UX Fundamentals: How People Interact with Things

Last updated on 1 April 2022

Different kinds of people interact with things in different ways, and to figure out what these ways are, here is a breakdown of the fundamental human factors that influence people’s interaction.

Factors of Interaction: Visual Aid

Models and Efficacy

As Bill Verplank shows in his famous illustration of Interaction Design,  human interaction consists of three sequential processes:

  1. Feel: A person senses her world and/or something in it.
  2. Know: That person’s brain interprets this sensory information, generating a thought, feeling, or idea.
  3. Do: The person acts upon the world or the thing, based on her thought, feeling, or idea.

If we view interaction this way, it is logical that the way we people interact is a function of how and how well these processes occur. The factors of interaction are thus:

  • Input Efficacy: how well we can sense the world around us
  • Processing Model: Our cognition (interpretation/thinking) about our sensory input
  • Output Efficacy: How well we express ourselves and exert our will onto the world

Differences Are Meaningful

If we can understand the people for whom we make things, then making those things great becomes much easier.

What Makes Us Different?

Differences in these factors can occur both between different people and within the same person between different contexts. A young child’s output efficacy is lower than an adult’s, due to motor skills development, but one person’s output efficacy is impaired as soon as she puts on a pair of gloves. Input efficacies between someone with perfect vision and someone who is visually impaired are different, while one adult driving at night has a lower input efficacy than when she drives the next day.

Processing models can also differ between people or in one person between different contexts. A dog-lover interprets a dog’s presence differently than does someone who is afraid of dogs. On the other hand, one young soldier might interpret a rapid series of flashing lights differently on a battlefield (gunfire) than she would in a night club (strobe lights).

Measuring Differences Between People

  1. Read: Many human factors patterns are well-known, like motor skills development in children. For these things, a literature study is the best first step, as long as the literature really is relevant.
  2. Ask: With nuanced differences, such as those in processing models, interviewing is important. To a point, people can report on their thoughts and give insight into their mental processing.
  3. Observe: Sometimes, reporting is not enough, because people are not enough aware of their processing or not articulate enough to express it. For those reasons, interviewing should be accompanied by some sort of observation.

Measuring Differences Within One Person

In short, the best way to learn about how user will behave and interact under different circumstances is to simulate those circumstances for that user and compare her behavior. This could be as simple as asking a test participant to imagine being in different scenarios or as complex as putting that participant into the actual circumstances and observing her behavior.

An Important Sidenote

So far, we have seen that different people can show different input/output efficacies or exhibit different processing models. We have also seen that one person can differ in these factors, depending on different contexts. What we must not forget is that these factors are dynamic, in a constant state of flux.

Visual Aid: Interaction Changes over Time

First of all, none of these factors is meaningful on its own. They all affect each other, and a person’s interaction is not the sum of these factors, but a synergy of their aggregated effects.

Secondly, interaction changes over time. As the three factors affect each other, they constantly change, and the person learns, adapts, and changes with it. Also, a person’s environment changes in response to her changing interaction. This does not even take into account the macro-level changes that occur as society changes the world and the world reciprocates.

Learn More to Create Better

To paraphrase Teresa Brazen, UX design is relatively simple:

  1. Make things for people.
  2. Those people aren’t you.
The second point reminds us that we need to learn about our users and design for them, rather than assuming they use things the same way(s) we do.
(This post’s cover image is from this YouTube video by Mike Wilson.)