Interaction loop

Now let’s review the interaction process, that happens between users and machines or computers.

Traditionally, two ways of interaction are considered — human-machine (HMI) and human-computer (HCI) interactions, but in fact there is no quite large difference between them, so I will use the words “machine”, “computer” or “device” as synonyms unless it is not important for the context.

Any interaction is a sequence of impacts or actions and responses between human and machine system. I’d prefer to call any chain of this sequence as interaction loop. This loop and its context can be presented in this diagram:

interaction loop overview

This interaction loop is very important, principal part of user experience, that we will refer and detalize in future chapters.


Let’s review an example of such interaction loop sequence, that is not too specific or complex. For instance, you want to make a call to your friend with your smartphone.

Loop 1  First of all, you take it into your hand. You want to unlock it — that is your internal intention (partially unconscious). You find the power button and press it with your finger — one of your most important “output devices”. The smartphone receives your action and lightens up the screen. You receive this feedback (the battery is not dead, the smartphone is turned on, and it is ready to be used).
 Loop 2 Now you type in the security code by touching the screen with fingers in certain positions, that you observe by your eyes. If the code is correct, the system responds with home screen (or previously opened app, but let’s skip it)
Loop 3 Next, you press the “phone” icon to make a call. The system responds by launching the phone “app” with contacts used. You observe this screen and see the name of the friend in the list of recent calls. This is what is needed.
Loop 4 Now you simply press the list item and the smartphone starts the call and changes its screen contents again to “dialing” view. You interpret this as correct behavior.
Loop 5 Now you move the smartphone to your ear. The system receives the proximity sensor level below the threshold, and because of its hidden logic, it reacts by turning the screen and touch surface off (to avoid extra battery draining and unnecessary spontaneous interactions).
And so on…

Based on this example, we see several smartphone inputs being used (physical button, touch screen surface, proximity sensor). If we add actual phone talk here, both our eyes and ears are used as our “inputs”, and both finger muscles and vocal folds as “outputs”, and both screen and speaker as outputs of smartphone. This is purely intermodal interaction — and it is absolutely seamless for us, because we do it everyday.

The same interaction loop process is used for other, more complex tasks, such as handling bulldozer, airplane, designing a book or anything else.

Is it something HMI specific?

Actually, if we change the machine with user, or change the user with machine, there will be no difference — this is a general interaction loop. You can place there animals, nature objects and even atoms and galaxies — and the picture will not change dramatically, because all interaction laws are derived from such fundamental sciences as biology, chemistry, physics and so on.

In some case it is the systems thinking approach — we have two complex systems (human and machine), that affect each other and there is some internal, hidden logic inside them.

Time factor

We should also mention very important aspect of interaction loop, that is hardly visualized — that is time.

All interactions require time, because there is some processing inertia inside each system. Also, if the time is too large, this interaction can be degraded to single actions without response. So, to make interaction, we need some time, but it shouldn’t be too long.

Next: What is user interface

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