Categories and conceptsintroduction
CS182/Ling109/CogSci110
Spring 2006
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
• What Concepts Are: Basic Constraints
– Concepts are the elements of reason, and
– constitute the meanings of words and linguistic
expressions.
Concepts Are:
•Universal: they characterize all particular
instances; e.g., the concept of grasping is the
same no matter who the agent is or what the
patient is or how it is done.
•Stable.
•Internally structured.
•Compositional.
•Inferential. They interact to give rise to inferences.
•Relational. They may be related by hyponymy,
antonymy, etc.
•Meaningful.
•Not tied to the specific word forms used to express
them.
Concepts: Traditional Theory
• The Traditional Theory
– Reason and language are what distinguish human
beings from other animals.
– Concepts therefore use only human-specific brain
mechanisms.
– Reason is separate from perception and action, and does
not make direct use of the sensory-motor system.
– Concepts must be “disembodied” in this sense.
The neural theory
Human concepts are embodied. Many
concepts make direct use of sensory-motor,
emotional, and social cognition capacities
of our body-brain system.
• Many of these capacities are also present in
non-human primates.
Classical vs prototype model of
categorization
• Classical model
– Category membership determined on basis of essential
features
– Categories have clear boundaries
– Category features are binary
• Prototype model
– Features that frequently co-occur lead to establishment
of category
– Categories are formed through experience with
exemplars
Prototype theory
1.
2.
3.
4.
5.
6.
Certain members of a category are prototypical – or
instantiate the prototype
Categories form around prototypes; new members added
on basis of resemblance to prototype
No requirement that a property or set of properties be
shared by all members
Features/attributes generally gradable
Category membership a matter of degree
Categories do not have clear boundaries
Prototype theory
1.
Certain members of a category are prototypical – or
instantiate the prototype
Category members are not all equal
a robin is a prototypical bird, but we may not want to say it is the
prototype, rather it instantiates (manifests) the prototype or ideal -- it
exhibits many of the features that the abstract prototype does
“It is conceivable that the prototype for dog will be unspecified for
sex; yet each exemplar is necessarily either male or female.”
(Taylor)
Prototype theory
3.
No requirement that a property or set of properties be
shared by all members -- no criterial attributes
–
–
Category where a set of necessary and sufficient attributes can be
found is the exception rather than the rule
Labov household dishes experiment
•
•
Necessary that cups be containers, not sufficient since many things
are containers
Cups can’t be defined by material used, shape, presence of handles
or function
Prototype theory
– Wittgenstein’s examination of game
• Generally necessary that all games be amusing, not
sufficient since many things are amusing
• Board games, ball games, card games, etc. have
different objectives, call on different skills and
motor routines
- categories normally not definable in terms of
necessary and sufficient features
Prototype theory
• What about mathematical categories like odd or even
numbers? Aren’t these sharply defined?
– (Armstrong et al.) Subjects asked to assign numbers a degree of
membership to the categories odd number or even number
 3 had a high degree of membership, 447 and 91 had a lower
degree (all were rated at least ‘moderately good’)
Categories - who decides?
• Embodied theory of meaning- categories are
not pre-formed and waiting for us to behold
them. Our need for categories drives what
categories we will have
• Basic level categories - not all categories
have equal status. The basic level category
has demonstrably greater psychological
significance.
Basic-level categories
furniture
Superordinate
chair
desk chair
easy chair
rocking chair
lamp
desk lamp
floor lamp
table
dining room table
coffee table
Basic
Subordinate
Categories & Prototypes:
Overview
Superordinate
Furniture
Sofa
leather
sofa
fabric
sofa
Basic-Level Category
Desk
L-shaped
desk
Reception
disk
Subordinate
• Three ways of examining the categories we form:
– relations between categories (e.g. basic-level category)
– internal category structure (e.g. radial category)
– instances of category members (e.g. prototypes)
Basic-level -- Criteria
• Perception –
– overall perceived shape
– single mental image
– fast identification
Basic-level -- Criteria
• Perception
• Function – motor program for interaction
Basic-level -- Criteria
• Perception
• Function
• Words –
– shortest
– first learned by children
– first to enter lexicon
Basic-level -- Criteria
•
•
•
•
Perception
Function
Communication
Knowledge organization –
– most attributes are stored at this level
Basic-Level Category
What constitutes a basic-level category?
