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The global mission of the NeuroCognition Lab is to provide a better understanding of the neuronal
basis of cognition in hearing adults and children as well as adults who are deaf. We are part of a
relatively new discipline known as Cognitive Neuroscience. To understand
this discipline you have to know something about the two parent fields:
Cognitive Psychology and Neuroscience. Traditional cognitive
psychologists seek to understand the general principles and properties
of cognitive processes such as perception, attention, problem solving
and language production (speaking and writing) and comprehension
(listening and reading) -- generally without much interest in the brain.
Neuroscientists come in a variety of flavors and study the nervous
systems of humans and other species, but by-in-large they focus on
relatively low level mechanisms within a specific system (e.g., some
neurophysiologists seek to understand the workings of the fundamental
units or cells of the nervous system known as neurons). Cognitive
Neuroscientists are specifically interested in how the brain
accomplishes the very complex tasks of perception, memory, attention
problem solving and language. They do this by using a combination of
theoretical and methodological techniques from both parent disciplines.
The
primary question our lab is interested in is how language and other,
possibly related, cognitive systems are organized and function in the
human brain. This turns out to be one of the most vexing questions in
psychology! This is partly because language use is such a
complex skill and partly because unlike many other cognitive
systems (e.g., memory, attention, object recognition) there are no
suitable animal models. Humans are the only species (on earth) that have
evolved a complex, learned communication system with a rich set of
structural rules. The lack of animal models has made it almost
impossible to perform the kind of invasive controlled manipulation of
the brain necessary to better understand how language works. Therefore,
we have been forced to rely on less invasive procedures.
In
the last several years a number of new and exciting non-invasive
techniques have become available for directly examining brain structure,
and more recently brain function.
CAT,
MRI, PET,
fMRI
and ERP are some
of the new techniques that allow the experimenter to take a
snap-shot of the awake and intact human brain. Using a computer the
experimenter can then construct a series of pictures of different
regions/areas of the brain. While CAT and traditional MRI show what the
brain looks like structurally (i.e., they show the anatomy of the
brain), PET, fMRI, MEG and ERP show areas of the brain that are active
or functioning (i.e., they show the physiology of the brain). It is
these latter techniques that have been a boon to Cognitive
Neuroscientists, as they allow the investigator to actually see brain
areas involved in different cognitive activities.
PET, fMRI
and MEG are very expensive (millions of dollars) as they require a
substantial investment in computer and imaging (scanner) hardware.
Typically these systems can only be afforded by large medical centers
that use them for clinical procedures. Psychologists interested in using
this equipment must squeeze in whenever a time slot opens (frequently in
the middle of the night). The advantage of these techniques is that they
have relatively good spatial resolution. This means that they can tell
with some accuracy where in the brain activity is occurring (within a
few centimeters or even millimeters in the latest equipment).
ERPs, which
record the electrical activity of the brain, are within the budget of
most psychological researchers, but traditionally they have suffered
from relatively poor spatial resolution. This means that while they can
measure different brain functions (i.e., activity in different cognitive
systems) they cannot easily determine where the activity is coming from.
However, recently advances in signal analysis and increases in electrode
arrays have improved the resolution of
ERPs and
there is now some hope that this technique, especially when coupled with
PET or fMRI, will be better able to determine which brain regions are
active in different cognitive tasks.
One thing
that has become very apparent in the study of human cognition is that
time is of the essence. Although neurons (the basic processing
units of the brain) operate at a relatively slow rate (they can fire at
best up to 1000 times per second), most of the higher level processes
that neurons are responsible for (and that we are interested in) take
place relatively rapidly -- on the order of less than a second. For
example, the typical reader can process, on average, about three to four
words a second. That means that, on average, a word is perceived,
recognized and understood in about 250 to 400 milliseconds! The rate for
processing spoken words is more variable, but is on the same basic time
scale. Therefore, any technique that aspires to measure word
comprehension as it unfolds in the brain will have to have sufficient
temporal resolution to differentiate the sub-processes (e.g.,
perceiving, recognizing, understanding) involved in the task of reading
or listening to words. PET and fMRI, because they measure the dynamics
of blood flowing in the brain, have resolutions on the order of, at
best, a few seconds (i.e., it takes a few seconds after a change in
brain state for it to show up in blood flow changes). Clearly, this is
too slow to resolve the sub-processes involved in word comprehension (or
most other cognitive skills for that matter). However, ERPs, because
they directly monitor the electrical activity of the brain, have
millisecond level resolution -- that is, they are on-line. ERPs are
therefore sensitive to brain activity well within the range of the
component processes of most cognitive tasks -- including word
comprehension. A substantial body of research now exists suggesting that
ERPs are sensitive to a variety of language subprocesses as well as
other cognitive processes.
In the
NeuroCognition Lab we use ERPs to study the neuronal basis of reading
and listening to language and more recently the production of language as well.
Since our arrival at SDSU in 2013 we have also begun an exciting new collaboration
with the Laboratory for Language and Cognitive Neuroscience. In this research we are
studying reading comprehension, comprehension of ASL signs and production of ASL in
individuals who are deaf.
Some of the
questions that we are interested in are reflected in our
on-going projects.
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