Playing video games can affect your memory and mood
A review has concluded that spatial training produces significant improvement, particularly for poorer performers, and that such training could significantly increase STEM achievement.
Spatial abilities have been shown to be important for achievement in STEM subjects (science, technology, engineering, math), but many people have felt that spatial skills are something you’re either born with or not.
In a comprehensive review of 217 research studies on educational interventions to improve spatial thinking, researchers concluded that you can indeed improve spatial skills, and that such training can transfer to new tasks. Moreover, not only can the right sort of training improve spatial skill in general, and across age and gender, but the effect of training appears to be stable and long-lasting.
One interesting finding (the researchers themselves considered it perhaps the most important finding) was the diversity in effective training — several different forms of training can be effective in improving spatial abilities. This may have something to do with the breadth covered by the label ‘spatial ability’, which include such skills as:
The review compared three types of training. Those that used:
The first two are examples of indirect training, while the last involves direct training.
On average, taken across the board, training improved performance by well over half a standard deviation when considered on its own, and still almost one half of a standard deviation when compared to a control group. This is a moderately large effect, and it extended to transfer tasks.
It also conceals a wide range, most of which is due to different treatment of control groups. Because the retesting effect is so strong in this domain (if you give any group a spatial test twice, regardless of whether they’ve been training in between the two tests, they’re going to do better on the second test), repeated testing can have a potent effect on the control group. Some ‘filler’ tasks can also inadvertently improve the control group’s performance. All of this will reduce the apparent effect of training. (Not having a control group is even worse, because you don’t know how much of the improvement is due to training and how much to the retesting effect.)
This caution is, of course, more support for the value of practice in developing spatial skills. This is further reinforced by studies that were omitted from the analysis because they would skew the data. Twelve studies found very high effect sizes — more than three times the average size of the remaining studies. All these studies took place in poorly developed countries (those with a Human Development Index above 30 at the time of the study) — Malaysia, Turkey, China, India, and Nigeria. HDI rating was even associated with the benefits of training in a dose-dependent manner — that is, the lower the standard of living, the greater the benefit.
This finding is consistent with other research indicating that lower socioeconomic status is associated with larger responses to training or intervention.
In similar vein, when the review compared 19 studies that specifically selected participants who scored poorly on spatial tests against the other studies, they found that the effects of training were significantly bigger among the selected studies.
In other words, those with poorer spatial skills will benefit most from training. It may be, indeed, that they are poor performers precisely because they have had little practice at these tasks — a question that has been much debated (particularly in the context of gender differences).
It’s worth noting that there was little difference in performance on tests carried out immediately after training ended, within a week, or within a month, indicating promising stability.
A comparison of different types of training did find that some skills were more resistant to training than others, but all types of spatial skill improved. The differences may be because some sorts of skill are harder to teach, and/or because some skills are already more practiced than others.
Given the demonstrated difficulty in increasing working memory capacity through training, it is intriguing to notice one example the researchers cite: experienced video game players have been shown to perform markedly better on some tasks that rely on spatial working memory, such as a task requiring you to estimate the number of dots shown in a brief presentation. Most of us can instantly recognize (‘subitize’) up to five dots without needing to count them, but video game players can typically subitize some 7 or 8. The extent to which this generalizes to a capacity to hold more elements in working memory is one that needs to be explored. Video game players also apparently have a smaller attentional blink, meaning that they can take in more information.
A more specific practical example of training they give is that of a study in which high school physics students were given training in using two- and three-dimensional representations over two class periods. This training significantly improved students’ ability to read a topographical map.
The researchers suggest that the size of training effect could produce a doubling of the number of people with spatial abilities equal to or greater than that of engineers, and that such training might lower the dropout rate among those majoring in STEM subjects.
Apart from that, I would argue many of us who are ‘spatially-challenged’ could benefit from a little training!
 Uttal DH, Meadow NG, Tipton E, Hand LL, Alden AR, Warren C, Newcombe NS. The Malleability of Spatial Skills: A Meta-Analysis of Training Studies. Psychological Bulletin [Internet]. 2012 . Available from: http://psycnet.apa.org/index.cfm?fa=search.displayRecord&id=B88373D4-D7A5-AA22-7CE9-6457D4AC5558&resultID=1&page=1&dbTab=pa
A comparison of skilled action gamers and non-gamers reveals that all that multitasking practice doesn’t make you any better at multitasking in general.
