New Experiment: The Language & Memory Test

There is a close relationship between language and memory, since of course whenever you use words and grammar, you have to access your memory for those words and that grammar. If you couldn't remember anything, you couldn't learn language to begin with.

The relationship between language and memory is not well understood, partly because they tend to be studied by different people, though there are a few labs squarely interested in the relationship between language and memory, such as the Brain and Language Lab at Georgetown University.

This week, I posted a new experiment, "The Language & Memory Test", which explores the relationship between memory and language. The experiment consists of two components. One is a memory test. At the end, you will see your score and how it compares with other people who took the test. This test is surprisingly hard for how simple it seems.

In the other part, you will try to learn to use some new words. We'll be studying the relationship between different aspects of your memory performance and how you learn these new words. As always, there will be a bit more explanation at the end of the experiment. When the experiment is done and the results are known, there will be a full description of them and what we learned here at the blog and at GamesWithWords.org.

Try the Language & Memory test here.

Findings: How memory changes with age

It's well-known that both long-term and short-term memory decline with age. However, most of these data come from verbal memory tests. The evidence for visual short-term memory is less clear. A few studies (Adamowicz, 1976; 1978; Fahle & Daum, 1997) show age-related declines, but more recent studies do not (Faubert & Bellefeuille, 2002; McIntosh et al., 1999; Sara & Faubert, 2000; Thompson, Cengelci & Ozekes, 1999).

In one of our longest-running experiments -- now archived -- we looked at visual short-term memory across a wide age range: from 14 years old to 90 years old. This has some advantages over the typical method, which is to test one group of young people (usually college students) and a group of older people (often recruited at a club or function frequented by folk of a certain age). With our data, we can find out not only whether visual working memory declines with age, but when it begins to decline and how rapidly.

The Memory Test

The experiment is simple. Participants are shown four novel objects for one second. Then they have to remember those objects for one second. After that, they are shown one object and asked if that is one of the four they just saw. A diagram of this method is on the right.

By the time the experiment stopped running, 8,374 people had completed the task (plus some who did not make it into this analysis -- for instance, people doing the experiment for the second time). This allowed us to look closely at the results year-by-year for the entire range of ages.

Results

Not surprisingly, performance did decline with age. Our statistical analyses suggest that the decline begins in the 30s (the best estimate was 36.6 years of age, with a 95% confidence interval from 32.2 to 41.1 years). Starting at 37 years old, performance on this task dropped by one percentage point every 2 1/2 years.



Why didn't those other recent studies show an age-related decline in visual short-term memory? One possibility is that the tasks those researchers used were simply too easy for differences to show up (the well-known ceiling effect), whereas our task and the ones used by the older experiments are all much harder.

Future Work

The exciting and novel part of this experiment is not that we showed age-related changes in memory performance. It would have been surprising if we didn't find any. What is more exciting is our ability to estimate the age at which it starts. My collaborators and I are currently running similar studies looking at aging for other types of mental tasks to see whether changes appear at similar ages. If changes appear at approximately the same age for two different tasks, that may suggest a common origin to the changes. We've run several more studies which I'll talk about in the future, and we're nearly ready to write up this work for publication.

Many thanks to the nearly 9,000 people who participated. Of course, we're always running new experiments at GamesWithWords.org. Please stop by.

See Also

This is not the only way the data from The Memory Test has been used. You read a compilation of previous posts on memory here.


Picture credit: http://www.flickr.com/photos/deepblue66/ / CC BY-NC-SA 2.0

Calling all 12 year olds

I've been analyzing data from the Memory Test. The response to that experiment has been fantastic, so I'm able to look at performance based on age, from about 14 years old to about 84 years old. Interestingly, by 14 years old, people are performing at adult levels. I have a few kids in the 10-13 range, but not quite enough. It would be nice to know at what age people hit adult competency.

So...if you or someone you know is in that age range, I'd like a few more participants in the near future. I should actually be able to put up a description of the results relatively quickly in this case, should I get enough participants.

