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Strong Emotions May Cause Temporary Blindness
Iphtashu Fitz writes "Ever been watching tv when a violent image comes on the screen and you don't even notice that somebody just entered the room? You've just encountered something known as emotion-induced blindness. Psychologists at Vanderbilt and Yale Universities have determined that people can suffer short periods of blindness, up to 1/2 a second in length, immediately after seeing highly emotional images. By displaying a series of images for 1/10 of a second each they were able to determine that test subjects couldn't identify images shown immediately after very erotic or gory images. You can try this out for yourself at the flash-based test site they have set up which also contains more details of the experiments."
Blindness is a poor and imprecise term for this finding and these findings are simply an extension of work performed in situational awareness. As one who's research deals with the neuroscience of vision and blindness, I have to say that "attention" or even "situational awareness: would be a better word/term, rather than "blindness". No offense to the authors of this study, but that sort of terminology might be expected of psychologists. :-) Seriously though, blindness implies a fundamental defect in the visual processing pathways as opposed to a failure to bring attention to a change in presentation due to conflicts of attention in higher or associative cortical processing. Now, if they demonstrated a lack of visual evoked potential in cortex, that might be something.
The failure to attend to or notice changes in your environment due to more traffic in cortical associative areas is not surprising really, and has long been known by cognitive scientists working with Air Force pilots. The more tasks required or stress induced upon a situation will degrade attentive performance and result in missing changes introduced into the environment.
For all you gamers out there, this is sort of an intuitive concept, right? How many times have you missed the doorbell, telephone or significant other trying to get ahold of you in the middle of a Doom/Marathon/Unreal fragfest? You increase the number of participants (and thus tasks to attend to) and you decrease your situational awareness of your immediate surroundings.
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This is very timely in light of recent news that the eyewitness accounts of the tube shooting of Charles de Menezes, were just completely wrong. Despite eyewitness accounts to the contrary, he was not wearing winter clothing, he had not jumped the turnstile, was not chased into the train by police, etc. Amazing.
When the eye moves, it temporarily shuts off the flow of visual data to the brain. That is why you don't experience the world swirling around as your eye darts from detail to detail. Experiments using an eye tracker found that one could change parts of the scene in the middle of the eye movement and the subject wouldn't notice the change. The tests looked at how severe a change was needed to make people notice that the scene was different -- colors of objects could change, people could be added to pictures, etc.
The coolest experiment used an eye tracker that painted words on the screen only where the fovea (the high resolution central portion of the retina) was looking and painted "X"s on the screen everywhere else (the low resolution bulk of the eye). Every time the subject's eye moved, the screen was redrawn to show the words where they were now looking and hide the words were they weren't looking. Subjects could read documents normally and were totally unaware that the screen was, in reality, full of "x"s except where their central field of vision happened to be pointing.
The point is that the eye & brain is not a simple pixel-based camera.
Two wrongs don't make a right, but three lefts do.
If you can't process or retain any visual information, you're blind. Why does it matter if it's a low level or high level failure?
The classic demonstration of low level versus high level functionality has to do with something called a "true cortical blindness". In these cases, trauma or stroke (whatever) that damages occipital cortex may in some rare cases render a person functionally blind. However, when you throw a ball at them, strangely, they are able to catch it. Obviously there is some visual function related to vision taking place. What is happening here is that the tectum or visual centers in the brainstem whose functionality is orienting to place and timing are perfectly intact. However, visual centers related to conscious perception of what is being seen are damaged. All other visual pathways are intact.
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My brothers and I operate a chain of grocery stores in Jamaica. Two months ago, one of the small stores was invaded by four gunmen who made the staff lie on the floor, shooting three of our employees in the process; fortunately their wounds were minor. While they attempted to open the safe in the manager's office, she surreptitiously placed a cell call to the police station, which is only about 100 meters away. When the police arrived, a 45-minute shootout ensued, during which the police shot and killed two of the assailants. The police eventually teargassed the building, and when the remaining two attempted to slip out by mingling with the staff as they left, they were attacked by a large, very angry, machete-carrying mob that had gathered on the scene, and hacked into mincemeat. I really have no sympathy for the bastards, but Jesus, they died horrible, horrible deaths. When I eventually reached the store after visiting the staff at the hospital, the police were still hosing away blood and fragments of flesh.
After seeing the three injured employees being treated, I arranged for the others, who were badly traumatized, to have a counseling session, and it was heartbreaking to hear them describe the ordeal of lying on the floor for 45 minutes while a firefight raged around them. The were showered with broken glass, lying in blood, having to look at the bodies of the two dead gunmen, one of whom had had his face shot away. They didn't believe that they were going to survive. While one of the group was recounting the events to the psychologist, he started sweating profusely, I mean veritable rivers running off his face and arms, and complained suddenly that he couldn't see. He didn't respond to hands being waved in front of his face, and the psychologist assured him that he'd seen this happen before as a result of extreme stress, and that his vision would return in a few minutes. I honestly don't know if he was just spinning a line of bullshit to calm down the guy, but sure enough, his vision returned in about five minutes. Clearly he hadn't suffered any physical injury apart from some cuts and bruises, but I can only surmise that the extreme psychological stress had screwed with his brain somehow. Can anyone shed any light as to the mechanism that could have caused this?