title: The secret world of shrimps: polarisation vision at its best.
abstract: BACKGROUND
  Animal vision spans a great range of complexity, with systems evolving to detect variations in light intensity, distribution, colour, and polarisation. Polarisation vision systems studied to date detect one to four channels of linear polarisation, combining them in opponent pairs to provide intensity-independent operation. Circular polarisation vision has never been seen, and is widely believed to play no part in animal vision.
  
  
  RESULTS
  Polarisation is fully measured via Stokes' parameters--obtained by combined linear and circular polarisation measurements. Optimal polarisation vision is the ability to see Stokes' parameters: here we show that the crustacean Gonodactylus smithii measures the exact components required.
  
  
  CONCLUSIONS
  This vision provides optimal contrast-enhancement and precise determination of polarisation with no confusion states or neutral points--significant advantages. Linear and circular polarisation each give partial information about the polarisation of light--but the combination of the two, as we will show here, results in optimal polarisation vision. We suggest that linear and circular polarisation vision not be regarded as different modalities, since both are necessary for optimal polarisation vision; their combination renders polarisation vision independent of strongly linearly or circularly polarised features in the animal's environment.
authors.affiliation: Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt am Main, Germany. Sonja.Kleinlogel@mpibp-frankfurt.mpg.de
authors.forename: Sonja
authors.initials: S
authors.lastname: Kleinlogel
authors.forename: Andrew G
authors.initials: AG
authors.lastname: White
mesh_terms: D000818:Animals; D003445:Crustacea / Q000502:physiology*; D008027:Light; D014785:Vision, Ocular