How good is your memory?

The average 20-29 year old scores a 2.5 on my Memory Test. How well can you do?

There are, of course, different types of memory. Most people think of 'memory' as an ability to recall facts and events from days or even years ago. This is what was destroyed in the famous amnesic H. M. However, H. M. was still able to remember new information for at least a few seconds; that is, his short-term ("working") memory was spared. There are also other types of memory, such as iconic memory, also knows as "sensory" memory. Moreover, memory for facts seems to dissociate from memory for skills ("know-how").

The Memory Test tests visual working memory.

Before you take the test, please do me one favor. If you want to test yourself multiple times, feel free to do so. But please check off the "have you done this experiment before" box. Failing to do this can screw up the data, so it's important.

What Does the Test Involve?

You try to remember four simple shapes for one second. Afterwards, you are shown a single shape. You have to decide if it is one of the four you were to remember. There are 40 trials, plus some practice trials.

A note about the practice: The practice trials are really, really hard. That is to get you warmed up, just like a runner tying weights to her ankles during her warm-up. The actual test is easier.

How is the Score Calculated?

On any given trial, you get the answer either right or wrong. We could just calculate what percentage you get right, but that would mean getting a score like "80%," which isn't very satisfying. 80% of what?

A formula developed by Nelson Cowan can be used to estimate how many of the shapes, on average, actually make it into your short-term memory store. The formula is this:

(% hits + % correct rejections - 1) / (Total number of objects)

A 'hit' means answering 'yes, this is one of the four objects,' when in fact that is the correct answer. A 'correct rejection' is saying 'no, this is not one of the four object,' when in fact it is not.

From the math, the score can run from -1/4, if you get every question wrong, to 4, if you get every question right (which has happened, but rarely). If you guessed at random, you should get half the questions right, in which case your score should be 0.

Keep in mind that this depends completely on the shapes. If the shapes are really hard to remember (as the practice shapes are), scores will be lower. If they are very easy, scores will be higher. What makes a shape easy is not just how complex it is, but how similar it is to the other shapes (how easy the shapes are to confuse with one another).

What Does the Score Mean?

You could have a higher or lower score for a number of reasons. For one thing, you might have guessed abnormally well or abnormally poorly. All tests are subject to a guessing effect. On average, guessing cancels itself out, but if the test is short enough and enough people take is, somebody is likely to get everything right (or wrong) just by chance.

Luck aside, a good score could mean that you have more "room" in your short-term memory. It might also mean you are better at avoiding interference. There are several types of interference in memory, and so you could be better at avoiding any one of them. You might also be better at paying attention, or you might have developed a useful strategy for success on this task. (That said, visual short-term memory does appear to be anywhere near as susceptible to strategies as verbal short-term memory.)

Remember one thing. This is not a clinical test. Though clinical tests for verbal short-term memory exist, I'm not sure there even are clinical tests for visual short-term memory. This is just for fun. Enjoy it.

Wait. How Do you Know What the Average Score Is?

The Memory Test is nearly identical to an experiment I ran previously. I used the data from that version to estimate what the scores will be on this version.

(Photo served from the National Geographic website)

Do you have the memory of a crow?

It appears that humans aren't the only ones with exceptionally good long-term memory. Crows not only remember individual faces over long periods of time and even seem to be able to communicate to other crows information about the people in question.

That animals, especially birds, have good memories is not all that surprising. That they remember human faces so well is striking.

There is an ongoing debate in the literature about whether the fact that humans are so good at processing faces is because we have specialized neural circuitry for human faces. Given that humans are an intensely social species, it would make sense for us to develop special face-recognition systems. It remains to be seen just how good crow memory for human faces is (the study in question is limited in some ways), but if their human face perception is very good, that would call for a very interesting explanation.

How many memories fit in your brain? More than we thought

One of the most obvious facts about memory is that it is not nearly so good as we would like. This definitely seems true in day-to-day life, and one focus of my research during the last couple years has been why our ability to remember what we see over even very short time periods is so very limited.

