Studies on the optic chiasm of the leopard frog.  I. Selective loss of visually elicited avoidance behavior after optic chiasm hemisection. 
We hemisected either the posterior or anterior portion of the optic chiasm and found that frogs were unresponsive to large looming stimuli anywhere in the visual field.  Nonetheless, the animals responded to prey stimuli throughout the visual field.  Responses to looming stimuli returned in 1 to 8 weeks post-surgery.  After complete transection of the chiasm animals were unresponsive to both prey and large looming stimuli.  Frogs responded normally to prey and looming stimuli if less than half the optic chiasm was cut or if the postoptic commissure was cut.  Since responses to looming stimuli returned before cut optic fibers could regenerate, these results suggest that visual information concerning prey and large looming objects are mediated by separate optic nerve fiber systems.