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

Right hemisphere

cortex

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., Nature1988: Fox et al., Science1988: Petersen et al., Nature1988: 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.