A difficult word, or sentence, on the printed page can be read again, whereas a word not clearly heard is rarely repeated.

The listeners therefore finds that he has to concentrate so hard on identifying the words correctly and on understanding them that he has little time left to remember.

In a foreign language, his brain simply has too much to do. In his own language, of course, he's able not only to identify and understand the words automatically, but also he can often even predict the words which are going to come. His brain, therefore, has much more time to remember.

Thirdly, I want to deal with a problem that worries most students in a lecture. The problem is this, they can't always follow the argument. This is of course partly due to the first two difficulties I've discussed.

When you have difficulty in identifying or remembering words and sentences, you obviously won't be able to follow the argument.

But even those students who can do these two things perfectly well have problems in following a quite straightforward argument. Why is this? I'll suggest three reasons here.