The Human-Machine Interaction Loop (HMIL) is a model of a single “interaction” between a user and a thing being used, and helps focus attention on all the HF aspects that must be attended to during design.
When a human interacts with any machine, the general set of activities that happen is always the same. These activities can be modelled in various ways.
A single HMIL represents a single task, like raising the volume of a radio or grasping a blender on an upper kitchen cabinet or setting the speed of a lathe. Every task can be represented with a HMIL.
A (slightly) better model for our purposes is shown in figure 2.
The Human-Machine Interaction Loop (HMIL) shown in figure 2 is the one we will refer to subsequently.
Consider the following examples.
Assuming you know how to adjust the volume on the particular radio in question, think of the specific activities involved with respect to the six elements of the HMIL (figure 2).
feedbackhas two components: the music coming from the radio, and the current position of the volume control.
observethis feedback; you hear the music and see the volume control setting.
cognitionto process the observations.
actuatethe volume control to change the volume.
A well-designed product will promote safe, easy, even enjoyable interactions. To understand the nature of that those interactions via analysis of HMILs is very important.
Consider the radio volume example above. Clearly, the design of the volume control will be dictated in large part by the need of the user to participate safely and easily in the HMIL outlined above.
Exercise for the reader Enumerate as many design decisions as you can think of that will help to ensure the volume control is safe, functional, and usable. Justify each decision by referring back to the HMIL above.
As usual, HMILs are analytic tools, so they don't actually help you design something. However, they do help you understand the design situation better so that you improve the odds of designing a good product.
An interesting case study about how humans can misunderstand what they see in a product designed by other humans - and that results in disaster - is the slide that led to the Columbia Shuttle disaster.
The problem of granularity can cause you to go into too much detail with HMILs.
In the example of the radio volume control, it may not be relevant if your job is to design a whole car dashboard. You will have to depend on the scope of the design brief to guide you: you may not need to design all the details of a product.
Furthermore, in scholastic settings, you may simply not have time to study all the HMILs of all the possible components of a design. In this case, you are advised to find a few particularly important components and focus on them. If you can demonstrate that you can (1) justify your choice of important components, (2) perform good HMIL analyses of those components, and (3) admit that the remaining components simply cannot be done within the timeframe of your project, then you'll have demonstrated appropriate mastery.