White killers of African Americans in New Orleans between 1921 and 1945, nearly half of whom were policemen, insisted that they acted in self-defense, only after their victims had threatened them, often by reaching for weapons. But many of their victims were unarmed. The conventional interpretation is that white residents invoked a formulaic justification of self-defense to mask their real intention, to uphold the city's racial hierarchy. Recent studies by cognition researchers, however, suggest a more complicated interpretation—that endemic racism can influence how the brain processes information, even to the extent of causing people to see a weapon where none exists.

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