Infradian rhythms

• How often do infrared rhythms occur?

  Less than one every 24 hours
• What is an example of an infrared rhythm?

  Female menstrual cycle
• What is the typical length/cycle of the female menstrual cycle?

  28 days
• Who conducted research into the female menstrual cycle?

  McClintock (1998)
• What did McClintock do?

  gathered samples of pheromones from 9 women with irregular periods (out of 29) at different stages of their cycle by sticking a cotton pad in their armpit for 8 hours. This cotton pad was then rubbed onto the upper lip of the women in a second group.
• What did McClintock find?

  that 68% of women experienced changes to their cycle which brought them closer to the cycle of their 'odour donor
• What do the findings of McClintock's study suggest?

  External factors must be taken into consideration when investigating infrared rhythms and that perhaps a more holistic approach should be taken, as opposed to a reductionist approach that considers only endogenous influences.
• What else does mcclintock's findings show about endogenous pacemakers and exogenous zeitgebers?

  They work as a blended system
• What is a weakness of infrared rhythms ? (Governed by exogenous zeitgebers)


  P) Research suggests that the menstrual cycle is, to some extent, governed by exogenous zeitgebers (external factors).

  
  

  E) Reinberg (1967) examined a woman who spent three months in a cave with only a small lamp to provide light. Reinberg noted that her menstrual cycle shortened from the usual 28 days to 25.7 days.

  
  

  T) This result suggests that the lack of light (an exogenous zeitgeber) in the cave affected her menstrual cycle, and therefore this demonstrates the effect of external factors on infradian rhythms.
• What is another weakness of infrared rhythms? (Evolutionary advantage)

  P) Evolutionary psychologists claim that the synchronised menstrual cycle provides an evolutionary advantage for groups of women.

  
  

  E) the synchronisation of pregnancies means that childcare can be shared among multiple mothers who have children at the same time.

  
  

  T) These findings indicate that external factors must be taken into consideration when investigating infradian rhythms and that perhaps a more holistic approach should be taken, as opposed to a reductionist approach that considers only endogenous influences.
• What is another weakness of infradian rhythms? (Deterministic)

  P) Research into biological rhythms is deterministic.

  
  

  E) Researching biological rhythms such as the menstrual cycle has led to a deterministic understanding of behavioural changes associated with pre-menstrual syndrome. The determinist argument has been used in court to defend women against charges of murder (Johnson)

  
  

  T ) To counter this, however, there is evidence that biological rhythms can be influenced by free will, for example Born et al (1999) found that people who will themselves to wake up earlier than usual had higher levels of ACTH in their blood (ACTH is part of the waking up cycle). Therefore, showing free will over our internal rhythms.
• What is another weakness of infradian rhythms? (Other factors affect menstrual cycle)

  P) There are also many other factors that may affect the menstrual cycle.

  
  

  E) such as stress and changes in diet and exercise. These may act as confounding variables which means that any supposed pattern of synchronisation is no more than would be expected to occur by chance.

  
  

  T) This suggests that menstrual synchrony research is flawed.