Meeting Abstract
The pitviper facial pit functions as a chamber-type “eye”. Uniquely, rather than quantum detection, sensory endings detect temperature contrasts on the pit membrane produced by thermal radiation. A novel neural pathway transmits this thermal image to the optic tectum, where it is merged with the visual image. Computer models of image formation suggest an indistinct thermal image. Neural processing in the hindbrain sharpens the image, but further sharpening may occur and so the quality of the thermal image informing behavior is unknown. However, it is critical to ecological questions such as detecting prey and thermoregulatory targets against a cluttered thermal background. We are approaching this question by testing the response of Pacific rattlesnakes (Crotalus oreganus) to a target moving against a patterned background. Temperatures are chosen so that it can be detected only if the background is resolved. Selection of experimental conditions required knowledge of how, singly or in combination, body, neurosensory ending, target, and background temperatures affect response. Using a target moving against a uniform background in a preliminary factorial experiment (body x target x background temperatures), we found response increased with target – background contrast. There was no response to varying absolute target temperature with fixed 6 °C contrast. But, contrary to nearly all other physiological processes, response increased as body temperature decreased. This response is integral to the facial pit sensory system, as we found the response to a moving visual target was independent of body temperature. We will describe the apparatus and present preliminary results of the resolution experiment.
