visual memory

Being overweight linked to poorer memory

  • A study of younger adults adds to evidence that higher BMI is associated with poorer cognition, and points to a specific impairment in memory integration.

A small study involving 50 younger adults (18-35; average age 24) has found that those with a higher BMI performed significantly worse on a computerised memory test called the “Treasure Hunt Task”.

The task involved moving food items around complex scenes (e.g., a desert with palm trees), hiding them in various locations, and indicating afterward where and when they had hidden them. The test was designed to disentangle object, location, and temporal order memory, and the ability to integrate those separate bits of information.

Those with higher BMI were poorer at all aspects of this task. There was no difference, however, in reaction times, or time taken at encoding. In other words, they weren't slower, or less careful when they were learning. Analysis of the errors made indicated that the problem was not with spatial memory, but rather with the binding of the various elements into one coherent memory.

The results could suggest that overweight people are less able to vividly relive details of past events. This in turn might make it harder for them to keep track of what they'd eaten, perhaps making overeating more likely.

The 50 participants included 27 with BMI below 25, 24 with BMI 25-30 (overweight), and 8 with BMI over 30 (obese). 72% were female. None were diagnosed diabetics. However, the researchers didn't take other health conditions which often co-occur with obesity, such as hypertension and sleep apnea, into account.

This is a preliminary study only, and further research is needed to validate its findings. However, it's significant in that it adds to growing evidence that the cognitive impairments that accompany obesity are present early in adult life and are not driven by diabetes.

The finding is also consistent with previous research linking obesity with dysfunction of the hippocampus and the frontal lobe.

http://www.eurekalert.org/pub_releases/2016-02/uoc-bol022616.php

https://www.theguardian.com/science/neurophilosophy/2016/mar/03/obesity-linked-to-memory-deficits

Reference: 

[4183] Cheke LG, Simons JS, Clayton NS. Higher body mass index is associated with episodic memory deficits in young adults. The Quarterly Journal of Experimental Psychology [Internet]. 2015 :1 - 12. Available from: http://dx.doi.org/10.1080/17470218.2015.1099163

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Physical activity linked to better memory for names and faces among older adults

  • A small study adds to evidence that walking improves memory in older adults, and indicates that this is particularly helpful for memory tasks the seniors find challenging.

A small study that fitted 29 young adults (18-31) and 31 older adults (55-82) with a device that recorded steps taken and the vigor and speed with which they were made, has found that those older adults with a higher step rate performed better on memory tasks than those who were more sedentary. There was no such effect seen among the younger adults.

Improved memory was found for both visual and episodic memory, and was strongest with the episodic memory task. This required recalling which name went with a person's face — an everyday task that older adults often have difficulty with.

However, the effect on visual memory had more to do with time spent sedentary than step rate. With the face-name task, both time spent sedentary and step rate were significant factors, and both factors had a greater effect than they had on visual memory.

Depression and hypertension were both adjusted for in the analysis.

There was no significant difference in executive function related to physical activity, although previous studies have found an effect. Less surprisingly, there was also no significant effect on verbal memory.

Both findings might be explained in terms of cognitive demand. The evidence suggests that the effect of physical exercise is only seen when the task is sufficiently cognitively demanding. No surprise that verbal memory (which tends to be much less affected by age) didn't meet that challenge, but interestingly, the older adults in this study were also less impaired on executive function than on visual memory. This is unusual, and reminds us that, especially with small studies, you cannot ignore the individual differences.

This general principle may also account for the lack of effect among younger adults. It is interesting to speculate whether physical activity effects would be found if the younger adults were given much more challenging tasks (either by increasing their difficulty, or selecting a group who were less capable).

Step Rate was calculated by total steps taken divided by the total minutes in light, moderate, and vigorous activities, based on the notion that this would provide an independent indicator of physical activity intensity (how briskly one is walking). Sedentary Time was the total minutes spent sedentary.

http://www.eurekalert.org/pub_releases/2015-11/bumc-slp112415.php

Reference: 

[4045] Hayes SM, Alosco ML, Hayes JP, Cadden M, Peterson KM, Allsup K, Forman DE, Sperling RA, Verfaellie M. Physical Activity Is Positively Associated with Episodic Memory in Aging. Journal of the International Neuropsychological Society [Internet]. 2015 ;21(Special Issue 10):780 - 790. Available from: http://journals.cambridge.org/article_S1355617715000910

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Clarity in short-term memory shows no link with IQ

December, 2010

The two measures of working memory capacity appear to be fully independent, and only one of them is related to intelligence.

The number of items a person can hold in short-term memory is strongly correlated with their IQ. But short-term memory has been recently found to vary along another dimension as well: some people remember (‘see’) the items in short-term memory more clearly and precisely than other people. This discovery has lead to the hypothesis that both of these factors should be considered when measuring working memory capacity. But do both these aspects correlate with fluid intelligence?

