Are biological cycles lasting around 24 hours, like the sleep wake
cycle, ehich is usually facilitated by checks and regular events
There is a free running cycle controlled by an
endogenous pacemaker working as a body clock
Another circadian rhythm is body temperature, rising and declining
as an indicator of metabolic rate, 4a.m. being the lowest point
Siffre 1975 spent 6 months in a cave with no
external cues as to time. Artifical lights would
come on when he moved and was awake but
gave no clue to whether it was light outside. His
sleep wake cycle ranged between 25-30hrs.
After 179 days had passed Siffre thought only
151 days had passed. This suggests human
body clocks do keep fairly reliable sleep/wake
cycle that on average very close to 24 hours
Could be an issue with this study in that the use of
artifical light is known to influence the circadian
rhythms. This means that the sleep/wale cycle is a
result of a combination between endogenous
pacemaker and exogenous zeitgeber
Aschoff and Weber; undergroud WWII
bunker, participants had no social or
enviromental cues, showed circadian
rhythm of 24/25 hours some up to 29
Folkard et al. 12 participants in a cave for three weeks, agreed to 11.45pm bedtime
and get up at 7.45 am, the clock started at 24 hours as normal and then speeded up to
22. All participants kept up at first but inly one was able to adapt to 22 hours. the
internal rhythm cannot be entrained by and external cue of less than 24 hours
Case study; man blind form birth had acircadian
rhythm of 24.9 hours despite clocks and social cues
Flawed methodology; Czeisler et al (1999) abl to adjust paricipants
circaidan rhythms in the range 22-28 hours with dim light
Individual differences; 1. cycle
length can vary 13-65 hours
(Czeisler) 2. Cycle onset
(duffy) morning people (6am to
10pm) evening people (10am
to 1pm)