How Hicks and Fitts Law Drive User Experiences

How to manage Hicks and Fitts law when building user interfaces for our users

When building user interfaces, there are many governing laws and recommendations that one should consider when designing how users should interact with applications or other user interfaces. There are two laws however that provide that individuals should always consider when designing them, Hick’s Law, and Fitts’ Law. Violations of Hick’s Law and Fitts’ Law will cause user error, panic, confusion, and drive people away from experiences. Hick’s Law and Fitts’ Law are the building blocks of creating user interfaces that help our users make informed choices and avoid confusion when trying to make any decision.

Fitt’s Law

Fitts’ law is defined as that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target. In other words, it means that the speed someone can find something is directly correlated with the size and how close it is to where they are currently looking. The motion we use to interact with something initially beings with a rapid movement and then a finer tune movement as we get closer to our intended target. We can find things better if they are bigger and closer to where we are currently drawing attention.

In Violation of Fitts’ Law

There are many examples of Fitts’ Law in action, but we will look at an example of where it can cause material harm and its importance when considering design decisions. Bradley provides a concise summary of an event where in 1996 Chrysler was being investigated over complaints that Jeep Cherokees were accelerating instead of braking as drivers intended. Chrysler cited the cause of this complaint was that drivers were hitting the gas pedal instead of the brake pedal and that users were at fault. However, during the design and creation of the Jeep, it was uncovered that the pedals were moved a few inches to the left reducing the distance between the gas and brake pedal. This then caused drivers to hit the gas pedal instead of the brake pedal as they were too close together. Chrysler had violated Fitts’ law by placing the pedals too closely together.

How to Design Towards Fitts’ Law

We can take Fitts’ law and help us design better interfaces for our users that better help them and guide them by providing what actions or information they need in bigger context as well as closer to what they are interacting it. Take for example a simple button. Budiu provides a recommendation that buttons that users interact with should include a label if also accompanied by an icon. By including this label as well as the icon, we naturally enlarge the area of the button for users to interact making our button easier to acquire according to Fitts’ Law.

On the other hand, we can make items that our users need to have, but should not normally interact with smaller than the other interactable elements on the screen or spacing them farther away from other elements. Examples of these sorts of interactions are things like opening the engine bay of a car. Normally on gas powered cars, opening the hood of the engine bay is much smaller than other elements in the driver’s view, and farther away from other elements that a driver would need to interact with. This can cause disaster for those who are driving if they inadvertently interact with it. Manufacturers have taken this interaction and moved it farther away from things like the steering wheel or turn signals and made it smaller than other elements, so it is harder for users to interact with unless they are specifically looking for it.

To further highlight the significance of Fitts’ law, we will review a study conducted by Juras, Slomka, and Latash (2009) in which participants were instructed to jump on targets of various sizes and distances, measuring preparation and movement times. In summary of this study, participants took longer to prepare for jumping on smaller targets than jumping on larger targets. When gathering information, we take longer to interact with something that is smaller as we adjust for our fine motor movement. In situations where individuals do not have time to adjust for these fine movements, like for example slamming on a brake pedal, this could potentially lead to mistakes.

Hick’s Law

As defined by Hick, Hick’s law states that the response time in simple decision tasks is a linear function of the transmitted information. To provide more context into this definition it can be said that the amount of time it takes to decide is directly correlated with the number of choices that are present. The more choices that are present to make means that it takes longer to decide.

In Violation of Hick’s Law

The New York Times reports of the story in June of 2008, individuals living in Hawaii were notified that a ballistic missile strike was incoming and to take immediate shelter. The alert was sent by mistake and was rolled back 38 minutes later. Citizens and guests of Hawaii were sent into a panic by this alert and caused numerous investigations into how a mistake of this magnitude could have been made. The cause was ultimately determined to be a bad user interface. The options to send out the alerts, including live and test alerts from the Hawaii Emergency Management Agency were many, bundled closely together, and had little contrast from each other. Hick’s law has been violated as a decision to send a test alert took too long as there were too many choices to make in one screen.

Which and When Should We Consider Each Law

Unlike the laws of gravity and thermodynamics, Fitts’ and Hick’s Laws can be moved and broken if it is the right place. Often one cannot place all the elements we need close together or separate out choices that users can interact with. One reason to use one over the other is the users understanding or mastery over the interface or process. To help us understand the differences we will refer to Logan, Ulrich, and Lindsey’s study (2016) in how users of varying types interacted with keyboards and typing tests. Here we will go over that experience with a system that can overcome the limitations of Fitts’ and Hick’s Laws.

In this study it was concluded that those who use a standard typing technique using the QWERTY keyboard layout can type faster and more consistently than those who use a nonstandard technique or use less fingers than the standard model. If we study a standard QWERTY keyboard, we are found with many keys that are very close together and are often the same size and dimension. Also, many keys that are commonly used together are spaced away from each other.

In studying this interaction and why it’s used to measure Fitts’ and Hick’s law, we need to understand that using more fingers to find a key is a complication of Hick’s law. Standard typists use all ten of their fingers to interact with a keyboard, while nonstandard typists use less than 10. According to Hick’s law those who use less than 10 fingers to type on a keyboard should be faster at typing a key as they have less choices to interact with that key. The inverse, however, is true. Mastery or repeated interaction with a system, even if it has a lot of choices, makes users faster with the intended system.

This is the case because with practice individuals learn that certain fingers play certain roles when interacting with systems. One finger oversees certain letters, and when using all those fingers, typists using a standard finger layout can outperform nonstandard typists as this mastery of which fingers are used for what role outperform those who give one finger more roles. Users naturally find a balance between Fitts’ and Hick’s law as they interact with a system more.

We can further balance our systems and user interfaces when designing it by considering how much training our users will have with a system. We do not need to remove choices from a system if the users of the system are well versed in the system. Other examples of this phenomenon are musical instruments like pianos and accordions where keys or notes are played with the same finger as they learn a new song. These instruments have many keys and choices, but users naturally find a balance between the two laws to create or reproduce music. When interacting with an interface repeatedly, users find the balance between these two laws to better help them be faster and more efficient than those who give themselves more options (fingers).

Conculsion

It is important to balance the Fitts’ and Hick’s law, however, users if given enough experience will find this balance and incorporate that into their workflow. Choices do not have to be removed if users are expected to be trained and develop mastery over specific interfaces. One does need to consider if their application will warrant enough interaction that users will naturally gain this affinity, or if design choices need to be made to help guide the user as they may be unfamiliar with the interface of do not interact with it often enough.

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