A new study presented 79 students with screen displays fleetingly showing either four or eight items. After a one-second blank screen, one item was returned and the subject asked whether that object had been in a particular location previously. Their ability to detect large and small changes in the items provided an estimate of how many items the individual could hold in working memory, and how clearly they remembered them. These measures were compared with individuals’ performance on standard measures of fluid intelligence.

Analysis of data found that these two measures of working memory — number and clarity —are completely independent of each other, and that it was the number factor only that correlated with intelligence.

This is not to say that clarity is unimportant! Only that it is not related to intelligence.

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Cognition impaired by low-level exposure to organophosphate pesticides

January, 2013

A meta-analysis has concluded that low-level exposure to organophosphates has a small-to-moderate negative effect on cognitive function.

Organophosphate pesticides are the most widely used insecticides in the world; they are also (according to WHO), one of the most hazardous pesticides to vertebrate animals. While the toxic effects of high levels of organophosphates are well established, the effects of long-term low-level exposure are still controversial.

A meta-analysis involving 14 studies and more than 1,600 participants, reveals that the majority of well-designed studies undertaken over the last 20 years have found a significant association between low-level exposure to organophosphates and impaired cognitive function. Impairment was small to moderate, and mainly concerned psychomotor speed, executive function, visuospatial ability, working memory, and visual memory.

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Spatial skills can be improved through training

October, 2012

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:

  • Perceiving objects, paths, or spatial configurations against a background of distracting information;
  • Piecing together objects into more complex configurations, visualizing and mentally transforming objects;
  • Understanding abstract principles, such as horizontal invariance;
  • Visualizing an environment in its entirety from a different position.

The review compared three types of training. Those that used:

  • Video games (24 studies)
  • Semester-long instructional courses on spatial reasoning (42 studies)
  • Practical training, often in a lab, that involved practicing spatial tasks, strategic instruction, or computerized lessons (138 studies).

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!

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How emotion keeps some memories vivid

September, 2012

Emotionally arousing images that are remembered more vividly were seen more vividly. This may be because the amygdala focuses visual attention rather than more cognitive attention on the image.

We know that emotion affects memory. We know that attention affects perception (see, e.g., Visual perception heightened by meditation training; How mindset can improve vision). Now a new study ties it all together. The study shows that emotionally arousing experiences affect how well we see them, and this in turn affects how vividly we later recall them.

The study used images of positively and negatively arousing scenes and neutral scenes, which were overlaid with varying amounts of “visual noise” (like the ‘snow’ we used to see on old televisions). College students were asked to rate the amount of noise on each picture, relative to a specific image they used as a standard. There were 25 pictures in each category, and three levels of noise (less than standard, equal to standard, and more than standard).

Different groups explored different parameters: color; gray-scale; less noise (10%, 15%, 20% as compared to 35%, 45%, 55%); single exposure (each picture was only presented once, at one of the noise levels).

Regardless of the actual amount of noise, emotionally arousing pictures were consistently rated as significantly less noisy than neutral pictures, indicating that people were seeing them more clearly. This was true in all conditions.

Eye-tracking analysis ruled out the idea that people directed their attention differently for emotionally arousing images, but did show that more eye fixations were associated both with less noisy images and emotionally arousing ones. In other words, people were viewing emotionally important images as if they were less noisy.

One group of 22 students were given a 45-minute spatial working memory task after seeing the images, and then asked to write down all the details they could remember about the pictures they remembered seeing. The amount of detail they recalled was taken to be an indirect measure of vividness.

A second group of 27 students were called back after a week for a recognition test. They were shown 36 new images mixed in with the original 75 images, and asked to rate them as new, familiar, or recollected. They were also asked to rate the vividness of their recollection.

Although, overall, emotionally arousing pictures were not more likely to be remembered than neutral pictures, both experiments found that pictures originally seen as more vivid (less noise) were remembered more vividly and in more detail.

Brain scans from 31 students revealed that the amygdala was more active when looking at images rated as vivid, and this in turn increased activity in the visual cortex and in the posterior insula (which integrates sensations from the body). This suggests that the increased perceptual vividness is not simply a visual phenomenon, but part of a wider sensory activation.

There was another neural response to perceptual vividness: activity in the dorsolateral prefrontal cortex and the posterior parietal cortex was negatively correlated with vividness. This suggests that emotion is not simply increasing our attentional focus, it is instead changing it by reducing effortful attentional and executive processes in favor of more perceptual ones. This, perhaps, gives emotional memories their different ‘flavor’ compared to more neutral memories.

These findings clearly need more exploration before we know exactly what they mean, but the main finding from the study is that the vividness with which we recall some emotional experiences is rooted in the vividness with which we originally perceived it.