The research is pretty clear by this point: humans are not (with a few rare exceptions) designed to multitask. However, it has been suggested that the modern generation, with all the multitasking they do, may have been ‘re-wired’ to be more capable of this. A new study throws cold water on this idea.
The study involved 60 undergraduate students, of whom 34 were skilled action video game players (all male) and 26 did not play such games (19 men and 7 women). The students were given three visual tasks, each of which they did on its own and then again while answering Trivial Pursuit questions over a speakerphone (designed to mimic talking on a cellphone).
The tasks included a video driving game (“TrackMania”), a multiple-object tracking test (similar to a video version of a shell game), and a visual search task (hidden pictures puzzles from Highlights magazine).
While the gamers were (unsurprisingly) significantly better at the video driving game, the non-gamers were just as good as them at the other two tasks. In the dual-tasking scenarios, performance declined on all the tasks, with the driving task most affected. While the gamers were affected less by multitasking during the driving task compared to the non-gamers, there was no difference in the amount of decline between gamers and non-gamers on the other two tasks.
Clearly, the smaller effect of dual-tasking on the driving game for gamers is a product of their greater expertise at the driving game, rather than their ability to multitask better. It is well established that the more skilled you are at a task, the more automatic it becomes, and thus the less working memory capacity it will need. Working memory capacity / attention is the bottleneck that prevents us from being true multitaskers.
In other words, the oft-repeated (and somewhat depressing) conclusion remains: you can’t learn to multitask in general, you can only improve specific skills, enabling you to multitask reasonably well while doing those specific tasks.
 Donohue S, James B, Eslick A, Mitroff S. Cognitive pitfall! Videogame players are not immune to dual-task costs. Attention, Perception, & Psychophysics [Internet]. 2012 ;74(5):803 - 809. Available from: http://www.springerlink.com/content/k7116k62242664p1/abstract/
Engaging in both moderate exercise and cognitively stimulating activities has an additive effect in reducing your risk of becoming cognitively impaired.
More findings from the long-running Mayo Clinic Study of Aging reveal that using a computer plus taking moderate exercise reduces your risk of mild cognitive impairment significantly more than you would expect from simply adding together these two beneficial activities.
The study involved 926 older adults (70-93), of whom 109 (12%) were diagnosed with MCI. Participants completed questionnaires on physical exercise and mental stimulation within the previous year. Computer use was targeted in this analysis because of its popularity as a cognitive activity, and because it was particularly associated with reduced odds of having MCI.
Among the cognitively healthy, only 20.1% neither exercised moderately nor used a computer, compared to 37.6% of those with MCI. On the other hand, 36% of the cognitively healthy both exercised and used a computer, compared to only 18.3% of those with MCI. There was little difference between the two groups as regards exercise but no computer use, or computer use but no exercise.
The analysis took into account calorie intake, as well as education, depression, and other health factors. Daily calorie intake was significantly higher in those with MCI compared to those without (respective group medians of 2100 calories vs 1802) — note that the median BMI was the same for the two groups.
Moderate physical exercise was defined as brisk walking, hiking, aerobics, strength training, golfing without a golf cart, swimming, doubles tennis, yoga, martial arts, using exercise machines and weightlifting. Light exercise included activities such as bowling, leisurely walking, stretching, slow dancing, and golfing with a cart. Mentally stimulating activities included reading, crafts, computer use, playing games, playing music, group and social and artistic activities and watching less television.
It should be noted that the assessment of computer activities was very basic. The researchers suggest that in future studies, both duration and frequency should be assessed. I would add type of activity, although that would be a little more difficult to assess.
Overall, the findings add yet more weight to the evidence for the value of physical exercise and mental stimulation in staving off cognitive impairment in old age, and add the twist that doing both is much better than doing either one alone.
 Geda YE, Silber TC, Roberts RO, Knopman DS, Christianson TJH, Pankratz SV, Boeve BF, Tangalos EG, Petersen RC. Computer Activities, Physical Exercise, Aging, and Mild Cognitive Impairment: A Population-Based Study. Mayo Clinic Proceedings [Internet]. 2012 ;87(5):437 - 442. Available from: http://www.mayoclinicproceedings.org/article/S0025-6196(12)00304-7/abstract
A small study has found that ten hours of playing action video games produced significant changes in brainwave activity and improved visual attention for some (but not all) novices.
