A model of the visual localization of prey by frog and toad.

In this paper we demonstrate how prey localization can be achieved rapidly and accurately by coupling prey-selection and lens-accommodation processes within a feedback loop. Information derived from prey selection supplies a setpoint for accommodation. In turn, adjustment of the lens modifies the visual input and can alter the prey selection process. The natural feedback of this goal-seeking system automatically corrects for the problem of ambiguity in binocular matching. Although it is of general interest as a depth algorithm, we tie the model to the known anatomy, physiology and behavior of frogs and toads. Instead of building a global depth-map we propose that the goal of catching a prey leads a frog or toad to select a particular region of its visual world for special scrutiny. We suggest that the first step of the prey-catching sequence is to adjust the accommodative state of the lenses and thus lock the visual apparatus on to a stimulus. We identify brain regions that could provide the neural substrates necessary to support the model's various functional stages and present experiments, with a computer simulation, that compare its functioning to animal behavior.