How Science Works Biological Approach
| For this section you need to be able to:
a Describe and evaluate twin and adoption studies as research methods. b Describe PET and MRI scanning techniques. c Identify, describe and apply the following terms: i alternative, experimental and null hypothesis Note: with regard to inferential tests, no calculations will have to be carried out in the examinations and formulae do not have to be learnt. d Describe and evaluate, including strengths and weaknesses, the use of animals in laboratory experiments in the biological approach. e Evaluate the use of animals in experiments in terms of credibility, ethical and practical issues. f Evaluate the use of laboratory experiments in terms of validity, reliability and generalisability. |
Twin and Adoption Studies
Both these methods are designed to separate nature from nurture. Twin studies change the genes and keep the environment steady, whereas adoption studies keep the genes steady and change the environment.
Twin Studies
Twin studies compare the amount of behavioural similarity between 2 types of twins.
Mono-zygotic (MZ) twins are genetically identical as they both developed from the same egg. Di-zygotic (DZ) twins only share 50% genes so are as genetically related as ordinary siblings.
Both types of twin will however share very similar environments as are born at the same time to the same family so will be treated the same. Any differences in the amount of behavioural similarity shared by each type of twin must therefore be due to the difference in genetic makeup. So if the behaviour of MZ twins is more similar than the behaviour of DZ twins we assume it is because they are genetically identical and therefore behaviour is a product of nature, not nurture.
Sometimes MZ twins are separated at birth and raised in different environments. They can be traced and tested for behavioural similarities to each other. Similar behaviour is therefore likely to be due to genetic influences. These cases though are quite rare.
Twin studies provide a good natural experiment as nurture is kept constant whilst genetic makeup varies so any differences between twins can credibly be assumed to be due to nature. However it is possible that twins used in research often answer advertisements, therefore they are a volunteer sample, meaning that they might only represent a certain type of person rather than be truly representative. It could be argued that MZ twins, because they look the same, are in fact treated more like each other than DZ twins who don’t look the same, therefore MZ have more similar environments too making it hard to draw conclusions about nature nurture.
Adoption studies
An adoption study tracks the behaviour of children adopted away from their biological parents at a young age. It looks for similarities between the child and their biological parents and their adoptive parents.
If adoptive children are more like their biological parents then we attribute the behaviour to nature – it is in the genes, but if they are more similar to their adoptive parents then it is due to nurture.
These studies tend to be quite ethical because there is no direct manipulation of the participants, the adoption occurs naturally so the psychologists simply track and measure behaviour. (sometimes this can even be done through the use of secondary data). However In practise adoption agencies try and place children with families similar to their birth family; this means that there is not a complete change of nurture, so it may overestimate the role of nature in causing any similarities between the children and their birth parents.
Sometimes MZ twins are separated at birth and raised in different environments. They can be traced and tested for behavioural similarities to each other. Similar behaviour is therefore likely to be due to genetic influences. These cases though are quite rare.
PET and MRI Scanning Techniques
Brain scanning techniques are a major advance in biological psychology. They allow researchers to examine the brains of living people and draw conclusions about the relationship between brain structure/activity and behaviour. There are 2 basic types of scan: functional e.g. PET and structural e.g. MRI. Structural scans take detailed pictures of the structure of the brain and functional ones show activity levels.
Magnetic Resonance Imaging (MRI) Scans
These are a form of structural scan that shows a picture of the brain inside the skull so that specialists can identify any areas of damage or tumours.
They allow a real, living brain to be seen without having to cut into the head of the patient.
Patients are placed in a very large scanner that sends a strong magnetic field through their head. The magnetic field causes the nuclei in hydrogen molecules in the brain to spin in a particular way, and this is picked up by the scanner. Because hydrogen concentrations vary in different parts of the brain, it is possible for the scanner to produce a detailed image of the brain based on the amount of hydrogen molecules it identifies in different areas.
Positron Emission Tomography (PET) Scans
PET scans are functional scans that show images that can illustrate how the brain is working during different tasks.
By identifying areas that are not working properly, doctors can see areas that are damaged or areas affected by tumours.
Patients are injected with water or glucose that has been labelled with a radioactive tracer substance. The substance travels around the body until it reaches the brain where the brain uses up the water or glucose as energy and the tracer begins to decay. As the tracer decays, it gives off positrons, so the more energy being used in different areas, the more positrons are being emitted. The positrons collide with electrons and form gamma rays that are picked up by the scanner and show the amount of energy being used by different areas of the brain
The biological approach is perhaps the most scientific of all the approaches in psychology and so it relies heavily on experimental methods to build its knowledge base.
At its most basic this will involve comparison between a control group who have experienced no direct manipulation of the independent variable with an experimental group who have.
The laboratory experiment is often used with animal subjects because of the level of control that can be applied to animals. Such controls cannot ethically be applied to human participants.
The Quasi (or natural) experiment is frequently used in this approach to test the effects of a variable that cannot be directly manipulated by the researcher. This could be for ethical reasons such as comparing the behaviour of people with some form of brain damage with a control group who do not have this damage. Or simply because it is not possible to manipulate the variable being investigated e.g. gender.
The quasi experiment has all the features of the laboratory experiment except that the independent variable occurs independently of the experiment and is not directly manipulated for the purpose of the study.
The independent variable is the causal variable; the one being tested by the research. The dependent variable is the measured variable, the one that is changed by the independent variable.
The control group is a comparison group of participants/subjects that do not experience the independent variable but are as similar as possible to the experimental group. The experimental group are the group of participants/subjects who do experience the independent variable and whose measure on the DV is compared to the control group to see if the independent variable has caused an effect.
A hypothesis is a testable prediction about the outcome of some research. The null hypothesis states no effect other than that which occurs by chance. A directional hypothesis states a specific difference of the outcome e.g. more/less faster/slower etc. (directional hypotheses are also known as one tailed) A non directional hypothesis states a difference but does not specify which direction. Non-directional hypotheses are also known as two tailed
Laboratory experiments with animal subjects are essentially the same as with human participants. An independent variable is manipulated in one condition and its effect is measured on the dependent variable and compared to the dependent variable in other conditions in order to establish cause and effect. All other variables are controlled and held constant across the conditions.
Animals are used when the independent variable is invasive and it would be unethical to apply it to humans e.g. administering a drug to see its effect on behaviour or to gain the maximum control over variables other than the independent variable/dependent variable e.g. animals can have all aspects of their lives controlled for the purpose of the experiment and you can breed animals for the experiment that are genetically similar so as you can remove the chance of individual differences affecting the results.