in The man who tried to redeem the world with logic. Apparently, one development that discouraged Pitts came at the age of 36 (he died atb the age of 46):
"[Jeorme Lettwin] Together with Pitts, McCulloch and the Chilean biologist and philosopher Humberto Maturana, he subjected the frogs to various visual experiences—brightening and dimming the lights, showing them color photographs of their natural habitat, magnetically dangling artificial flies—and recorded what the eye measured before it sent the information off to the brain. To everyone’s surprise, it didn’t merely record what it saw, but filtered and analyzed information about visual features like contrast, curvature, and movement. “The eye speaks to the brain in a language already highly organized and interpreted,” they reported in the now-seminal paper “What the Frog’s Eye Tells the Frog’s Brain,” published in 1959.
The results shook Pitts’ worldview to its core. Instead of the brain computing information digital neuron by digital neuron using the exacting implement of mathematical logic, messy, analog processes in the eye were doing at least part of the interpretive work. “It was apparent to him after we had done the frog’s eye that even if logic played a part, it didn’t play the important or central part that one would have expected,” Lettvin said. “It disappointed him. He would never admit it, but it seemed to add to his despair at the loss of Wiener’s friendship.”"
Some of the work related to the frog's eye is described here and the break up with Norbert Weiner in this review of a book about Norbert Weiner.
Some more developments of frog vision studies and applications to education are discussed in this 2010 paper of Luis Radford The eye as a theoretician: Seeing structures in generalizing activities.