Richard Boydell suffered from cerebral palsy and acquired language as a child through listening and reading alone. His first attempt at communication was at age 30, with the aid of a typewriter. He later became a computer programmer. A short excerpt from a computer-related book:
"Richard Boydell was born with a first-class brain, indomitable and resourceful
parents, ... He was born in 1933 with severe jaundice and cerebral palsy, ..."
"I acquired an understanding of language by listening to those around me. Later, thanks to my mother's tireless, patient work I began learning to read and so became familiar with written as well as spoken language. As my interest developed, particularly in the field of science, I read books and listened to educational programs on radio and, later, television which were at a level that was normal, or sometimes rather above, for my age. Also when people visited us ... I enjoyed listening to the conversation even though I could only play a passive role and could not take an active part in any discussion ... As well as reading books and listening to radio and television .... I read the newspaper every day to keep in touch with current events".
Stephen Krashen "The Input Hypothesis: Issues and Implications" (1985), citing Adrian Fourcin's 1975 article "Visual feedback and the acquisition of intonation".
Fourcin's article is also mentioned in "Foundations of language development" by Elizabeth Lenneberg (1975). Also mentioned in "Language development in exceptional circumstances" by Dorothy Bishop and Kay Mogford.
According to Fourcin, Boydell's writing was "elegantly phrased" although he had never written anything before. Krashen believes that Boydell's ability to express himself was due to his listening and reading and he uses this as an example for his input hypothesis.
Krashen uses Boydell as an argument against the "comprehensible output" theory.
Anyone seeking parallels with adults trying to learn a foreign language through passive exposure should keep in mind that Boydell learned English as a child. English was his mother tongue. Native speakers use the language internally, during abstract reasoning and problem solving. How often we actually "think" in our mother tongue is a separate issue but internal use of language is definitely a native speaker characteristic. A passive adult consuming foreign entertainment will not behave as a child acquiring his mother tongue. Advanced speakers of a foreign language would most likely start using their new language internally only after a prolonged period of habitual daily language production and interaction with native speakers. Another issue is that Boydell could speak only with extreme difficulty due to cerebral palsy. His writing was impeccable, but I cannot find any information about his spoken language skills.
See: Case Histories and the Comprehension Hypothesis by Stephen Krashen