Abstract
Like many animals, humans are sensitive to the polarization of light. We can detect the angle of polarization using an entoptic phenomenon called Haidinger's brushes, which is mediated by dichroic carotenoids in the macula lutea. While previous studies have characterized the spectral sensitivity of Haidinger's brushes, other aspects remain unexplored. We developed a novel methodology for presenting gratings in polarization-only contrast at varying degrees of polarization in order to measure the lower limits of human polarized light detection. Participants were, on average, able to perform the task down to a threshold of 56%, with some able to go as low as 23%. This makes humans the most sensitive vertebrate tested to date. Additionally, we quantified a nonlinear relationship between presented and perceived polarization angle when an observer is presented with a rotatable polarized light field. This result confirms a previous theoretical prediction of how uniaxial corneal birefringence impacts the perception of Haidinger's brushes. The rotational dynamics of Haidinger's brushes were then used to calculate corneal retardance. We suggest that psychophysical experiments, based upon the perception of polarized light, are amenable to the production of affordable technologies for self-assessment and longitudinal monitoring of visual dysfunctions such as age-related macular degeneration.
Highlights
Polarization is another dimension of light, just like colour and intensity, which can provide distinct and useful information about a visual scene
We found that humans can detect a visual stimulus in polarization-only contrast using Haidinger’s brushes when per cent polarization is as low as 56%
Haidinger’s brushes give humans, on average, the ability to detect the orientation of a polarized light field even when the per cent polarization is as low as 56%
Summary
Polarization is another dimension of light, just like colour and intensity, which can provide distinct and useful information about a visual scene. We detect the orientation of polarized light using ‘Haidinger’s brushes’, an entoptic visual phenomenon described by Wilhelm Karl von Haidinger in 1844 [2]. He reported [3] that when viewing a polarized light field, with no spatial variation in intensity or colour, it was possible for someone with normal sight to perceive a faint pattern of yellow and blue bowtie-like shapes that intersect at the viewer’s point of fixation (electronic supplementary material, figure S1). The effect vanishes within about 5 s, but can be maintained and/or increased in salience by rotating the eye around the primary visual axis relative to the light field, e.g. tilting one’s head side to side
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call