I'm a big fan of Stephen Krashen's research and the comprehension hypothesis. I'm garnering enough experience learning Thai that I'm now convinced that input is the only way to truly acquire a language.

Recently, I've been thinking about how to determine a level of input that provides optimally efficient acquisition. That is, how can I tell when input is at level "i+1"? The American University Alumni language school uses a very pure input approach, and they provide some guidelines. AUA instructors target 80% or greater understanding for all of their students. For AUA, "understanding" includes not only familiar vocabulary, but also the context of visual and experiential cues. For example, a beginning student playing Uno in Thai might understand fewer than 80% of the words, but most people who already know the game would understand at least 80% of the experience. After a large amount of comprehensible experience in the foreign language, words acquire meaning without resorting to translation.

I think an 80% rule-of-thumb is good, and an inclusive definition of understanding is also good. In fact, I cannot imagine a pure input approach which does not allow for understanding by contextual cues. Without contextual cues, there would be no way to "get started" without introducing translation of some sort and breaking the input model.

This definition of understanding means that all sorts of material is available. For the months of May and June, I studied primarily by watching children's movies in Thai. I avoided subtitles, since they can interfere with acquisition. By using visual and contextual cues, I was able to have 80% or greater comprehension while only following 30% of the spoken dialogue. Watching the same movies again and again, my comprehension of the spoken dialogue improved, and for one those movies it's now around 60-70% and still growing.

My vocabulary is bigger than it was in May, and a new source of comprehensible input is radio news stories. If I already know something about the subject, I can fill in gaps left by unfamiliar vocabulary. If I don't know much about the subject, I have to understand more of the vocabulary. The vocabulary is usually easiest in human interest stories, like a review of the week's top movies.

It's not always possible to understand 80% of everything. Like Tony, an enthusiastic ESL blogger, I place the highest priority on my level of interest. If I am very interested, I will listen again and again with a great desire to uncover the meaning. Even if I only understand 50%, the listening is very productive.

I am not a purist. A very pure input approach doesn't seem practical without a teacher. I own a dictionary, and I do use it. However, I strongly emphasize input over anything else, and I avoid memorization, letting words and phrases build themselves into my vocabulary naturally.