Elon Musk’s Neuralink Corp. used a brain implant to enable a monkey to see something that wasn’t physically there, according to an engineer, as it moves toward its goal of helping blind people see.

T here’s a 3D hand on a black screen. J. Galen Buckwalter concentrates on the image, trying to move one of the virtual hand’s fingers — with his mind. For more than 50 years, Buckwalter hasn’t felt ...