A high-resolution, low-cost, and easy-to-implement technique for measuring eye movements will be developed. This will accelerate the pace of research on vision by allowing widespread integration of eye movement measurements into increasingly sophisticated studies of visually- guided behavior, including studies in freely moving mice. Historically, research on sensory processing has focused to a great extent on the visual system. However, as neuroscientists turn increasingly to using mice in their research, they are turning increasingly away from the visual system in favor of other sensory systems. This is limiting the extent to which our understanding of the visual system can reap the benefits of the powerful molecular-genetic tools available in mice for analyzing neural circuits in health and disease. Mice are sometimes misperceived as being not very visual. Although less dependent on vision than some species, mice clearly use vision for a variety of functions, including navigation and evasion of predators. Thus, there is great potential for the molecular-genetic approaches available uniquely in mice to advance our understanding of the fundamental visual processing operations supporting such visually-guided behavior. Nevertheless a technical barrier is limiting studies of vision in mice, namely the difficulty of measuring and controlling ee movements and hence knowing what the input was to the visual system at the level of the retina. This technical barrier will be eliminated by developing a novel technique for measuring eye movements in mice, based on magnetic sensing. A small but powerful neodymium magnet will be used to create a rotating external magnetic field as the eye rotates in its socket. The angle of the magnetic field will then be detected by an external magnetic field sensor. To optimize performance of the system for measuring eye movements in mice, various magnet shapes, magnetic sensors, and geometric configurations of magnet and sensor will be rigorously tested. Performance will be compared against existing methods for measuring eye movements, namely video-oculography and the scleral search coil techniques. The magnetic system will then be assessed in mice that are free to move, and will be used to examine the coordination of eye and head movements during natural behaviors. Importantly, the techniques developed in mice will be readily adaptable to a broad range of species.