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Did you see the gorilla?
(Filed: 05/05/2004)
Our Stone Age brains may simply be unable to cope with the pace of modern life, says Roger Highfield
Look around, and you could be forgiven for believing that you can see a vivid and detailed picture of your surroundings. Indeed, you may even think that your eyes never deceive you. Unfortunately, the same cannot be said for your brain.
Scientists have gathered some remarkable evidence which shows that it is possible to see something without observing it, in research that sheds new light on traffic accidents that occur when a driver "looked but failed to see", and other examples of mayhem and mishap in everyday life.
The astonishing lack of attention we pay to our surroundings has been highlighted by research conducted by Dr Daniel Simons of the University of Illinois and Dr Daniel Levin of Vanderbilt University. At the end of this article, Dr Simons invites readers to explore the limitations of their own brains.
In one experiment, people who were walking across a college campus were asked by a stranger for directions. During the resulting chat, two men carrying a wooden door passed between the stranger and the subjects. After the door went by, the subjects were asked if they had noticed anything change.
Half of those tested failed to notice that, as the door passed by, the stranger had been substituted with a man who was of different height, of different build and who sounded different. He was also wearing different clothes.
Despite the fact that the subjects had talked to the stranger for 10-15 seconds before the swap, half of them did not detect that, after the passing of the door, they had ended up speaking to a different person. This phenomenon, called change blindness, highlights how we see much less than we think we do.
Working with Christopher Chabris at Harvard University, Simons came up with another demonstration that has now become a classic, based on a videotape of a handful of people playing basketball. They played the tape to subjects and asked them to count the passes made by one of the teams.
Around half failed to spot a woman dressed in a gorilla suit who walked slowly across the scene for nine seconds, even though this hairy interloper had passed between the players and stopped to face the camera and thump her chest.
However, if people were simply asked to view the tape, they noticed the gorilla easily. The effect is so striking that some of them refused to accept they were looking at the same tape and thought that it was a different version of the video, one edited to include the ape.
Prof Richard Wiseman of the University of Hertfordshire recently repeated this experiment before a live audience in London (as part of his Theatre of Science, performed with the author Dr Simon Singh) and found that only 10 per cent of the 400 or so people who saw the show managed to spot the gorilla.
In the past few days, two teams have reported complementary studies that underline our limited capacity to hold a visual scene in short-term memory (VSTM), such as a passing gorilla, revealing how our "visual scratch pad" is controlled by a penny-sized region of the brain called the posterior parietal cortex, near the back of the head.
The studies were published in the journal Nature by Drs Edward Vogel and Maro Machizawa of the University of Oregon, Eugene, and by Prof René Marois and Jay Todd of Vanderbilt University, Nashville.
Subjects are good at remembering all of the objects in scenes containing four or fewer objects but frequently make mistakes describing displays containing a larger number of objects, indicating that the storage capacity of our VSTM is about four.
To find out more about the mechanism of visual memory, Prof Marois used a technique called magnetic resonance imaging to monitor the VSTM in action in a living brain. In subjects, activity in the posterior parietal cortex matched the number of items stored in the VSTM, increasing up to about four objects and levelling off thereafter.
In a similar way, Dr Vogel found that electrical activity in this same part of the brain, measured by electrodes stuck to the scalp, was also related to short-term memory – also reaching a peak of activity with four items.
"Though we have the impression we are taking in a great deal of information from a visual scene, we are actually very poor at describing its contents in detail once it is gone from our sight," said Prof Marois.
In the case of the door experiment of Drs Simons and Levin, for example, it seems that the limited visual short term memory capacity of the subjects meant that they did not retain enough details to spot that they were talking to a new person.
This visual memory may also be linked to intelligence. In the same way that a computer with a larger working memory can tackle problems more quickly, people with a greater capacity for holding images in their heads may have better reasoning and problem-solving skills.
And there may be a link with mathematical skills, notably subitising - the ability to instantly know the exact number of objects on a screen without the need to count, according to Prof Brian Butterworth of University College London, though he emphasised that more work is needed to flesh out this relationship.
"There have been some arguments that limits on visual memory are related to limits on the number of items we can attend to at once as well as to limits on the number of items we can count at a glance (typically both have capacity estimates of around three to four)," added Dr Simons.
"I'm not sure that the link is direct or if there are any causal relationships between these processes, but three to four does crop up a lot in cognitive psychology.''
This research has more serious implications. This memory limitation could contribute to traffic accidents, said Dr Vogel, because it "allows us to maintain and monitor information about the objects (for example, other cars, bicyclists, pedestrians) that are within our immediate vicinity so that we can avoid colliding with them.
While this hasn't been tested directly, it seems highly plausible that racing drivers have higher VSTM capacity than normal drivers which would allow them to monitor more cars within the field."
