When a person's view of reading is delayed on unfamiliar words, one can judge about the lack of knowledge of a foreign language.
During reading, the person's view is progressing along the lines of the written text is not the same: some words are read quickly, and the other eyes "stop" (this "stop" lasts about 200-250 ms, while the progress from word to word continues 1/20 seconds).
In addition, during the reading the person periodically returns to some of the passages just read. However, for a quick reading (for example, when the text is unproblematic) such "stops" are extremely insignificant and almost invisible: the person glances as if looking at the lines.
When reading a foreign text with an unimportant knowledge of the language, the look stops on unfamiliar words for a long time. Specialists representing the Massachusetts University of Technology found that the movement of the eyes can determine whether a person knows the language well.
Nearly 150 students from all over the world were involved in the experiment: for all of them, English was a non-native language. Students were asked to read the text in English (this text was the same in some cases, but differed in others). The movement of the eye was controlled by special equipment, which simultaneously recorded what words caused the participant the greatest "inhibition".
As suggested by researchers, this simple method really pointed to the quality of knowledge of a foreign language.
Most likely, the described method can become universal: it will help to determine the quality of knowledge of a foreign language, regardless of what language was native to the subject (in the experiment participated volunteers who considered their native language Chinese, Portuguese, Spanish, etc.).
Experts believe that a larger number of participants representing cardinally opposite language groups should be involved in the study. Perhaps the definition of knowledge by sight will be one of the ways to test students.
But, according to the researchers, the information obtained during the experiment has not only practical meaning. The results give an opportunity to understand how the study of the language as a whole is going on: how the brain perceives the new task, how the learning of new linguistic data is moving.
Recall that today in many countries - including, and in the United States - to assess the language knowledge is used a common test TOEFL (Test of English as a Foreign Language). This test contains a number of levels and is highly complex.
A detailed description of the experiment is presented on the pages of the "Material of the Sixteenth Regular Conference of the North American Division of the Association of Computer Linguistics" (https://arxiv.org/abs/1804.07329).