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Matthew J. Wadas, Amanda M. Scalise, Angel J. Rivera, Amy E. Lindsey; Tiger Salamanders Are More Sensitive To Higher Spatial Frequencies And Less Sensitive To Red/Green Stimuli Following Metamorphosis From Aquatic Into Terrestrial Phase. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1176.
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© ARVO (1962-2015); The Authors (2016-present)
During metamorphosis from the aquatic to the terrestrial phase, the retina of the tiger salamander (Ambystoma tigrinum) loses blue-sensitive cones and gains more rods. This experiment examined how these changes affect vision.
Stimuli were either drifting spatial black/white contrast gratings (0.17-2.0 cycles/degree visual angle) or red/green luminance gratings (0.47 cpd; 2-97% contrast) presented on a screen in front of the animal. Salamanders (N=8; 11.2-16.0 cm body length) were first tested during the aquatic phase, then metamorphosis was induced and measures were repeated. A "response" to the visual stimulus was defined as swimming in the direction of the moving grating for at least 10 seconds. A staircase method, starting with a 50% contrast stimulus, was used to determine contrast threshold. "Threshold" was defined as P (response) = 0.5.
Four aquatic animals metamorphosed to the terrestrial phase. Peak contrast sensitivity (1/contrast threshold) to moving black/white sinusoidal gratings was higher (p<0.05) for terrestrial (0.47 cpd visual angle) compared to aquatic (0.39 cpd visual angle) salamanders. Aquatic salamanders had a lower (t(3) = 2.91, p = 0.03) average contrast detection threshold (56%) compared to terrestrial (66%) for moving red/green luminance gratings.
(1) The ability to respond to visual stimuli changes after tiger salamander retina undergoes changes in photoreceptor morphology during metamorphosis. The changes are generally predictable from the morphology, and may serve to enhance visual function in a terrestrial environment such as increased acuity and sensitivity in dim light. (2) The relationship between retinal morphology and vision can be studied before and after metamorphosis using the same psychophysical techniques.
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