HCI-Lect-08.pdf

HCI LECTURE 08 1  INTRODUCTION In the previous two chapters we have looked at the human and the computer respectively. We are interested in how the human user uses the computer as a tool to perform, simplify or support a task. There are a number of ways in whi...

HCI LECTURE 08 1  INTRODUCTION In the previous two chapters we have looked at the human and the computer respectively. We are interested in how the human user uses the computer as a tool to perform, simplify or support a task. There are a number of ways in which the user can communicate with the system. At one extreme is batch input, in which the user provides all the information to the computer at once and leaves the machine to perform the task 2  INTRODUCTION At the other extreme are highly interactive input devices and paradigms, such as direct manipulation and the applications of virtual reality. Here the user is constantly providing instruction and receiving feedback. These are the types of interactive system we are considering. 3  MODELS OF INTERACTION Interaction involves at least two participants: the user and the system. Both are complex, as we have seen, and are very different from each other in the way that they communicate and view the domain and the task. The interface must therefore effectively translate between them to allow the interaction to be successful. The use of models of interaction can help us to understand exactly what is going on in the interaction and identify the likely root of difficulties. They also provide us with a framework to compare different interaction styles and to consider interaction problems. 4  MODELS OF INTERACTION We begin by considering the most powerful model of interaction, Norman’s execution– evaluation cycle; then we look at another model which extends the ideas of Norman’s cycle. Both of these models describe the interaction in terms of the goals and actions of the user. 5  The Terms of Interaction Traditionally, the purpose of an interactive system is to aid a user in accomplishing goals from some application domain. A domain defines an area of expertise and knowledge in some real-world activity. Some examples of domains are graphic design, authoring and process control in a factory. 6  The Terms of Interaction Tasks are operations to manipulate the concepts of a domain. A goal is the desired output from a performed task. An intention is a specific action required to meet the goal. 7  The execution–evaluation cycle Norman’s model of interaction is perhaps the most powerful in Human–Computer Interaction, possibly because of its closeness to our intuitive understanding of the interaction between human user and computer. The user formulates a plan of action, which is then executed at the computer interface. 8  The execution–evaluation cycle The interactive cycle can be divided into two major phases: execution and evaluation. These can then be subdivided into further stages, seven in all. The stages in Norman’s model of interaction are as follows: 9 The execution–evaluation cycle 1. Establishing the goal. 2. Forming the intention. 3. Specifying the action sequence. 4. Executing the action. 5. Perceiving the system state. 6. Interpreting the system state. 7. Evaluating the system state with respect to the goals and intentions. 10  The execution–evaluation cycle Each stage is, of course, an activity of the user. First the user forms a goal. This is the user’s idea of what needs to be done. Therefore needs to be translated into the more specific intention. 11  The execution–evaluation cycle The user perceives the new state of the system, after execution of the action sequence, and interprets it in terms of his expectations. If the system state reflects the user’s goal then the computer has done what he wanted and the interaction has been successful; otherwise the user must formulate a new goal and repeat the cycle. 12  The execution–evaluation cycle Turning on the Light 1. Establish the goal – Increase light in the room 2. Form the intention – To turn on the lamp 3. Specify the action sequence – Walk to the lamp, reach for the knob, twist the knob 4. Execute the action sequence – [walk, reach, twist] 5. Perceive the system state – [hear “click” sound, see light from lamp] 6. Interpret the system state – The knob rotated. The lamp is emitting light. The lamp seems to work 7. Evaluate the system state with respect to the goals and intentions – The lamp did indeed increase the light in the room [goal satisfied] 13  The execution–evaluation cycle Norman uses this model of interaction to demonstrate why some interfaces cause problems to their users. He describes these in terms of the gulfs of execution and the gulfs of evaluation. 14  The execution–evaluation cycle The gulf of execution is the difference between the user’s formulation of the actions to reach the goal and the actions allowed by the system. The gulf of evaluation is the difference between the physical presentation of the system state and the expectation of the user. 15 The execution–evaluation cycle 16  Human error - slips and mistakes Human errors are often classified into slips and mistakes. We can distinguish these using Norman’s gulf of execution. Slip: you have formulated the right action, but fail to execute that action correctly. Mistake: if you don’t know the system well you may not even formulate the right goal. 17  Human error - slips and mistakes Slip example: – If you understand a system well you may know exactly what to do to satisfy your goals and you have formulated the correct action. – However, perhaps you mistype or you accidentally press the mouse button at the wrong time. Mistake example: – you may think that the magnifying glass icon is the ‘find’ function, but in fact it is to magnify the text. 18  Human error - slips and mistakes slip understand system and goal correct formulation of action incorrect action mistake may not even have right goal! Fixing things? slip – better interface design mistake – better understanding of system 19 Thank You 20