So far as our brains are concerned, these studies suggest that the old adage "out of sight, out of mind" may be true. Indeed, it is a wonder that scientists are here to discuss the issue at all, given that the ability of our ancestors to dodge spears, clubs and pouncing lions may have been curbed by the limited capacity of human visual memory.
But, Prof Marois said that a VSTM capacity of four was probably not much of a problem in the relatively slower-paced lives of our hunter-gatherer ancestors. Not so today, however. The fast pace of modern life is stretching our Stone Age brains to the limit.
Telegraph readers can test their brains using online demos at Dr Simons's website: http://viscog.beckman.uiuc.edu/media/dailytelegraph.html
http://www.telegraph.co.uk/connected/main.jhtml?xml=/connected/2004/05/05/ecfgorilla05.xml
Personally I prefer the headline here:
http://www.smh.com.au/articles/2004/05/07/1083911408990.html
"A gorilla in the midst: how our brains deceive us"
Another report:
GORILLA? WWHAT GORILLA
May 6 2004
Bizarre experiment shows how we can be blind to the obvious
By Donna Watson
THE next time you catch your husband looking at a busty blonde, don't be too hard on him ... he might not even have noticed her.
New research suggests our brain is capable of storing such a small number of visual details that we often look at things without really seeing them.
One study found we only remember four things or fewer from any given scene.
So a man may not even notice a beautiful woman in a busy room or even someone dressed as a gorilla.
Dr Daniel Simons, of the University of Illinois, is behind some of the new research. In one experiment, he asked volunteers to look at a tape of two teams passing a ball and count how many passes were made.
Around half were so engrossed in their task they failed to spot a woman crossing the screen dressed in a gorilla outfit.
Distraction But when asked just to watch the tape, they spotted the ape right away. Many refused to believe it was the same tape.
Professor Richard Wiseman, of the University of Hertfordshire, repeated the experiment in front of a live audience and only 10 per cent spotted the gorilla.
In another experiment, Dr Simons found half the population wouldn't even notice if they were still talking to the same person after a distraction.
He sent a stranger to stop people and ask for directions. After a few seconds, two men passed between the pair carrying a board and the stranger was replaced by another man of a different height and build, in different clothes.
Only half of those tested noticed the change. This phenomenon, known as change blindness, shows we take in far less than our eyes actually see.
It can also explain whywe often forget where we left our keys.
Prof Rene Marois, of Vanderbilt University in Nashville, has carried out similar, but more scientific, research.
He said: 'We have the impression we are taking in a great deal of information from a visual scene but we are actually very poor at describing its contents in detail once it is gone from our sight.
'We found the upper limit for visual short-term memory is just four objects.
'So if you put your keys down with a load of shopping bags on a crowded table, you could almost immediately have problems remembering where you put them.
'Once you turn away to do something else, the image of the keys in a certain location is quickly replaced because they are in an area with more than four items.'
Prof Marois showed people between one and eight objects. The items were removed and the group was asked to recall as many as possible.
They could almost always remember all the objects when presented with four or fewer. But when shown more, their recall rapidly diminished.
Asked to recall eight objects, they scored an average of only 68 per cent.
Some researchers think the number of details stored is linked to intelligence in the same way that a computer with more memory can store more information.
Dr Edward Vogel, of the University of Oregon, has also studied the visual scene in short term memory (VSTM) capacity.
He said the research highlights serious safety implications as memory limitation could contribute to traffic accidents.
He added: 'It seems highly plausible racing drivers have higher VSTM capacity than normal drivers, allowing them to monitor more cars within the field.'
STRANGER THAN FICTION
Dr Simons's experiment involved a stranger asking a man for directions
The man, right, gives the stranger directions
But they are interrupted by passing workmen ......
and a different person takes the stranger's place
The subject is oblivious and carries on talking
Source
It does sound more like Jeremy Beadle science but as he is 'One Of Us' that might be a good thing
Another broader report:
Brain signal predicts working memory prowess
17 Apr 2004
Some people are better than others at remembering what they have just seen – holding mental pictures in mind from moment to moment, it seems that a brain signal predicts working memory prowess. An individual's capacity for such visual working memory can be predicted by his or her brainwaves, researchers funded by the NIH's National Institute of Mental Health have discovered.
A key brain electrical signal leveled off when the number of objects held in mind exceeded a subject's capacity to accurately remember them, while it continued to soar in those with higher capacity, report University of Oregon psychologist Edward Vogel, Ph.D., and graduate student Maro Machizawa, in the April 15, 2004 Nature.
Analogous to a computer's RAM, working memory is the ever-changing content of our consciousness. It's been known for years that people have a limited capacity to hold things in mind that they've just seen, varying from 1.5 to 5 objects. "Our study identifies signals from brain areas that hold these visual representations and allows us to coarsely decode them, revealing how many objects are being held and their location in the visual field," explained Vogel.
