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Low retinal noise in animals with low body temperature allows high visual sensitivity
Nature
|July 28, 1988
Summary
We cannot see single photons due to retinal noise from thermal isomerizations. Lowering temperature enhances visual sensitivity in cold-blooded animals, suggesting thermal events limit vision across species.
Area of Science:
- Vision science
- Neurobiology
- Phototransduction
Background:
- Human vision detection limits are near the 100-photon level.
- Retinal noise from thermal isomerizations is a proposed barrier to single-photon detection.
- Electrical 'dark' rod events, indistinguishable from photoisomerization signals, have been recorded.
Purpose of the Study:
- To investigate the role of thermal isomerizations in limiting visual performance.
- To compare visual sensitivity across species and temperatures.
- To determine if thermal events limit visually guided behavior.
Main Methods:
- Recording electrical dark rod events in amphibian retinas.
- Studying visually guided behavior in dark-adapted toads and frogs.
- Comparing absolute threshold intensities and estimated thermal isomerization rates across species.
Main Results:
- Electrical dark events match the rate and thermal parameters of spontaneous thermal isomerizations.
- Visually guided behavior in amphibians is limited by thermal isomerizations.
- Lower temperatures correlate with higher visual sensitivity in poikilothermic vertebrates.
Conclusions:
- Thermal isomerizations, not just photon capture, fundamentally limit visual sensitivity.
- Cold-blooded vertebrates achieve higher light sensitivities at low temperatures due to reduced thermal noise.
- This suggests a universal limit on visual performance imposed by thermal noise across different vertebrate classes.
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