WORD SEMANTICS 2 DAY 27 – OCT 30, 2013 Brain & Language LING 4110-4890-5110-7960 NSCI...
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Transcript of WORD SEMANTICS 2 DAY 27 – OCT 30, 2013 Brain & Language LING 4110-4890-5110-7960 NSCI...
WORD SEMANTICS 2DAY 27 – OCT 30, 2013
Brain & Language
LING 4110-4890-5110-7960
NSCI 4110-4891-6110
Harry Howard
Tulane University
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Course organization• The syllabus, these slides and my recordings are
available at http://www.tulane.edu/~howard/LING4110/.• If you want to learn more about EEG and neurolinguistics,
you are welcome to participate in my lab. This is also a good way to get started on an honor's thesis.
• The grades are posted to Blackboard.
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REVIEW
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Linguistic model, Fig. 2.1 p. 37
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Discourse model
SyntaxSentence prosody
MorphologyWord prosody
Segmental phonologyperception
Acoustic phonetics Feature extraction
Segmental phonologyproduction
Articulatory phonetics Speech motor control
INPUT
SEMANTICS
Sentence level
Word level
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Semantic networks
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LEXICAL SEMANTICS 2Ingram: III. Lexical semantics, §10.
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The linkages in such a network are …
• associative …• established by the fact that certain words are often used together,
such as pig and farm;• these are ‘accidental’, in the sense that there is nothing in the
meaning of pig that requires them to be associated with farms;• they are often defined in a free association test, by giving a subject
the prime word and asking her to say the first word that comes mind;
• or semantic …• the relationships of meaning mentioned yesterday, such as part-
whole;• these are necessary, in the sense that a hand is by definition made
up of fingers.
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Caveat• I grant that the distinction between associative and
semantic relationships can be difficult to pin down.• Note that psychologists would call semantic networks ‘semantic
memory’, • while linguists would say that most of these networks contain real-
world knowledge, which is different from linguistic semantics.
• So let us look at an experiment that tries to tease these two domains apart.
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Semantic + associative vs. non-associative prime-probe relationsTable 10.4, Moss et al. (1995)
Semanticrelation
Category coordination[taxonomy]
Function
Natural Artifact Instrumental Scripted
Associated cat – dog boat – ship bow – arrow theater – play
brother – sister coat – hat umbrella – rain beach – sand
Non-associated
aunt – nephew airplane – train knife – bread party – music
pig – horse blouse – dress string – parcel zoo – penguin
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Increased priming with respect to control condition in which there is no relationship between prime and probe:
unrelated (control) < semantic + non-associative < semantic + associative
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Leftovers• The modality of presentation has a large influence.
• Auditory priming fades much more quickly than visual priming.
• Priming has shown that multiple word meanings are activated before a word is actually recognized. • This reminds of the TRACE model, which is reviewed in the next
slide.
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An alternative: the TRACE II model
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Activation in a semantic network
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Some results from brain imaging• I have mentioned a few times a general division of the
brain into posterior or sensory cortex (occipital, temporal & parietal lobes) and anterior or motor cortex (frontal lobe).
• Should this have any relevance for language?• Nouns vs verbs
• Many nouns have ‘high imageability’ and so should require more activation from visual cortex (temporal-occipital lobes)
• Verb should require more activation from motor cortex (frontal lobe)
• Not all results are consistent, but by and large this is true.
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Levels of categorization
• On a scale of 1 to 7, rate the following items as a good example of the category furniture.
• 1 chair • 1 sofa • 3 couch • 3 table • 5 easy chair • 6 dresser • 6 rocking chair • 8 coffee table • 9 rocker • 10 love seat • 11 chest of drawers • 12 desk • 13 bed
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Hierarchy of categories
furniture
|
chair
|
bench
domain-level
|
basic/prototype
|
subordinate
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Basic is special
1. Response Times: in which queries involving a prototypical member (e.g. is a robin a bird) elicited faster response times than for non-prototypical members.
2. Priming: When primed with the higher-level (superordinate) category, subjects were faster in identifying if two words are the same. Thus, after flashing furniture, the equivalence of chair-chair is detected more rapidly than stove-stove.
