Transcript Perfusion Measurement with Dynamic Contrast MRI

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

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.
Research Methodology in
Psycholinguistics
Left
hemisphere
cortex
Right
hemisphere
Lesion Study
Split-brain patients –those who
have a damaged corpus callosum
but an undamaged brain.
Research Methodology in
Psycholinguistics
Results:
The left hemisphere is a language
hemisphere. (dominant).
• General Comments on Lesion
Studies:
1. The association between language
processing (e.g. syntactic processing)
and the damaged brain areas is direct.
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.
• Can we reliably investigate
normal people’s intact brain by
using noninvasive techniques??
No, before mid 1980’s.
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.
• 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.
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
• 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.
Massachusetts General Hospital
(Harvard University):
1992: K.K. Kwong et al. (PNAS)
S. Ogawa et al. (PNAS)
“Brain Imaging ” -- visualize the
activity of the intact human brain
• Brain science is (over-)interdisciplinary
and is a team’s work. Psycholinguistics
and Linguistics are parts of it.
fMRI & PET
Scanner for
image
acquisition
Workstation
for image
analysis
Image data
interpretation
Ideas &
designs for
the study
MRI physicist
or/& medical
doctor
Computer
programming
expert
Neurologist &
physiologist
Mind workers
(language,
perception…)
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.
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.
Milestones in Brain Science:
Hong Kong: ?????????????.
Everything depends on the vision of the
local community leaders.
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
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.
It takes about 400 milliseconds (msec) to
name common words.
But can we say 400 msec is the time to
identify a word? NO.
dog
dog
/dawg/
What is the time for the participant’s 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.
What is “identification”? Does identification
include access to a word’s 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.
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.
reda
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 won’t take more than 700
msec to identify a common word.
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.
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.
Conclusion:
Word identification takes place very
rapidly.
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.
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)?
dog
cat
dog
cup
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.
Thus, when reading a word, you do
NOT see it, but you have identified it.
This is an example of subliminal
perception.
Identifying words and letters
How does the processing of words relates
to the processing of letters?
Two hypotheses:
Hypothesis 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.
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
Ruling out the letter-by-letter hypothesis
Reicher’s 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.
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.