Last Monday I was invited to be a guest speaker for a group of language teachers and to tell more about teaching languages using Comprehensible Input. 

What is Comprehensible Input (CI)? In short: a student acquires language through a lot of input (listening and reading) of this language and the input needs to be comprehensible. 

But what is this 'input' exactly?

I see 'input' as the message that is presented to the learner. A teacher who says in the target language: "Today is a bad day, it rains", that's input.

A list with the different types of weather is not input.

A text about Juan who is very hungry and wants to eat a lot and says to his friend Paco: "I am very hungry, I want to eat a lot", that's input.

An explanation of how 'to want + infinitive' is used as a construction, is not input.

In our courses we advise to limit the new vocabulary to about 3 target structures (chunks) per lesson series.

Why so little?

Simple, the human brain cannot process many new things at once. If you use many new words in a lesson, your students encounter these words, but they don't acquire them. The acquisition of new vocabulary takes much more time; the learner must be able to recognize the word in sound and in written form, the learner must know the meaning of the word, must experience how this word might change (plural, past tense, etc) and the learner must be able to use this word in language production. Only then is it acquired. This cannot be done if you present 20 or more new words every lesson. Our brain is simply not capable of processing so much.

How much can the brain handle? dr. Gianfranco Conti wrote an interesting blog about this. Young children could learn about 3-5 items (word or better: chunks) per lesson. With teenagers this could be about 6-8 items per lesson.

As you might understand, it's not easy to determine the exact number of new items per lesson and not all the research give the same outcome. But it is clear from all the research that cognitive overload happens fast.

It is very important that any new item gets repeated in the upcoming lessons, otherwise it doesn't get enough opportunity to be transferred into the long-term memory.