Figure 1. Experimental design.

The subjects were trained on a modified version of a serial reaction time task. Four colored response buttons were positioned at distinct spatial locations and the subjects had to press on the response button matching the color shown on a computer screen. The subjects were intensively trained on a fixed eight-item sequence (Blue-Yellow-Green-Red-Yellow-Blue-Red-Green). They were asked to use their left hand for the blue and green buttons and the right hand for the red and yellow buttons. The task involved a sequence of ample and uncommon movements (e.g., crossing arms, pronated forearm, flexed and extended hand) that would be unambiguously recognized if replayed during sleep.