So memory is crap, right?

It may be hard to remember a visual scene over a very short time period, but new evidence suggests that it is remarkably easy to remember a visual image over a longer period of time (several hours).

Researchers at MIT showed participants nearly 3,000 visual images (see some of them here) over the course of 5 1/2 hours. Afterwards, their memory was tested. They were able to discriminate the pictures they actually saw from slightly altered versions of the same picture nearly 90% of the time.

This is frankly incredible. When I show participants much, much simpler images and then ask them to recognize the same images just 1 second later, accuracy is closer to 80%!

These results are going to necessitate some re-thinking the literature. It suggests that our brains are storing a lot more information than many of us thought just a little while ago. It also suggests a very strange interaction between time and memory strength that will need to be better understood.

So this is a surprise?

Yes, and no. The results are surprising, but their publication last week in the Proceedings of the National Academy of Sciences was not, at least not for me. I had the opportunity to first be stunned by these data nearly a year ago, when the third author gave a talk at Harvard. It came up again when he gave another talk during the winter. (Oh, and I've known the first author since we sat next to each other during a graduate school application event at MIT, and we still regularly talk about visual memory).

So I and many others have had the opportunity to think through the implications for a long time now, which means it is very possible that there are labs which have already completed follow-up studies.

While this has nothing to do with the big story itself -- the sheer massiveness of visual memory elicited in this study -- I bring it up as an example of my point from last week: the fact that America is (for now) the center of the scientific world gives us tremendous institutional advantages, the least of which is that it is much easier to stay fully up-to-date. If that mantle passes to another country, we will be the ones reading about old news only when it finally comes out in press.

Parting Thoughts

If you yourself have done research like this, the first thing you probably wondered was where they got 3,000 carefully controlled visual images, not to mention all the test images.

Google Images, baby, Google Images. It still took a great deal of time, but as I hear the story told, the ability to download huge numbers of web images via Google was immensely helpful. This is just one more example of Web search as a tool for science.

The verbal memory hegemony

One fact about the world is that the most famous memory researchers did most of their work on verbal memory. Alan Baddeley and George Miller both come to mind -- and I doubt anybody can think of more famous memory researchers in the last 50 years.

Another fact about the world is that many researchers -- not necessarily Baddeley or Miller -- have assumed that anything discovered using memory tests involving words should apply to other forms of memory as well. To pick unfairly on one person, Cowan notes in his masterful paper "The magical number 4 in short-term memory" that out of several related experiments, one has results that diverge from the others. Cowan attempts an explanation but basically throws up his hands. He doesn't notice that of all the experiments discussed in that section, the divergent one was the only one to use visual rather than verbal stimuli.

Similarly, a reviewer of my paper which just came out complained that the results reported in the paper only "told us things we already knew." As evidence, the reviewer cited a number of other papers, all of which had investigated verbal rather than visual short-term memory.

As it happens, the results in this case were very similar to what had been reported previously for verbal memory. But it could have come out differently. That was the point of doing the experiment.

Partly because of this bias in favor of verbal materials, not enough is known about visual memory, though this has been changing in recent years, thanks in part to folks like Steve Luck, George Alvarez, Yuhong Jiang, Edward Vogel and several others.

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Cowan, N. (2001). The magical number 4 in short-term memory: a reconsideration of mental storage capacity. Behavioral and brain sciences, 24, 87-185.

Hartshorne, J.K. (2008). Visual working memory capacity and proactive interference. Public Library of Science One

Miller, G.A. (1956). The magical number seven, plus or minus two: some limits on our capacity for processing information. Psychological Review, 63, 81-97.

Results from an Experiment: The Time Course of Visual Short-Term Memory

The first experiment I ran on the Web has finally made it into print. Rather fittingly, it has been published in a Web-based journal: The Public Library of Science One.

