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Andrew E. Silva, Dusan Sarenac, Connor kapahi, David G. Cory, Ivar Taminiau, Dmitry A. Pushin, Ben Thompson; Psychophysical discrimination of structured light exhibiting spatially-dependent polarization. Journal of Vision 2020;20(11):265. doi: https://doi.org/10.1167/jov.20.11.265.
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© ARVO (1962-2015); The Authors (2016-present)
Haidinger’s brush is an entoptic image of a central oblong smudge elicited when the macular pigment preferentially absorbs specific direction of polarized light. Because Haidinger’s brush is dependent on macular pigment, it may have value as a screening tool for macular dysfunction. We examined whether healthy human observers could use Haidinger’s brush to psychophysically discriminate between two beams of structured light exhibiting different patterns of spatially-dependent polarization, called spin-coupled Orbital Angular Momentum (OAM) states. Because the direction of polarization changes across the beam, OAM discrimination requires the perception of a spatially-dependent pattern of multiple Haidinger’s brush orientations. This richer stimulus may provide more precise information about macular function than a traditional linearly polarized stimulus. We examined the discriminability of OAM states by monocularly presenting OAM light to the eyes of 12 healthy participants. On each trial, one of two possible OAM states was presented. Participants made self-directed saccades to observe the Haidinger’s brush pattern and verbally indicated the perceived state. Overall, participants successfully performed the discrimination task (68% accuracy, SD = 22%, p = 0.013). This study provides foundational confirmation that humans can discriminate quantized modes of structured light with varying degrees of success. Structured light may therefore serve as a sensitive psychophysical probe of individual differences in macula structure and function in normal and clinical populations.
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