Viper Vision 2: Adaptive noisy vision systems reproduce pit viper ambush behavior

A pit viper can see you, decide whether to strike you, and attack you faster than any human vision system can initiate a motor response. A unique set of sensory organs in pit vipers allow for sub-100 ms reaction with 5 degree accuracy in low light environments without the use of opsin based conformation-change photon detection that is nearly ubiquitous in natural systems. The capabilities of these organs center around a thin membrane sparsely populated with thermally sensitive 'pixels'. Each membrane is situated in a shallow cavity or 'pit', with an entrance smaller than the area of the heat detecting membrane creating a rough pinhole camera. While much has been learned about the biochemistry of these sensory organs, questions of the mechanism of photon absorption, the reasons behind their geometry, how accurate imaging is obtained from a noisy environment, and how visual information is reconstructed all remain unanswered. To address these, we employ a noisy vision system model that incorporates the fundamental physics of thermal fluctuations to perform exquisite edge detection. We show that our thermal edge detection mechanism is optimized in the neural response of the snake vision system, results from strong threshold sensitivity known to be evident in snakes, and reproduces recently measured ambush behavior in live snakes.