Polarization vision is the ability of animals to detect the oscillation plane of the electric field vector of light (E-vector) and use it for behavioral responses. This ability is widespread across animal taxa but is particularly prominent within invertebrates, especially arthropods. Polarized light can be either used implicitly for enhancing image contrast and for adding another dimension to the color vision system, or it can be explicitly used as a separate vision channel for communication purposes and for encoding global directions for an internal compass. Polarized light in nature is produced either by reflection at shiny surfaces or by scattering (e.g., in the atmosphere) of unpolarized sunlight. This results in the presence of polarized light in many different habitats, including underwater. The most prominent source of polarized light is the skylight polarization pattern, which contains information about the position of the sun in the sky and is thus used for navigation purposes. In insects, E-vectors are detected through specialized regions of the compound eyes. Neurons downstream of the involved photoreceptors respond to changes in E-vectors with mod- ulations of their action potential frequency, so that each neuron is tuned to one particular E-vector. Over the last decade, an extensive, conserved network of such neurons has been uncovered in the brains of locusts, crickets, and monarch butterflies, spanning many processing stages, from the photoreceptors to the motor control centers in the thorax. At the boundary of sensory processing and motor planning, a brain region called the central complex plays an integral part in polarized- light processing. It comprises an ordered array of neurons that use polarized-light information to encode a representation of the azimuthal space surrounding the animal. How this network is proposed to process polarized-light information, integrates it with other sensory modalities, and transforms sensory signals into motor commands that guide behavior is the main focus of this entry. To put this neuronal network into the context in which it has to function in the natural world, results obtained from behavioral experiments in a variety of species are discussed as well.
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