Boston policeman Kenny Conley said he didn't see his colleagues brutally beating an undercover officer on a January night in 1995. He claimed he was too busy chasing down a murder suspect.
But the jury didn't buy it, instead concluding that he must be lying to protect his comrades. Convicted of perjury and obstruction of justice, Conley was sentenced to 34 months in jail.
New research, however, suggests most people would have missed the fight that night, and that Conley might well have been telling the truth.
In their book "The Invisible Gorilla," neuroscientists Christopher Chabris and Daniel Simons explain the phenomenon of inattentional blindness -- the failure to see "salient scenes" while paying attention to something else.
Studies have shown that it can cause a person busy counting something in front of him to miss a gorilla, and someone chatting on a cell phone to unintentionally ignore a clown on a unicycle.
It could also explain Conley's account of the 1995 incident, which inspired "The Invisible Gorilla."
For their latest study, published today in the journal iPerception, Chabris and Simons simulated Conley's ordeal in a "real world experiment," and nearly two thirds of the subjects said they saw nothing of the staged fight.
"Just because an event is emotionally significant, that doesn't mean it's going to grab our attention," said Chabris, assistant professor of psychology and co-director of the neuroscience program at Union College in Schenectady, N.Y. "Our attention seems to be captured much less by important things than we think it will."
Union College students were asked to run behind a male volunteer at night and count the number of times he tapped his head. Along the route, three other volunteers pretended to fight. At the end of the three-minute dash, the students were asked to recall how many times the "suspect" tapped his head and whether they had noticed anything unusual along the way. Only 35 percent said they saw the fight.
"Most people were very surprised that they could have missed it," Chabris said.
Similarly, about half of the subjects in another study were shown a video of a gorilla walking through a game of basketball and were shocked to discover they missed it -- an experiment Chabris and Simons published in 1999.
"People would accuse us of switching the tape," said Simon, professor of psychology at the University of Illinois in Champaign, Ill.
The gorilla experiment showed that people who are focused on one thing can miss something else as obvious as, well, a gorilla. But the researchers wanted to show that the theory held up in real-world scenarios, like Conley's.
"Lab research is great, in that you can precisely control what you're doing. But it's always good to check that it does translate," said Simons. "Everything we know about the limits of focused attention told us it should work."
And it did. Nevertheless, Chabris and Simons are instinctively surprised when their "salient scenes" go unnoticed.
"I still feel like everyone's going to notice the gorilla," said Simons, who showed the famous video to students for years. "Whenever I would show it, I'd hold my breath because I was convinced everyone would see it."
That, they say, gets to the heart of what they're studying -- the way intuitions can be deceiving. In Conley's case, the jury assumed he must have seen the assault, and therefore must have been lying.
"When somebody claims plausibly not to have seen something, they may be telling truth -- they may not be intentionally lying or obscuring," Simons said. "Based on what we know about the limits of attention, it was plausible that someone could have run past the fight if they were really focused on something else."
After a long legal battle, Conley's conviction was overturned and he's back on the force. He still maintains he didn't see the fight that night.
Ironically, when Conley was invited to watch the gorilla video with Chabris and Simons, he spotted the animal right away, Simons said.