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We also measured the V1 surface area of the peripheral 15~60deg and compared it
with that of the central 0~15deg. The area on peripheral cortex is almost the same size
with that on central cortex (P=0.889). A mean of 49.6% of striate cortex was devoted
to the representation of the peripheral vision in 15-60deg. The data is not significantly
different from the post-mortem data of which the peripheral cortex is about 46.9%.
The percentage was significantly larger than the 39.1% of striate cortex devoted to
peripheral vision in the macaque.
4 Discussion
Our results indicate that peripheral representation most reach dorsorostral by the POS
and most subjects' representation was located in the ventrocaudal bank of the POS.
Previous fMRI studies of human retinotopic mapping have identified the V1 using the
visual stimulus of limited to central and/or peri-central visual field. The stimuli used
did not directly activate much of the periphery in V1, V2, V3 and it was hard to com-
pare with physiological studies of human peripheral vision above 30° of eccentricity
[14]. Using wide-view visual presentation system, we estimated that the V1 has an
average surface size of approximately 2223 mm^2, which represents the portion of
visual field eccentricity from 0° to 60°. Our estimates are consistent with the results
of those physiological and fMRI studies.
Were the cortical surface a plane, one could calculate the gray matter volume from
the surface area and knowledge of the mean cortical thickness. The cortical surface is
not flat, and in regions of high curvature the local volume can differ measurably from
the estimate based on planarity. Specifically, volume is underestimated on the crowns
of gyri and overestimated in the fundi of sulci. For large regions that include sulci and
gyri, these two errors tend to cancel one another. For smaller regions these two types
of errors may not cancel well. In a subset of the regions reported in this paper, we
calculated the difference between estimates of gray matter volume assuming planarity
and estimates that account for local curvature. The difference between the two esti-
mates never exceeded 5 percent, even in small regions such as V3 or the sub-regions
used to estimate cortical magnification. Hence, for the regions we report here, it is
reasonable to estimate the gray matter tissue volume as surface area multiplied by
cortical thickness.
Does surface area correlate with performance? Duncan and Boynton (2002) have
reported a correlation between cortical magnification estimates (based on surface
area) and a visual acuity task [15]. If such a correlation is observed in several con-
texts, then a theory relating the size of the neuronal substrate, say based on signal-to-
noise ratio, may become accepted. Should this connection become secure, then the
analysis of correlation between surface area and performance may provide a means
for uncovering the functional role of visual areas.
V1 surface area (mean = 2202 mm^2) is larger than previous research which focus
on central vision [16]. The area mapped out to 60 deg is about twice of which in cen-
tral vision. The area for V1 surface agrees with the post-mortem data.
The previous research found a correlation between the surface area of V1 and the
size of the retinal and geniculate input streams. And, Dougherty et al. made the