The study highlights how emotion can sharpen our attention, building on previous findings that emotional events are more easily detected when visibility is difficult, or attentional demands are high. It is also not inconsistent with a study I reported on last year, which found some information needs no repetition to be remembered because the amygdala decrees it of importance.

I should add, however, that the perceptual effect is not the whole story — the current study found that, although perceptual vividness is part of the reason for memories that are vividly remembered, emotional importance makes its own, independent, contribution. This contribution may occur after the event.

It’s suggested that individual differences in these reactions to emotionally enhanced vividness may underlie an individual’s vulnerability to post-traumatic stress disorder.

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Latest London taxi driver study shows brain changes driven by learning

January, 2012

A comparison of the brains of London taxi drivers before and after their lengthy training shows clearly that the increase in hippocampal gray matter develops with training, but this may come at the expense of other brain functions.

The evidence that adult brains could grow new neurons was a game-changer, and has spawned all manner of products to try and stimulate such neurogenesis, to help fight back against age-related cognitive decline and even dementia. An important study in the evidence for the role of experience and training in growing new neurons was Maguire’s celebrated study of London taxi drivers, back in 2000.

The small study, involving 16 male, right-handed taxi drivers with an average experience of 14.3 years (range 1.5 to 42 years), found that the taxi drivers had significantly more grey matter (neurons) in the posterior hippocampus than matched controls, while the controls showed relatively more grey matter in the anterior hippocampus. Overall, these balanced out, so that the volume of the hippocampus as a whole wasn’t different for the two groups. The volume in the right posterior hippocampus correlated with the amount of experience the driver had (the correlation remained after age was accounted for).

The posterior hippocampus is preferentially involved in spatial navigation. The fact that only the right posterior hippocampus showed an experience-linked increase suggests that the right and left posterior hippocampi are involved in spatial navigation in different ways. The decrease in anterior volume suggests that the need to store increasingly detailed spatial maps brings about a reorganization of the hippocampus.

But (although the experience-related correlation is certainly indicative) it could be that those who manage to become licensed taxi drivers in London are those who have some innate advantage, evidenced in a more developed posterior hippocampus. Only around half of those who go through the strenuous training program succeed in qualifying — London taxi drivers are unique in the world for being required to pass through a lengthy training period and pass stringent exams, demonstrating their knowledge of London’s 25,000 streets and their idiosyncratic layout, plus 20,000 landmarks.

In this new study, Maguire and her colleague made a more direct test of this question. 79 trainee taxi drivers and 31 controls took cognitive tests and had their brains scanned at two time points: at the beginning of training, and 3-4 years later. Of the 79 would-be taxi drivers, only 39 qualified, giving the researchers three groups to compare.

There were no differences in cognitive performance or brain scans between the three groups at time 1 (before training). At time 2 however, when the trainees had either passed the test or failed to acquire the Knowledge, those trainees that qualified had significantly more gray matter in the posterior hippocampus than they had had previously. There was no change in those who failed to qualify or in the controls.

Unsurprisingly, both qualified and non-qualified trainees were significantly better at judging the spatial relations between London landmarks than the control group. However, qualified trainees – but not the trainees who failed to qualify – were worse than the other groups at recalling a complex visual figure after 30 minutes (see here for an example of such a figure). Such a finding replicates previous findings of London taxi drivers. In other words, their improvement in spatial memory as it pertains to London seems to have come at a cost.

Interestingly, there was no detectable difference in the structure of the anterior hippocampus, suggesting that these changes develop later, in response to changes in the posterior hippocampus. However, the poorer performance on the complex figure test may be an early sign of changes in the anterior hippocampus that are not yet measurable in a MRI.

The ‘Knowledge’, as it is known, provides a lovely real-world example of expertise. Unlike most other examples of expertise development (e.g. music, chess), it is largely unaffected by childhood experience (there may be some London taxi drivers who began deliberately working on their knowledge of London streets in childhood, but it is surely not common!); it is developed through a training program over a limited time period common to all participants; and its participants are of average IQ and education (average school-leaving age was around 16.7 years for all groups; average verbal IQ was around or just below 100).

So what underlies this development of the posterior hippocampus? If the qualified and non-qualified trainees were comparable in education and IQ, what determined whether a trainee would ‘build up’ his hippocampus and pass the exams? The obvious answer is hard work / dedication, and this is borne out by the fact that, although the two groups were similar in the length of their training period, those who qualified spent significantly more time training every week (an average of 34.5 hours a week vs 16.7 hours). Those who qualified also attended far more tests (an average of 15.6 vs 2.6).

While neurogenesis is probably involved in this growth within the posterior hippocampus, it is also possible that growth reflects increases in the number of connections, or in the number of glia. Most probably (I think), all are involved.

