[visionlist] Re: CVNet - RE: Request for references: Architectural specializationof "foveal" visual cortex.

Mark Schira mark.schira at gmail.com
Fri Oct 17 20:32:22 PDT 2008


Dear David
There is actually very little work on the organization of the very
foveal representation in primates (or any other animal for that
matter).
There is some nice work  in marmosett monkeys (Rosa, M.G., and
Tweedale, R. (2000). Visual areas in lateral and ventral extrastriate
cortices of the marmoset monkey. J Comp Neurol 422, 621-651.). The
fovea is usually avoided since small eye movements or worse small and
slow drifts of the eye position (which are hard to detect with
implanted coils) are a big confounder.
There is also some work by Dow et al. 1981 in macaque monkey, but that
is only on V1.
So when you are interested in mircorarchitecture like columnar
organization etc, you are probably out of luck.
For Human you might want to take a look at:  Schira, M.M., Wade, A.R.,
and Tyler, C.W. (2007). Two-dimensional mapping of the central and
parafoveal visual field to human visual cortex. J Neurophysiol 97,
4284-4295.)
 To my best knowledge this is the most accurate published measurement
of parafoveal visual cortex in Human to date. We used fMRI to measure
the retinotopic organization of V1 and V2 down to 0.5 and 0.75
including areal and linear magnification in both directions. We also
made detailed model predictions for more foveal cortex and discuss
possible consequences of the projection of the visual field onto a
folded manifold – the human cortex.
Recently, we measured the remaining 0.75 - 0 degree for V1 V2 and V3
(and some V4 and DLO) using high resolution fMRI (1.2mm). The
manuscript is almost completed and just an eye blink away from initial
submission. We presented some of the data on conferences, and I can
send you the citations if you like.
So far I can tell you so much as there is no surprise for V1 (i.e. our
model from 2007 is a very accurate prediction), but each V2 and V3
span a larger area than expected.
So in short: nothing special foveal for V1, but for V2 and V3.
When it comes to reading, however, I doubt that this organization is
due to reading, since it looks as marmoset monkeys have a very similar
organization and they are not recognized as particular skilled
readers.
Is this organization critical for reading? Probably.  I certainly
agree with you that foveal vision is most critical for reading, and
the fact that the foveal confluence is terra incognita isn't helping
to understand reading.
Cheers
M.

On Sat, Oct 18, 2008 at 10:48 AM, Bullough, John <bulloj at rpi.edu> wrote:
>
> Dear David,
>
> I am not sure if the following answers your questions directly, but in our laboratory we have been looking at vision at mesopic light levels, when both rods and cones contribute to vision. Since the fovea is essentially a "cone-only" island, foveal processing (e.g., on-axis detection, processing of details) is characterized (more or less) by the photopic luminous efficiency function. Peripheral processing (e.g., off-axis detection) is characterized (more or less) by a mixture of the photopic and scotopic luminous efficiency functions.
>
> In one experiment (He et al., 1997) we found that reaction times to
> on-axis stimuli of different spectra (but equated for photopic luminance) followed a single monotonic function, but reaction times to off-axis stimulu showed  a bifurcation between spectra below a photopic luminance of 1 cd/m^2 and in a way that could be modeled by a combination of photopic and scotopic luminous efficiency. Similar findings have been made in other studies from our laboratory (many of which are summarized by Rea et al., 2004)--most of these studies have a very applied research context, involving street lighting and driving contexts (we have been looking at the implications of using light sources with more short-wavelength/rod-stimulating energy in outdoor lighting applications) and from these kinds of results have developed a system of "unified" photometry linking photopic and scotopic vision based on reaction time data. Since the fovea is populated only by cones, that part of the retina always is characterized by "photopic" photometry.
>
> If the publications mentioned above might be useful to you, I would be happy to send them to you or to any others on the list. They are found in the lighting literature, and not so much in the vision literature.
>
> He, Y., M. S. Rea, A. Bierman and J. Bullough. 1997. Evaluating light source efficacy under mesopic conditions using reaction times. Journal of the Illuminating Engineering Society 26(1): 125-138.
>
> Rea, M. S., J. D. Bullough, J. P. Freyssinier-Nova and A. Bierman. 2004. A proposed unified system of photometry. Lighting Research and Technology 36(2): 85-111.
>
> John
>
> --
> John D. Bullough, Ph.D. - bulloj at rpi.edu
> Senior Research Scientist, Adjunct Assistant Professor
> Lighting Research Center, Rensselaer Polytechnic Institute, Troy, NY
> tel +1.518.687.7100, fax +1.518.687.7120, web www.lrc.rpi.edu
>
>
>
>
>
> ________________________________
>
> From: visionlist-bounces at visionscience.com [mailto:visionlist-bounces at visionscience.com] On Behalf Of David Todd
> Sent: Thursday, October 16, 2008 8:06 AM
> To: visionlist at visionscience.com
> Subject: [visionlist] Request for references: Architectural specializationof "foveal" visual cortex.
>
>
>
> Good morning vision people!
>
> I am looking for any solid references, literature or ongoing work in the existence of architectural specialization of the portion of the visual (esp. =
> V1) cortex that is retinotopically mapped to the fovea. I am currently preparing a paper/ argument that:
>
>          The "foveal" cortex must, by nature of functional evolution be physiologically specialized to preferentially process "foveal" input i.e. character detail, texture, hue, text. This is a presumption that contrasts with the idea that visual cortex (esp V1) is uniform in column, hypercolumn etc. characteristics throughout.
>
>          The "foveal" cortex has unique and preferential projections to the language centers (letter, word, sentence recognition, interpretation, association) as opposed to "non-foveal" cortex.
>
>
>
> Does anyone have recommendations, input, criricisms?
>
>
>
> Full Signature
>
> David P. Todd, O.D.
> Director, Clinical Affairs
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-- 
Mark M. Schira, Ph.D.
School of Psychology
University of New South Wales
Sydney 2052

office:+ 61 (0) 2 9385 8849
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