they do not even see this correcttly!
>>see everything in black and white.<<
A lack of vision
You don't see as much as you think you do
By Carey Goldberg, Globe Staff, 4/15/2003
ook up and around you, then back at these words. How much did you see of your surroundings? Pretty much all of it, and in rich detail, right?
Wrong. In recent years, a rash of experiments, spurred by new technology, have demonstrated that people often take in far less of the world around them than previously thought.
Tests have found that subjects miss even major changes right before their eyes - say, the sudden disappearance of an airplane's jet engine, or a woman's bright scarf.
But most remain oblivious to their own blindness.
In the making, some researchers say, is a quiet revolution in the thinking about visual perception.
And that reconception of what people can and cannot see, they say, could be felt in a multitude of ways: Juries could assign blame differently in traffic-accident cases. Designers could devise different computer interfaces. And any individual could look at the world with fresh eyes, newly aware of the limits imposed on him or her by the brain.
''It used to be thought that perception was about us creating a copy of our environment inside our heads,'' something like a recording videocamera, said Ron Rensink, a noted vision researcher at the University of British Columbia.
But now, he said, scientists increasingly realize that perception works more like a Web browser: People can take in and store only a tiny portion of the scene around them - just as only a bit of the Web fits onto one computer screen - but they can gain access to an enormous array of information by choosing to focus on any piece of it.
Rensink started studying ''change blindness'' - people's blindness to scene changes - back in the 1990s while working at Cambridge Basic Research, a now-defunct lab that Nissan financed to look into the psychology of driving.
He was prompted in part by the frequent city-driving accidents categorized as ''driver looked but failed to see,'' he said. Drivers sometimes even plow right into trains that are already crossing the road, he noted.
As he and his colleagues came to realize the powerful effects of change blindness, he said, they became more than a little afraid to cross the street.
''You stop trusting your visual system,'' he said.
It is not exactly clear why such blindness strikes, researchers say, but it follows that if a person's brain is not building up a thorough picture of what's around him, it cannot notice whether something changes, unless cued by a motion.
Most of the time, of course, that system works pretty well. But research into change blindness indicates that it can fail more than previously suspected.
Much of the work on change blindness hinges on showing people scenes, then briefly interrupting their view so they will not be tipped off by the motion of the change, and then restoring the scene with something significantly different. (Several of Rensink's demonstrations can be found at www.cs.ubc.ca/ rensink/flicker/download/.)
Researchers have been shocked, they say, by the enormity of the changes that people fail to see.
Some experiments have people look at a scene, say, of soldiers boarding a plane. Then the screen briefly goes blank - the ''flicker effect'' devised by Rensink to keep subjects from noticing the motion of a change - and then the scene reappears with a large chunk of it different. A large patch of color may come and go, or a large object.
Other experiments use ''mud splashes'' - distracting patches of color on the screen - to distract attention from the change. Still others, using more expensive laboratory technology, have made sure the change happens while a subject shifts his gaze, to make sure, once again, that he or she missed the motion of change.
In many of the experiments, subjects performed surprisingly poorly at trying to detect the changes, taking many seconds to notice differences that seem glaring once identified. A whole tree would come and go, for example, or a large patch would change color but remain undetected for a relatively long time.
Change blindness also plays into the danger of cellphones, Rensink noted. Because people mistakenly believe they've got a good picture of the road built up in their heads, they don't realize how damaging their distraction by the cellphone can be to the accuracy of their visual perception.
These days, change blindness is scientifically hot, the subject of special sessions at recent conferences and special issues of journals, such as the online Journal of Vision.
Psychological work exploring visual perception goes back decades, but new software, leaning heavily on Photoshop and video-editing programs, has allowed researchers to approximate the natural scenes that actually make up the world. They have thus provided much more powerful data than the dots and other simple displays used in the old days.
What surprised some researchers even more than change blindness was how overconfident people were about being able to detect changes. They call that effect ''change blindness blindness'' - that people are blind to their own inability to detect change.
In one experiment by Dan Levin, an associate professor at Kent State University in Ohio, 90 percent of subjects predicted that they would notice if the scarf on a woman in a video disappeared. But, in fact, when another group of subjects actually watched the video, none of them noticed.
''The key is that people really have intuitions that are a mile off base,'' he said.
''You think you're aware of all this visual information in front of you when in fact you're aware of very little of it at any given time. And because of that, people believe they'll see these changes when in fact they'll almost always go unnoticed.''
Levin is now working on a National Science Foundation grant to assess the impact that misunderstandings about vision can have on jurors when they hear cases about traffic accidents.
It has long been known that jurors often have misconceptions about memory, he noted, and think, mistakenly, that if a witness is confident of a memory, that must mean it is accurate.
Similarly, he said, jurors may be mistaken about vision, presuming that if a driver missed seeing something, he must have been negligent.
''But it may be the case that even if something's right in front of you, you might not be aware of it,'' he said.
Researchers say that computer designers may make wrong assumptions as well, about screen prompts that they believe a user cannot miss seeing.
One piece of that, Levin said, is ''banner blindness,'' a newly coined term for a phenomenon related to change blindness - that sometimes, when big banners are blazoned across the computer screen, they somehow fail to register with viewers.
Work on change blindness is inextricably linked to memory, said Daniel J. Simons, associate professor at the University of Illinois and a noted change-blindness researcher.
It is prompting many researchers to explore and debate whether change blindness stems from a failure to store information or failure to compare the current scene with the past one.
In the late 1990s, he said, many argued that ''maybe you don't retain much of anything'' from second to second. More recently, he said, many are arguing that ''maybe you retain a bit more than we thought but we fail to compare what's there to what was there before.''
Overall, said Jeremy Wolfe, a vision researcher at MIT, change blindness experiments have provided ''a very gripping set of phenomena,'' but, he said, they are still ''in search of a completely convincing theory.''
The basic bottom line, however, is this, according to Rensink: ''You don't realize you're missing all kinds of stuff. Even when it's right in front of you, you're missing stuff all the time.''
Carey Goldberg may be contacted at goldberg@globe.com.
This story ran on page C1 of the Boston Globe on 4/15/2003.
© Copyright 2003 Globe Newspaper Company.
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