Two Key Studies of Hormones & Their Effect on Behaviour: Morhenn et al. (2008) & Zak et al. (2009) (HL IB Psychology)
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Key Study (Testosterone): Zak et al. (2009)
Aim: To investigate the role played by testosterone in prosocial behaviour.
Participants: 25 males (mean age = 20.8 years) of whom 44% were Asian; 36% were Caucasian; 8% were Hispanic and 12% were of other ethnicities.
Procedure: A double-blind procedure with an independent variable of two conditions:
half of the participants received testosterone in gel form (Androgel) while the other half of the participants were given a placebo. Testosterone levels were measured via blood samples during the experimental phase. The participants took part in the Ultimate Game (UG), a decision-making task borrowed from economic theory involving making decisions as to whether to donate money.
Results: The participants in the Androgel condition (i.e. heightened testosterone levels) donated 27% less money than their first, pre-experiment baseline measurement suggested. The testosterone group were also more likely to agree to share money compared to their own baseline measurements.
Conclusion: Men with heightened testosterone levels may exhibit less prosocial behaviour than those with lower testosterone levels.
Evaluation of Zak et al. (2009)
Strengths
The study sheds some light on a possible link between heightened testosterone and lack of prosocial behaviour which could be used to inform therapies for men who may struggle with aggressive or anti-social behaviour
The use of objective measures such as the blood samples increases the reliability and scientific nature of the findings
Limitations
It is difficult to determine the extent of the males’ pre-existing and post-experiment prosocial tendencies as the researchers used a snapshot design rather than a longitudinal design
Agreeing to donate or share money in an artificial environment and task such as in this study reduces the ecological validity of the study - would this be the same result if it were to be tested as a field experiment? Might other variables affect whether they donate?
Key terms:
Testosterone
Androgel
Prosocial behaviour
Key Study (Oxytocin): Morhenn et al. (2008)
Aim: To investigate the relationship between oxytocin, massage, and monetary sacrifice.
Participants: 96 students (mean age = 22.3 years, 53% female, 47% male) who were randomly allocated to one of three conditions:
The Massage and Trust group (MT) – the participants received a 15-minute back massage followed by a trust game in which each participant was a decision-maker and had to decide whether to match the donations made by another player (each had been given $10) which was measured as monetary sacrifice made per participant
The Rest and Trust group (RT) – the participants were asked to rest for 15 minutes and then to play the trust game as described above
The Massage-only group (M) – the participants received a 15-minute massage
The participants’ blood was sampled before and after the procedure to compare the pre-experiment and post-experiment oxytocin levels.
Results: The MT group showed the biggest increase in oxytocin levels (16%) than the RT group. The MT group also sacrificed 243% more money than the RT group with women showing higher levels of oxytocin and more monetary sacrifice overall than men. The M group showed no difference in oxytocin levels, possibly because they were not asked to engage in a trust game i.e. the massage alone was not enough to increase oxytocin. The RT group showed decreased oxytocin levels compared to the other two groups.
Conclusion: Massage followed by a trust game appears not only to increase oxytocin levels but also to predict the direction of monetary sacrifice i.e. increasing oxytocin levels is matched by increasing monetary sacrifice.
Evaluation of Morhenn et al. (2008)
Strengths
Using the M condition as a control group ensured that the researchers were able to demonstrate that the combination of touch and trust raised oxytocin and resulted in monetary sacrifice
Using objective measures such as MRS increases the reliability and scientific nature of the findings
Limitations
Attempting to operationalise trust in an artificial game is beset with difficulty as this is a variable which is subjective and may fluctuate according to mood or situation
The study was conducted in an individualistic culture and it could be that a collectivist culture would view trust differently
Key terms:
Oxytocin
Trust
Sacrifice
Exam Tip
Don’t forget that culture is a key evaluation point in IB Psychology. Most research is conducted in individualistic cultures so it is always good to consider how the results might have been affected if the research was replicated in a collectivist culture – or even if such replication would be possible (e.g. some cultures may not allow the procedure to be carried out as it is in the original study).
Worked Example
Extended Response Question - 22 marks
Evaluate research into the effect of hormones or pheromones on behaviour. [22]
In an ‘Evaluate’ ERQ, you need to make sure that you weigh up the strengths and limitations of either a theory, an explanation or research (which can include theories as well as studies). Here are two paragraphs to give you an idea of how to do this:
One strength of Morhenn et al. (2008) is that the participants were randomly allocated to condition (MT, RT, or M) which increases the reliability of the study as it is a control put in place to ensure lack of bias in participant-condition selection. However, a limitation of random allocation to condition is that it is always possible that participants who possess similar qualities or characteristics may end up in the same group. In the case of Morhenn et al. (2008) it could be that participants who were already predisposed to having higher levels of oxytocin and trust were allocated to the MT group. This is a limitation as it impairs the internal validity of the study as the researcher cannot then be confident that the IV has truly affected the DV.
Another strength of the procedure is that both the MT and the M groups were massaged for the same length of time which is a control that ensures that neither group received more massage time than the other. This increases the reliability of the study as it is a standardised procedure which can then be replicated to test for reliability. However, the actual massage itself could not be exactly replicated per participant, even if the same massage technique was used each time. Some participants may have received a slightly softer or more robust massage than others and it is possible that the massage therapist may have become tired as the procedure went on. This is a limitation as it would reduce the reliability.
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