Mark Dow
Research
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Functionally
active areas during viewing of moving images compared to a static
image. The alternating green and yellow spots highlight significant
activity in the middle-temporal (V5/MT)
regions, on the left and right near the back of the brain, during two fMRI
scans separated by several months. This gives a sense of how spatially
specific and repeatable fMRI can be, at least for some classes of
neuronal activity.
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I work on software
for image and functional MRI time
series analysis,
and am involved with fMRI studies involving human tactile-visual
processing, visual spatial attention and retinotopy.
Cross-modal
Plasticity
This fMRI and ERP study examines how different
sensory modalities, such as hearing, vision and touch, interact in the
human brain, and how these interactions are shaped by external factors
in environment and internal factors such as attention.
Segmentation software
tools for
neuroimaging
These include 3-D
surface extraction and
segmentation algorithms, and volume navigation and editing tools that
provide a framework for semi-automatic region of interest generation
and landmark specification. The approach we are developing is based on
edge/surface detection using Gaussian derivative filters,
over-segmentation, and hierarchical region combination. The goal is to
quickly identify primary surfaces, landmarks, and other image based
features, and to use maps
of these features to inform segmentation or parcellation of 3-D images.
Far
peripheral human vision
These fMRI
experiments are designed to investigate
the organization, operation, and plasticity of cortical areas involved
in visual processing at large (20-80 degree) eccentricities. We use
light guiding fibers to present flashing stimuli at peripheral
locations during functional imaging. Retinotopically mapped visual
areas and areas that preferentially respond to peripheral visual
stimulation are identified. We are investigating the extent and
organization of these visual areas, and how they are modulated by
spatial attention. Comparison of hearing and congenitally deaf adults
results will elucidate how visual cortical networks are modified and
modulated by different auditory experience.
Geek art, geometric images and the
algorithms that generate them
Geek software
Video
motion estimation and quantification
Space
Software
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Free volume navigation, visualization, and
editing software (MS Windows). In active development, in collaboration
with Greg Scott.
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Scale
Space Edges software
Presentations, papers, posters,
teaching materials, etc.
Emergence
of the neural network for reading in five-year-old beginning readers of
different levels of pre-literacy abilities: An fMRI study
Yoshiko Yamada, Courtney Stevens,
Mark Dow, Beth A. Harn, David J. Chard and Helen J. Neville
NeuroImage, Volume 57, Issue 3, 1 August 2011,
Pages 704-713
...
Following 3 months of kindergarten and, for AR children,
supplemental reading instruction, OT children showed left-lateralized
activation in the temporo-parietal region, whereas AR children showed
bilateral activation and recruitment of frontal regions including the
anterior cingulate cortex. These data suggest that typical reading
development is associated with initial recruitment and subsequent
disengagement of right hemisphere homologous regions while atypical
reading development may be associated with compensatory recruitment of
frontal regions.
Arithmetical
Self-Similarity (seminar slides)
Mark Dow, Jörg Endrullis, Dimitri Hendriks, Jan Willem Klop
Streams Seminar, Nijmegen, April 20, 2010
What is the underlying construction for
scale-invariant sequences? We determine the arithmetical
self-similarity of several classes of streams. What is their
relation to fractals: is scale-invariance a sufficient criterion for
turtle drawings to converge to a fractal curve?
BOLD localization of
short
visual events (seminar slides)
Mark Dow
LCNI science meeting, February
2005
An
edge based image segmentation
method (poster)
Mark Dow, Ray Nunnally
ISMRM 2004 conference, [abstract
.doc]
Neuroscience, disease progression and
clinical trial studies, using MRI and other imaging modalities, benefit
from unbiased and repeatable image feature quantification. We describe
a general method for segmentation of 2-D images that reduces the burden
of manual region of interest (ROI) selection while increasing
repeatability. The method uses an objective edge definition and edge
linking criteria to over-segment an image, and hierarchical clustering
of the resulting elemental segments. The algorithms have been tested on
a range of imagery, and are suitable for several MRI tissue
segmentation purposes. The algorithms do not require thresholds that
are image or image modality dependant, and can be extended to 3-D for
segmentation and feature extraction tasks, such as landmark
identification.
Human
retinotopic mapping of the far periphery (poster)
Greg Scott, Mark Dow, Helen Neville
Society for Neuroscience
2003 conference
We used fMRI to map cortical areas
sensitive to visual stimuli in the far periphery. Discrete flashing
light stimuli at eccentricities of 2-80° presented in each visual
field quadrant of one eye induced a BOLD response in cortical visual
areas. By tracing these activations at increasing eccentricities,
several retinotopic paths were delineated for each visual field
quadrant. Some of these regions can be identified with known visual
areas by their spatial arrangement and mirroring of neighboring
representations.Cortical distance between activation locations of
spatially adjacent stimuli were estimated. This provides a measure of
the cortex used as a function of eccentricity, for each identified
visual area.
Measuring the
earth's shape: Maximum solar
elevation observations, through space and time (seminar slides,
.ppt)
Mark Dow, Ansel Dow
Road trip report at Brain Development Lab
[print/high res. version:
.ppt
(32 MB)]
Dressed
basis for highly excited molecular vibrations (.pdf)
Michael E. Kellman,
Mark W. Dow,
and Vivian Tyng
J. Chem. Phys.
118, 9519
(2003)
[The following abstract is the way a theoretical chemist would describe
how the vibrations of a water molecule (stretching an bending of bonds
between the atoms of H
2O) might be modeled. While we often
know how molecules behave experimentally by
spectrum analysis,
there is no easy way to predict the complexities without some
simplifiing model that retains the richness of interactions.]
Starting from
a multiresonance spectroscopic Hamiltonian fit by Baggott to
experimental levels of H2O,
an approximate Hamiltonian is devised using a prediagonalized
“dressed” zero-order basis, within which a residual,
effective single-resonance coupling operator acts. The dressed basis
incorporates many of the effects of nonintegrability, while the
effective resonance furnishes much of the simplicity of integrable
systems. Numerical tests are performed for two distinct dressed bases,
in which different resonance operators are chosen as the residual
effective coupling. Excellent agreement with the energies and
eigenvectors of the exact system is obtained for each of the two
dressed bases.
miscellaneous, BDL and LCNI
Some of my other stuff
inordinate detail, a blog
including current Programmers Anonymous notes, miscellaneous references
and some project details.
Miscellaneous
Mark's photos
Family and friends
Other people's great
stuff
Science is Beauty, thumbnails
The Geometry
Junkyard
Sean Michael Ragan,
great ideas
deviantART, great art,
searchable. Here are a few of my favorites.
Mathematical
imagery, Jos Leys
The
Brain From
Top To Bottom, tour of human brain functional neuroanatomy
fMRI 4
Newbies, tutorials
Tatjana van Vark's instuments,
particularly her
The Harmonium for
mechanical Fourier analysis and synthesis
Making Art the Otto
Lange Way (I recommend subscribing to the blog through email)
Some great free software
World Wind, virtual
spherical navigation
MRIcron,
Chris Rorden's free, great volume display software
IrfanView,
Irfan
Skiljan's free, great 2-D image software
Nvu, free, great web
page
generation, web authoring software
Google Desktop, hard drive
indexed search
MRIConvert,
Jolinda Smith's free, great GUI batch DICOM file conversion program
Some great books
