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Why is it harder the farther away? How does Fitts' law explain the effect of target distance on speed?
In our daily digital operations, whether we are clicking buttons while controlling a mouse or sliding our fingers on a touch screen, the distance and size of the target will directly affect the efficiency of performing tasks. This phenomenon is due to the existence of Fitts' law, which explains a core law of human movement.
Fitts' law was originally proposed by psychologist Paul Fitts in 1954. Its core idea is that the time required to quickly move to a target area is a function of the ratio of target distance to target width. Specifically, the greater the distance, the more difficult it is to contact a relatively small target. Research shows that this principle applies not only to human hand movements, but also to movements of other body parts such as feet or heads.
"The depth and distance of the target will directly affect the selection time."
Basic principles of Fitts’ law
In Fitts' law, the most important indicator is the difficulty index (ID), which is used to quantify the difficulty of the target selection task. This index is calculated based on the ratio between distance (D) and width (W). The greater the distance, or the smaller the width of the target, the longer it will take to complete the task. This means that choosing the difficulty of a task depends not only on the distance, but also on the accuracy of the target.
Two-stage moving process
Fitts' law divides the human movement process into two stages:
- Initial Movement: Move quickly but imprecisely toward the target.
- Ultimate movement: Slower but more precise, designed to reach targets with precision.
In the first stage, the effect of distance is most obvious. You can quickly close the distance, but fine-tuning near the target takes more time and effort. Therefore, for tasks of the same difficulty, the impact of distance on overall task completion time will exceed the impact of target size.
"Fitts' law has been shown to be valid in many situations, even in the context of different movements and behaviors."
The impact of design and interface
Based on Fitts' law, a well-designed user interface (UI) should take into account the size and location of the target. A common design strategy is to make objects (such as buttons) as large as possible, which makes them easier for users to operate. In addition, gathering frequently used functions together and placing them at the edge of the screen can maximize user operation efficiency.
For example, in the Mac operating system, the menu bar is always located in the upper left corner of the screen. This design allows users to effectively click on the menu while moving the mouse quickly. In the Microsoft Windows system, the "Start" button is placed in the lower left corner, which also uses edge strategies to simplify user operations.
The challenge of a new perspective
Many studies have shown that the application of Fitts' law is not limited to traditional 2D environments, but also extends to 3D motion and time target selection. Traditionally, Fitts' law only considers the placement of targets in space, but its core guiding principles still apply when we are faced with targets such as those that flicker or move.
"Whether it is in space or time, the difficulty of selecting a target can be improved by understanding Fitts' law."
Conclusion
Whether it is to enhance work efficiency or improve user experience, it is crucial to have a deep understanding of Fitts’ Law and the design implications it brings. However, the fact that each person perceives and responds to distance and purpose in a unique way not only makes us reflect on the nature of design, but also makes us think about how you might apply this principle in your own work or life.
