Fitts's law, Hick's law and the Gestalt laws
Fitts's law (reaching a target), Hick's law (choosing among n options) and six Gestalt laws (how the eye groups things), applied to layout choices.
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Fitts's law: what is it?
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The time to reach a target with the pointer grows with the distance to travel and shrinks as the target gets larger.
In its usual form, T = a + b·log2(D/W + 1), where D is the distance, W the target's width, and a and b are measured. The logarithm means doubling the size does not halve the time.
At the same distance, a button grows from 40 to 80 px wide. What does Fitts's law predict for the pointing time?
- It falls, though not by half
- It is halved, as the width is doubled
- It does not change: only distance matters
- It rises, a larger target is harder to aim at
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It falls, though not by half
Size enters through a logarithm: the gain exists but is diminishing. Doubling a large target gains less than doubling a tiny one.
The six Gestalt laws covered here: proximity, similarity, …, …, figure-ground and ….
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The six Gestalt laws covered here: proximity, similarity, continuity, closure, figure-ground and common region.
These laws describe how the eye organises what it sees into groups and shapes before even reading. A designer uses them to show what belongs together.
Hick's law: what is it?
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Decision time grows with the number of choices, as the logarithm of that number: doubling the choices adds a nearly constant amount, not twice the time.
It is written T = a + b·log2(n + 1). It assumes the user already knows the options: when they must scan an unfamiliar list entry by entry, time grows rather in proportion to its length.