There are two important points to take away from this study. One is its clear demonstration that training can produce measurable changes in a brain region. The other is the indication that this development may come at the expense of other regions (and functions).

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Frequent 'heading' in soccer can lead to brain injury and cognitive impairment

December, 2011

A small study extends the evidence that even mild concussions can cause brain damage, with the finding that frequent heading of the ball in soccer can cause similar damage.

American football has been in the news a lot in recent years, as evidence has accumulated as to the brain damage incurred by professional footballers. But American football is a high-impact sport. Soccer is quite different. And yet the latest research reveals that even something as apparently unexceptional as bouncing a ball off your forehead can cause damage to your brain, if done often enough.

Brain scans on 32 amateur soccer players (average age 31) have revealed that those who estimated heading the ball more than 1,000-1,500 times in the past year had damage to white matter similar to that seen in patients with concussion.

Six brain regions were seen to be affected: one in the frontal lobe and five in the temporo-occipital cortex. These regions are involved in attention, memory, executive functioning and higher-order visual functions. The number of headings (obviously very rough estimates, based presumably on individuals’ estimates of how often they play and how often they head the ball on average during a game) needed to produce measurable decreases in the white matter integrity varied per region. In four of temporo-occipital regions, the threshold number was around 1500; in the fifth it was only 1000; in the frontal lobe, it was 1300.

Those with the highest annual heading frequency also performed worse on tests of verbal memory and psychomotor speed (activities that require mind-body coordination, like throwing a ball).

This is only a small study and clearly more research is required, but the findings indicate that we should lower our ideas of what constitutes ‘harm’ to the brain — if repetition is frequent enough, even mild knocks can cause damage. This adds to the evidence I discussed in a recent blog post, that even mild concussions can produce long-lasting trauma to the brain, and it is important to give your brain time to repair itself.

At the moment we can only speculate on the effect such repetition might have to the vulnerable brains of children.

The researchers suggest that heading should be monitored to prevent players exceeding unsafe exposure thresholds.

Reference: 

Kim, N., Zimmerman, M., Lipton, R., Stewart, W., Gulko, E., Lipton, M. & Branch, C. 2011. PhD Making Soccer Safer for the Brain: DTI-defined Exposure Thresholds for White Matter Injury Due to Soccer Heading. Presented November 30 at the annual meeting of the Radiological Society of North America (RSNA) in Chicago.

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Another challenge to idea that men are better at spatial thinking

October, 2011

A cross-cultural study finds a significant gender difference on a simple puzzle problem for one culture but no gender difference for another. The difference was only partly explained by education.

Here’s an intriguing approach to the long-standing debate about gender differences in spatial thinking. The study involved 1,279 adults from two cultural groups in India. One of these groups was patrilineal, the other matrilineal. The volunteers were given a wooden puzzle to assemble as quickly as they could.

Within the patrilineal group, men were on average 36% faster than women. Within the matrilineal group, however, there was no difference between the genders.

I have previously reported on studies showing how small amounts of spatial training can close the gap in spatial abilities between the genders. It has been argued that in our culture, males are directed toward spatial activities (construction such as Lego; later, video games) more than females are.

In this case, the puzzle was very simple. However, general education was clearly one factor mediating this gender difference. In the patrilineal group, males had an average 3.67 more years of education, while in the matrilineal group, men and women had the same amount of education. When education was included in the statistical analysis, a good part of the difference between the groups was accounted for — but not all.

While we can only speculate about the remaining cause, it is interesting to note that, among the patrilineal group, the gender gap was decidedly smaller among those who lived in households not wholly owned by males (in the matrilineal group, men are not allowed to own property, so this comparison cannot be made).

It is also interesting to note that the men in the matrilineal group were faster than the men in the patrilineal group. This is not a function of education differences, because education in the matrilineal group was slightly less than that of males in the patrilineal group.

None of the participants had experience with puzzle solving, and both groups had similar backgrounds, being closely genetically related and living in villages geographically close. Participants came from eight villages: four patrilineal and four matrilineal.

Reference: 

[2519] Hoffman M, Gneezy U, List JA. Nurture affects gender differences in spatial abilities. Proceedings of the National Academy of Sciences [Internet]. 2011 ;108(36):14786 - 14788. Available from: http://www.pnas.org/content/108/36/14786.abstract

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Visual Memory

Older news items (pre-2010) brought over from the old website

More light shed on distinction between long and short-term memory

The once clear-cut distinction between long- and short-term memory has increasingly come under fire in recent years. A new study involving patients with a specific form of epilepsy called 'temporal lobe epilepsy with bilateral hippocampal sclerosis' has now clarified the distinction. The patients, who all had severely compromised hippocampi, were asked to try and memorize photographic images depicting normal scenes. Their memory was tested and brain activity recorded after five seconds or 60 minutes. As expected, the patients could not remember the images after 60 minutes, but could distinguish seen-before images from new at five seconds. However, their memory was poor when asked to recall details about the images. Brain activity showed that short-term memory for details required the coordinated activity of a network of visual and temporal brain areas, whereas standard short-term memory drew on a different network, involving frontal and parietal regions, and independent of the hippocampus.

