In the last decade or two, Dominic ffytche and his colleagues in London have done pioneering research on the neural basis of visual hallucinations. Based on the detailed reports of dozens of subjects, they developed a taxonomy of hallucinations, including categories like figures with hats, children or small people, landscapes, vehicles, grotesque faces, text, and cartoonlike faces. (This taxonomy is described in a 2000 paper by Santhouse et al.)
