Figure 4.

Simulations of phase advance shifts in 2-h increments between the original phase position (A₀) and an 8-h phase advance (A_-8) of sleep onset. As in Figure 3, the shifts are supposed to be independent from each other. S (filled circles) and R (open circles) are represented in the lower panel, the resulting SP functions (open squares) in the upper panel. The direction of the shifts and corresponding changes in the SP function are indicated by arrows. In all simulations an 8-h sleep episode begins at a given point A_n (indicated by horizontal hatched bars). The effects of the advance shifts on SP are described in the text.