Core principle

FCE is based on a simple principle:

functional change is more meaningfully detected by comparing a person to their own normal range than by comparing them to population averages.

This does not eliminate uncertainty. It makes the comparison more personally relevant, more fair, and more sensitive to change over time.

What FCE measures

FCE measures short-task execution under time and attention constraints. Depending on the task, this includes:

• reaction speed
• response control and inhibition
• attention under divided load
• motor precision and consistency

FCE measures functional signals. It does not measure cause, diagnosis, intelligence, knowledge, or character.

The model: signal → comparison → interpretation

FCE works in three layers:

1. Signal: the instrument records observable performance such as reaction times, errors, hits, misses, and variability.
2. Comparison: those signals are compared to the person’s own baseline, not to an outside norm.
3. Interpretation: the result is presented as a structured signal of relative position, not as a diagnosis or verdict.

This matters because the output is not “reality.” It is a comparison derived from measured performance.

What a baseline is

A baseline is not a single fixed value.

It is a distribution of a person’s typical performance across repeated sessions. In practice, FCE builds that reference from multiple sessions and uses both central tendency and variability to define the person’s normal range.

A stronger baseline comes from repeated use under reasonably consistent conditions.

Why baseline-relative measurement matters

• Fairness: people differ naturally; baseline-relative comparison reduces overreliance on population norms.
• Sensitivity: deviation from personal normal can be visible even when absolute performance still appears acceptable.
• Practicality: the reference is built from repeated sessions on the same device and input style.
• Clarity: the result becomes a signal of change, not a label placed on the person.

What FCE does not try to do

• FCE does not infer why performance changed.
• FCE does not determine whether the cause is sleep, stress, illness, medication, distraction, recovery, or anything else.
• FCE does not convert performance into diagnosis, legal status, or moral judgment.

FCE shows that execution changed relative to baseline. It does not claim to explain the cause of that change.

Why trends matter more than single sessions

A single session is a noisy signal. Repeated sessions form a pattern.

This is why FCE is designed for repeated comparison over time rather than one-off interpretation. Trends, recurrence, and consistency are more meaningful than isolated results.

The instrument is strongest when used as a structured history of comparison, not as a one-time verdict generator.

Refusal is part of the concept

FCE may refuse to produce a usable comparison when session quality is too low.

• too little valid data
• too much noise or execution failure
• conditions that make interpretation unreliable

Refusal is not a failure of the user. It is part of the instrument’s integrity.

Next reading

After this page, continue with:

• Scope & Limits — what FCE is not and what it cannot do
• How to Use — how to build baseline and run checks properly
• How the tests work — what each task measures