Visual Memory is a Scrawny Creature

That experiment, The Time Course of Visual Short-Term Memory, was part of a larger study probing a fundamental question about memory: why is visual working (short-term) memory so lousy? In recent years, visual memory folk like Edward Vogel and George Alvarez have debated whether we can store as many as four items in visual memory, while on the other hand researchers looking more at verbal memory, such as Nelson Cowan, have been arguing over whether verbal memory can store only four items. There are memory tricks that can allow you to keep a hundred words in short-term memory; nobody has reported any similar tricks for visual memory.

There are many other ways in which visual memory is piddly compared to verbal memory, and I go into them in depth in the paper. Interestingly, previous researchers have not made much out of this difference, possibly because people seem to work on either visual memory or verbal memory, but not both.

Does Verbal Memory Explain the Differences between Humans and Apes?

One possibility that occurred to me is that if verbal memory in fact is considerably more robust and more useful than visual memory, that would endow verbal animals (i.e., adult humans) with significant advantages over non-verbal animals (e.g., human infants and all other animals). Just as writing has allowed some human cultures to supplement our limited memory capacity -- try doing a complicated math problem in your head; the real limitation is memory -- language could allow us to supplement limited non-verbal memory systems.

In fact, I found that many of the differences between adult humans on the one side and young children and apes on the other are found in tasks with large working memory demands. More examples are given in the paper, but this includes theory of mind tasks.

Is Verbal Memory Really Better?

Of course, this is fruitless speculation unless visual working memory is really inferior. The problem is that visual and verbal memory capacity is tested in somewhat different ways. The easiest way to test verbal memory capacity is to give people a list of words to remember and then ask them to repeat that list back (this forms an important part of many IQ tests).

This is obviously impossible with visual memory tests.

In a visual memory test, the participant is usually shown several images to remember. Then, after a delay, they are shown another image and asked if that is the same as one of the original images. Notice that you can be right 50% of the time just by guessing. Thus, to get a good measure, you need to do this many times.

Proactive Interference

This brings up the specter of proactive interference. I have written about proactive interference recently and won't belabor it here. The basic intuition is that if you do many trials of a memory test, it becomes hard to remember which stimuli were on which trial. So if you have been asked to remember circles of different colors, and then you are asked if the last trial contained a blue circle, you might remember that you have seen a blue circle recently but not remember if it was on the last trial or not.

So if visual working memory capacity tasks require many trials and verbal working memory tasks do not, one possible reason for the poor performance observed for visual working memory might be greater proactive interference.

Nope -- not proactive interference

The short version of the results of the published paper is that proactive interference does decrease measured capacity for visual working memory, but not by very much (about 15%). So it cannot account for the differences between visual and verbal working memory. The search must go on.

I hope to describe how the Web-based experiment contributed to this result in a future post. But interested readers can also read the paper itself. It is fairly short and reasonably non-technical.

Participate in current Web-based experiments at my lab by clicking here.

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Hartshorne, J.K. (2008). Visual working memory capacity and proactive interference. Public Library of Science One

Interference in Memory

I wrote recently about interference processes that cause memory failure. As I wrote before, retroactive interference is when learning new information causes you to forget what you learned previously. In proactive interference, old information makes it hard to learn new information.

It turns out that there are (maybe) two types of proactive interference, and this may tell us a great deal about how memory works.

How Specific?

Half a century ago, Keppel & Underwood found that people quickly get worse at memory tasks. A basic task works like this: Remember the following letters: "etnmwo"

Now look away from the screen. After a few seconds, ask yourself what the letters were. How many could you remember?

Keppel & Underwood task was slightly different, but this gives you the basic idea. Again, what they found was that as people play this game, they actually do best on the first trial, worse on the 2nd, even worse on the 3rd, etc. (People bottom out fairly quickly, as we'll see in a future post.)

Keppel & Underwood suggested that this was due to proactive interference, which now seems pretty well established.

Later researchers discovered a curious thing. If the memory task is done with letters for a while, and then the experimenter switches to numbers, the participants suddenly get better. It doesn't have to just be letters and numbers. Switching from one type of item (say, names of car manufacturers) to another type (say, names of animal species) typically leads to an improvement in performance.

