The dual coding theory, a theory of cognition, was first advanced by Allan Paivio of the University of Western Ontario. The theory postulates that the human cognition consists of two subsystems that process knowledge simultaneously, one processing the verbal objects and one dealing with visual objects. The two systems have different functions; the verbal subsystem processes and stores linguistic information whereas the visual subsystem processes and stores images and pictorial information. While the two subsystems can be activated independently, the interrelations and connections of the two systems allow the dual coding of information.

When reviewing examples where this theory was applied, one can clearly see the importance of presenting information in both visual and verbal representations. When designing instructional interfaces, the designer should consider that proper application of this principle could result in enhancement of recall and recognition of content.

The dual coding theory also discusses limitations of the verbal and visual subsystem processes. Humans have difficulty simultaneously attending to multiple auditory or visual cues, depending on expertise with the task or prior knowledge with the subject area. A multimedia presentation that shows multiple visuals such as an image of a speaker as well as the text that the speaker is reading could overwhelm the viewer because he/she must now attend to two images. On the other hand, an eLearning module that shows images of person using a digital camera or iPod while also simultaneously providing narration that describes the images could potentially provide for improved learning because the visual and verbal information does not compete with each other.