To find out if the amplitude of detectable signals reflects the number of object representions held in visual memory, the researchers presented 36 subjects with a series of trials containing an increasing number of objects.
Subjects briefly viewed a picture containing colored squares, followed by a one-second delay, and then a test picture.
They pressed buttons to indicate whether the test picture was identical to -- or differed by one color -- from the one seen earlier. The more squares a subject could correctly identify having just seen, the greater his/her visual working memory capacity. Subjects averaged 2.8 squares.
Electrodes on the scalp recorded neural activity during the one-second delay to pinpoint signals reflecting activity of brain areas involved in holding the images in working memory. Asking subjects to remember just one of two sets of colored squares that appeared on the left and right sides of the screen revealed signals near the opposite rear side of the head as emanating from the brain area involved.
The researchers found that the more squares a subject correctly identified, the higher the spike of corresponding brain activity – up to a point. Amplitude of the signal for correct trials was much higher than incorrect ones, suggesting that the delay activity specifically reflects the maintenance of successful representations in visual memory.
Neural activity of subjects with poorer working memory scores leveled off early, showing little or no increase when the number of squares to remember increased from 2 to 4, while those with high capacity, who correctly remembered more squares, showed large increases.
Using a similar task with functional magnetic resonance imaging (fMRI), a research team at Vanderbilt University reports in the same issue of Nature that the posterior parietal cortex, an area at the top rear part of the brain, is the brain area responsible for holding representations in visual working memory – and likely source of the signal in the Oregon study.
"Simply by measuring the amplitude increase across memory array sizes, we can accurately predict an individual's memory capacity," said Vogel.
Since working memory capacity is strongly predictive of performance on a broad array of of cognitive abilities - reasoning, language, flexible problem solving - Vogel foresees the physiological measure as finding applications in assessing individuals who are behaviorally or verbally impaired, such as in cases of stroke or paralysis. The technique has also been used to study development of cognitive abilities in pre-verbal children.
NIMH is part of the National Institutes of Health (NIH), the Federal Government's primary agency for biomedical and behavioral research. NIH is a component of the U.S. Department of Health and Human Services.
Source
The papers refered to are in this issue of Nature:
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v428/n6984/index.html
and are:
Nature 428, 748 - 751 (15 April 2004);
Neural activity predicts individual differences in visual working memory capacity
EDWARD K. VOGEL AND MARO G. MACHIZAWA
Department of Psychology, University of Oregon, Eugene, Oregon 97403-1227, USA
Correspondence and requests for materials should be addressed to E.K.V. ([email protected]).
Contrary to our rich phenomenological visual experience, our visual short-term memory system can maintain representations of only three to four objects at any given moment. For over a century, the capacity of visual memory has been shown to vary substantially across individuals, ranging from 1.5 to about 5 objects. Although numerous studies have recently begun to characterize the neural substrates of visual memory processes, a neurophysiological index of storage capacity limitations has not yet been established. Here, we provide electrophysiological evidence for lateralized activity in humans that reflects the encoding and maintenance of items in visual memory. The amplitude of this activity is strongly modulated by the number of objects being held in the memory at the time, but approaches a limit asymptotically for arrays that meet or exceed storage capacity. Indeed, the precise limit is determined by each individual's memory capacity, such that the activity from low-capacity individuals reaches this plateau much sooner than that from high-capacity individuals. Consequently, this measure provides a strong neurophysiological predictor of an individual's capacity, allowing the demonstration of a direct relationship between neural activity and memory capacity.
and:
Nature 428, 751 - 754 (15 April 2004);
Capacity limit of visual short-term memory in human posterior parietal cortex
J. JAY TODD AND RENÉ MAROIS
Vanderbilt Vision Research Center, Department of Psychology, Vanderbilt University, 530 Wilson Hall, Nashville, Tennessee 37203, USA
Correspondence and requests for materials should be addressed to R.M. ([email protected].).
At any instant, our visual system allows us to perceive a rich and detailed visual world. Yet our internal, explicit representation of this visual world is extremely sparse: we can only hold in mind a minute fraction of the visual scene. These mental representations are stored in visual short-term memory (VSTM). Even though VSTM is essential for the execution of a wide array of perceptual and cognitive functions, and is supported by an extensive network of brain regions, its storage capacity is severely limited. With the use of functional magnetic resonance imaging, we show here that this capacity limit is neurally reflected in one node of this network: activity in the posterior parietal cortex is tightly correlated with the limited amount of scene information that can be stored in VSTM. These results suggest that the posterior parietal cortex is a key neural locus of our impoverished mental representation of the visual world.
Emps
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