This has been called "release from proactive interference." But it is not the only kind.

More Specific

The type of proactive interference discussed above has been called "item-nonspecific" proactive interference. Learning information about one item made it harder to remember information about similar items.

This can be contrasted with "item-specific" proactive interference. As an example, go back to the sample memory test above. You were asked to remember "etnmwo." Suppose in the next trial, I asked you to remember "oaqzp" for a few seconds, after which I asked you:

"Is one of the letters are are supposed to remember an E?"

There is a decent chance you would incorrectly say "yes." This is because, although E was not one of the letters on this trial, it was one of the letters on the previous one. If I had instead asked about the letter C, which was not in either trial, you would be more likely to respond correctly and say "No."

This effect was discovered by Monsell using what is called the "Recent Probes Paradigm" -- which is basically what I just described.

Two Types or One?

One could legitimately wonder if these are really two different phenomena. That is, maybe item-specific proactive interference is simply a stronger version of item-nonspecific proactive interference.

It is hard to answer that question using behavioral experiments. Luckily, this is one of those places where neuroimaging can be helpful in understanding behavior. Recent neuroimaging results have found a strong overlap between the brain regions involved in the two types of proactive interference.

What Does this Say about Models of Memory?

Jonides and colleagues have been developing a model of memory that may both describe and predict the data on proactive interference.

In the model, to the extent that I understand it, you perform a short-term memory task like the ones described above by activating representations of the items. That is, to remember "aort," you would activate your long-term memory representations of A, O, R & T. But you do not actually hold those representations in consciousness; it is more that you make them easy to retrieve.

Now, suppose I ask you to repeat back those letters. You have to retrieve each of the four letters into consciousness so that you can give me your answer. You do this via something vaguely akin to a keyword search. That is, you search your memory for relevant features (e.g., a letter, recently encountered, seen on a blog, etc.). Since A, O, R & T all match those features and are all activated in memory, you retrieve them successfully.

Suppose on the next trial, though, you have to remember W, Z, P & E. So you activate those representations in memory. But A, O, R & T also remain somewhat active. And they also match most of the features (i.e., "keywords"). So you might accidentally retrieve one of them (item-specific proactive interference). In addition, since memories overlap, the still-active A, O, R & T representations make it harder to activate and maintain the representations of W, Z, P & E, since the compete for use of some of the same neurons. This might just make you fail to activate or retrieve anything at all.

Notice that if on the next trial, I ask you to remember 9, 3, 5, & 2, these items share fewer features with the letters on the previous trials, making the "keyword search" easier. Also, the representations of 9, 3, 5 & 2 in the brain are more distinct from the representations of the letters in trials one and two than either were from each other. Thus, you get release from item-nonspecific proactive interference.

Monsell, S. (1978). Recency, immediate recognition memory, and reaction time. Cognitive Psychology, 10(4), 465-501.

Keppel, G., Underwood, B.J. (1962). Proactive inhibition in short-term retention of single items. Journal of Verbal Learning & Verbal Behavior, 1, 153-161.

Jonides, J., Lewis, R.L., Nee, D.E., Lustig, C.A., Berman, M.G. (2008). The mind and brain of short-term memory. Annual Review of Psychology, 59, 193-224.

Forgetting what you haven't yet learned

More than one student has complained that the space in their head is limited, and new information is simply pushing the old information out. In the terms of memory research, this is retroactive interference: learning new information causes you to forget old information.

The way this is typically studied in the laboratory is to have the participant learn something -- often a paired associate (think "Concentration") -- then learn something else, and then finally be tested on the original memory item(s). This way, one can vary that middle task in order to study how different activities cause different amounts/types of retroactive interference.

The is another type of interference: proactive interference. This is the effect that learning one piece of information has on future learning. That is, the books a student has already read make it harder to learn new information.

