Abstract
Research on the visual system of non-primates, such as birds and rodents, is increasing. Evidence that neural responses can differ dramatically between head-immobilized and freely behaving animals underlines the importance of studying visual processing in ethologically relevant contexts. In order to systematically study visual responses in freely behaving animals, an unobtrusive system for monitoring eye-in-orbit position in real time is essential. We describe a novel system for monitoring eye position that utilizes a head-mounted magnetic displacement sensor coupled with an eye-implanted magnet. This system is small, lightweight, and offers high temporal and spatial resolution in real time. We use the system to demonstrate the stability of the eye and the stereotypy of eye position during two different behavioral tasks in chickens. This approach offers a viable alternative to search coil and optical eye tracking techniques for high resolution tracking of eye-in-orbit position in behaving animals.
Highlights
Spatial vision research in non-primate species, such as birds and rodents, is becoming increasingly common (Harmening et al, 2011; Huberman and Niell, 2011; Sridharan et al, 2013; Starosta et al, 2013)
This study reports on the performance of magnetic eye tracking in chickens that are engaged in goal directed behaviors
The movements consisted of saccadic shifts in eye position and rapid eye oscillations (15–30 Hz) that occurred during each shift
Summary
Spatial vision research in non-primate species, such as birds and rodents, is becoming increasingly common (Harmening et al, 2011; Huberman and Niell, 2011; Sridharan et al, 2013; Starosta et al, 2013). In order to measure the effects of visual stimuli at specific locations in the visual field, the positions of the eyes relative to the locations of stimuli must be known; monitoring eye positions accurately in freely moving animals has proven difficult. We describe a method for tracking eye-in-orbit positions that can be applied to freely moving animals, even in species with small heads. A classical method for monitoring eye-in-orbit position is the electro-oculogram (EOG). The advantage of EOG recordings is that they can be measured in freely behaving animals with minimal hardware attached to the head. The disadvantage is that the amplitude of the eye’s dipole drifts with ambient illumination (Arden and Kelsey, 1962), and can change within tens of seconds, making EOG recordings unreliable for measuring absolute eye-in-orbit position
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