Transcript WORD SEMANTICS 2 DAY 27 – OCT 30, 2013 Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Harry Howard Tulane University.

WORD SEMANTICS 2
DAY 27 – OCT 30, 2013
Brain & Language
LING 4110-4890-5110-7960
NSCI 4110-4891-6110
Harry Howard
Tulane University
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Brain & Language - 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
Discourse model
Sentence level
Word level
Syntax
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M
A
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T
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C
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Sentence prosody
Morphology
Word prosody
Segmental phonology
production
Segmental phonology
perception
Articulatory phonetics
Speech motor control
Acoustic phonetics
Feature extraction
INPUT
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Semantic networks
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LEXICAL SEMANTICS 2
Ingram: 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 partwhole;
• 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 realworld 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 relations
Table 10.4, Moss et al. (1995)
Semantic
relation
Associated
Nonassociated
Category coordination
[taxonomy]
Function
Natural
Artifact
Instrumental
Scripted
cat – dog
boat – ship
bow – arrow
theater – play
brother – sister
coat – hat
umbrella – rain
beach – sand
aunt – nephew
airplane – train
knife – bread
party – music
pig – horse
blouse – dress
string – parcel
zoo – penguin
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.
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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 vision
early 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
•
•
•
•
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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/singlestage 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
RECOGNITION
Grill-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.
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NEXT TIME
Q7
Continue with word semantics
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