Maguire et al.

what was the background for Maguire?

In some species, hippocampal volumes (plastic as brain develops) enlarge specifically during seasons when spatial ability is greatest; i.e. animals which migrate or store food for the winter. ​

This suggests that the hippocampus is plastic as it changes & develops to adapt to different situations & experiences. Spatial awareness is developed.

what was the aim?

to investigate if the hippocampus was involved in storing spatial memory in humans, and was plastic in adult humans, as had been found in research on small mammals and birds. 

what was the method, why?

quasi exp bc IV is not being directly manipulated by the researcher; already taxi drivers

why were taxi drivers used, why specifically London taxi drivers?

As observable changes to the Hippocampus were likely to require extensive learning, and therefore would require a lot of participants’ time and resources, they decided to compare the volume of the hippocampus of individuals who had had to undergo extensive navigational training as part of their job, and individuals who had not. They decided to use London taxi drivers because they undertake a course called ‘The Knowledge’.

what were the IV conditions?

taxi drivers vs non-taxi drivers

what was the DV

changes to volume of hippocampus

what sampling method was used?

self-selected/volunteer

What brain imaging technique was used?

MRI

How were brain scans analysed?

voxel-based morphometry (compared to control group) & pixel counting

What are the 2 variables measured for the correlation in the study?

length of time taxi-driving & brain size

Where was the hippocampul volume greatest for the non-taxi drivers?

anterior

• no other brain diffs

• greater spatial memory may result in less capacity to store new spatial memory (e.g. Ldn taxi drivers may be so used to Ldn, they struggle learning routes outside of it)

outline the sample and evaluate it

outline the procedure

The data was collected using magnetic resonance imaging (MRI) which collects data about the structure of the brain. It was analysed using two techniques:

• Voxel based morphometry - an automatic procedure that "normalises" the scans of a template to elimnate overall brain size as an extraneous variable & then identifies differences in grey matter volume in diff regions of the brain. (shrinks brain in proportion, using template to observe vol of grey matter)

• Pixel counting - compared the vol of anterior body & posterior section of the taxi driver & control ps' hippocampi. These regions are divided into slices. On each slice, the analyst traces around hippocampus, a grid is placed over the area, then the analyst counts no. of pixels in hippocampus.

  • imgs analysed by one person experienced in the technique & blide to whether the scan was of a taxi driver or control & VBN findings - no researcher bias, increases internal val

This procedure allowed total hippocampul volume to be calculated 

what are the ethical issues of using an MRI?

• MRIs are relatively harmless, consent was also given to take part in study & have MRI scan

• could cause psychological distress if ps is claustrophobic/not keen on loud sounds as MRI's are loud & small

outline the results of the study

From the graph, the 2 correlations found:

• the longer the time spent as a taxi driver, the larger grey matter vol in posterior hippocampus - positive correlation

• the longer the taxi driver, the smaller the volume of grey matter in the anterior hippocamus (negative correlation)

what conclusions were drawn?

• the hippocampus is plastic in adults

• the posterior hippocampus functions as a store for spatial memory

• posterior hippocampus may be larger in taxi drivers as they had more navigational experience, and posterior hippocampus is used for spatial memory

• extra grey matter vol in posterior hippocampus may have come from anterior hippocampus

evaluate the research method and technique

• quasi exp - allows variable to be studied that cannot be easily controlled (e.g. long-term experience of using spatial memory - using taxi drivers' experience was a convenient way to assess the effect of spatial experience

• quasi exp do not allow causal conclusions as ps are not randomly allocated to conditions. Other characteristics unique to taxi drivers may explain diffs in hippocampul vol (e.g. taxi driving is a v social job - talking to people all day may have an affect on hippocampul vol, however matched ps design was used, so this may have been overcome

evaluate reliability

• using MRI to measure brain volume is a standardised technique conducted in a highly controlled env & conditions - creates consistency - reliability & replicability

• only one person counted pixels, results were not cross-checked