"The experimenters used functional magnetic resonance imaging (fMRI) to scan the brains of Harvard and other Boston-area students while showing them pictures of other college-age people whom the researchers randomly described as either liberal northeastern students or conservative Midwest fundamentalist Christian students.
The categories were a ruse. The pictures were actually downloaded from an online dating website and randomly assigned to the two groups (which were an invention of the researchers), with each group holding similar racial and gender mixes.
The experimental participants, however, thought each person pictured really was from one group or the other because the experimenters contrived demographic information about each photo; this information was randomly reassigned to different pictures with each new experimental subject. The participants, then, were confronted with pictures of people who had randomly generated but coherent cultural and political identities already attached to them."