The Electrodynamic Basis of Dichroism-Mediated Polarization Perception

Humans see the polarization of light through entoptic percepts arising from the macula’s Henle fiber layer, where xanthophyll pigments absorb preferentially across the radiating fibers. From the layer’s complex dielectric tensor alone, Maxwell’s equations in Berreman $4\times 4$ form yield its Mueller matrix, set by four scalars $\{A,B,C,D\}$. Its intensity channel depends only on the dichroic pair $A$ and $B$, which fix the percepts at a maximum contrast $\mathrm{\mid }B\mathrm{\mid }\mathrm{/}A\approx 0.05$. One relation generates the whole dichroism-mediated family: Haidinger’s brushes under a uniform field, their dark arms perpendicular to the $\mathbf{E}$-vector; fractured brushes under spatially varying fields; and $N$-fold brushes under vector-vortex illumination.