Chen Qin, Liu Yang, Brauth Steven E, Fang Guangzhan, Tang Yezhong
Department of Herpetology, Chengdu Institute of Biology, Chinese Academy of Sciences, No.9 Section 4, Renmin South Road, Chengdu, Sichuan 610041, P.R. China.
Department of Psychology, University of Maryland, College Park, MD 20742, USA.
J Exp Biol. 2017 Sep 1;220(Pt 17):3103-3109. doi: 10.1242/jeb.155382.
The thermal infrared (IR) sensing system of pit vipers is believed to complement vision and provide a substitute imaging system in dark environments. Theoretically, the IR system would best image a scene consisting of a homothermal target in cold surroundings as a bright spot on a dark background. To test this hypothesis, we evaluated how the pit viper () discriminates and strikes prey when the background temperature is either higher or lower than that of the prey (approximately 32-33°C) in different parts of the scene. Snakes were tested in a modified predation cage in which background temperatures were set to 26°C on one side and either 33 or 40°C on the opposite side when the eyes, the pit organs or neither sensory system was occluded. When the eyes were blocked, snakes preferred to strike prey on the 26°C side rather than on the 33°C side but showed no bias in the other conditions. Snakes showed no preference for 26 versus 40°C background temperature, although more missed strikes occurred when the eyes were occluded. The results thus revealed that the pit viper IR system can accomplish a 'brightness constancy' computation reflecting the difference between the target and background temperatures, much as the visual system compares the luminance of a figure and the background. Furthermore, the results show that the IR system performs less well for locating prey when the background is warmer than the target.
蝰蛇的热红外（IR）传感系统被认为可补充视觉功能，并在黑暗环境中提供替代成像系统。从理论上讲，IR系统能将寒冷环境中由等温目标构成的场景最佳地成像为暗背景上的亮点。为验证这一假设，我们评估了在场景不同部位背景温度高于或低于猎物温度（约32 - 33°C）时，蝰蛇（）如何辨别并攻击猎物。蛇在一个经过改装的捕食笼中接受测试，当眼睛、颊窝器官或两者都不被遮挡时，捕食笼一侧的背景温度设置为26°C，另一侧设置为33°C或40°C。当眼睛被遮挡时，蛇更倾向于攻击26°C一侧的猎物而非33°C一侧的猎物，但在其他条件下没有表现出偏好。蛇对26°C和40°C的背景温度没有偏好，不过当眼睛被遮挡时，未命中攻击的情况更多。结果因此表明，蝰蛇的IR系统能够完成反映目标与背景温度差异的“亮度恒常性”计算，就如同视觉系统比较图形和背景的亮度一样。此外，结果表明当背景比目标温暖时，IR系统在定位猎物方面表现较差。
