Pointing usually comprises a fast ballistic stroke and slower corrections

What it is

The submovement model treats target acquisition as a rapid, approximately ballistic initial stroke toward the target, followed by one or more slower feedback-driven corrections into the hit area. It explains why pointing trajectories and velocity are often not a single smooth movement, and why target width primarily affects the final stage.

Why it happens

The first movement quickly covers most distance but cannot reliably stop at the endpoint because sensory and motor noise remain. Visual and proprioceptive feedback estimates residual error after the stroke and triggers smaller corrections. Narrower targets or larger initial error require more correction. Repeated proportional reduction of remaining error is one mechanism for Fitts's logarithmic relation.

Studying it

Capture high-frequency pointer or hand trajectories and analyse velocity peaks, pauses, reversals, and endpoints to separate initial and later submovements. Vary distance, width, feedback delay, and device, then compare phase duration and correction count. Total reaction time alone hides which phase a design changed.

Where it stops holding

Submovement segmentation is an idealised analytic model; trajectories are not always clearly separable, and skilled users, automatic gain, or complex paths can alter form. Drags, tracking, and feedback-deprived action have other control structures. A velocity trace alone does not reveal subjective strategy.

Related

• Same group: B1.16.2 Correction count rises with relative ballistic endpoint error · B1.16.3 Proportional error reduction per correction yields a logarithmic time relation · B1.16.4 Enlarging a target primarily shortens correction, not the ballistic phase · B1.16.5 Without visual feedback, correction cannot occur and movement becomes ballistic
• Nearby: B1.01 Fitts's law · B1.05 Steering law
• Search terms: submovement model · ballistic movement · endpoint correction