Meeting Abstract

3.8  Jan. 4  What do pitvipers see? Computer visualizations based on anatomy, optics, heat transfer, and neurophysiology BAKKEN, George S.*; COLAYORI, Samantha E.; Indiana State University; Indiana State University gbakken@indstate.edu

The facial pit of pitvipers (Viperidae: Crotalinae) appears to function as a pinhole eye, using thermal infrared radiation to form temperature-contrast images on a sensory membrane suspended in the pit. The facial pit has a complex 3-dimensional shape, both internally and externally, that determines the nature of the image falling on the membrane. Image strength and sharpness interact; reducing the pinhole aperture increases sharpness but decreases irradiance. However, neural image sharpening may partly break this interaction. We present an improved model of facial pit function based on combined optical and heat transfer analysis, extending previous work by including a proper estimate of atmospheric transmittance for thermal infrared radiation and adding the effect of convection-conduction heat loss from the membrane. Pit aperture characteristics, membrane sensitivity, image sharpening and tonic (constant) vs. phasic (rate of change) neural response interact to produce the final image. We combined our model and published neurophysiological data to explore these interactions by creating video representations of the thermal infrared view of prey items active outdoors. Convective heat loss from the membrane significantly reduces estimated temperature contrast, and has a larger effect on smaller pit organs, e.g. immature snakes. Consequently, membrane receptors must be sensitive to temperature differences on the order of 0.001°C if snakes can detect a mouse at ca. 1m as suggested by Ebert and Westhoff, J. Comp Physiol A, 2006. The results suggest behavioral studies to better characterize the limits of the facial pit sense and laboratory studies to better define the physical and neurological aspects of the facial pits.