The next time you drive in the fog, check your speedometer. You may be speeding and not know it. That’s because–when the visual landscape lacks contrast–people perceive objects moving much slower than they actually are. A new study debuts the first convincing, quantitative explanation for this potentially dangerous visual mistake.
In 1982, psychologist Peter Thompson of York University, United Kingdom, first noticed that when two objects of different contrast are moving at the same speed, people always say the higher contrast object is moving faster. Researchers brushed off this misperception, dubbed “the Thompson effect,” as a kink in an otherwise precisely tuned visual machine. But a few years ago, Eero Simoncelli, a computational neuroscientist at New York University in New York City, and his colleagues wondered if they could explain this phenomenon using basic principles of human vision.