First, Frank patched one eye of each of the animals and allowed them to play for six hours. Then, some cats slept while others were kept awake for the same period of time in the dark. Later, when the cats were shown visual patterns on a screen, in cats that had slept, the eye that had not been patched was favored even more strongly (plasticity in the visual systems was enhanced). In cats that stayed awake, on the other hand, the brain reverted to using both eyes almost equally.