[996] Cashdollar N, Malecki U, Rugg-Gunn FJ, Duncan JS, Lavie N, Duzel E. Hippocampus-dependent and -independent theta-networks of active maintenance. Proceedings of the National Academy of Sciences [Internet]. 2009 ;106(48):20493 - 20498. Available from: http://www.pnas.org/content/106/48/20493.abstract

http://www.eurekalert.org/pub_releases/2009-11/ucl-tal110909.php

Individual differences in working memory capacity depend on two factors

A new computer model adds to our understanding of working memory, by showing that working memory can be increased by the action of the prefrontal cortex in reinforcing activity in the parietal cortex (where the information is temporarily stored). The idea is that the prefrontal cortex sends out a brief stimulus to the parietal cortex that generates a reverberating activation in a small subpopulation of neurons, while inhibitory interactions with neurons further away prevents activation of the entire network. This lateral inhibition is also responsible for limiting the mnemonic capacity of the parietal network (i.e. provides the limit on your working memory capacity). The model has received confirmatory evidence from an imaging study involving 25 volunteers. It was found that individual differences in performance on a short-term visual memory task were correlated with the degree to which the dorsolateral prefrontal cortex was activated and its interconnection with the parietal cortex. In other words, your working memory capacity is determined by both storage capacity (in the posterior parietal cortex) and prefrontal top-down control. The findings may help in the development of ways to improve working memory capacity, particularly when working memory is damaged.

[441] Edin F, Klingberg T, Johansson P, McNab F, Tegner J, Compte A. Mechanism for top-down control of working memory capacity. Proceedings of the National Academy of Sciences [Internet]. 2009 ;106(16):6802 - 6807. Available from: http://www.pnas.org/content/early/2009/03/31/0901894106.abstract

http://www.eurekalert.org/pub_releases/2009-04/i-id-aot040109.php

Some short-term memories die suddenly, no fading

We don’t remember everything; the idea of memory as being a video faithfully recording every aspect of everything we have ever experienced is a myth. Every day we look at the world and hold a lot of what we say for no more than a few seconds before discarding it as not needed any more. Until now it was thought that these fleeting visual memories faded away, gradually becoming more imprecise. Now it seems that such memories remain quite accurate as long as they exist (about 4 seconds), and then just vanish away instantly. The study involved testing memory for shapes and colors in 12 adults, and it was found that the memory for shape or color was either there or not there – the answers either correct or random guesses. The probability of remembering correctly decreased between 4 and 10 seconds.

[941] Zhang W, Luck SJ. Sudden death and gradual decay in visual working memory. Psychological Science: A Journal of the American Psychological Society / APS [Internet]. 2009 ;20(4):423 - 428. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19320861

http://www.eurekalert.org/pub_releases/2009-04/uoc--ssm042809.php

Where visual short-term memory occurs

Working memory used to be thought of as a separate ‘store’, and now tends to be regarded more as a process, a state of mind. Such a conception suggests that it may occur in the same regions of the brain as long-term memory, but in a pattern of activity that is somehow different from LTM. However, there has been little evidence for that so far. Now a new study has found that information in WM may indeed be stored via sustained, but low, activity in sensory areas. The study involved volunteers being shown an image for one second and instructed to remember either the color or the orientation of the image. After then looking at a blank screen for 10 seconds, they were shown another image and asked whether it was the identical color/orientation as the first image. Brain activity in the primary visual cortex was scanned during the 10 second delay, revealing that areas normally involved in processing color and orientation were active during that time, and that the pattern only contained the targeted information (color or orientation).

[1032] Serences JT, Ester EF, Vogel EK, Awh E. Stimulus-Specific Delay Activity in Human Primary Visual Cortex. Psychological Science [Internet]. 2009 ;20(2):207 - 214. Available from: http://dx.doi.org/10.1111/j.1467-9280.2009.02276.x

http://www.eurekalert.org/pub_releases/2009-02/afps-sih022009.php
http://www.eurekalert.org/pub_releases/2009-02/uoo-dsm022009.php

The finding is consistent with that of another study published this month, in which participants were shown two examples of simple striped patterns at different orientations and told to hold either one or the other of the orientations in their mind while being scanned. Orientation is one of the first and most basic pieces of visual information coded and processed by the brain. Using a new decoding technique, researchers were able to predict with 80% accuracy which of the two orientations was being remembered 11 seconds after seeing a stimulus, from the activity patterns in the visual areas. This was true even when the overall level of activity in these visual areas was very weak, no different than looking at a blank screen.

