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Abstract:
Abstract: The cortical magnification factor (CMF), which
quantifies the relationship between location in visual space and
area of activation in primary visual cortex, has been estimated
with varying success using indirect methods such as psychophysics
and functional magnetic resonant imaging (fMRI). To directly
estimate the CMF using neuronal activity, we have combined
multi-input stimulation and analysis with multi-electrode
event-related potential (ERP) dipole source localization (Slotnick
et al., 1999). For each of 60 independently modulated checkerboard
patches within the central 18 degrees of the visual field, the
location, magnitude, and time-course of the dipole current source
which best described the ERP distribution was obtained. Distances
between each pair of adjacent patches and the corresponding
distances between adjacent cortical sources were used to calculate
the CMF. This estimate corresponds well with the CMF provided by
fMRI. One of the major concerns of fMRI has been its dependence on
cerebral bloodflow which may respond quite differently than neural
activity. By independently validating fMRI using a direct method of
estimating CMF, our study has shown that, at least in primary
visual cortex, fMRI results are in accordance with results based on
neural activity.
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