POLARIZATION CONTRAST: A NEW KIND OF VERTEBRATE VISION

Project: Research project

Description

Many vertebrates--including various fish, amphibians and birds, but
not humans-- have been proven in behavioral experiments to be
capable making orienting responses based upon the angle of
polarization of linearly polarized light. Although the biophysical
basis of a similar capability in invertebrates is well established,
there is no accepted hypothesis that explains the vertebrate
ability. We hypothesize that in vertebrates the ability is
conferred by the manner in which light is trapped and propagates
in a unique class of photoreceptors possessed by all the
vertebrates with the ability: the double cone. We propose to test
the hypothesis that the double cone, with its approximately
elliptical inner segment cross section, is a polarization detector
both by solving numerically Maxwell's equations for modal
propagation in a dielectric waveguide model of the double cones of
Lepomis cyanellus (green sunfish), and by measuring directly the
light power throughput through double cones as a function of input
polarization. We further hypothesize that the expected weak
polarization modulation of the individual double cone is greatly
enhanced by a class of "polarization-opponent" neurons in the inner
retina which receive opposite signed inputs from double cones with
their major elliptical axes arranged in orthogonal "tetradic"
mosaics in sunfish and other species. We propose to locate and
record from these hypothetical inner retinal neurons with voltage-
sensitive dyes. Finally, we hypothesize that the role of this
system of polarization-opponent neurons is to serve as a common
mode rejection system for randomly polarized light (such as the
underwater spacelight), and to confer on the animals which possess
it polarization contrast sensitivity. This latter constitutes a
heretofore undescribed kind of vision in vertebrates, and should
enable those possessing it to segregate objects on the basis of
the polarization distribution of the light reflected from them.
We propose behavioral experiments in sunfish to characterize this
predicted novel visual ability. Whilst the proposed work will have
no immediate transfer to the study of human vision, we expect
important spinoffs in the practical implementation of waveguide
theory to human vision, in understanding underwater biology and
ecology, and in instrumentation for stimulating and recording from
tissue-mosaics.
StatusFinished
Effective start/end date7/1/896/30/93

Funding

  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health

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vertebrates
cones
polarization
neurons
polarized light
invertebrates
photoreceptors
birds
dielectric waveguides
fishes
biology
Maxwell equation
rejection
animals
dyes
recording
modulation
cross sections
electric potential

ASJC

  • Medicine(all)