• Perception:
– similar overall
perceived shape
– single mental image
– (gestalt perception)
– fast identification
• Function:
– general motor program
• Communication:
–
–
–
–
–
shortest
most commonly used
contextually neutral
first to be learned by children
first to enter the lexicon
• Knowledge Organization:
– most attributes of category
members stored at this level
Other Basic-level categories
• Objects
• Colors
• Motor-routines
Concepts are not categorical
Mother
• The birth model
The person who gives birth is the mother
• The genetic model
The female who contributes the genetic material is the mother
• The nurturance model
The female adult who nurtures and raises a child is the mother of the
child
• The marital model
The wife of the father is the mother
• The genealogical model
The closest female ancestor is the mother
(WFDT Ch.4, p.74, p.83)
Radial Structure of Mother
Genetic
mother
Stepmother
Unwed
mother
Surrogate
mother
Biological
mother
Adoptive
mother
Central
Case
Foster
mother
Birth
mother
Natural
mother
The radial structure of this category is
defined with respect to the different
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 categories
Concepts 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"); antiideal 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)
Prototype
• Cognitive reference point
• Ideal case / Nightmare case
– standards of comparison
– e.g. ideal vacation
– can be abstract
– may be neither typical nor
stereotypical
• Social stereotypes
– snap judgments
– defines cultural expectations
– challengeable
• Typical case prototypes
– default expectation
– often used unconsciously in
reasoning
• Paragons / Anti-paragons
– an individual member that
exhibits the ideal
• Salient examples
– e.g. 9/11 – terrorism act
• Generators
– central member + rules
– e.g. natural number = singledigit numbers + arithmetic
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
Left middle temporal gyrus
ACC
Premotor
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.
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 the
words 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?
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)
TR
– The bike is near the house
– ? The house is near the bike
• Boundary / Bounded Region
LM
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)
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
English
AROUND
ON
OVER
IN
Bowerman & Pederson
Dutch
OP
OM
AAN
BOVEN
IN
Bowerman & Pederson
Chinese
ZHOU
LI
SHANG
Bowerman & Pederson
Spatial schemas
•
•
•
•
•
TR/LM relation
Boundaries, bounded region
Topological relations
Orientational Axes
Proximal/Distal
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 A
Region B
Boundary
Roles:
Boundary
Region A
Region 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
above
upright
below
down
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
left
back
front
right
Relative frame of reference
right??
back
front
left??
Absolute frame of reference
west
south
north
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
TR/LM + Container
out
in
TR
C
TRC
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
Representing image schemas
semantic schema Source-Path-Goal
roles:
source
path
goal
trajector
semantic schema Container
roles:
interior
exterior
portal
boundary
Boundary
Source
Trajector
Interior
Portal
Goal
Path
Exterior
These are abstractions over sensorimotor experiences.
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
construction WALKED
form
selff.phon  [wakt]
meaning : Walk-Action
constraints
selfm.time before Context.speech-time
selfm..aspect  encapsulated
“Harry walked into the cafe.”
Utterance
Analysis Process
Constructions
General
Knowledge
Semantic
Specification
Belief State
CAFE
Simulation
The INTO construction
construction INTO
subcase of spatial-prep
form
selff .phon  [Inthuw]
meaning
evokes Trajector-Landmark as tl
evokes Container as cont
evokes Source-Path-Goal as spg
tl.trajector  spg.trajector
tl.landmark  cont
cont.interior  spg.goal
cont.exterior  spg.source
Simulation specification
A simulation specification consists of:
- schemas evoked by constructions
- bindings between schemas
Simulation-based language understanding
construction WALKED
form
selff.phon  [wakt]
meaning : Walk-Action
constraints
selfm.time before Context.speech-time
selfm..aspect  encapsulated
“Harry walked into the cafe.”
Utterance
Analysis Process
Constructions
General
Knowledge
Semantic
Specification
Belief State
CAFE
Simulation
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
Forced choice
Free form
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
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?
Language and Thought
Language
Thought
cognitive processes
• 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