Perfusion Measurement with Dynamic Contrast MRI

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Research Methodology in Psycholinguistics

• 4. Neurolinguistic Approach
• It studies the brain mechanism for language
  functioning where is language functioning
  localized in the brain?
• Lesion study using brain-damage patients
• Functional brain imaging study using the intact
  human brain

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• Basic Neuroanatomy
• The outer layer of the brain cerebral cortex
• Hidden underneath the cortex are subcortical
  parts of the brain
• The left and right hemispheres are connected by a
  band of nerve fibers corpus callosum
• An important feature of the human nervous system
  is that each cerebral cortex is connected to the
  opposite side of the body. This is termed
  contralateral connections.

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Research Methodology in Psycholinguistics

Left hemisphere
Right hemisphere
cortex
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Lesion Study

• Split-brain patients those who have a damaged
  corpus callosum but an undamaged brain.

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Research Methodology in Psycholinguistics
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• Results
• The left hemisphere is a language hemisphere.
  (dominant).

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• General Comments on Lesion Studies
• The association between language processing (e.g.
  syntactic processing) and the damaged brain areas
  is direct.

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2. The primary limitation is that lesions studies
rely on damaged brains. This has several
drawbacks because patients with distinct
lesions and specific functional impairments are
rare in many case, lesions are large
following brain damage, performance may not
reflect normal language processing because
patients may compensate for their deficits by
using unusual processing strategies.
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• Can we reliably investigate normal peoples
  intact brain by using noninvasive techniques??
• No, before mid 1980s.

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Research Methodology in Psycholinguistics

• Brain Imaging Techniques
• (PET fMRI)
• Language processing requires energy. Brain
  imaging techniques depend on the fact that
  working brain tissue calls more blood its way and
  consumes more glucose.

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• PET (positron emission tomography)
• Subjects are injected with glucose that has been
  tagged with a radioactive substance through
  this, brain images can be got indicating which
  regions of the brain have the greatest blood flow
  are are using the most energy.

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Washington University at St. Louis 1986
Fox et al., Nature 1988 Fox et al.,
Science 1988 Petersen et al., Nature 1988
Posner et al. Science
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• fMRI (functional magnetic resonance imaging)
• When subjects perform a task (e.g., reading),
  neural activity in specific areas of the brain
  increases. This results in greater need for
  glucose and oxygen, both of which are met by
  increasing blood flow. There is a small
  difference in magnetic susceptibility (a property
  of molecules) between oxygenated hemoglobin and
  de-oxygenated hemoglobin. With increased blood
  flow to active brain areas, there is a change in
  the proportion of oxygenated to de-oxygenated
  hemoglobin. This difference is detected by MRI
  scanners.

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Massachusetts General Hospital (Harvard
University) 1992 K.K. Kwong et al. (PNAS)
S. Ogawa et al. (PNAS)
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Brain Imaging -- visualize the activity of
the intact human brain
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• Brain science is (over-)interdisciplinary and is
  a teams work. Psycholinguistics and Linguistics
  are parts of it.

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fMRI PET
Scanner for image acquisition
Ideas designs for the study
Workstation for image analysis
Image data interpretation
MRI physicist or/ medical doctor
Mind workers (language, perception)
Computer programming expert
Neurologist physiologist
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Milestones in Brain Science 1990 Presidential
Proclamation 6158 signed by George Bush,
proclaiming that 1990-2000 is Decade of the
Brain. 1993 The Human Brain Project (HBP) is
launched in USA. Participating units included
National Institute of Health, National Institute
of Mental Health, Harvard University, Washington
University at St. Louis, Stanford University,
MIT, Dartmouth College etc. Now the HBP is
jointly researched by scientists over more than
15 countries.
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Milestones in Brain Science 1996-2000 Research
on the human brain is put in national strategic
development plans of more than 20 countries and
regions including England, China, Japan, France,
Spain, Canada, Australia, Singapore, Taiwan.
Functional brain imaging research centers were
rapidly established in many countries. 2001
With the completion of the human genome project,
the HBP has become a second word-wide project and
has been in the frontier of science.
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Milestones in Brain Science Hong Kong
?????????????. Everything depends on the vision
of the local community leaders.
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Word Recognition The Mental Lexicon I

• This chapter covers several basic issues on
  word recognition
• Word identification is relatively automatic,
  compared to syntactic process of sentences.
• Words are not processed letter by letter the
  relation between parts and wholes.
• 2 routes in visual word recognition graphic
  meaning and graphic-phonologic-meaning

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Automaticity of word recognition

• How long does it take to identify a word?
• Response-time methods.
• We present a participant a word on some sort of
  visual display and measure how long it takes the
  participant to speak the word aloud. Suppose that
  we can precisely control when the presentation of
  the word begins and can precisely measure when
  the participant begins making the response, we
  would have a measure of response time.