3. Exemplars: When asked to name a few exemplars, the more prototypical items came up more frequently.
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Basic is really special• 1) It is the highest level at which a single mental image
can represent the entire category (you can’t get a mental image of vehicle or furniture).
• 2) It is the highest level at which category members have a similarly perceived overall shape.
• 3) It is the highest level at which a person uses similar motor actions for interacting with category members.
• 4) It is the level at which most of our knowledge is organized.
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The fMRI experiment
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Why we are interested in vision• The easiest stimuli to use are visual, so we will be
gathering information about vision anyway• pictures (name this picture)• text
• Reading disorders (dyslexia) have a linguistic component• We are ultimately more interested in audition, however,
but perhaps some of what we learn from vision will generalize to it
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Early and late visionearly vision is beneath the surface; late vision is on it
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Norman (2002)• Constructivist approach
• ventral ~ identification• the stimulation is inherently
insufficient, necessitating an “intelligent” perceptual system that relies on inference
• perception is indirect/multistage process between stimulation and percept
• memory, stored schemata, and past experience play an important role in perception
• excels at analyzing the processes and mechanisms underlying perception
• Ecological approach• dorsal ~ visual control of motor
behavior• the information in the ambient
environment suffices and is not equivocal, and thus, no “mental processes” are needed to enable the pick-up of relevant information
• perception is direct/single-stage process
• no role for memory or related phenomena
• excels at the analysis of the stimulation reaching the observer
• affordances
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The what / ventral pathway (Palmeri & Gauthier 2004)
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CATEGORY-SPECIFIC DEFICITS
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THE FUNCTIONAL ORGANIZATION OF THE VENTRAL VISUAL PATHWAY AND ITS RELATIONSHIP TO OBJECT RECOGNITIONGrill-Spector 2004
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Introduction• Humans recognize objects and faces instantly and
effortlessly.• What are the underlying neural mechanisms in our brains
that allow us to detect and discriminate among objects so efficiently?
• Here we examine whether the human ventral stream is organized more around stimulus content or recognition task.
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Previous discoveries• Multiple ventral occipitotemporal regions anterior to retinotopic cortex
respond preferentially to various objects compared to textures.• Functional imaging studies have revealed that some of these regions
respond maximally to specific object categories, such as:• faces (fusiform face area)• places (parahippocampal place area)• body parts• letter strings • tools• animals
• These results suggest that areas that elicit a maximal response for a particular category are dedicated to the recognition of that category.
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Problems• Comparing activation between a handful of object
categories is problematic because it depends on the choice of categories.
• While there is maximal activation to one category the activation to other categories is not negligible
• Comparing the amplitude of activation to object categories does not exclude the possibility that the underlying representation might not be of whole objects.
• Objects from different categories differ in many dimensions and it is possible that the source of higher activation for a category is not restricted to visual differences.
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Three ways to represent objects• Kanwisher (2000): ventral temporal cortex contains a
limited number of modules specialized for the recognition of special categories (faces, places, body parts) and the remaining cortex is a general-purpose mechanism for the perception of any shape
• Haxby et al.(2001): occipitotemporal cortex is organized according to form attributes. The representation of an object is reflected by a distinct pattern of response across ventral cortex, and this distributed activation produces the visual percept
• Tarr and Gauthier (2000): occipitotemporal cortex is organized according to the perceptual processes carried out and not by the content of information processed – different cognitive processes require different computations
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Experimental tasks• Detection
• subjects decide whether or not a gray-scale image contains an object
• Identification• subjects discriminate between objects belonging to the same basic
level category• for instance, a particular subordinate member of a category (e.g.
electric guitar) from other members of that category (e.g. acoustic guitars)
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Results• When the category was held constant but subjects performed different recognition tasks (detection vs. identification) similar regions in the human ventral stream were activated.
• When the task was kept constant and subjects were required to identify different object categories, different regions of the human ventral stream were activated.
• This suggests that the human ventral stream is organized more around visual content than visual process.
NEXT TIMEQ7
Continue with word semantics
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