Following on from research finding that people who regularly play action video games show visual attention related differences in brain activity compared to non-players, a new study has investigated whether such changes could be elicited in 25 volunteers who hadn’t played video games in at least four years. Sixteen of the participants played a first-person shooter game (Medal of Honor: Pacific Assault), while nine played a three-dimensional puzzle game (Ballance). They played the games for a total of 10 hours spread over one- to two-hour sessions.
Selective attention was assessed through an attentional visual field task, carried out prior to and after the training program. Individual learning differences were marked, and because of visible differences in brain activity after training, the action gamers were divided into two groups for analysis — those who performed above the group mean on the second attentional visual field test (7 participants), and those who performed below the mean (9). These latter individuals showed similar brain activity patterns as those in the control (puzzle) group.
In all groups, early-onset brainwaves were little affected by video game playing. This suggests that game-playing has little impact on bottom–up attentional processes, and is in keeping with earlier research showing that players and non-players don’t differ in the extent to which their attention is captured by outside stimuli.
However, later brainwaves — those thought to reflect top–down control of selective attention via increased inhibition of distracters — increased significantly in the group who played the action game and showed above-average improvement on the field test. Another increased wave suggests that the total amount of attention allocated to the task was also greater in that group (i.e., they were concentrating more on the game than the below-average group, and the control group).
The improved ability to select the right targets and ignore other stimuli suggests, too, that these players are also improving their ability to make perceptual decisions.
The next question, of course, is what personal variables underlie the difference between those who benefit more quickly from the games, and those who don’t. And how much more training is necessary for this latter group, and are there some people who won’t achieve these benefits at all, no matter how long they play? Hopefully, future research will be directed to these questions.
 Wu S, Cheng CK, Feng J, D'Angelo L, Alain C, Spence I. Playing a First-person Shooter Video Game Induces Neuroplastic Change. Journal of Cognitive Neuroscience [Internet]. 2012 ;24(6):1286 - 1293. Available from: http://dx.doi.org/10.1162/jocn_a_00192
A large, long-running study suggests both that children with attention difficulties tend to spend more time playing video games, and that extensive video game playing is bad for attention.
A three-year study involving 3,034 Singaporean children and adolescents (aged 8-17) has found that those who spent more time playing video games subsequently had more attention problems, even when earlier attention problems, sex, age, race, and socioeconomic status were statistically controlled. Those who were more impulsive or had more attention problems subsequently spent more time playing video games, even when initial video game playing was statistically controlled. These findings suggest that the cause-effect relationship between video game playing and attention problems/impulsiveness goes both ways.
While the particular content may have an effect on attention problems and impulsiveness (violent games appeared to be an additional, independent, factor in attention problems), it was the total time spent that was more important.
Participants completed questionnaires about their video game playing habits annually for three years running. They also completed questionnaires aimed to measure attention and impulsiveness (the Current ADHD Symptoms Scale Self-Report, and the Barratt Impulsiveness Scale-11, respectively). Regarding attention, the children answered questions such as how often they "fail to give close attention to details or make careless mistakes" in their work or "blurt out answers before questions have been completed." For the impulsivity test, they selected points they felt described themselves, such as "I often make things worse because I act without thinking" or "I concentrate easily."
How does this finding relate to other evidence showing that playing video games can improve visual attention for rapid and accurate recognition of information from the environment? The answer lies in the different nature of attention — the attention needed for visual search differs in important ways from the attention necessary for sustained concentration in contexts that are often effortful and/or boring.
The example of many attention-challenged individuals makes this more understandable. Many parents of children with ADHD find that the only thing their child can concentrate on for a lengthy period is video games. The answer to that riddle is the rapidly changing nature of video games, and the way they are designed to grab the attention, with flashing lights and loud noises and moving images etc. The young person is not, therefore, improving their ability to focus in a way that is helpful for the school environment, or indeed for everyday life.
Unfortunately, this study suggests that it is precisely those people who are most in need of such ‘external supports’ for attention (‘grabbing’ stimuli such as lights and sounds and movement) — that is, those individuals who are least able to control their own attention — who are most likely to spend a lot of time playing such games. The games then weaken their attentional control even more, and so the cycle continues.
