The aim of the study was to see whether the brains of London taxi drivers would be somehow different as a result of their exceptional knowledge of the city and the many hours that they spend behind the wheel navigating the streets of London.

The participants for this study were 16 right-handed male London taxi drivers. The taxi drivers were compared with the MRI scans of 50 right-handed males who did not drive taxis. In order to take part in the study, the participants had to have completed the "Knowledge" test and have their license for at least 1.5 years. The controls were taken from an MRI database. The sample included a range of ages so that age would not be a confounding variable.

The study is correlational in nature as the IV is not manipulated by the researcher. The researchers were looking to see if there was a relationship between the number of years of driving a taxi and the anatomy of one's brain. It was also a single-blind study - that is, the researcher did not know whether she was looking at the scan of a taxi driver or a control.

The data from the MRI was measured using two different techniques: voxel-based morphometry (VBM) and pixel counting. Voxel-based morphology (VBM) was used in this study to measure the density of grey matter in the brain. Pixel counting consists of counting the pixels in the images provided by the MRI scans in order to calculate the area of the hippocampus.

There were two key findings of the study. First, pixel counting revealed that the posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects and the anterior hippocampi were significantly smaller.  VBM showed that the volume of the right posterior hippocampi correlated with the amount of time spent as a taxi driver. No differences were observed in other parts of the brain. Maguire argues that this demonstrates that the hippocampus may change in response to environmental demands.

How does this relate to localization of function?  It appears that the posterior hippocampus is involved when previously learned spatial information is used, whereas the anterior hippocampal region may be more involved during the encoding of new environmental layouts.

• The study was a quasi-experiment, so no cause and effect relationship can be established. The researchers were unable to manipulate the independent variable; it was naturally occurring.
• The brain scans were coded so that analysis could be done blindly - that is, the researchers did not know which brain scan belonged to which participant in order to avoid researcher bias.
• Some might argue that those with larger hippocampi might be more spatially talented and thus chose to be taxi drivers; however, this is disproven by the correlation between the size of the hippocampus and the number of years driving.
• You cannot argue that the MRI has low ecological validity because the participants were not asked to do anything while in the scanner.  They simply had their brain anatomy measured.
• Although the study appears to have sampling bias, it is a reality that the vast majority of London cabbies are male.  However, it still does make it difficult to generalize the findings.
• The study is ethically sound as the MRI does not pose any health risks to the participants and all gave consent.

Eleanore Maguire has done a lot more research than the study above.  The following presentation by Maguire looks at the role of the hippocampus - as well as other aspects of memory.