Unlike humans, numerous animals are differentially sensitive to the vector orientation of linearly polarized light. However as early as 1844 Haidinger noted that weak blue-yellow brushes appear, centered on the fovea, when the sky is observed through a slowly rotating polarizer. Different models have been proposed to try to understand this phenomenon, but the precise mechanism remains unknown and the polarization unexploited. We suggest that when Fresnel's laws are applied to the unguided oblique rays, that the cylindrical geometry of the blue cones in the fovea along with their distribution induces an extrinsic dichroism and could explain why the human eye is sensitive to polarization. We have constructed an artificial eye model system using the same laws and were able to photograph the appearance of entoptic-like blue-dark brushes, confirming the observations and our mathematical simulations. Moreover, our in vivo and in vitro tests show that in addition to the usual 3s fading time measured using a stationary stimulus, there exists for this entoptic image a short extra creating and erasing time of about 0.1s, using a dynamical stimulus. We have also found that, surprisingly, the rotating pattern is more regular and symmetrical with one of our two eyes around a more circular blue cone-free area, the dominant eye. Our results suggest that the polarization sense can provide important information in many areas that remain to be explored.
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