So this research answers the question ADHD parents tend to have: should I encourage my child to play video games a lot (given that it’s the only thing that holds their attention) or not? The answer, unfortunately, would seem to be: not. However, all is not lost. There are computer ‘games’ that are designed to help those with ADHD learn to concentrate in a way that is more useful (see the Topic collection on ADHD for more on this).
The American Academy of Pediatrics recommends one hour per day of total media screen time (including TV, DVDs, video games, Internet, iPad, etc.) for children in elementary school, and two hours for children in secondary school.
Gentile, D.A., Swing, E.L., Lim, C.G. & Khoo, A. 2012. Video game playing, attention problems, and impulsiveness: Evidence of bidirectional causality. Psychology of Popular Media Culture, Vol 1(1), Jan 2012, 62-70. doi: 10.1037/a0026969
Full text available at http://www.apa.org/pubs/journals/releases/ppm-1-1-62.pdf
A study has found that playing a cognitively complex video game improved cognitive performance in some older adults, particularly those with initially poorer cognitive scores.
A number of studies have found evidence that older adults can benefit from cognitive training. However, neural plasticity is thought to decline with age, and because of this, it’s thought that the younger-old, and/or the higher-functioning, may benefit more than the older-old, or the lower-functioning. On the other hand, because their performance may already be as good as it can be, higher-functioning seniors may be less likely to benefit. You can find evidence for both of these views.
In a new study, 19 of 39 older adults (aged 60-77) were given training in a multiplayer online video game called World of Warcraft (the other 20 formed a control group). This game was chosen because it involves multitasking and switching between various cognitive abilities. It was theorized that the demands of the game would improve both spatial orientation and attentional control, and that the multiple tasks might produce more improvement in those with lower initial ability compared to those with higher ability.
WoW participants were given a 2-hour training session, involving a 1-hour lecture and demonstration, and one hour of practice. They were then expected to play the game at home for around 14 hours over the next two weeks. There was no intervention for the control group. All participants were given several cognitive tests at the beginning and end of the two week period: Mental Rotation Test; Stroop Test; Object Perspective Test; Progressive Matrices; Shipley Vocabulary Test; Everyday Cognition Battery; Digit Symbol Substitution Test.
As a group, the WoW group improved significantly more on the Stroop test (a measure of attentional control) compared to the control group. There was no change in the other tests. However, those in the WoW group who had performed more poorly on the Object Perspective Test (measuring spatial orientation) improved significantly. Similarly, on the Mental Rotation Test, ECB, and Progressive Matrices, those who performed more poorly at the beginning tended to improve after two weeks of training. There was no change on the Digit Symbol test.
The finding that only those whose performance was initially poor benefited from cognitive training is consistent with other studies suggesting that training only benefits those who are operating below par. This is not really surprising, but there are a few points that should be made.
First of all, it should be noted that this was a group of relatively high-functioning young-old adults — poorer performance in this case could be (relatively) better performance in another context. What it comes down to is whether you are operating at a level below which you are capable of — and this applies broadly, for example, experiments show that spatial training benefits females but not males (because males tend to already have practiced enough).
Given that, in expertise research, training has an on-going, apparently limitless, effect on performance, it seems likely that the limited benefits shown in this and other studies is because of the extremely limited scope of the training. Fourteen hours is not enough to improve people who are already performing adequately — but that doesn’t mean that they wouldn’t improve with more hours. I have yet to see any interventions with older adults that give them the amount of cognitive training you would expect them to need to achieve some level of mastery.
My third and final point is the specific nature of the improvements. This has also been shown in other studies, and sometimes appears quite arbitrary — for example, one 3-D puzzle game apparently improved mental rotation, while a different 3-D puzzle game had no effect. The point being that we still don’t understand the precise attributes needed to improve different skills (although the researchers advocate the use of a tool called cognitive task analysis for revealing the underlying qualities of an activity) — but we do understand that it is a matter of precise attributes, which is definitely a step in the right direction.
The main thing, then, that you should take away from this is the idea that different activities involve specific cognitive tasks, and these, and only these, will be the ones that benefit from practicing the activities. You therefore need to think about what tasks you want to improve before deciding on the activities to practice.
