When You Don’t See What’s Visible: The Inattentional Blindness Factor & More

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Experiments mirroring a real-world case that resulted in an officer going to prison for perjury have confirmed that a trick of the mind called inattentional blindness—the failure to see something important that is clearly within your field of view—can occur under stressful circumstances on the street.

The officer’s conviction was described in detail in a book called The Invisible Gorilla, which Force Science News reviewed  [10/8/10. Click here to read it]. He’d been in foot pursuit of a shooting suspect at 0200 in Boston and had run past three fellow officers who were brutally beating a black male. In a public furor that arose over the beating, the officer insisted he didn’t see the incident even though he ran right past it.

Investigators, prosecutors, and a jury figured he was lying in a classic case of “blue silence” and he was sentenced to 34 months behind bars. They assumed that because he could easily have seen the beating, he must have seen it.

Authors of the book, behavioral scientists Dr. Christopher Chabris of Union College in Schenectady, NY, and Dr. Daniel Simons of the University of Illinois-Champaign, argue that the officer could have experienced inattentional blindness, which occurs when you are so intently focused on a particular subject or task that your mind, without your realizing it, automatically screens out other, unrelated stimuli.

There is a “common but mistaken belief,” the authors explain, “that people pay attention to, and notice, more of their visual world than they actually do.” (What the researchers call “the illusion of attention” is explored from the perspective of investigating officer-involved shootings in the certification course on Force Science Analysis.)

Inattentional blindness has been well documented in laboratory experiments, but some months ago Chabris and a research team that included Simons decided to test it on the street in conditions similar to what the Boston officer had experienced.

First they asked 20 college students one by one to pursue a male confederate for about three minutes while he jogged for about three minutes along a 1,300-ft. route at night in an area lit with streetlamps. While running about 30 ft. behind, each participant was to count the number of times the runner touched his head with either his left or right hand—“a task that required focused attention.”

About a third of the way into the chase, in a driveway just off the path, three volunteers staged a fight in which two of them beat the third. These subjects “shouted, grunted, and coughed,” the researchers report—and were visible to each pursuing runner for at least 15 seconds before the chaser passed by.

At the end of the route, the researchers asked the subjects how many head-touches they had counted. “Then we asked whether [they] had seen anything unusual along the route and then whether they had seen anyone fighting,” the researchers write. Only seven out of 20 (35%) had seen the brawl.

To check if darkness had affected visibility, the team repeated the experiment in daytime with 16 fresh pursuers. Even though in this test the simulated beating was visible for at least 30 seconds (twice as long as at night), 44% of the subjects failed to notice it.

Finally, in a third iteration of the scenario 58 new pursuers were assigned by coin flip either to keep separate counts of head touches by the runner’s left and right hands during a daylight run or just to follow the runner without counting. “One hallmark of inattentional blindness is that increasing the effort required by the primary task decreases noticing of unexpected events,” the researchers explain.

Sure enough, 58% those with the so-called “high-load condition” of needing to count touches did not see the fight, while 28% of those only chasing (in “no-load condition”) failed to do so.

Across the three experiments “with 94 total participants,” the research team writes, “a substantial number of subjects failed to notice a three-person fight as they ran past it…both at night and during the day….” Dr. Bill Lewinski, executive director of the Force Science Institute, who was not involved in these experiments, observes:

“If the stress involved in merely counting head touches provokes this level of inattentional blindness in ordinary people, just imagine how extensive the phenomenon can be when police officers are intently focused on a threat to their lives or on taking custody of a deadly suspect, where the stakes are tremendously higher.

“Investigators, force reviewers, and jurors need to be educated that the mind can play many tricks under stress and that surprising gaps in observation and memory are not necessarily evidence of evasion or deceit.”

He points out that the results of the Chabris team’s experiments are consistent with findings by Force Science who with researchers from the United Kingdom tested the effect of cognitive work load on attention and perception as part of a ground-breaking 2010 study of officer performance when exhausted.

“After they were thoroughly stressed,” Lewinski explains, “officers were sent into an incident in a room where they were confronted by a very aggressive and hostile assailant who was within reach of a number of dangerous weapons, including an assault rifle, sawed off shotgun, handgun and knife. Most of the officers saw only one of the weapons, even though they were all within reach and constituted potential threats to their lives in that scenario. Shortly after, only 27% of the stressed officers could correctly identify the assailant from a photo line up whereas 54% of the non-exerted officers correctly identified the assailant.

It is very clear that officers in the midst of a dynamic encounter tend to see far less than what the public believes they should.

For free access to the full report on the Chabris team’s experiments, click here.

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