According Paivio’s theory, people use two systems of Mental Representation. They are independent from each other, yet connected. They are the verbal system and the non-verbal system and this is the basic assumption of Dual Coding Theory.
Each one of these systems has different types of information. Paivio defended that the non-verbal system deals with images and its equivalents in other sensory organs, while the verbal system dealt with the language processing. But, as I stated above, theses two systems are connected and each and any concept is associated to other concepts, in both systems, at the same time.
In 1971, a memory test was made in order to support this theory and provide some answers about this dual coding system. A long list of words and photos was given to the test subjects for memorizing. The results were unanimous: the subjects always recalled more photos than words.
In order to understand these results, some comparisons and analysis were required. First off, it was necessary to compare the verbalizable photographs with the non-verbalizable ones, as well as, the words that were more or less imagetic.
The differences between the subjects who were told to build a mental image for any presented word and the ones who were not instructed in that way were also analyzed.
Cognitive performance is mediated by two interrelated systems which are different in structure, organization and information representation. In the verbal system (logogens) the information is represented in an abstract, logical and sequential manner, while in the non-verbal system, the representation is made through images in a concrete and analogical manner.
Paivio studies’ show that the mnesic performance increases directly with the quantity of alternative codes in memory, which means, that if you can make the subject memorize a piece of information in the two systems of representation, the probability of him recalling it increases.
Although, these studies also show that if you give the test subject the information in a single code and ask him to create a second one, it will interfere with his memory capacity, which hypothesizes that sometimes, dual coding some sort of information can just be redundant.
Some modern neurocognitive studies support this theory.