Proceedings of the Annual Meeting of the Cognitive Science Society

It has been found behaviorally that visual habituation in toads exhibits locus specificity and partial stimulus specificity. Dishabituation among different configurations of visual worm stimuli forms an ordered hierarchy. This paper presents a computational model of the toad visual system involved in pattern discrimination, including retina, tectum, and anterior thalamus. In the model w e propose that the toad discriminates visual objects based on temporal responses, and anterior thalamus has differing representations of different stimulus configurations. This theory is developed through a large scale neural simulation. With a minimum number of hypotheses, we demonstrate that anterior thalamus in response to different worm stimuli shows the same hierarchy as shown in the behavioral experiment. The successful simulation allows us to provide an explanation of neural mechanisms for visual pattern discrimination. This theory predicts that retinal R 2 cells play a primary role in the discrimination via tectal small pear cells (SP) while R 3 cells refine the feature analysis by inhibition. The simulation also demonstrates that the retinal response to the trailing edge of a stimulus is as crucial for pattern discrimination as to the leading edge. N e w dishabituation hierarchies are predicted by shrinking stimulus size and reversing stimulus-background contrast.