[652] Harrison SA, Tong F. Decoding reveals the contents of visual working memory in early visual areas. Nature [Internet]. 2009 ;458(7238):632 - 635. Available from: http://dx.doi.org/10.1038/nature07832

http://www.eurekalert.org/pub_releases/2009-02/vu-edi021709.php
http://www.physorg.com/news154186809.html

Even toddlers can ‘chunk' information for better remembering

We all know it’s easier to remember a long number (say a phone number) when it’s broken into chunks. Now a study has found that we don’t need to be taught this; it appears to come naturally to us. The study showed 14 months old children could track only three hidden objects at once, in the absence of any grouping cues, demonstrating the standard limit of working memory. However, with categorical or spatial cues, the children could remember more. For example, when four toys consisted of two groups of two familiar objects, cats and cars, or when six identical orange balls were grouped in three groups of two.

[196] Feigenson L, Halberda J. From the Cover: Conceptual knowledge increases infants' memory capacity. Proceedings of the National Academy of Sciences [Internet]. 2008 ;105(29):9926 - 9930. Available from: http://www.pnas.org/content/early/2008/07/11/0709884105.abstract

http://www.eurekalert.org/pub_releases/2008-07/jhu-etg071008.php

Full text available at http://www.pnas.org/content/105/29/9926.abstract?sid=c01302b6-cd8e-4072-842c-7c6fcd40706f

Working memory has a fixed number of 'slots'

A study that showed volunteers a pattern of colored squares for a tenth of a second, and then asked them to recall the color of one of the squares by clicking on a color wheel, has found that working memory acts like a high-resolution camera, retaining three or four features in high detail. Unlike a digital camera, however, it appears that you can’t increase the number of images you can store by lowering the resolution. The resolution appears to be constant for a given individual. However, individuals do differ in the resolution of each feature and the number of features that can be stored.

[278] Zhang W, Luck SJ. Discrete fixed-resolution representations in visual working memory. Nature [Internet]. 2008 ;453(7192):233 - 235. Available from: http://dx.doi.org/10.1038/nature06860

http://www.physorg.com/news126432902.html
http://www.eurekalert.org/pub_releases/2008-04/uoc--wmh040208.php

And another study of working memory has attempted to overcome the difficulties involved in measuring a person’s working memory capacity (ensuring that no ‘chunking’ of information takes place), and concluded that people do indeed have a fixed number of ‘slots’ in their working memory. In the study, participants were shown two, five or eight small, scattered, different-colored squares in an array, which was then replaced by an array of the same squares without the colors, after which the participant was shown a single color in one location and asked to indicate whether the color in that spot had changed from the original array.

[437] Rouder JN, Morey RD, Cowan N, Zwilling CE, Morey CC, Pratte MS. An assessment of fixed-capacity models of visual working memory. Proceedings of the National Academy of Sciences [Internet]. 2008 ;105(16):5975 - 5979. Available from: http://www.pnas.org/content/105/16/5975.abstract

http://www.eurekalert.org/pub_releases/2008-04/uom-mpd042308.php

Impressive feats in visual memory

In light of all the recent experiments emphasizing how small our short-term visual memory is, it’s comforting to be reminded that, nevertheless, we have an amazing memory for pictures — in the right circumstances. Those circumstances include looking at images of familiar objects, as opposed to abstract artworks, and being motivated to do well (the best-scoring participant was given a cash prize). In the study, 14 people aged 18 to 40 viewed 2,500 images, one at a time, for a few seconds. Afterwards, they were shown pairs of images and asked to select the exact image they had seen earlier. The previously viewed item could be paired with either an object from a novel category, an object of the same basic-level category, or the same object in a different state or pose. Stunningly, participants on average chose the correct image 92%, 88% and 87% of the time, in each of the three pairing categories respectively.

[870] Brady TF, Konkle T, Alvarez GA, Oliva A. Visual long-term memory has a massive storage capacity for object details. Proceedings of the National Academy of Sciences [Internet]. 2008 ;105(38):14325 - 14329. Available from: http://www.pnas.org/content/early/2008/09/10/0803390105

Full text available at http://www.pnas.org/content/105/38/14325.abstract

Attention grabbers snatch lion's share of visual memory

It’s long been thought that when we look at a visually "busy" scene, we are only able to store a very limited number of objects in our visual short-term or working memory. For some time, this figure was believed to be four or five objects, but a recent report suggested it could be as low as two. However, a new study reveals that although it might not be large, it’s more flexible than we thought. Rather than being restricted to a limited number of objects, it can be shared out across the whole image, with more memory allocated for objects of interest and less for background detail. What’s of interest might be something we’ve previously decided on (i.e., we’re searching for), or something that grabs our attention.  Eye movements also reveal how brief our visual memory is, and that what our eyes are looking at isn’t necessarily what we’re ‘seeing’ — when people were asked to look at objects in a particular sequence, but the final object disappeared before their eyes moved on to it, it was found that the observers could more accurately recall the location of the object that they were about to look at than the one that they had just been looking at.

