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The program did so by analysing the signs that accompanied each of those words whenever it appeared in the subtitles. Where it was not obvious which part of a signing sequence relates to the given keyword, the system compared multiple occurrences of a word to pinpoint the correct sign.
Starting without any knowledge of the signs for those 210 words, the software correctly learnt 136 of them, or 65 per cent, says Everingham. "Some words have different signs depending on the context – for example, cutting a tree has a different sign to cutting a rose." he says, so this is a high success rate given the complexity of the task.
http://www.newscientist.com/article/dn17431-computer-learns-sign-language-by-watching-tv.html