Day 48 of 150 Speed Difficulty 4/10
Fitts's law: movement time scales with log of distance/width
Quick answer
Fitts's law: movement time scales with log of distance/width. Today's question (Fitts's law) asks about a finding from Fitts, P. M. in 1954. The correct option is log₂(2D / W) — the index of difficulty — full explanation, primary source, and glossary cross-links below.
Today's question
Fitts's law (1954) predicts that movement time to a target scales with:
Reveal the answer and explanation
Correct: B — log₂(2D / W) — the index of difficulty
Fitts modelled rapid aimed movement (e.g., reaching for a button) as a noisy information channel: the time required is a linear function of log₂(2D / W), where D is movement distance and W is target width. The relationship is one of the most robust laws in psychology — it holds across mice, fingers on touchscreens, head movements, eye gaze, and underwater pointing. Modern UI design uses Fitts's law to size buttons (large is fast) and to reason about screen-edge "infinite" targets in operating systems.
About the source
Fitts, P. M. (1954). The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology, 47(6), 381–391.
Every Cognition Bible question cites a primary source — a paper, book chapter, or monograph that exists, that we can point to on Google Scholar, and whose finding the question accurately summarizes. No fabricated authority strings, no name-drops without paper-level grounding.
More from the Cognition Bible
Done with today's question? Play the FOKIQ Daily — six puzzles across six cognitive domains, free, every day.