Short term memory is an instruction that briefly stores information before it can be transferred to the long-term memory. Based on Cognitive Load Theory (CLT) there is capacity limitation for working memory to selectively attend and process the words and pictures that located in the sensory memory. This theory states that the working memory should be used and managed efficiently via finding the way of how we can optimize the working memory especially when the process of learning is complicated.
First when the worlds and pictures involved in the multimedia presentation delivered by the learner, will be hold temporarily in sensory memory. Spoken words that have been intruded on the ears will be hold as sounds in verbal sensory memory and pictures will be hold as image in visual sensory memory. Then attended sounds and images will be transferred to working memory. Some of this attended words and images in working memory will be organized and words will be converted to verbal model and images will be converted to a pictorial model. At last learner integrate some of verbal and pictorial model and also his previous knowledge and information (if exist in the long-term memory) altogether and after integration, it will be stored in the long term memory for the future (Mayer 2009, p. 58).
As illustrate in figure 4., a cognitive theory of multimedia learning include two channels; Verbal/auditory channel that is shown on top and visual/pictorial channel that is shown in bottom. There are three memory stores that consist of sensory memory (capable of retaining sounds and images that intruding in the ears and eyes respectively), working memory (capable of temporarily storing and managing the information required for active processing) and long term memory (capable of storing unlimited capacity of knowledge for a lengthy period of time). Also there are three main cognitive processes consist of selecting, organizing and integrating (SOI). Based on this theory, learners engage in three cognitive processes throughout learning. The first process is selecting the information (selecting words and selecting images), organizing the selected information (organizing words and organizing images) and integrating the organized information with prior knowledge in long-term memory (Mayer 2009, p. 58).
“Multimedia learning involves learning from words (such as printed or spoken text) and pictures (such as animation, video, illustrations, or photographs).” (Mayer 2009, p. 57)
The science of learning has three principles in view of how people learn. Dual learning (there are two divided channels that people use for processing verbal and visual material), Limited capacity (there is a limited capacity for processing the material at any one time) and Active processing (engaging students in proper cognitive processing in learning time).
Computer engineers for recalling a long sequence of binary digits first categorize it into triplets and finally convert each of categorized group to a single octal digit. For example a binary digit like 010111001001000110 first is grouped to 11-001-001-000-110 and finally can be converted to 271106. Via this trick, 18 binary digits that exceeds the span of immediate memory, can easily be converted to six recoded octal digits and properly will be remembered. Also this procedure helps engineers to contract with three times as much as information as before (Miller, 1956).
If the limitation of memory span is constant number of chunks, we can create larger chunks by increasing the number of bits of information in it. For example if we have to carry a purse with full of money, it’s rational to fill the purse with silver dollars instead of coins. Miller for introducing the definition of recoding talked about radio-telegraphic codes. If we change a radio-telegraphic codes that contains many chunk with few bits per chunk, to a fewer chunks that contains more bits per chunk, we have done the recoding action (Miller, 1956).
Millers for declaring and proving the definition of chunk and the differences between bits and chunks cited Hayes memory span experiment. In this experiment participants had to recall different kinds of test materials such as nine binary digits (about 25 bits), seven letters of the alphabet (about 33 bits) and five monosyllabic English words (about 50 bits). The results of this experiment shows that with binary items the memory span is about nine and with monosyllabic English words, it is about five (Miller, 1956, pp. 8-9).
This experiment proves that the amount of information transmitted is not invariable and it rises linearly while the amount of information per item in the input rose therefore Miller declared that limitation of absolute judgment is based on the amount of information (bits) and limitation of the immediate memory is based on the number of items (chunks) (Miller, 1956, pp. 8-9). “I can say that the number of bits of information is constant for absolute judgment and the number of chunks of information is constant for immediate memory.” (Miller, 1956, p. 10)
The value of the channel capacity will be increased if we don’t force the observer to respond as accurate as possible and let him make relatively crude judgments of several attributes simultaneously. The observer is not able to answer extremely accurate and has definite limit. Miller defined this clear and definite limit “the span of absolute judgment” and estimated this value for single dimensional judgment to be near seven. He declared that by increasing the dimensions and not requiring the precise respond, the value of the span of the absolute judgment will be increased from seven to 150 (Miller, 1956, pp. 8-9).