Why some gorillas go unseen

For poor multitaskers, unexpected sights are more likely to go unseen

Eat your heart out, Houdini. Average schmoes can make a gorilla-suited dude pounding his chest go poof, thanks in part to a common difficulty with focusing on distractions.

WHAT APE? A new study used video from the original 1999 “invisible gorilla” experiment, which showed people passing a basketball in a circle (a still from the video shown above, although the basketball isn’t visible in this view). Subjects asked to count basketball passes were more likely to notice an intervening gorilla if they could focus on two things at once in another lab task. Daniel Simons

People who don’t see unexpected happenings, such as a gorilla strolling by, while concentrating on a task often have difficulty with what amounts to mental multitasking, says a team led by psychology graduate student Janelle Seegmiller of the University of Utah in Salt Lake City.

Individuals who do poorly on a test requiring them to perform two mental operations at once are especially prone to an experimental effect dubbed “the invisible gorilla,” Seegmiller and her colleagues report in the May Journal of Experimental Psychology: Learning, Memory and Cognition.

Previous studies of this effect have instructed participants to count the number of times people in a video pass a basketball to one another. Nearly half of volunteers don’t notice a person in a gorilla suit walk among the players, pause for a few chest thumps and depart.

Why people counting passes sometimes overlook a wandering ape is poorly understood. Explaining this effect is no laughing matter, though, since it corresponds to real-life attention mishaps, such as drivers gabbing on cell phones who fail to see pedestrians in crosswalks or red lights at intersections.

“Some people may have enough extra flexibility in their attention to notice distractions while talking on a cell phone behind the wheel, or while counting basketball passes,” says Utah psychologist and study coauthor Jason Watson.

Previous work has shown that only about one in 40 people can operate a car safely while concentrating on a cell-phone conversation (SN Online: 3/31/10).

A flair for allocating one’s attention to different objects at the same time may help to flush out intrusive gorillas, but everyone overlooks unexpected events on occasion, cautions psychologist Daniel Simons of the University of Illinois at Urbana-Champaign. “We all have limits on our attention capacity,” says Simons, who codirected the original study in 1999 that documented the invisible gorilla phenomenon.

Seegmiller’s group first tested the ability of 197 college students, ages 18 to 35, to solve simple math problems and remember individual letters that followed each problem. After completing sets of problems, participants tried to recall, in order, the letters they had seen.

Volunteers correctly answered most math problems, which showed that they did not focus just on remembering letters.

Students then watched a gorilla video, in which two teams with three players each passed basketballs. One team wore black outfits and the other white. Participants simultaneously counted the black team’s bounce and aerial passes.

Overall, 58 percent of volunteers noticed the gorilla while counting passes. Importantly, 67 percent of those who remembered letters especially well after solving math problems spotted the gorilla, versus 36 percent of those with the poorest letter memory.

It’s not clear, Simons remarks, whether people with flexible attention control are better at noticing unexpected events in general or surprising occurrences with obvious links to what they’re already focusing on — such as a black gorilla walking among black-garbed basketball players.

Bruce Bower

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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