An action is programmed in full before it is launched

What it is

Before a finger or arm actually starts moving — a single tap, a throw, a continuous handwriting stroke — the brain has already packaged the whole timing, direction, and force profile into one complete instruction, called a motor program. Motor program theory holds that the execution phase merely releases this pre-assembled instruction in sequence; it doesn't decide what to do next on the fly while the movement is underway. This is often misread as "movement is a frame-by-frame decision process" — the opposite is true: the faster, shorter, and more practiced a movement is, the closer it comes to handing the entire trajectory to a program that was fully specified in advance, with no further decision-making during execution.

Why it happens

The evidence comes from movements too fast to allow on-the-fly decisions. Getting visual information from the eye through sensory processing, comparison, and back out as a new motor command takes a minimum amount of time; yet many fast actions — a brief tap, a throw, a quick handwriting stroke — finish in less time than it takes that loop to run once. If a movement is shorter than the time feedback would need to matter, the only way to explain its accuracy is that direction, force, and timing were all fixed before execution began, with execution simply releasing the plan rather than depending on information relayed mid-movement. This is also why patients with severely impaired proprioceptive input can still produce movements with correct temporal structure: the program itself doesn't need continuous sensory input to run — sensory input mainly helps set the parameters beforehand or check the outcome afterward, not steer the movement while it's happening.

Studying it

The standard approach gives participants a task fast and brief enough that, in principle, there's no time for online correction, then uses electromyography to record when muscle activation begins relative to when the limb visibly starts moving — if a whole sequence of muscle activations is already ordered to match the final trajectory before the movement is visible, the instruction was clearly packaged and released as a unit. A second paradigm cuts or delays visual feedback and checks whether accuracy is barely affected: if removing feedback doesn't noticeably hurt precision, the movement was never depending on feedback during execution in the first place. Typical dependent measures include the preparation latency before movement onset, how far ahead of movement onset EMG activity begins, and the accuracy difference between feedback-present and feedback-absent conditions.

Where it stops holding

This account is about short, fast, well-practiced movements — it doesn't apply to long, slow movements that allow mid-course adjustment, which mix in feedback-based correction during execution and aren't purely pre-packaged releases. Also, "programmed in advance" doesn't mean "unchangeable": a program can still be replaced or cancelled before it actually launches, though doing so takes extra processing time. Being pre-programmed only means that once execution begins there's no more on-the-fly deciding — it says nothing about how much room for change exists in the window before launch, or how long that window lasts.

Related

• Same group: A8.05.2 Movement complexity increases the preparation time needed to program it · A8.05.3 A launched action has a non-cancelable window · A8.05.4 Cancelling an already-programmed action itself takes time and carries a cost · A8.05.5 Changing the target inside that window guarantees a mis-hit
• Nearby: A8.06 Open-Loop Control · A8.23 Stages of Motor Learning
• Search terms: motor program · feedforward control · motor programming