They were brought into play because of multiple intelligence theory. Dr. Howard Gardner of Harvard University first advanced the theory of multiple intelligences in his 1983 book, Frames of Mind . His theory says there are 7 different ways people think and learn, so there are 7 different ways to be intelligent. This theory has held up in many experiments, and is under continued study at Harvard Project Zero. Educators who adopt Gardner's theory try to use instructional approaches that will appeal to all 7 different types of students.
Most people think and learn best through visual activity.
Reading, pictures, overheads, Powerpoint presentations, and movies are geared toward these visual thinkers. The soundtrack of a movie helps them, as well as tapes, lecture and hearing others read aloud. These students sometimes develop the habit of mouthing the words when they read to themselves. They are often musically talented. They learn by doing.