[1398] Bays PM, Husain M. Dynamic shifts of limited working memory resources in human vision. Science (New York, N.Y.) [Internet]. 2008 ;321(5890):851 - 854. Available from: http://www.ncbi.nlm.nih.gov/pubmed/18687968

http://www.physorg.com/news137337380.html

More on how short-term memory works

It’s been established that visual working memory is severely limited — that, on average, we can only be aware of about four objects at one time. A new study explored the idea that this capacity might be affected by complexity, that is, that we can think about fewer complex objects than simple objects. It found that complexity did not affect memory capacity. It also found that some people have clearer memories of the objects than other people, and that this is not related to how many items they can remember. That is, a high IQ is associated with the ability to hold more items in working memory, but not with the clarity of those items.

[426] Awh E, Barton B, Vogel EK. Visual working memory represents a fixed number of items regardless of complexity. Psychological Science: A Journal of the American Psychological Society / APS [Internet]. 2007 ;18(7):622 - 628. Available from: http://www.ncbi.nlm.nih.gov/pubmed/17614871

http://www.eurekalert.org/pub_releases/2007-07/uoo-htb071107.php
http://www.physorg.com/news103472118.html

Support for labeling as an aid to memory

A study involving an amnesia-inducing drug has shed light on how we form new memories. Participants in the study participants viewed words, photographs of faces and landscapes, and abstract pictures one at a time on a computer screen. Twenty minutes later, they were shown the words and images again, one at a time. Half of the images they had seen earlier, and half were new. They were then asked whether they recognized each one. For one session they were given midazolam, a drug used to relieve anxiety during surgical procedures that also causes short-term anterograde amnesia, and for one session they were given a placebo.
It was found that the participants' memory while in the placebo condition was best for words, but the worst for abstract images. Midazolam impaired the recognition of words the most, impaired memory for the photos less, and impaired recognition of abstract pictures hardly at all. The finding reinforces the idea that the ability to recollect depends on the ability to link the stimulus to a context, and that unitization increases the chances of this linking occurring. While the words were very concrete and therefore easy to link to the experimental context, the photographs were of unknown people and unknown places and thus hard to distinctively label. The abstract images were also unfamiliar and not unitized into something that could be described with a single word.

[1216] Reder LM, Oates JM, Thornton ER, Quinlan JJ, Kaufer A, Sauer J. Drug-Induced Amnesia Hurts Recognition, but Only for Memories That Can Be Unitized. Psychological science : a journal of the American Psychological Society / APS. 2006 ;17(7):562 - 567.

http://www.sciencedaily.com/releases/2006/07/060719092800.htm

Discovery disproves simple concept of memory as 'storage space'

The idea of memory “capacity” has become more and more eroded over the years, and now a new technique for measuring brainwaves seems to finally knock the idea on the head. Consistent with recent research suggesting that a crucial problem with aging is a growing inability to ignore distracting information, this new study shows that visual working memory depends on your ability to filter out irrelevant information. Individuals have long been characterized as having a “high” working memory capacity or a “low” one — the assumption has been that these people differ in their storage capacity. Now it seems it’s all about a neural mechanism that controls what information gets into awareness. People with high capacity have a much better ability to ignore irrelevant information.

[1091] Vogel EK, McCollough AW, Machizawa MG. Neural measures reveal individual differences in controlling access to working memory. Nature [Internet]. 2005 ;438(7067):500 - 503. Available from: http://dx.doi.org/10.1038/nature04171

http://www.eurekalert.org/pub_releases/2005-11/uoo-dds111805.php

Language cues help visual learning in children

A study of 4-year-old children has found that language, in the form of specific kinds of sentences spoken aloud, helped them remember mirror image visual patterns. The children were shown cards bearing red and green vertical, horizontal and diagonal patterns that were mirror images of one another. When asked to choose the card that matched the one previously seen, the children tended to mistake the original card for its mirror image, showing how difficult it was for them to remember both color and location. However, if they were told, when viewing the original card, a mnemonic cue such as ‘The red part is on the left’, they performed “reliably better”.

The paper was presented by a graduate student at the 17th annual meeting of the American Psychological Society, held May 26-29 in Los Angeles.

http://www.eurekalert.org/pub_releases/2005-05/jhu-lc051705.php

An advantage of age

A study comparing the ability of young and older adults to indicate which direction a set of bars moved across a computer screen has found that although younger participants were faster when the bars were small or low in contrast, when the bars were large and high in contrast, the older people were faster. The results suggest that the ability of one neuron to inhibit another is reduced as we age (inhibition helps us find objects within clutter, but makes it hard to see the clutter itself). The loss of inhibition as we age has previously been seen in connection with cognition and speech studies, and is reflected in our greater inability to tune out distraction as we age. Now we see the same process in vision.

