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Santoshi Ramachandran, Vallabh Das; A comparison of spatial patterns of fixation preference during visual & auditory tasks in strabismic monkeys. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1555.
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© ARVO (1962-2015); The Authors (2016-present)
Strabismic subjects often develop the ability to fixate visual targets with either eye and can choose the eye of fixation depending on spatial location of the target. Fixation preference for visual targets likely results from suppression of specific regions of the retina. The purpose of this experiment was to compare spatial patterns of fixation preference, when strabismic monkeys are presented with a) visual stimuli and b) auditory stimuli with no visual feedback.
21 coincident visual and auditory targets (red LEDs & speakers) were arranged 10° apart in a 7x3 array, (X: -30° to 30°; Y: -10° to 10°) at a distance of 57 cm. Binocular eye movements were measured in two head-fixed strabismic monkeys [M1 (XT~30°), M2 (XT~25°)] in a saccadic task. Each trial began with presentation of a central visual target for 1s followed by an eccentric visual target or a band-pass white noise auditory target for 2s. Spatial patterns of fixation preference were calculated by recording the incidence of using a specific eye to acquire the target at each spatial location.
M1 & M2 initiated 70% & 67%, respectively, of all trials with their left eye, therefore exhibiting an eye preference. Irrespective of which eye fixated the center target, they fixated on far right target locations with their right eye and far left locations with their left eye. The border for a change in fixation preference, in response to visual targets, occurred approximately between the lines of fixation of the two foveae, e.g., in M1, the border was at ~R15° when the left eye was viewing the center target. This pattern was different for auditory stimuli where the border for change in fixation preference for both animals passed through horizontal 0°. The area between left and right fixation zones where either eye obtained the target at equal instances was broader for auditory targets (~25°) than it was for visual targets (~10°).
We found that, in strabismic monkeys, spatial fixation preference was also observed during auditory stimulation, i.e., despite the absence of visual feedback. Therefore, even in the absence of retinal error, the brain chose one eye over the other to acquire targets depending on spatial location of the target. Our data suggests that spatial fixation preference is multi-modal and retinal suppression additionally influences fixation preference during visual tasks.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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