Independent visual threshold measurements in the two eyes of freely moving rats and mice using a virtual-reality optokinetic system
Slow horizontal head and body rotation occurs in mice and rats when the visual field is rotated around them, and these optomotor movements can be produced reliably in a virtual-reality system. If one eye is closed, only motion in the temporal-to-nasal direction for the contralateral eye evokes the tracking response. When the maximal spatial frequency capable of driving the response (“acuity”) was measured under monocular and binocular viewing conditions, the monocular acuity was identical to the binocular acuity measured with the same rotation direction. Thus, the visual capabilities of each eye can be measured under binocular conditions simply by changing the direction of rotation. Lesions of the visual cortex had no effect on the acuities measured with the virtual optokinetic system, whereas perceptual thresholds obtained previously with the Visual Water Task are. The optokinetic acuities were also consistently lower than acuity estimates from the Visual Water Task, but contrast sensitivities were the same or better. These data show that head-tracking in a virtual optokinetic drum is driven by subcortical, lower frequency, and contralateral pathways.(Received February 1 2005)
(Accepted May 18 2005)
Key Words: Optomotor; Acuity; Contrast sensitivity; Accessory optic system; Visual cortex.
c1 Address correspondence and reprint requests to: Robert M. Douglas, Department of Ophthalmology and Visual Sciences, University of British Columbia, 2550 Willow Street, Vancouver, British Columbia, Canada V5Z 3N9. E-mail: [email protected]