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Visual performance of the toad (Bufo bufo) at low light levels: retinal ganglion cell responses and prey-catching accuracy
Authors:A -C Aho  K Donner  S Helenius  L Olesen Larsen  T Reuter
Institution:(1) Department of Zoology, University of Helsinki, SF-00100 Helsinki, Finland;(2) Laboratory for Comparative Physiology, August Krogh Institute, University of Copenhagen, Denmark
Abstract:The accuracy of toad snapping towards moving worm dummies under various levels of dim illumination (from absolute threshold to ldquomoonlightrdquo) was videorecorded and related to spike responses of retinal ganglion cells exposed to equivalent stimuli. Some toads (at ca. 16 °C) successfully snapped at dummies that produced only one photoisomerization per 50 rods per second in the retina, in good agreement with thresholds of sensitive retinal ganglion cells. One factor underlying such high sensitivity is extensive temporal summation by the ganglion cells. This, however, is inevitably accompanied by very long response latencies (around 3 s near threshold), whereby the information reaching the brain shows the dummy in a position where it was several seconds earlier. Indeed, as the light was dimmed, snaps were displaced successively further to the rear of the dummy, finally missing it. The results in weak but clearly supra-threshold illumination indicate that snaps were aimed at the advancing head as seen by the brain, but landed further backwards in proportion to the retinal latency. Near absolute threshold, however, accuracy was ldquotoo goodrdquo, suggesting that the animal had recourse to a neural representation of the regularly moving dummies to correct for the slowness of vision.
Keywords:Visual sensitivity  Visual latency  Toad  Bufo bufo  Prey-catching
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