The reality was much closer to full compensation. Missing the right side of his occipital lobe, UD’s brain never fully compensated for the loss of the region that handles visual input from the left side of his visual field. As such, he essentially has a permanent blind spot on his left side. He easily deals with this by simply moving his eyes and head to capture full peripheral vision on his left side, though.

The authors of the case report, led by cognitive neuroscientist Marlene Behrmann of Carnegie Mellon University, concluded that UD had not regained function in the “lower-order” visual cortex, meaning basic functions like peripheral vision. But, they note, he did regain all the more complex functioning in the “higher-order” visual cortex based on the results of more extensive testing.

In the three-year followup of UD’s recovery from surgery, the researchers tracked how his brain was functioning using fMRI—functional magnetic resonance imaging, which measures brain activity by monitoring changes in blood flow. They also had him take cognitive and perception tests.

As was the case prior to his brain surgery, UD scored above average on IQ tests and was within a normal range of visual perception for his age. UD performed just fine at recognizing faces, discriminating objects, perceiving global forms, and on reading-proficiency tests.