New findings expand understanding of tunnel vision, auditory blocking and lag time


In both cases, the findings will help advance studies at the Force Science Research Center regarding officer behavior during shootings.

The Hopkins study, led by Dr. Steven Yantis, a professor in the Dept. of Psychological and Brain Sciences, tracked how the human brain handles competing demands for attention.

In a neuroimaging lab, adults ranging in age from 19 to 35 were asked to view a rapidly changing computer display of multiple numbers and letters while listening through headsets to 3 voices simultaneously speaking numbers and letters. This was intended to simulate “the cluttered visual and auditory input people deal with every day.” Using sophisticated imaging equipment, Yantis and his team recorded the subjects’ brain activity.

They found that when the subjects directed their attention to visual tasks (“tunneling in” on the computer screen), the parts of the brain that record auditory stimuli registered decreased activity. By the same token, when they focused on listening to spoken messages, brain areas that respond to visual images showed diminished activity.

In effect, when a subject concentrated on one source of sensory input--looking at something, in this case--that essentially “turned down the volume” on the part of the brain that monitors hearing. And vice versa. As Yantis puts it:

“When attention is deployed to one modality, it necessarily extracts a cost on another modality. The brain can’t simultaneously give full attention to both.”

Yantis uses this finding, reported in last November’s issue of the Journal of Neuroscience, to explain why cell phone conversations diminish a driver’s visual acuity for what’s happening on the road. But Dr. Bill Lewinski, executive director of the Force Science Research Center at Minnesota State University-Mankato, sees important law enforcement implications.

“This explains why officers defending themselves in a shooting may not hear things accurately--or at all,” he told Force Science News. “Their intense focus on a powerful visual stimulus--a threat to their life--causes their brain’s hearing receptors to shut down.

“We’ve known for a long time that shooting survivors often don’t hear their rounds going off, can’t remember hearing their partner screaming in their ear, may have perceived their gunshots as puny pops and so on--many sound distortions or omissions. Now we know why this so-called auditory blocking takes place.

“Likewise, we understand why they may not see something within their field of vision--where their partner was standing, where civilians were--when they are focused on listening to audible stimuli. And we know that these phenomena are real, an unavoidable part of the human condition, not just something cops imagine.”

In a web-posted video explaining his experiments, Yantis references work at the University of Utah that, like his study, would seem to most civilians to have primarily road safety implications.

(The video can be accessed here.)

You can click on the photo of Professor Yantis to launch the video or click the link at the end of the printed news release.)

At Utah, researchers monitored subjects talking on a cell phone while “operating” a visual driving simulator. This study measured reaction time and found, for example, that a driver’s reaction to the brake lights of a car ahead is “significantly slower” if he or she is engaged in a phone conversation.

Lewinski believes this finding, too, “has important law enforcement implications, concerning the impact of distraction. In this case, if you are listening to something (a cell phone conversation) it will delay your reaction to something that occurs in your visual field.”

But distractions within a particular sensory realm--within your visual field, say--will produce delays, too, he points out. “If you are focused on watching one thing you won’t detect changes as rapidly in the other parts of your visual field that you aren’t concentrating on.

“For example, if you are intently watching a suspect’s right hand because you think he might produce a weapon there and instead he comes up with a weapon in his left hand, your reaction time will be significantly impaired.”

In the practical world of the street and in court the ramifications of these perceptual studies are “profound and wide ranging,” Lewinski stresses.

They show, for instance, how “dealing with multiple suspects in a high-stress encounter presents an extreme challenge to you as an officer. Not only will you be able primarily to see only what you are focused on at any given moment but your own brain may sabotage or delay your ability to perceive and react to threats outside your immediate focus. If you’re not anticipating a threat from beyond your point of concentration, you can be caught flat-footed and be way behind the reactionary curve when a threat is presented.”

Moreover, you may be held to unrealistic standards in court or during departmental investigations after a major use of force if the persons probing or judging your actions don’t understand the psychological influences involved. “People questioning you are seriously deluding themselves if they think you can perceive, pay attention to, react to and remember everything with clarity and precision, even if it happened directly in front of you,” Lewinski says.

“The reality is that most of us are pretty poor—in fact, incapable—of perceiving and recording everything that occurs to us at any particular moment. Not perceiving the totality of an event is how we normally operate. Even in non-stress situations, not to mention a life-threatening confrontation, once we focus on anything, even if it’s a thought in our own head, we significantly compromise our ability to perceive and remember what else is occurring around and to us.

“The uninformed person will wonder why in a lethal situation you can’t remember how you moved or shot or how many rounds you fired or the movement of the very person you are shooting at to save your life.

“The bottom line of Dr. Yantis’ work is that the brain has limited capacity for paying attention and recording what it perceives. It shifts among competing stimuli to accommodate what seems most important, and blocks out the rest.

“In reality, you may be capable only of vague generalizations after an experience like a shooting. Those investigating or judging you need to realize you are not feigning lack of memory. Details that were not important to your survival during the microseconds of a shooting may not have been recorded. You will simply remember what you were focused on at the time, not what someone who was not there at the moment of crisis may think later is important.”

Part of FSRC’s mission is to research how officers can cope with the phenomena revealed in the university studies cited above. A number of experiments are underway or planned at the Center to explore perception and reaction time in complex new ways, Lewinski says, and these latest studies will assist in that research. “Later,” he says, “we will investigate how training can best be designed to help officers better overcome the challenges they face.”

For a more complete discussion of the recent university studies and their implications for law enforcement, click here.

There you’ll find a special report Lewinski has prepared, including a detailed examination of one reaction-time challenge in particular, the time it takes officers to respond to a change in circumstances and stop shooting at a previously perceived threat.

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