The first experiment was conducted in San Francisco in 2012, when the state of California was considering a reform to its "three-strikes" law. Researchers showed white commuters a short video that featured a series of inmate mugshots. One version of the video reflected the total prison population: 25-percent black. The other reflected the population imprisoned under the three-strikes law: 45-percent black.
Both groups agreed that the three-strikes law was too harsh. But if the video they'd seen had more black inmates in it, they were less likely to agree to sign a petition to change it. More than half of the first group signed the petition; only a quarter of the second group did.
In other words, according to the researchers, "the blacker the prison population, the less willing registered voters were to take steps to reduce the severity of a law they acknowledged to be overly harsh."