An open-loop action does not draw on feedback once it has launched

What it is

Motor control runs in two fundamentally different modes. Open-loop control means a movement, once launched, executes from start to finish according to instructions fixed before launch — even if new sensory information comes in during execution, it isn't used to adjust the movement in progress. Closed-loop control, by contrast, continuously compares incoming feedback against the target while the movement is underway and keeps correcting course. What separates the two isn't whether a movement is fast or accurate — it's whether feedback arriving during execution actually gets used to change the movement. Open-loop doesn't mean "no feedback exists"; it means feedback either arrives too late to be used, or was never going to be used at all.

Why it happens

Whether a movement can use feedback during execution depends on which is longer: the time it takes the feedback loop to run once, or the movement's own duration. For feedback to actually do anything, it has to go through sensing, comparison against the expected state, generating a correction, and conducting that correction to the muscle — and that chain has a minimum duration of its own. If a movement finishes before that chain completes, feedback simply arrives too late to be used, and the movement has no choice but to run entirely on the parameters fixed before launch — that is open-loop control. Open-loop isn't a matter of the body refusing feedback; it's that the time window is too short for feedback to have any effect at all.

Studying it

The standard way to determine whether a movement is open-loop or closed-loop is to artificially cut or delay a participant's sensory feedback — occluding vision, or delaying its display — and compare accuracy and trajectory: if performance is barely affected once feedback is removed, that segment of execution was open-loop to begin with; if performance clearly degrades, the original execution was relying on in-flight correction. A second approach analyzes the movement's velocity profile: open-loop-dominated movements tend to show a single, smooth velocity curve without the deceleration-adjust-decelerate-again segmentation that is the typical signature of feedback correction kicking in.

Where it stops holding

Open-loop and closed-loop are rarely an all-or-nothing pair — the same movement often starts closer to open-loop and picks up closed-loop correction later on. Purely open-loop execution only holds when a movement is short and brief enough, the target is simple enough, or feedback is genuinely unavailable (anesthesia, complete visual occlusion). Judging which mode dominates a given class of movement requires comparing total movement duration against the feedback loop's own latency — not just whether a movement looks fast, or whether users report not feeling like they're adjusting.

Applying it

• For actions brief enough that feedback simply can't arrive in time to matter — a quick tap, a flick-style swipe — put the design effort into what's set before launch: target size, starting position, grip posture — rather than into visual or haptic feedback during execution, since that feedback has essentially no chance to correct anything at this point.
• Don't layer real-time in-flight correction cues onto these actions (a mid-flight trajectory-correction animation, for instance) — users can't process and use them in time, so all they add is visual load without improving accuracy; the thing actually worth optimizing is target reachability before launch.
• How to check: record the movement's velocity-versus-time curve and check whether it's a single smooth peak or a compound curve with multiple deceleration-adjustment segments. A single-peak curve signals open-loop dominance, meaning investment in in-flight feedback for that movement is essentially wasted.

Related

• Same group: A8.06.2 Fast, short movements are dominated by an open-loop component · A8.06.3 Open-loop error comes from programming precision, not execution correction · A8.06.4 Without any feedback, control has to stay open-loop, and accuracy has a fixed ceiling
• Nearby: A8.05 Motor Programming and Movement Preparation · A8.07 Closed-Loop Control
• Search terms: open-loop control · feedforward execution · motor control loop