 B. A. Farrell had earlier presented a similar thought experiment featuring a Martian; in this version, it is humans who lack knowledge of what it is like for the Martian to exercise his sensory capacities (1950, 183; though Farrell ultimately argues that this thought experiment does not present a challenge to physicalism). Paul E. Meehl, responding to Feigl, describes two individuals who each have complete neurophysiological knowledge, one of whom is congenitally blind; he takes it as intuitive that this person does not know something which the other does, namely “what red looks like” (1966, 151).