Supplementary material from "Asymmetric Playback Speeds for Ascent and Descent Phases Produce Natural Jump Impressions"

Judging how natural others' jump motion appears is crucial for estimating the physical states. While previous research on motion perception has typically assumed jump motions have physically symmetrical trajectories between ascent and descent phases, the human visual system exhibits asymmetry in motion perception across the phases. If naturalness judgments depend on the perceptual symmetry of the jump trajectory rather than its physical symmetry, naturalness should peak when trajectories are physically asymmetric. To test this, we presented jump motions with independently modulated phase playback speeds to participants for naturalness evaluation. Results showed that naturalness peaked when the ascent was physically faster than the descent. The asymmetry between the phases was observed regardless of the jumper's form, occurring in both human-shaped and scrambled displays. These findings suggest that the perceptual—rather than physical—symmetry of the trajectory serves as a reference for naturalness.