Cortically Magnified

Last week I went to see an optometrist. As he examined my eye with a strong light, I was amazed that I saw an image of the blood vessels on the retina. This phenomenon is called the entoptic image. It was first described by Purkinje about 200 years ago. I read about it in “How we perceive our own retina” by Kuno Kirschfeld (published in Proc. Bio. Sci.)

The lens is the component in the eye that reflects light. They are not always shape liked pancakes or magnifying glasses. In small mammals, the lens is very often looks like the chewy tapioca balls in Asian boba milk tea. Primate lenses are more like magnifying glasses:

A recent paper shows that our vision is so sensitive to light that human subjects can detect the presence of one single photon shot into their retinas. While scientists have been trying to establish the lower limit of visual sensitivity for a very long time, and it is generally accepted that a small number of photons are sufficient for detection since the 40’s, new advances in quantum optics finally allow us to manipulate light at single photon precision, and it is the first time that direct evidence for single photon sensitivity is demonstrated in a psychological experiment.

The visuotopic map of the marmoset dorsomedial visual cortex (area DM; see references) is sufficiently complex that it is probably worthwhile to design a few visual aides to make it more intuitive. The figure above is my first attempt. In this figure, DM is divided into three segments, with the most medial segment representing central upper visual field (nose and eye of Sir Isaac Newton), the middle segment representing the entire lower visual field, and the medial segment representing the peripheral upper visual field (the forehead and hair of Newton).

I created this figure to illustrate the retinotopic map of the primary visual cortex of the marmoset. The eccentricity contours are plotted in red, and polar angles are in blue. It’s very easy to create it in 3D so that you can rotate it around and see it from different angles. This is how you do it: Download ParaView, the open source 3D data visualization package.