Biological rhytms are recurring cycles of biological processes.
There are different kinds of biological rhythms, and each has a different time/length.
Ultradian Less than 24 hours
Circadian About a day
Infradian More than 24 hours (usually monthly)
The control of biological rhythms
Biological Clock - Endogenous pacemakers
External Cues - Exogenous Zeitgebers e.g. light, temperature, social cues (such as meal times)
Research into circadian rhythms
Key Study: Siffre (1975)
Aim: Siffre aimed to investigate the free running time of his sleep/wake cycle.
Method: He spent 6 months in a cave with no external cues i.e. light, clocks, tv or radio. He was wired up in order to monitor bodily functions.
Findings: At first his sleep wake cycle was erratic ranging from 13 to 48 hours. However after a while this pattern settled at 24.9 hours.
Conclusions: The circadian sleep wake cyle exists however external cues are needed in order to maintain/correct it.
Evaluation Points Conducted in a cave and so therefore lacks ecological validity.
The study fails to take into account any individual differences in circadian cyles.
Research methadology may have lacked internal validity as cave lights may have been seen to act as exogenous zeitgebers.
Research into circadian rhythms 2
Key Study: Folkard (1985)
Aim: Conducted a study to see if external cues could be used in order to override the external clock.
Method: Isolated in a cave, volunteers had to go to sleep at 11.45pm and wake at 7.45am. At first the clock ran as normal however it soon quickend so that when 24 hours had passed it was only 22.
Findings: At first the circadian cyle mathed the clock, however after a while they no longer matched and participants continued to follow the 24 hours rhythm during the 22 hour state.
Conclusions: The circadian rhythm can only be guided to a certain extent by external cues.
Evaluation Points: Larger sample compared to Siffre so results can be generalised to others.
Also conducted in a cave so lacked eco-logical validity.