An optimal path is not necessarily the most legible
Aliases: legibility efficiency trade-off · human-aware motion planning · predictable versus legible motion
What it is
The efficiency–legibility trade-off arises because a path minimising distance, time, or energy need not reveal its goal early. Efficient motion optimises robot cost; legible motion also values observer uncertainty and may introduce a small deviation, postural cue, or velocity change.
Why it happens
When candidate goals share an initial shortest-path segment, efficiency delays distinguishing information until the branch. People wait for evidence, begin collaboration late, or avoid the wrong side. A legible path exchanges modest robot motion for information gain. If reduced human waiting and conflict exceed detour cost, whole-system efficiency can improve.
Studying it
Distance-optimal, legibility-optimised, and compromise paths can be compared for the same goal. Goal-recognition curves, coordination onset, conflicts, energy, and end-to-end completion expose the trade-off. Both local robot cost and joint-system cost should be reported. Goal layout and strategy familiarity alter the result and belong in the model.
Where it stops holding
Motion need not become a performance when nobody is nearby, the goal is unique, or energy is severely constrained. Optimisation against the wrong human inference model can produce strange or misleading gestures. Safety dominates legibility, and an explicit display may cost less than a large detour.
Applying it
- Compare candidates using total task cost, including waiting, erroneous action, and avoidance rather than robot travel alone.
- Add diagnostic motion only where ambiguity affects coordination or safety; return to efficient motion elsewhere.
- Measure recognition lead against added time and energy across goal layouts, then choose the smallest deviation meeting safety and coordination criteria.
Related
- Same group: X2.02.1 A trajectory itself communicates the goal · X2.02.3 Hesitation and deceleration can communicate yielding
- Adjacent: X2.05 Predictability and discontinuity in motion · X4.04 Shared control
- Search terms:
efficiency legibility trade-off·trajectory optimization·human-aware motion planning