Whereas HTA is concerned with establishing an accurate description of the steps that are required in order to complete a task, the focus of this article is on a technique that captures some representation of the knowledge that people have, or that they need to have in order to complete a task. Cognitive task analysis is concerned with informing the design process through the application of cognitive theories. We don’t use cognitive task analysis (CTA) as often as we should. It’s an overlooked and for some an unknown tool.
A task is accomplished by performing actions in some order and CTA recognizes that some actions are physical (such as pressing buttons, moving pointers, or speaking) but some of them are mental, or cognitive operations. Undertaking such as deciding which button to press or where to place a pointer, recalling previously-stored knowledge from memory, or comparing two objects are cognitive rather than physical operations.
Humans perceive the world and produce some representation of it in his or her mind (sometimes called the "problem space"). This representation is what we would usually call "knowledge". It may be described in terms of the concepts that we have, the relationships between those concepts, and our capacity to make use of those concepts. The human then manipulates that representation and produces some output - some behavior - that can be observed. Cognitive task analysis seeks to model the internal representation and processing that occurs for the purpose of designing tasks that can be undertaken more effectively by humans. It is the basic characteristics of human actions in terms of perceiving the world, representing it internally, manipulating it, and expressing it which underlies Norman's seven-stage model and the other cognitive theories.
There are a number of cognitive task analysis techniques that focus on the different aspects of the cognitive processing assumed to be necessary for a person to complete a task. In addition to the levels of description, most of these focus attention on the mappings between levels - how a description at one level is translated into a description at another level. The two principal levels of cognitive activity are: the tasks-action representations and mappings and the goal-task representations and mappings.
Some CTA techniques
When done well, the outcome of CTA is a description of the actual performance objectives, conceptual and procedural knowledge for the performance, performance standards, and tools as used by experts as they perform the task
There are many different CTA methods that distinguish four main categories (interviews, observation, textual, and psychometric) and within those categories, there are around 75 (!) different methods.
Of the various cognitive models, historically, the most important was the human processor which described a psychological model of humans consisting of three interacting systems: the perceptual, motor, and cognitive systems, each of which has its own memory (that is, internal representation or knowledge) and processor. This model led to the GOMS (goals, Operations, Methods, and Selection rules) and Cognitive Complexity Theory (CCT) methods of task analysis. A more "natural" method of expressing the GOMS model is NGOMSL which assumes that as people learn and perform tasks, they develop knowledge structures. A method known as Knowledge Analysis of Tasks (KAT) is utilized "to identify the elements of knowledge represented in a task knowledge structure". There are several other influential cognitive task analysis techniques that focus on different aspects of the general information processing model. Task Action Grammar (TAG) is concerned with an evaluation of the learnability of systems, whereas both Moran's External Task Internal Task (ETIT) and Payne's Yoked State Space (YSS) are concerned with the mapping of tasks from the external task space to the internal task space. We can see where various techniques are applicable by relating them to our general model of task analysis which consisted of three levels of description: goals, tasks, and actions.
Conclusion
The recognition that users have tasks is fundamental to the grain of analysis appropriate for user-centered design. The term "task analysis" is, however, somewhat misleading, as frequently task analysis techniques simply describe what happens as opposed to offering any analytic capability. The danger here is that if analysts spend too long describing current processes and task structures, they will be reluctant to abandon those designs. People interacting with a computer system will transfer knowledge from their previous experiences - of both computerized and non-computerized systems - and will make use of that knowledge to guide their behavior. Understanding the content and structure of that knowledge can be used to inform HCI design.
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