Anatomy and Physiology of Vision in the Frog (Rana pipiens)

Abstract

Frogs arc essentially dependent on vision. They fccd on worms, flies, and other insects which they catch directly with the mouth or by striking them with the tongue; for this they use only visual clues. Furthermore, frogs prey only on moving insects, and their attention is never attracted by stationary creatures or objects. Nor do they respond with feeding behavior to a large moving object, instead it provokes an escape reaction. For them, a form deprived of movement SCClnS to bc behaviorally meaningless. Frogs, then, appear to recognize their prey and select it for attack from among all other environmental objects because it exhibits a number of features such as movement, a certain size, some contrast, and, perhaps, also a certain color. Furthermore, this ability of frogs to recognize their prey and to snap at it is not altered by changes in the general environment. Just as wc arc able to read and to recognize shapes under the most varied conditions, so arc frogs able to scc their prey and to fccd upon it under the bright light of midday or under the twilight of morning or evening, whether this bc in their natural environment or in a small cage in the laboratory. How is this accomplished? How do frogs recognize the universals, prey and enemy? To survive, a frog needs to react rapidly, either to catch a prey or to escape an enemy. To do this, the pat tern of light and dark that is the original image formed on the retina has to be anaJyzed, sooner or later, to select from it the features which define the universals. In these circumstances we can ask: Does the retina perform an analysis and abstract the meaningful parameters that will permit the recognition of the universals or is this analysis performed only later in the visual centers? Any