BAKKEN, George S.*; KROCHMAL, Aaron R.; Indiana State University; University of Houston, Downtown: Pitviper thermal vision: An optical analysis of spatial resolution and signal strength

The long-standing belief that the facial pit of pitvipers is strictly a specialization for detecting and striking at warm prey has led studies of the pit organ to focus on a �maximum detection range� of the organ. However, demonstrations that the pit organ can direct thermoregulatory movements have supported earlier speculation that facial pits are used for general navigation. The imaging quality of the facial pit and associated neural processing centers is particularly relevant to navigation. But, optical studies of the pit are few and do not use standard optical analysis. Thus, the resolution of the thermal images formed by the facial pit is unknown. We therefore studied image formation in the facial pit with combined optical and heat transfer analysis techniques. We first recorded quantitative thermal images of typical prey items against laboratory and field backgrounds over a natural range of microclimate conditions. We then used MATLAB image processing routines to combine these images with optical point-spread functions to estimate the differential irradiance of the facial pit sensory membrane. We constructed the spread functions on the basis of approximate facial pit geometry and angular resolution from published neurological studies. Finally, we estimated the distribution of pit membrane temperatures resulting from the irradiance distribution using heat transfer analysis, and adjusted the range and contrast of the final digital image to reflect the published 0.001&degC � 0.003&degC temperature sensitivity of the membrane. Preliminary results indicate a need for detailed studies of pit organ geometry, behavioral responses in complex environments, and the role of neurological image sharpening in order to resolve the difference between computed and observed capabilities.