 Whitlock LA, McLaughlin AC, Allaire JC. Individual differences in response to cognitive training: Using a multi-modal, attentionally demanding game-based intervention for older adults. Computers in Human Behavior [Internet]. Submitted . Available from: http://www.sciencedirect.com/science/article/pii/S0747563212000143
Games that use the n-back task, designed to challenge working memory, may improve fluid intelligence, but only if the games are at the right level of difficulty for the individual.
It has been difficult to train individuals in such a way that they improve in general skills rather than the specific ones used in training. However, recently some success has been achieved using what is called an “n-back” task, a task that involves presenting a series of visual and/or auditory cues to a subject and asking the subject to respond if that cue has occurred, to start with, one time back. If the subject scores well, the number of times back is increased each round.
In the latest study, 62 elementary and middle school children completed a month of training on a computer program, five times a week, for 15 minutes at a time. While the active control group trained on a knowledge and vocabulary-based task, the experimental group was given a demanding spatial task in which they were presented with a sequence of images at one of six locations, one at a time, at a rate of 3s. The child had to press one key whenever the current image was at the same location as the one n items back in the series, and another key if it wasn’t. Both tasks employed themed graphics to make the task more appealing and game-like.
How far back the child needed to remember depended on their performance — if they were struggling, n would be decreased; if they were meeting the challenge, n would be increased.
Although the experimental and active control groups showed little difference on abstract reasoning tasks (reflecting fluid intelligence) at the end of the training, when the experimental group was divided into two subgroups on the basis of training gain, the story was different. Those who showed substantial improvement on the training task over the month were significantly better than the others, on the abstract reasoning task. Moreover, this improvement was maintained at follow-up testing three months later.
The key to success seems to be whether or not the games hit the “sweet spot” for the individual — fun and challenging, but not so challenging as to be frustrating. Those who showed the least improvement rated the game as more difficult, while those who improved the most found it challenging but not overwhelming.
You can try this task yourself at http://brainworkshop.sourceforge.net/.
Jaeggi, Susanne M, Martin Buschkuehl, John Jonides, and Priti Shah. “Short- and long-term benefits of cognitive training.” Proceedings of the National Academy of Sciences of the United States of America 2011 (June 13, 2011): 2-7. http://www.ncbi.nlm.nih.gov/pubmed/21670271.
 Jaeggi SM, Buschkuehl M, Jonides J, Perrig WJ. From the Cover: Improving fluid intelligence with training on working memory. Proceedings of the National Academy of Sciences [Internet]. 2008 ;105(19):6829 - 6833. Available from: http://www.pnas.org/content/early/2008/04/25/0801268105.abstract
http://www.latimes.com/health/la-he-iq-boost-20110614-1,0,2455553.story http://consumer.healthday.com/Article.asp?AID=653856 http://health.usnews.com/health-news/family-health/brain-and-behavior/ar... http://medicalxpress.com/news/2011-05-brain_1.html
A twin study suggests prenatal testosterone may be a factor in the innate male superiority in mental rotation*.
Because male superiority in mental rotation appears to be evident at a very young age, it has been suggested that testosterone may be a factor. To assess whether females exposed to higher levels of prenatal testosterone perform better on mental rotation tasks than females with lower levels of testosterone, researchers compared mental rotation task scores between twins from same-sex and opposite-sex pairs.
It was found that females with a male co-twin scored higher than did females with a female co-twin (there was no difference in scores between males from opposite-sex and same-sex pairs). Of course, this doesn’t prove that that the differences are produced in the womb; it may be that girls with a male twin engage in more male-typical activities. However, the association remained after allowing for computer game playing experience.
The study involved 804 twins, average age 22, of whom 351 females were from same-sex pairs and 120 from opposite-sex pairs. There was no significant difference between females from identical same-sex pairs compared to fraternal same-sex pairs.
* Please do note that ‘innate male superiority’ does NOT mean that all men are inevitably better than all women at this very specific task! My words simply reflect the evidence that the tendency of males to be better at mental rotation is found in infants as young as 3 months.
 Vuoksimaa E, Kaprio J, Kremen WS, Hokkanen L, Viken RJ, Tuulio-Henriksson A, Rose RJ. Having a Male Co-Twin Masculinizes Mental Rotation Performance in Females. Psychological Science [Internet]. 2010 ;21(8):1069 - 1071. Available from: http://pss.sagepub.com/content/21/8/1069.short
Male superiority in mental rotation is the most-cited gender difference in cognitive abilities. A new study shows that the difference can be eliminated in 6-year-olds after a mere 8 weeks.
