Cognitive load is a term that refers to the load on working memory during instruction.
Instruction may be aimed at teaching learners problem solving skills, thinking and reasoning skills (including perception, memory, language, etc.) Many would agree that people learn better when they can build on what they already understand (known as a schema), but the more a person has to learn in a shorter amount of time, the more difficult it is to process that information in working memory. Consider the difference between having to study a subject in one's native language versus trying to study a subject in a foreign language. The cognitive load is much higher in the second instance because the brain must work to translate the language while simultaneously trying to understand the new information.
Another aspect of cognitive load theory involves understanding how many discrete units of information can be retained in short term memory before information loss occurs. An example of this principle that seems to be commonly cited is the use of 7-digit phone numbers, based on the theory that most people can only retain seven "chunks" of information in their short term memory.
"Cognitive load theory has been designed to provide guidelines intended to assist in the presentation of information in a manner that encourages learner activities that optimize intellectual performance" (Sweller, van Merriënboer, and Paas, 1998, p. 251). Sweller's theory employs aspects of information processing theory to emphasize the inherent limitations of concurrent working memory load on learning during instruction. It makes use of schemas as the unit of analysis for the design of instructional materials.
The history of cognitive load theory can be traced back to the beginning of Cognitive Science and the work of G.A. Miller. Miller was perhaps the first to suggest our working memory capacity was limited in his classic paper . His experimental results suggested that humans are only able to hold seven plus or minus two digits of information in their short term memory. Simon and Chase used the term "chunk" to describe how people might organize information in their short term memory, this chunking of memory components has also been described as schema construction.
John Sweller developed cognitive load theory (CLT) while studying problem solving . While studying learners as they solved problems, he and his associates found that learners often use a problem solving strategy called means-ends analysis. He suggests problem solving by means-ends analysis requires a relatively large amount of cognitive processing capacity, which may not be devoted to schema construction. Instead of problem solving, Sweller suggests Instructional designers should limit cognitive load by designing instructional materials like worked-examples, or goal-free problems.
In the 1990s, Cognitive load theory was applied in several contexts and the empirical results from these studies led to the demonstration of several learning effects: the completion-problem effect ; Modality effect [7 ]; Split-attention effect [8 ]; the Worked-example effect[9 ] [10 ] and the expertise reversal effect .
Cognitive load theory has broad implications for Instructional design. This theory provides a general framework for instructional designers for it allows them to control the conditions of learning, within an environment, or more generally within most instructional materials. Specifically, it provides empirically-based guidelines that help instructional designers to decrease extraneous cognitive load during learning, and refocus that learner's attention toward germane materials, increasing germane (schema related) cognitive load. This theory differentiates between three types of cognitive load: intrinsic cognitive load, germane cognitive load, and extraneous cognitive load 
The term "Intrinsic cognitive load" was first described by Chandler and Sweller.[13 ] Accordingly all instruction has an inherent difficulty associated with it (e.g., the calculation of 2 + 2, versus solving a differential equation). This inherent difficulty may not be altered by an instructor. However many schemas may be broken into individual "subschemas" and taught in isolation, to be later brought back together and described as a combined whole [14 ].
Extraneous cognitive load is generated by the manner in which information is presented to learners and is under the control of instructional designers. This load can be attributed to the design of the instructional materials.
An example of extraneous cognitive load occurs when there are two possible ways to describe a square to a student [14 ]. A square is a visual and should be described using a visual medium. Certainly an instructor can describe a square in a verbal medium, but it takes just a second and far less effort to see what the instructor is talking about when a learner is shown a square, rather than having one described verbally. In this instance, the efficiency of the visual medium is preferred. This is because it does not unduly load the learner with unnecessary information. This unnecessary cognitive load is described as extraneous cognitive load.
Germane load is that load devoted to the processing, construction and automation of schemata. While intrinsic load is generally thought to be immutable, instructional designers can manipulate extraneous and germane load. It is suggested that they limit extraneous load and promote germane load .
Paas and van Merriënboer[15 ] developed a construct (known as relative condition efficiency) which helps researchers measure perceived mental effort, an index of cognitive load. This construct provides a relatively simple means of comparing instructional conditions. It combines mental effort ratings with performance scores. Group mean z-scores are graphed and may be compared with a one-way ANOVA.
Paas and van Merriënboer used relative condition efficiency to compare three instructional condition (worked examples, completion problems, and discovery practice). They found learners who studied worked examples were the most efficient, followed by those who used the problem completion strategy. Since this early study many other researchers have used this and other constructs to measure cognitive load as it relates to learning and instruction.
The ergonomic approach seeks a quantitative neurophysiological expression of cognitive load which can be measured using common instruments, for example using the heart rate-blood pressure product (RPP) as a measure of both cognitive and physical occupational workload.[17 ] They believe that it may be possible to use RPP measures to set limits on workloads and for establishing work allowance.
Evidence has been found that individuals systematically differ in their processing capacity.  [19 ] A series of experiments support the assumption that each individual has a fixed capacity for processing information, irrespective of the task in question, or more accurately, irrespective of the processes an individual uses in solving any given task. Tasks ranged from remembering simple lists, lists supplemented with a fixed constant and simple arithmetic.
Identifying the processing capacity of individuals could be extremely useful in further adapting instruction (or predicting the behavior) of individuals. Accordingly, further research would clearly be desirable. First, it is essential to compute the memory load imposed by detailed analysis of the processes to be used. Second, it is essential to ensure that individual subjects are actually using those processes. The latter requires intensive pre-training.
For ergonomics standards see