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01 Jun 2018

Principles of Interaction Design: What It Takes to Create Positive Human-Computer Interactions

Every time you find yourself engrossed in a video game, you experience a good interaction. Another example? Cashing out at an ATM in less than a minute. Ditto?—?when an app automatically fills in the verification code sent via SMS, when you use a widget on your home screen instead of opening an app, and, of course, seeing a green checkmark when correctly filling in a form.

Unfortunately, everyone?—?even the best of us?—?experiences bad interactions. Father of user-centered design Don Norman wrote a whole book describing good and bad designs, and most of all?—?sinfully bad doors. “My problems with doors have become so well known that confusing doors are often called ‘Norman doors.’ Imagine becoming famous for doors that don’t work right,” he laments in The Design of Everyday Things. Norman doors are the doors that you always push when they need to be pulled and pull when they need to be pushed.

Bad interactions?—?in both physical and virtual worlds?—?create obstacles between a user and a product, like a push door that they keep mistakenly pulling by the handle. They distract people from getting to their goal and often make them give up altogether. That’s when interaction design comes to the rescue.

Interaction design (abbreviated to IxD) has been around at least since the 1980s but only fairly recently has it come to gain shape and form like any other discipline. And it is a separate discipline. User experience (UX) design shapes the overall encounter with the use of a product, including programming, building information architecture, doing usability engineering, and user research. Interaction design is involved in helping a user reach their goal via smooth, pleasurable, and quick interactions with an object or a machine.

Relationships between different subsets of UX design

If a software product is a house and UX design is everything that makes this house a cozy and convenient place to live in, then interaction design is a light switch near the entrance to each room, a heated bathroom floor, a dinner table big enough to accommodate the whole family. While you only remember your overall experience of living in this house, it’s the small details like nicely colored walls and comfy armchairs that make up this experience.

You will often find IxD mentioned together with another term?—?human-computer interaction (HCI). When the first personal computers invaded people’s homes and offices, the idea that conversations between humans and machines should resemble human-human conversations gained popularity.

Since then, a lot of scientific research, including cognitive science and computer science, has been put to use to explore ways of shaping better communication between machines and humans. As a founder of the field, John M. Carroll notes, “HCI expanded from its initial focus on individual and generic user behavior to include social and organizational computing, accessibility for the elderly, the cognitively and physically impaired, and for all people, and for the widest possible spectrum of human experiences and activities.

Laws and Principles of Interaction Design

Interaction design lies at the intersection of many different methodologies and therefore designers are still figuring out the discipline’s hard and fast rules. But, there are many principles interaction designers apply in their practice that can be described as a foundation of the whole field. Let’s explore them now.

1. Fitts’ Law

Introduced in 1954 and targeted to calculate performance of assembly workers, Fitts’ law describes one of the most basic phenomena of human-computer interactions. It illustrates the relation between the distance to the target, your speed, and the size of the target. It basically says that the bigger the object, the faster you can point to it. Whether you point with a cursor or a finger, you can calculate how big a button should be to decrease the time spent aiming for it and increase the accuracy of pointing.

You can check out this demonstration that calculates the time it takes for you to click on circles of different sizes placed different distances from each other.

How to apply it in practice?

  • Shorten the distance between action A and action B
  • Place common elements in like manner

Reddit’s user jbu311 suggested an interface improvement that was later implemented on the website

  • Make interactive elements big enough so users can aim easily
  • Provide a lot of clickable space around a link (or just make it a button)

2. Hick’s Law

Named after psychologist William Edmund Hick, Hick’s law dictates that the greater the number of choices, the longer it takes to make a decision. This leads to a simple conclusion: Giving a lot of choice is not always a good thing. Despite the fact that users are instinctively drawn to products with more features, simpler solutions bring more satisfaction.

Imagine entering a frozen yoghurt shop and seeing endless rows of toppings. You’ll spend hours choosing between them. And while picking desserts may be fun, scrolling through a list of book genres in an online store is not. Amazon, by the way, generously applies Hick’s law to categorize its vast choice of listings. You do have to read through them all to find the needed department, but you do it in measured amounts, by looking through different sections step by step.


Hick’s law on Amazon

How to apply it in practice?

  • Reduce the number of menu elements and put them in categories
  • Highlight Search and Filter features
  • Break down the checkout or any long form-filling process into manageable steps
  • Leave out excessive customization options

3. Tesler’s Law

In the mid-1980s, Apple computer scientist and then vice president at Apple Larry Tesler came up with a model that states: “Every application must have an inherent amount of irreducible complexity. The only question is who will have to deal with it.” This law is basically the foundation of today’s trend toward minimalist interfaces, in which users don’t have to deal with complexity?—?because developers do.

“The senior designer won’t stop simplifying until the design is simple enough,” says Tesler in an interview for Bill Moggridge’s book Designing for Interaction. Even if it takes extra days or weeks, you’ll have to remove clutter from the interface and deal with it on the back-stage level.

How to apply it in practice?

  • Embrace radical decisions and start with the final and cleanest state of the design.
  • Never skip user testing.

4. Five Languages (Dimensions) of Interaction Design

In Designing for Interaction, a usability academic Gillian Crampton Smith offered a concept of four dimensions (or languages) of interactive design. According to Crampton Smith, these languages are the essence of all interactions that help humans and machines communicate effectively. Later, designer Kevin Silver proposed the fifth dimension thus establishing the concept now known as 5 dimensions of interaction design. Designers use them to analyze the current interactions and ask questions within each dimension.

1D: Words. This is the language we use to describe interactions and the meaning behind every button, label, or signifier. Words should be clear and familiar to end users, used consistently and appropriately to the setting.

SoundCloud uses effective wording to describe the scope of the service’s functionality

  • What words should we use so our end users can understand them?
  • Do we use words consistently throughout the interface?
  • What meaningful information can we provide to let users know what will happen after they perform an action?

2D: Visual representations. These are all typography, imagery, icons, and a color palette that users perceive involuntarily.