Categories and concepts- introduction

1. Categories and concepts- introduction CS182/Ling109/CogSci110 Spring 2007

2. 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

3. Embodiment Of all of these fields, the learning of languages would be the most impressive, since it is the most human of these activities. This field, however, seems to depend rather too much on the sense organs and locomotion to be feasible. Alan Turing (Intelligent Machines,1948)

4. The WCS Color Chips • Basic color terms: • Single word (not blue-green) • Frequently used (not mauve) • Refers primarily to colors (not lime) • Applies to any object (not blonde)

5. Concepts • What Concepts Are: Basic Constraints • Concepts are the elements of reason, and • constitute the meanings of words and linguistic expressions.

6. 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 words used to express them.

7. 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.

8. 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.

9. 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

10. Prototype theory • 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

11. Prototype theory • 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)

12. 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 • Cups vs. bowls is graded and context dependent

13. 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

14. 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’)

15. 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.

16. Basic-level categories

17. chair desk chair easy chair rocking chair furniture lamp desk lamp floor lamp table dining room table coffee table Superordinate Basic Subordinate

18. Categories & Prototypes: Overview Furniture Superordinate • 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) Sofa Desk Basic-Level Category leathersofa fabricsofa L-shapeddesk Receptiondisk Subordinate

19. Basic-level -- Criteria • Perception – • overall perceived shape • single mental image • fast identification

20. Basic-level -- Criteria • Perception • Function – motor program for interaction

21. Basic-level -- Criteria • Perception • Function • Words – • shortest • first learned by children • first to enter lexicon

22. Basic-level -- Criteria • Perception • Function • Communication • Knowledge organization – • most attributes are stored at this level

23. 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 Basic-Level Category What constitutes a basic-level category?

24. Other Basic-level categories • Objects • Colors • Motor-routines

25. Concepts are not categorical

26. 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)

27. Radial Structure of Mother Geneticmother Stepmother The radial structure of this category is defined with respect to the different models Unwedmother Adoptivemother CentralCase Surrogatemother Birthmother Biologicalmother Naturalmother Fostermother

28. 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?

29. Concepts and radial categories Concepts can 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, 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)

30. 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)

31. Cognitive reference point standards of comparison Social stereotypes snap judgments defines cultural expectations challengeable Typical case prototypes default expectation often used unconsciously in reasoning Ideal case / Nightmare case e.g. ideal vacation can be abstract may be neither typical nor stereotypical 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 = single-digit numbers + arithmetic Prototype

32. Neural Evidence for category structure • Are there specific regions in the brain to recognize/reason with specific categories?

33. 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)

34. A PET Study on categories (Nature 1996)

35. 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.

36. 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

37. Left middle temporal gyrus ACC Premotor

38. Calcarine Sulcus

39. 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.

40. 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

42. 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

43. 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)

44. Somatotopy in STS and MC

45. 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.

46. 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).

47. 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).

48. Movement vs. Actions

49. Correlation with BOLD Signal