 Some authors have raised doubts about the thought experiment itself. It is sometimes pointed out, for example, that merely confining Mary to a monochromatic environment would not prevent her from having color experiences (see Thompson 1995, 264) or that, after release, she would not be able to see colors. But the example can be refined to meet these objections. Mary might be monochromatic from birth and changed into a normal perceiver by some medical procedure. It is sometimes objected that already accepted or future results of visual science are or might be incompatible with the existence of a Mary-case (a person with monochromatic experience who becomes a normal color perceiver later) or that such results might require (to preserve consistence with visual science) the introduction of so many additional assumptions that the conceivability of the example becomes doubtful. To this one might reply that the thought experiment need not be compatible with visual science. If the case of a person with monochromatic vision who turns into a normal perceiver really does involve serious difficulties for materialism, then the mere fact (if it were one) that our visual apparatus excludes the actual existence of such a case does not seem to provide a convincing reply for the materialist. But this point (the relevance or irrelevance of visual science in this context) has not received much discussion in the literature. It has, however, been pointed out (see Graham and Horgan, 2000, footnote 4 with its reference to Shepard 1993) that at least presently available results of color vision science do not exclude a Mary-case. (The psychologist Knut Nordby was a real life case of a color vision specialist who was also a complete achromat. See his paper ‘Vision in a Complete Achromat: A Personal Account’, linked into in the Other Internet Resources section and Nordby, 2007.)