For a few minutes at APA's 2006 Annual Convention, an annual G. Stanley Hall Lecture morphed into a magic show.

University of Illinois at Urbana-Champaign psychology professor Dan Simons, PhD, projected six playing cards onto the meeting room's screen and recruited a volunteer from the audience.

"Pick one [card] and point to it so everyone can see which one it is," Simons said to the audience member as he covered his eyes and looked away from the screen.

The participant chose the queen of clubs. Simons uncovered his eyes, clicked his mouse and only five cards remained on the screen. The queen of clubs was not one of them. The audience gasped-and chortled.

So how did he do it?

While the audience focused on the queen of clubs' absence, the other cards had changed as well.

Simons's research suggests that what we actually see is very different from what we think we see. The reason we fail to detect changes in our environment is because of our need to focus-if we noticed everything around us, it would be too distracting.

"People believe that...the mind keeps track of everything like a video camera, when in reality that doesn't seem to be the case," he said, noting that instead of recording an entire scene, people tend to focus on a specific task.

Change blindness

Illustrating people's inattention is a Simons study in which an experimenter held a map and asked a random pedestrian for directions. As the pedestrian provided directions, two people-Simons and his collaborator, Daniel Levin, PhD, of Vanderbilt University-walked in between him and the pedestrian holding a wooden door.

After the interruption, the experimenter was no longer there: He was replaced with Simons-who looks markedly different and has a distinctly different voice. However, nearly 50 percent of pedestrians failed to notice that they were talking to a different person after the door passed, according to the results, published in a 1998 article published by Simons and Levin in Psychonomic Bulletin & Review (Vol. 5, No. 4, pages 644-649).

The phenomenon, known as change blindness, is shocking to most people, he said.

"Nobody would be surprised...if I told you, 'Hey look at his picture-I changed one grain of sand on a beach and nobody noticed,'" he said. "[But] it's counterintuitive that people can miss things that are substantial and right in front of them."

'Change blindness blindness'

Even when people are on the lookout for changes-and insist that they will detect errors-they still fail to find them, Simons's research suggests.

The reason for the metacognitive error, or "change blindness blindness," is simple, said Simons. People often don't believe that they are prone to change blindness, even after they've been alerted to the phenomenon.

In a 2000 study in Visual Cognition (Vol. 7, No. 1, pages 397-412), Levin and Simons had an experimenter read to participants a description of changes in a four different short film scenes-ranging from one actor alternating between wearing and not wearing a scarf to a change in actors. The experimenter then showed participants both the pre-change and post-change views and pointed out the changes. Next the participants recorded whether they thought they would have noticed the change, as well as their confidence in their response.

Nearly 83 percent of participants insisted with reasonable confidence that they would be able to detect the changes, even though only around 11 percent of participants in previous studies using the same clips detected the changes. The reason, Simons suggested, is that the original participants were unaware of where to focus their attention.

"Distinctive things, things that are unusual, things that are highly salient, don't necessarily draw attention to themselves if you're engaged in some other task," he said, noting that the audience's focus on the queen of clubs kept them from tracking the other cards.

The real world

One possible explanation for change blindness is that focus is essential to complete any task, said Simons.

"In order to function in the world, you have to be able to focus on what you're intending to do-not on other things," he said.

Yet people's overestimation of their abilities to detect anomalies can have dramatic consequences.

For instance, when people drive and talk on their cell phones they often fail to notice unexpected events-such as a motorcycle starting to turn in front of them. In fact, that is one of the most common type of motor-cycle accident, according to the Insurance Institute for Highway Safety.

"Drivers often say that they never saw the motorcycle," Simons said. "And in most contexts, motorcycles are rarer than cars-you're not looking for motorcycles, you're looking for cars."