Visual acuity of the midland banded water snake estimated from evoked telencephalic potentials |
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Authors: | Robert A Baker Timothy J Gawne Michael S Loop Sheena Pullman |
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Institution: | (1) Animal Resources Program, University of Alabama at Birmingham, Birmingham, USA;(2) Department of Vision Sciences, School of Optometry, University of Alabama at Birmingham, Birmingham, AL 35294-4390, USA;(3) Oakwood College, Huntsville, AL 35896, USA |
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Abstract: | The visual acuity of seven midland banded water snakes was measured by recording evoked responses from telencephalon to temporally
modulated square wave grating patterns. Using conventional electrophysiological techniques and signal averaging, high contrast
square wave gratings of different spatial frequencies were presented. Acuity was estimated by extrapolating relative response
amplitude/log10 spatial frequency functions which yielded an average acuity of 4.25 cycles/degree. Refractive state was also estimated by
recording evoked potentials to intermediate spatial frequencies with different lenses in front of the eye. Polynomial fits
indicated that under the experimental conditions the snakes were around 6.4 diopters hyperopic suggesting a corrected acuity
of 4.89 cycles/degree. Reduction of grating luminance resulted in a reduction in evoked potential acuity measurements. These
results indicate that the spatial resolution of midland banded water snakes is the equal of cat; about 20/120 in human clinical
terms. |
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Keywords: | Snake Vision Acuity Evoked potential |
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