M&P: The participants for this study were 16 healthy, right-handed male licensed London taxi drivers. The taxi drivers were compared with the scans of 50 healthy right-handed males who did not drive taxis. All of the participants had been licensed London taxi drivers for more than one and a half years. The average time spent training to be a taxi driver before passing the licensing tests fully (i.e., time on “The Knowledge”) was 2 years. All of the taxi drivers were described as having healthy general medical, neurological, and psychiatric profiles. The scans of the 50 control participants were selected from the structural MRI scan database at the same unit where the taxi drivers were scanned. Participants below 32 and above 62 years of age were excluded as were females, left-handed males, and those with any health problems. The study is an example of a quasi or natural experiment because the researchers are comparing the data of taxi drivers and non-taxi drivers. The researchers have no control of this variable as it is naturally occurring. The researchers also make use of correlation analysis as they are investigating a relationship between the brain scans and length of time the taxi drivers have been licensed. The data were collected using structural magnetic resonance imaging (MRI) which collects data about the structure or anatomy of the brain.