Fig. 3.

Top image frames extracted from video recordings of a male infant, together with the large-displacement optical flow [94, 95]. Left infant at 69 days post-term, showing not yet fidgety movements. Right corrected age of 84 days post-term age, performing typical fidgety movements.

Bottom acceleration measured at the right upper arm of the infant within a time window of 5 s around the frames showing the optical flow. The acceleration vector is represented in spherical coordinates, i.e. radius (r), azimuth (phi) and polar angle (theta). For better readability, the means of r, phi and theta have been removed