Complex sentence: He raised the chickens in an environment where the light came perpetually from below and trained them to peck at pictures of dented (concave) or domed (convex) spheres, which were lit from both the left and right sides simultaneously.
Split into simpler sentences: He raised the chickens in an environment where the light came perpetually from below and trained them to peck at pictures of concave or convex spheres. In the photographs, the spheres were lit from both the left and right sides simultaneously.