Rats maintain an overhead binocular field at the expense of constant fusion

• Published in: Nature (London) Vol. 498; no. 7452; pp. 65 - 69
• Main Authors: Wallace, Damian J., Greenberg, David S., Sawinski, Juergen, Rulla, Stefanie, Notaro, Giuseppe, Kerr, Jason N. D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06-06-2013; Nature Publishing Group
• Subjects: 631/378/2613; Animals; Biological and medical sciences; Escape Reaction - physiology; Exploratory Behavior - physiology; Eye; Eye and associated structures. Visual pathways and centers. Vision; Eye movements; Eye Movements - physiology; Eyes & eyesight; Fundamental and applied biological sciences. Psychology; Head - physiology; Humanities and Social Sciences; Mammals; Methods; Models, Biological; Movement - physiology; Movements; multidisciplinary; Optic Disk - physiology; Physiological aspects; Predatory Behavior; Rats; Rattus; Retina - physiology; Rodents; Science; Standard deviation; Vertebrates: nervous system and sense organs; Vision, Binocular - physiology; Visual acuity; Visual Fields - physiology; Germany; Reflex; Rat; Visual field; Rodentia; Eye movement; Eye; Visual system; Vertebrata; Visual stimulus; Mammalia; Animal; Binocular vision; Behavior
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature12153

Fusing left and right eye images into a single view is dependent on precise ocular alignment, which relies on coordinated eye movements. During movements of the head this alignment is maintained by numerous reflexes. Although rodents share with other mammals the key components of eye movement control, the coordination of eye movements in freely moving rodents is unknown. Here we show that movements of the two eyes in freely moving rats differ fundamentally from the precisely controlled eye movements used by other mammals to maintain continuous binocular fusion. The observed eye movements serve to keep the visual fields of the two eyes continuously overlapping above the animal during free movement, but not continuously aligned. Overhead visual stimuli presented to rats freely exploring an open arena evoke an immediate shelter-seeking behaviour, but are ineffective when presented beside the arena. We suggest that continuously overlapping visual fields overhead would be of evolutionary benefit for predator detection by minimizing blind spots.
In freely moving rodents, eye movements serve to keep the visual fields of the two eyes continuously overlapping overhead at the expense of continuous alignment, a strategy that may have evolved to maintain constant overhead surveillance of predators.
Rats have their eyes on higher things
Animals with front-facing eyes such as primates align both eyes in order to fuse left and right eye images, regardless of head movement. Jason Kerr and colleagues show here that coordination of the eyes follows a different strategy in rodents. Using a custom-built miniaturized ocular-videography system, they find that in freely moving rats, eye movements serve to keep the visual fields of the two eyes continuously overlapping overhead, although not necessarily aligned. Rats are ground-dwelling animals often threatened from above, so this strategy may have evolved as a means of maintaining constant overhead surveillance of predators.