Research method

Quasi-experiment

where participants are not randomly assigned to conditions but are instead placed into pre-existing groups based on a naturally occurring variable. This method is often used in psychology when variables such as occupation or experience cannot be ethically manipulated.

used to examine differences in brain structure using strong magnetic fields. for example hippocampus

memory
spatial memory
navigation

Maguire et al 2000

To investigate the effect of spatial navigation on size of hippocampus

Quasi correlational experiment
single blind (the researcher analyzing scans did not know whether they belonged to a taxi driver or a control).
Participants: 16 right-handed male London taxi drivers and 50 right handed male non-taxi drivers (control group)
Methods:
Taxi Drivers had completed the "Knowledge" test and held their licenses for at least 1.5 years.
placed in MRI and compared
Voxel-Based Morphometry (VBM) measured the density of grey matter in the brain.
Pixel Counting calculated the hippocampal area in MRI images.

Taxi drivers had larger posterior hippocampi and smaller anterior hippocampi compared to controls.
Correlation: The size of the posterior hippocampus increased with the number of years driving a taxi
This suggests that the hippocampus adapts to environment
posterior hippocampus involved in using previously learned spatial information
the anterior hippocampus linked to learning new spatial layouts.

This shows how a quasi-experimental method can be used to study the relationship between brain structure and behaviour in real-world settings, where manipulation of the independent variable (becoming a taxi driver) would not be possible.