Dale, an American audio-visual educator, wrote a book "Audio-visual Teaching Method" on 1946, in which he put forward the theory of "experience cone" and thought that experience came from some direct ways and some indirect ways.

After World War I, with the progress of science and technology, more and more media were applied to education. The appearance of audio-visual movies and recordings finally promoted the "audio-visual teaching movement" in American education. And Dell's Audio-visual Teaching Method, with the "Tower of Experience" as the core, is the representative work of audio-visual teaching theory.

Edgar Dale is the main representative of audio-visual teaching theory, and the research results of other audio-visual teaching experts such as Weber and Hou Ben have also had an important influence on the formation of this theory.

The experience under the pagoda is the most concrete, and the more abstract it is. But this doesn't mean that you have to go through the bottom-up ladder to gain any experience, nor does it mean that the experience at the next level is more useful than the experience at the previous level. Stratification is to explain the concrete or abstract degree of each experience.

In the "tower of experience", we can see that learners begin as participants in actual experience, then as observers of real events, then as observers of indirect things (providing some media to present these events), observing substitutes of real things, and finally, learners observe abstract symbols of an event.

Dell believes that students have accumulated some concrete experience and can understand the abstract expression of real things. On this basis, they can effectively participate in more abstract teaching activities.

Education and teaching should start with concrete experience and gradually rise to abstraction. Effective learning methods should be full of concrete experience. The biggest failure of education and teaching is that students remember many common laws and concepts, but there is no specific experience as a pillar.

Education and teaching should not stay in concrete experience, but should develop to abstraction and universality and form concepts. Concepts can be used for reasoning and are the most economical thinking tools. It simplifies and saves people's wisdom of seeking truth. It is dangerous to take concrete direct experience too seriously.

In school, the application of various teaching media can make learning more concrete and lead to better abstraction.

Audio-visual media located in the middle layer of pagoda can provide students with concrete and understandable experience more than language and visual symbols, and can break through the limitations of time and space and make up for the shortcomings of other direct experience methods.