Aschoff and Wever

• Aschoff and Wever: found evidence for a free-running sleep/wake cycle of about 25 hours
• This suggests that light has an influence on circadian rhythms.
• This is because the absence of light (in a bunker) meant this zeitgeber could not entrain the natural cycle, suggesting this is the normal function of zeitgebers
• . However, the findings also showed that there is an endogenous pacemaker controlling the sleep/wake cycle because each participant had a regular and predictable rhythm.