UX Laws: How the human motor system can be applied to UX

UX laws are some practices that designers can use to improve their products. In this article, I will go through some UX laws, explain why it’s great to use these laws, and find real-life examples of those. So let’s start with the first one.

Fitts’s Law

It all began in 1954, when the psychologist Paul Fitts, who was investigating how the human motor system worked, informed us that the time necessary to travel to a target depended on the distance to it and, inversely to its size:

“The time to acquire a target is a function of the distance to and size of the target.”

This law can be applied to UX if you want something to be easy to select, making it big and in a location where the users can easily reach (near the thumb if you are working on a mobile app). Here are the reachability spots on a mobile phone:

That’s also why iOS and Android recommend using buttons with a minimum size of 44x44 CSS pixels.

Fitts’s law can also be used for the opposite reasons, making things harder to reach or select. This can usually be applied for options like deleting an account or signing out, where we want to ensure that users don’t press those accidentally and their action is intentional.

Hick’s law

This law is named after a British and American psychologist team of William Hick and Ray Hyman. It was initially made on 1952, and this is one of my favorites. So basically, the team tested the relationship between stimuli and an individual’s reaction time to any given stimulus. Given that, the results were that the more stimuli to choose from, the longer the user would take to decide.

“The amount of time it takes to make a decision grows with the quantity and complexity of choices.”

That has a significant impact on UX, telling us that we don’t need to bomb users with choices that they would take time to absorb and interact with, plus giving them work they don’t want.

Let’s get a real-life example here. In the picture below, you can see two remotes, the standard remote that everyone is used to and the Apple TV remote. The difference here is that Apple took the right approach and applied Hick’s law perfectly well, maintaining only the necessary option that users would use and removing all the unnecessary stuff.

Jakob’s Law

This law is also fundamental for each designer to use in their products. It was coined by Jakob Nielsen, a user advocate and principal of the Neilsen Norman Group. To simplify this law’s meaning, I’m gonna use the famous quote: “If ain’t broke, don’t fix it.”

This means we must adjust to the user’s familiarity with other applications. We don’t want them to have entirely new interactions whenever they open another application, and that’s because they will transfer expectations they have built from another application that they are familiar with to another that appears similar.

When making changes, we need to keep in mind to focus on changing the things that users find hard to use and can be better, and not changing how we interact with an application.

Let’s take Google as an example; below, we see the first version of Google and the most current one. Here you can notice that even though Google now is faster and looks way prettier, it didn’t change how we search on Google. We can still see the big logo and search bar; because it works perfectly well, they applied Jakob’s law of not changing something familiar.

Miller’s Law

“Most people have a working memory capacity of only seven things at a time (plus or minus two).”

This is what George Miller came out within 1956. He said that the span of immediate memory and absolute judgment were limited to around seven pieces of information, and they could be overwhelmed.

To prevent this overwhelm, we need to make sure that we use Miller’s Law to focus on chunking, meaning grouping information by its features to make them more memorable.

Let’s take some real-world examples. I am sure we can better memorize this number:+383 47 700 800 rather than +38347700800.

Or let’s take this example of credit cards; as we can see, numbers here are chunked into groups; if designers wouldn’t apply Miller’s law here, it could result in a 16-digit card number that would be a nightmare to write.

Thanks for coming this far!