Perceiving polarization with the naked eye: characterization of human polarization sensitivity.
Bottom Line: 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.
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.
No MeSH data available.
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Mentions: The relationship between orientation of Haidinger's brushes and the stimulus polarization orientation for each individual was typically nonlinear (figure 4a,b), and in some cases there was a rapid switching/change in orientation relative to the change in stimulus orientation (e.g. around 200° incident polarization angle in figure 4a). The values of corneal retardance ranged from 0° to a maximum of 72°, or 0.199λ, which corresponds to 91 nm at 460 nm (peak wavelength for spectral sensitivity curve of Haidinger's bushes ). The mean corneal retardance was 40° ± 17° s.d., corresponding to 51 ± 20 nm s.d. (figure 4c,d). Mean corneal azimuth was −4° ± 19° s.d. (nasally upwards; figure 4d). The mean offset was 83° ± 6° s.d. Three participants' datasets were rejected, as the fit to equation (2.2) gave r2 values lower than 0.4 indicating that the individuals were unable to perform the alignment task, the reasons for which were not investigated. All 21 remaining datasets had r2 values above 0.9.Figure 4.
No MeSH data available.