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In 2005, Robert James Fourie researched how efficiently a normally hearing adult could learn sign language vocabulary from a teacher versus three types of media, namely a CD-ROM, a video and a book.
There was only 1 subject.
The author's conclusion:Results suggested that the subject learned sign language vocabulary most efficiently from the teacher followed closely by the video, then the CD-ROM, and then the book. These differences were probably due to the feedback and personal contact provided only by the teacher, as well as the greater clarity of the teacher's signs as opposed to the clarity of the media.