– Analysis– Semantic Specification– Enactment or Simulation

• Semantic Specification (SemSpec)– Combines Schemas and Frames– Links (bindings) determine particular meaning

• Enactment – Based on system goals– Uses SemSpec and world knowledge