Neurobiology of polarization vision.

Insects can perceive the pattern of polarized light (e-vector pattern) in the sky and use it as a compass. To accomplish this navigational task they employ a specialized part of the retina in which the polarization analysers (ultraviolet receptors) are arranged in a way that mimics, by and large, the distribution of e-vector directions in the sky. By sweeping this 'matched polarization filter's across the sky, the insect translates the complex spatial information provided by the celestial e-vector patterns into rather simple temporal modulations of summed receptor outputs. This mechanism provides a striking example of peripheral coding by matched filtering in sensory systems.