Question about dental decomposition experiment?

Hey there, I was reading an interview with Fight Club author Chuck Palahniuk when he said, ""In college, we read about a group of people who were shown photographs of dental decomposition in various stages. The people who were shown photographs of mild deterioration and mild tooth loss increased their dental care, their dental hygiene. But people who were shown severely deteriorated mouths, hideous photographs, those people just shut down entirely. They quit brushing their teeth and flossing altogether. It actually made them worse." Does anyone know what he was talking about?
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THAT DOES NOT MAKE SENSE
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