The spectral indices show the transition from local quality to pattern structure. The Spectral Centroid reads the concentration of energy across frequencies: SEQ 4, made of pure sustained movements, remains the lowest and most continuous profile (1.1 Hz), whereas the mere presence of an accent is enough to shift the gesture toward faster components. In the 4-movement sequences, however, the Centroid tends to level out at high values: motor density increases for all configurations and the index is no longer sufficient to distinguish them.

This is where Spectral Irregularity comes into play, describing the jaggedness of the spectrum. Its increase in the 4-movement sequences indicates that it is not only the quantity of energy that changes, but also the way energy is internally organized. SEQ 9 reaches the maximum because it combines accents at the extremes and central sustained movement, generating a more articulated spectral structure; SEQ 12 remains lower because the block logic produces a less varied distribution. The spectral signature no longer speaks only of the single gesture, but of its temporal arrangement.

These indexes measure order, predictability and internal complexity. The Spectral Entropy isolates SEQ 4 as the most ordered configuration: in pure sustained movements, energy remains concentrated on a few components and the movement appears more continuous. The Sample Entropy, by contrast, increases with event density: when movements become four, the signal is richer and less predictable in detail.

The most important result is Spectral Dominance. Dominance is low when energy does not gather around an underlying frequency and becomes higher in sequences with cyclic organization, especially SEQ 7 and SEQ 8. These two configurations build a recognizable pulse because they alternate accented and sustained movements regularly. It is the first kinematic signature of the greater regularity and fluidity perceived in cyclic alternation sequences.

The jerk indices clarify that physical fluidity does not coincide with the mere absence of abrupt movement. The MeanAbsoluteJerk measures absolute discontinuity: SEQ 4 is the most continuous pole, SEQ 2 the jerkiest pole and the mixed sequences lie in between. In complex sequences, absolute jerk converges on high values because four gestures compressed into five seconds accumulate discontinuity.

The Jerk Metric introduces a finer reading: by normalizing jerk by velocity, it shows that pure sustained movement can require high relative control. Fluid movement is therefore not passive, but implies constant micro-corrections to maintain continuity and release. The ExcursionRange remains stable, indicating that spatial amplitude is not what explains the differences. The signature of fluidity arises from the relationship among continuity, control and execution density.

Temporal indices distinguish local fragmentation from rhythm proper. The Peak Count is highest in SEQ 2: two accents produce many micro-peaks because the impulse is internally fragmented. This means that having many peaks does not automatically mean having a more regular rhythm. The Duty Cycle completes the picture, showing how long the gesture remains above its own mean velocity: SEQ 4 maintains more continuous activity, whereas SEQ 2 works through concentrated impulses.

The Dominant Frequency is the decisive index for reading rhythmic structure. In the 2-movement sequences it remains low, because the sequence is too short to stabilize a pulse. In the 4-movement sequences it increases when the pattern creates a recognizable cadence, but drops in SEQ 11 and SEQ 12, where the arrangement of accents does not produce clear cyclicity. This prepares the perceptual result: SEQ 7 and SEQ 8 are judged more regular and more fluid because their alternation makes rhythm legible.

The spatial indices serve first and foremost as a control for the paradigm. ROM_Tot remains substantially constant: the sequences do not differ because they occupy more or less space, but because they traverse that space with different dynamic organizations. This is an essential methodological point, because it rules out the possibility that perceptual judgments depend on accidental variations in amplitude.

The Path Length increases in 4-movement sequences due to greater motor density, whereas Path Efficiency describes how direct or tortuous the trajectory is. SEQ 4 is more efficient because sustained movement tends to produce a continuous trajectory; some complex sequences, such as SEQ 7 and SEQ 11, are less efficient because the transition between different qualities introduces deviations. The spatial structure confirms that the manipulation does not change the scale of the gesture, but the syntax of its traversal.

The intensity and variability indices show how energy accumulates and is distributed. The Total Velocity mainly follows density: more movements in the same interval produce greater overall activity. The Total Jerk and theAcceleration Variance, by contrast, describe the dynamic quality of energy: SEQ 4 remains the most stable and least abrupt profile, SEQ 2 reaches the highest values among the short sequences and the complex sequences sit on a high plateau.

The central result is the equivalence between local intensity and combinatorial density: two concentrated accents can produce a discontinuity comparable to four distributed movements. This explains why perceived energy remains a very robust dimension: the viewer can anchor it to immediate physical variations such as acceleration, jerk and duration of activity. Regularity and fluidity depend more on the pattern; energy remains more directly anchored to gesture dynamics.