[1356] Betts LR, Taylor CP, Sekuler AB, Bennett PJ. Aging Reduces Center-Surround Antagonism in Visual Motion Processing. Neuron [Internet]. 2005 ;45(3):361 - 366. Available from: http://www.cell.com/neuron/abstract/S0896-6273(05)00013-9

http://psychology.plebius.org/article.htm?article=739
http://www.eurekalert.org/pub_releases/2005-02/mu-opg020305.php

Why working memory capacity is so limited

There’s an old parlor game whereby someone brings into a room a tray covered with a number of different small objects, which they show to the people in the room for one minute, before whisking it away again. The participants are then required to write down as many objects as they can remember. For those who perform badly at this type of thing, some consolation from researchers: it’s not (entirely) your fault. We do actually have a very limited storage capacity for visual short-term memory.
Now visual short-term memory is of course vital for a number of functions, and reflecting this, there is an extensive network of brain structures supporting this type of memory. However, a new imaging study suggests that the limited storage capacity is due mainly to just one of these regions: the posterior parietal cortex. An interesting distinction can be made here between registering information and actually “holding it in mind”. Activity in the posterior parietal cortex strongly correlated with the number of objects the subjects were able to remember, but only if the participants were asked to remember. In contrast, regions of the visual cortex in the occipital lobe responded differently to the number of objects even when participants were not asked to remember what they had seen.

[598] Todd JJ, Marois R. Capacity limit of visual short-term memory in human posterior parietal cortex. Nature [Internet]. 2004 ;428(6984):751 - 754. Available from: http://www.ncbi.nlm.nih.gov/pubmed/15085133

http://www.eurekalert.org/pub_releases/2004-04/vu-slo040704.php
http://tinyurl.com/2jzwe (Telegraph article)

Brain signal predicts working memory capacity

Our visual short-term memory may have an extremely limited capacity, but some people do have a greater capacity than others. A new study reveals that an individual's capacity for such visual working memory can be predicted by his or her brainwaves. In the study, participants 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, and the higher the spike of corresponding brain activity – up to a point. 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 showed large increases. Subjects averaged 2.8 squares.

[1154] Vogel EK, Machizawa MG. Neural activity predicts individual differences in visual working memory capacity. Nature [Internet]. 2004 ;428(6984):748 - 751. Available from: http://dx.doi.org/10.1038/nature02447

http://www.eurekalert.org/pub_releases/2004-04/niom-bsp041604.php

Learning without desire or awareness

We have long known that learning can occur without attention. A recent study demonstrates learning that occurs without attention, without awareness and without any task relevance. Subjects were repeatedly presented with a background motion signal so weak that its direction was not visible; the invisible motion was an irrelevant background to the central task that engaged the subject's attention. Despite being below the threshold of visibility and being irrelevant to the central task, the repetitive exposure improved performance specifically for the direction of the exposed motion when tested in a subsequent suprathreshold test. These results suggest that a frequently presented feature sensitizes the visual system merely owing to its frequency, not its relevance or salience.

[594] Watanabe T, Nanez JE, Sasaki Y. Perceptual learning without perception. Nature [Internet]. 2001 ;413(6858):844 - 848. Available from: http://dx.doi.org/10.1038/35101601

http://www.nature.com/nsu/011025/011025-12.html
http://tinyurl.com/ix98

Visual memory better than previously thought

Why is it that you can park your car at a huge mall and find it a few hours later without much problem, or make your way through a store you have never been to before? The answer may lie in our ability to build up visual memories of a scene in a short period of time. A new study counters current thinking that visual memory is generally poor and that people quickly forget the details of what they have seen. It appears that even with very limited visual exposure to a scene, people are able to build up strong visual memories and, in fact, their recall of objects in the scene improved with each exposure. It is suggested these images aren't stored in short-term or long-term memory, but in medium-term memory, which lasts for a few minutes and appears to be specific to visual information as opposed to verbal or semantic information. "Medium-term memory depends on the visual context of the scene, such as the background, furniture and walls, which seems to be key in the ability to keep in mind the location and identity of objects. These disposable accumulated visual memories can be recalled in a few minutes if faced with that scene again, but are discarded in a day or two if the scene is not viewed again so they don't take up valuable memory space."

Melcher, D. 2001. Persistence of visual memory for scenes. Nature, 412 (6845), 401.

http://www.eurekalert.org/pub_releases/2001-07/rtsu-rrf072501.php

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