[visionlist] [*Email Suspect*] is this visual illusion already existing?

[Kenneth KNOBLAUCH]

Hi Laurent,

There is considerable individual differences in the density of macular pigment.  See papers by Jack Werner for example. It’s most dense in the fovea and then I don’t remember if it is the transmission or optical density but one of them declines exponentially with eccenticity. The cones are shorter too outside the macula and in the periphery in general so the optical densities of the photopigment will be lower and this will change their spectral sensitivities which will change the chromatic contrast between fovea and periphery.

Ken

Kenneth Knoblauch
Inserm U1208
Stem-cell and Brain Research Institute
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France
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On 14 Sep 2026, at 17:59, PERRINET Laurent <laurent.perrinet at univ-amu.fr> wrote:

 Hi Ken

Thanks for the feedback.

The idea is that the two colors are defined by Gaussian densities in the spectral range of visible wavelengths such that:

- both colors have the same mode (~470 nm, see below)
- the background color is narrow (std of 4 nm) while that of the shape is broader (40 nm)
- these colors are normalized to be of the same luminance (relying on the very practical `colormath` package)

In summary, the colors are the same except one (the background) is more precise in spectral space ad the other less (shape).

Your mention of the Maxwell spot is clearly the good direction. It gave me pointers to interesting papers including :

- Marina Gardasevic, Robert J. Lucas, Annette E. Allen Appearance of Maxwell’s spot in images rendered using a cyan primary https://spam.inserm.fr/fmlurlsvc/?fewReq=:B:JVo+NTc0PiJyOTYqNCJtYDk0NT40NSJ3bWNqZXBxdmE5YTdlPTA1MjYzPDI1MGZnNDU9MmE8PDQ3YTQ0MjY9PDRnPTc9M2UzYSJwOTUzPD0wNDY0NTwidW1gOTI8QUMycD08NDQxMzU8KTI8QUMycD1GNDQxMzU8InZndHA5Imc5NzQibGBoOTQ=&url=https%3a%2f%2fwww.sciencedirect.com%2fscience%2farticle%2fpii%2fS0042698919301889 

- Akiyoshi Kitaoka  https://spam.inserm.fr/fmlurlsvc/?fewReq=:B:JVo+NTc0PiJyOTYqNCJtYDk0NT40NSJ3bWNqZXBxdmE5PDYxZmJmYDFhMjxgNTAwNj1iZzJnYGBiNzY1MTY2YjMzPT0yPDA8YSJwOTUzPD0wNDY0NTwidW1gOTI8QUMycD08NDQxMzU8KTI8QUMycD1GNDQxMzU8InZndHA5Imc5NzQibGBoOTQ=&url=https%3a%2f%2fwww.psy.ritsumei.ac.jp%2fakitaoka%2fshitsukan-shikikaku2024.html 

This paper pointed to a peak wavelength of 460nm (for the blue in OLED displays) which makes the effect a bit different. The notebook explores the range of 460 to 490 nm giving differential effects.


Thanks, Laurent



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Le 14 sept. 2026 à 16:09, Kenneth KNOBLAUCH <ken.knoblauch at inserm.fr> a écrit :

Telln us some more about the spectral characteristics of the stimuli. I suspect that you are seeing the differential filtering by macular pigment in fovea and parafovea, like Maxwell’s spot but sampled discretely.  I am a protanope and see it.

thanks   very cool


ken
Kenneth Knoblauch
Inserm U1208
Stem-cell and Brain Research Institute
18 avenue du Doyen Lépine
69500 Bron
France
tel: +33 (0)4 72 91 34 77
fax: +33 (0)4 72 91 34 61
portable: +33 (0)6 84 10 64 10
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