When Gazzaniga asked Jenkins what he saw, Jenkins was able to describe the square. Then Gazzaniga tried the same thing on the other side, flashing the same image to the left of Jenkins’ gaze. When he asked Jenkins again what he saw, though, Jenkins said he saw nothing.

Intrigued, Gazzaniga pulled another image, this time of a circle, to flash on Jenkins’s right and left sides separately, as he had done with the square.

Instead of asking Jenkins to describe the object, though, he asked him to point to it. When the image was on Jenkins’ right side (left brain), he lifted his right hand (controlled by the left brain) to point to it. When the circle flashed on his left side (right brain), he lifted his left hand (controlled by the right brain) to point to it.

The fact that Jenkins was able to point to the circle with both hands told Gazzaniga that each of Jenkins’ hemispheres had processed the sight of the circle. It also meant that in the previous trial, both of Jenkins’s hemispheres had processed the square—even though Jenkins said, when his right brain processed the sight, that he saw nothing. At that point, scientists had known for about a century that language arises from the left hemisphere; given that, the researchers later reasoned, Jenkins could only talk about the square when its picture was flashed to his right eye (left brain). On the other side, even though Jenkins had seen the square, he could not speak about it.

Between 1962 and 1967, Sperry and Gazzaniga worked together to perform dozens of additional experiments with Jenkins and other split-brain patients. In one set of studies conducted in 1962 and 1963, Gazzaniga presented Jenkins with four multicolored blocks. Then, he showed Jenkins a picture of the blocks arranged in a certain order, and asked him to make the same arrangement with the blocks in front of him.

Because the right brain handles visual-motor capacity, Gazzaniga was unsurprised to see that Jenkins’ right hemisphere excelled at this task: Using his left hand, Jenkins was immediately able to arrange the blocks correctly. But when he tried to do the very same task with his right hand, he couldn’t. He failed, badly.

“It couldn’t even get the overall organization of how the blocks should be positioned, in a 2x2 square,” Gazzaniga later wrote of Jenkins’ left hemisphere in his memoir, Tales from Both Sides of the Brain. “It just as often would arrange them in a 3+1 shape.”

But more surprising was this: As the right hand kept trying to get the blocks to match up to the picture, the more capable left hand would creep over to the right hand to intervene, as if it realized how incompetent the right hand was. This occurred so frequently that Gazzaniga eventually asked Jenkins to sit on his left hand so it wouldn’t butt in.

When Gazzaniga let Jenkins use both hands to solve the problem in another trial, he again saw the two brain hemispheres at odds with one another. “One hand tried to undo the accomplishments of the other,” he wrote. “The left hand would make a move to get things correct and the right hand would undo the gain. It looked like two separate mental systems were struggling for their view of the world.”