Boundary crossing needs its own feedback, distinct from recognition-failure feedback

What it is

A hand leaving the interaction volume and a gesture not being recognized are two events for the system. If they share the same silence or the same red cross for the user, they collapse into one. Crossing the boundary needs an independent feedback signal: it can say “you are outside the volume,” and it must not be readable as “that motion is not in the vocabulary.” What must differ is the identity of the signal, not merely louder volume.

Why it happens

Recognition failure comes from the classifier: the trajectory is not close enough to a template, or confidence is below threshold. Crossing comes from geometry: the point already failed containment, so the classifier may never have run, or it ran and policy discarded the result. If both pipelines present only “no command,” users can only change the shape of the motion—repairing a class error, which cannot repair a geometry error. An independent signal has to occupy a channel that is hard to confuse with class failure: for example an out-of-volume cursor that turns into a translucent arrow with a “step forward” hint, versus a vocabulary shake or an “unrecognized” phrase on class failure. Once the channels mix (both a single “ding”), users still treat them as one fault after a few trials.

Studying it

Construct two kinds of no-command: an intentionally unlike motion inside the volume, and a canonical motion outside it. Compare shared feedback with split-channel feedback. Dependent measures are whether the next repair is stance or hand shape, spoken attribution, and attempts to first success. Add a third no-command—not yet engaged—and see whether the three signals remain separable. Do not teach “what out-of-volume looks like” in the briefing, or the test measures memory rather than signal discriminability.

Where it stops holding

An exhibit with one discrete gesture and a mat that already locks stance rarely sees crossing, so a dedicated signal pays little. Continuous scrub tasks cross often; shared silence is expensive. Users who cannot see cursor-shape changes need the independent signal on audio or haptics, or “independent” holds only for people with unimpaired vision. Localization can write “unrecognized” and “please come closer” as confusable phrases; copy is part of the channel.

Applying it

• Give out-of-volume, recognition failure, and not-engaged each a feedback that does not share modality or wording. Write it as a state table. Forbid all three as “nothing happens.”
• Out-of-volume signals should carry a direction or stance suggestion (forward, left). Recognition failure should not carry a stance suggestion, so the two are not heard as one sentence.
• Accept with two scripts: wrong gesture inside, right gesture outside. Watch whether the first repair is the hand or the place; repairing the wrong object means the signals did not split.

Related

• Same group: C4.22.1 The boundary itself is invisible; users perceive it only through whether actions take effect · C4.22.3 Without boundary feedback, users misread out-of-bounds as a system fault or a wrong gesture · C4.22.4 Actions near the boundary should receive progressive cues rather than failing abruptly at the edge
• Adjacent: C4.24 Recognition confidence and bias direction · C4.26 Distinguishing three-state feedback
• Search: boundary feedback · error differentiation · out-of-range cue