Ever since the 35mm slide projector gave way to PowerPoint, the default mode of instruction in a wide variety of fields has been the "words-on-the-wall" presentation. Sometimes this takes the form of the presenter reading aloud the text projected on the screen. Sometimes the relationship between the projected text and the spoken word is less rigid. At all times, such a presentation creates situations in which members of the audience are asked to read and listen at the same time.
The authors of the attached articles argue that asking students to listen and read at the same time creates a form of cognitive overload that inhibits learning.