The role of neural adaptation in the perception of Haidinger’s brushes

Haidinger's brushes are an entoptic phenomenon consisting in the perception of a yellowish bow tie when linearly polarized white light enters the eye. The pattern arises from the particular spatial distribution of dichroic carotenoid molecules in the macula, creating a sort of embedded radial polarizer for blue light. In the past years, we conducted the broadest test ever performed to identify the polarization degree threshold on healthy individuals in conditions of maximum contrast. The setup was based on the combination of two different sources, one of which was polarized using a linear polarizer, rotating to elude neural adaptation. In the last months, we further upgraded the original system by introducing an additional degree of freedom, represented by the rotation speed, and conducted for the first time psychophysical tests to investigate the correlation between polarization degree and Haidinger's brushes angular frequency.