The Tentative Hypothesis

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The Tentative Hypothesis

• There is more to polarization vision in humans
  than has previously been thought.
• or
• The human visual system extracts useful and
  useable information from the polarization
  properties of objects.

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Haidingers Brush
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Explanation

• Dichroism of the macular pigment lutein

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Motivators

• Blue polarization filters attenuate epileptic
  seizures. (Kepecs, 2004)
• They dont know why. Suggest Lutein and
  connection to Haidingers brush.
• We speculate that cross-polarized lenses may
  attenuate the PPR by inducing binocularly
  disparate patterns of retinal activation that
  result in altered patterns of cortical activation
  in the early but not, ordinarily, later stages of
  visual processing, and that these alterations
  render the stimulus less epileptogenic.

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An assumption

• Polarized light is not processed separately or on
  a different channel. But it doesnt need to be in
  order to be used.
• In some butterflies (Papilio aegeu) horizontal
  polarized green is differentially allowed to pass
  through its optical filter.

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Polarization Vision in Invertebrates

• We all know the capabilities of mantis shrimp and
  other interesting sea creatures, who use
  polarized light to get about given varying
  underwater lighting conditions.
• As it turns out, nearly all marine animals which
  live near the surface have some sensitivity to
  polarized light. They use the refracted
  celestial polarization pattern, which is highly
  correlated with the sun position, for
  navigational tasks. (Sabbah et al., 2006)
• But what about life above the waters surface?

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Polarization vision in insects and vertebrates

• Ants and some other insects seem to use the
  polarized skylight for navigational purposes
  (Wehner 1997)
• Salamander and other lizards respond to polarized
  light and can be trained to perform tasks with
  polarized stimuli (Taylor Alder, 1973)
• Many species of birds are sensitive to polarized
  light, and use the skylight polarization
  information for migration and orientation
  purposes (Munro Wiltschko, 1995)
• It is a generally accepted fact that mammals
  (including humans, of course) are insensitive to
  polarized light.
• But, is it really that simple?...

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• How much useful polarization information could
  there be?
• Probably more than you would expect.

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False Colour Polarization of Rainforest Leaves
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How might mammals use polarization information?

• Polarization information seems useful in
  distinguishing figure from ground, even when
  color and luminance are fairly constant.
• This could be helpful when foraging,
  discriminating shadows, or looking for the ripest
  berries in the bush, which may have different
  polarization distribution, but nearly identical
  color and luminance.
• In desert regions, polarization is the only way
  to tell a mirage from a real water source at
  distance. (Gabor Horvath, Jozsef Gal, 1997)

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So, can humans use this information?

• Given that we may have some contrast sensitivity
  to polarization after all, is it possible for
  humans to use this information, even though we
  have no phenomenological experience of
  polarization itself?
• Is the information simply confounded with color
  and luminance, or can it be used in low level
  cortical processes?