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It takes about 400 milliseconds (msec) to name
common words. But can we say 400 msec is the
time to identify a word? NO.
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dog
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dog
/dawg/
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• What is the time for the participants brain to
  achieve a state that we call identification?
• For naming, besides identification time (IT),
  several other processes must occur
• a) What kind of response to make? (naming here)
• b) The participant must retrieve the motor
  program for making the response
• c) The command must be sent down to the mouse.
• IT a b c 400 msec.

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What is identification? Does identification
include access to a words meaning? If it does,
we can use a semantic categorization task to
measure the time to identify a word. e.g. we can
ask the participant to judge if a word is an
animal. (cat, stone). In this case, it takes
about 700 msec to complete the task.
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We can also use a lexical decision task to
measure how long it takes tom judge whether a
viewed stimulus is a real word or not. It takes
about 500-600 msec for this task.
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reda
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Return to the question how long does it take to
identify a word? We do not know the exact time
to identify a word, because we cannot partial out
processes irrelevant to identification itself.
But we know it wont take more than 700 msec to
identify a common word.
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• How long does it take to identify a word?
• Brief presentation methods
• We present a word on some sort of visual display
  very briefly (say, 60 msec). Then immediately
  following the exposure to the word, we present a
  pattern mask usually consisting of letterlike
  forms in the same location. Thus, the subject
  sees the word for 60 msec followed immediately by
  the mask.
• It is found that we can identify words in 60
  msec.

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• How long does it take to identify a word?
• Eye movement methods
• Our eyes fixate on a word for 200-250 msec on
  average, followed by a saccade (one eye movement)
  of 25 msec.

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Conclusion Word identification takes place very
rapidly.
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Automaticity of word recognition
Because a word can be recognized so quickly, can
we say word identification occurs automatically?
How to define automatic? --we are unaware
of the process --the execution of the process is
not under the conscious control of the subject.
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To examine the automaticity of word
identification, the following priming paradigm
may be adopted In a priming experiment, the
researcher exposes two words in sequence, the
prime and the target (e.g., DOG - CAT). The
researcher is interested in how quickly the
target is processed. Specifically, is CAT
processed more quickly when it follows a related
word (DOG) than it follows an unrelated word
(FAN)?
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dog
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cat
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dog
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cup
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When the prime is exposed for 30 or 50 msec,
subjects response to the related target is much
faster. In this case, subjects are not aware of
the prime they cannot view the prime clearly or
even cannot realize there is a prime word before
the target. This is true even if the proportion
of related to unrelated prime-target pairs is
manipulated. However, the prime is indeed
processed and influences target identification.
This priming effect indicates that word
identification occurs automatically.
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Thus, when reading a word, you do NOT see it, but
you have identified it. This is an example of
subliminal perception.
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Identifying words and letters
How does the processing of words relates to the
processing of letters? Two hypotheses Hypothesi
s 1 Because word recognition takes place so fast
and automatic, the process of letter
identification is bypassed by skilled readers.
Smith (1971) assumes that skilled readers
identify english words pretty much the same way
they identify a picture.
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Hypothesis 2 Words are encoded as the sequence
of letters. Words are processed letter-by-letter
serially from left to right. (Gough,
1972) Iconic memory
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Ruling out the letter-by-letter
hypothesis Reichers study (1969). Following the
fixation point, he presented a target stimulus
(either a word such as WORD, a letter such as D,
or a nonword such as ORWD). The target stimulus
was followed by the pattern mask and 2 probe
letters, one above the critical letter of the
target and the other below it. (Forced-choice
) Subjects task was to choose which of the two
probe letters was exposed in the target stimulus.
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Reicher found that the critical letter in the
target word was reported more accurately than the
same letter in isolation. The letter in
isolation was reported with about the same
accuracy as the letter in the nonword
(ORWD). Thus, letters in words are identified
more accurately than letters in isolation. This
is termed the word superiority effect.