Figure 3. Subdivision of sleep states by velocity.

States of sleep were subdivided into high velocity states (i.e. transitions and fluctuations) (a), and slow states (i.e. stable clusters) (b), by a heuristic velocity limit. Points are colour coded according to velocity (right side: colour bar legend: arbitrary velocity units). Comparison of the manual classification (c) with automatic probability based classification (d) for a whole night data set for one representative subject is shown. Colour coding: WAKE (red), NREM stage 1 (yellow), stage 2 (green), stage 3 (blue), and REM sleep (magenta).