Following a monkey study that found training in spatial memory could raise females to the level of males, and human studies suggesting the video games might help reduce gender differences in spatial processing (see below for these), a new study shows that training in spatial skills can eliminate the gender difference in young children. Spatial ability, along with verbal skills, is one of the two most-cited cognitive differences between the sexes, for the reason that these two appear to be the most robust.
This latest study involved 116 first graders, half of whom were put in a training program that focused on expanding working memory, perceiving spatial information as a whole rather than concentrating on details, and thinking about spatial geometric pictures from different points of view. The other children took part in a substitute training program, as a control group. Initial gender differences in spatial ability disappeared for those who had been in the spatial training group after only eight weekly sessions.
A study of 90 adult rhesus monkeys found young-adult males had better spatial memory than females, but peaked early. By old age, male and female monkeys had about the same performance. This finding is consistent with reports suggesting that men show greater age-related cognitive decline relative to women. A second study of 22 rhesus monkeys showed that in young adulthood, simple spatial-memory training did not help males but dramatically helped females, raising their performance to the level of young-adult males and wiping out the gender gap.
Another study showing that expert video gamers have improved mental rotation skills, visual and spatial memory, and multitasking skills has led researchers to conclude that training with video games may serve to reduce gender differences in visual and spatial processing, and some of the cognitive declines that come with aging.
 Tzuriel D, Egozi G. Gender Differences in Spatial Ability of Young Children: The Effects of Training and Processing Strategies. Child Development [Internet]. 2010 ;81(5):1417 - 1430. Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1467-8624.2010.01482.x/abstract
 Lacreuse A, Kim CB, Rosene DL, Killiany RJ, Moss MB, Moore TL, Chennareddi L, Herndon JG. Sex, Age, and Training Modulate Spatial Memory in the Rhesus Monkey (Macaca mulatta). Behavioral Neuroscience [Internet]. 2005 ;119(1):118 - 126. Available from: http://psycnet.apa.org/journals/bne/119/1/118/
 Dye MWG, Green SC, Bavelier D. Increasing Speed of Processing With Action Video Games. Current Directions in Psychological Science [Internet]. 2009 ;18(6):321 - 326. Available from: http://dx.doi.org/10.1111/j.1467-8721.2009.01660.x
Current study: www.physorg.com/news203744243.html Monkey study: http://www.eurekalert.org/pub_releases/2005-02/apa-ima022205.php http://www.eurekalert.org/pub_releases/2005-02/euhs-npm020905.php http://www.sciam.com/article.cfm?articleID=000560D5-7252-12B9-9A2C83414B... Video game study: http://www.eurekalert.org/pub_releases/2009-12/afps-rsa121709.php
A new study shows improvement in visual working memory in older adults following ten hours training with a commercial brain training program. The performance gains correlated with changes in brain activity.
While brain training programs can certainly improve your ability to do the task you’re practicing, there has been little evidence that this transfers to other tasks. In particular, the holy grail has been very broad transfer, through improvement in working memory. While there has been some evidence of this in pilot programs for children with ADHD, a new study is the first to show such improvement in older adults using a commercial brain training program.
A study involving 30 healthy adults aged 60 to 89 has demonstrated that ten hours of training on a computer game designed to boost visual perception improved perceptual abilities significantly, and also increased the accuracy of their visual working memory to the level of younger adults. There was a direct link between improved performance and changes in brain activity in the visual association cortex.
The computer game was one of those developed by Posit Science. Memory improvement was measured about one week after the end of training. The improvement did not, however, withstand multi-tasking, which is a particular problem for older adults. The participants, half of whom underwent the training, were college educated. The training challenged players to discriminate between two different shapes of sine waves (S-shaped patterns) moving across the screen. The memory test (which was performed before and after training) involved watching dots move across the screen, followed by a short delay and then re-testing for the memory of the exact direction the dots had moved.
 Berry AS, Zanto TP, Clapp WC, Hardy JL, Delahunt PB, Mahncke HW, Gazzaley A. The Influence of Perceptual Training on Working Memory in Older Adults. PLoS ONE [Internet]. 2010 ;5(7):e11537 - e11537. Available from: http://dx.doi.org/10.1371/journal.pone.0011537
Full text available at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0011537
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