[visionlist] Request for references: Architectural specializationof "foveal" visual cortex.

[Bullough, John]

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/m² 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?

 

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