Just like retroactive interference, proactive interference is seen in both short-term and long-term memory. 

Memory Systems: How Does Memory Work?

The existence of interference tells us a lot about how memory works, because there is nothing necessary about it.

Consider a computer. We don't expect each new file we add to our computer to cause the computer to lose other files, short of copying over those original files. Similarly, the file I added today should not affect a file I add tomorrow, short of causing me to run out of disk space.

So why is human memory affected this way?

Overlapping Memories

There are a couple reasons it could be. One is that memory is probably overlapping. A computer -- at least, in its basic forms -- saves each file in a unique place in memory. The human brain, however, probably reuses the same units for different memories. Memories are overlapping.

How exactly this works is still very much a matter of research and debate, but it makes a certain amount of sense. Suppose you have several different memories about your mother. It would make sense for your mental representation of your mother to show up in each of those memories. For one thing, that should make it easier to relate those memories to one another.

Searching for Memories

Another way interference might appear in memory is in how it effects memory retrieval. The more files you put on your computer, the harder it is to find the files you want. This is especially true if you keep them all in one directory and use keyword searches.

Human memory retrieval probably does not work like a keyword search, but nonetheless it is reasonable to assume that the more memories you have, the more similar memories you have. Thus, finding the right memory is harder, because you have to distinguish it from similar memories.

How exactly this plays out depends on your model of memory. I will talk about one I particularly like in a future post.

Upcoming Posts

Although  my main research is in semantics and pragmatics -- aspects of language -- I have also worked on working memory. I have a paper coming out shortly based partly on an experiment I ran at my Web-based lab. Over the next week or two, I plan to write about some of the fundamental questions about memory addressed in that paper, as well as write about the paper and lay out its results.

The Heat Death of Science

Several years ago, I was fairly up-to-date on dyslexia research. A couple colleagues and I were writing a comprehensive review of the literature. Several drafts of the pape were written, but for various reasons that project got put aside and was never finished.

I'm currently preparing to overhaul that paper and update it based on recent research. To put this in perspective, 147 papers on dyslexia were published in 2007 alone (according to PsychInfo*).

Like the physical universe, the universe of knowledge has been expanding at an accelerated rate. It's hard to be current in several fields. By the time you are current in psychology, sociology has moved on. With time, it seems increasingly difficult to stay on top of multiple subfields (e.g., autism and dyslexia).

I wonder how long it will be before it is impossible to stay on top of even a single, narrow topic. This postulated moment would be the equivalent of heat death for science. Or not. Perhaps science will end in a big crunch instead.

Or will we find ways of dealing with massive amounts of information. While our technologies in this arena have improved, I take it as self-evidence that they have not improved as fast as information has increased.

Thoughts?

*If anybody for some reason wants to check for themselves, I searched for papers with the word "dyslexia" in the abstract. If you search for "dyslexia" in any field, you get 177.

Having solved the question of monkeys & humans, I move on to children and adults

Newborns are incredibly smart. They appear to either be born into the world knowing many different things (the difference between Dutch and Japanese, for instance), or they learn them in a blink of an eye. On the other hand, toddlers are blindingly stupid. Unlike infants, toddlers don't know that a ball can't roll through a solid wall. What is going on?

First, the evidence. Construct a ramp. Let a ball roll down the ramp until it hits a barrier (like a small wall). The ball will probably bounce a little and rest in front of the wall. Now let an infant watch this demonstration, but with a screen blocking the infant's view of the area around the barrier. That is, the infant sees the ball roll down a ramp and go behind a screen but not come out the other side. The infant can also see that there is barrier behind the screen. If you then lift the screen and show the ball resting beyond the barrier -- implying that the ball went through the solid barrier, the infant acts startled (specifically, the infant will look longer than if the ball was resting in front of the barrier as it should be).

Now, do a similar experiment with a toddler. The main difference is there are doors in the screen, one before the barrier and one after. The toddler watches the ball roll down the ramp, and their task is to open the correct door to pull out the ball. Toddlers cannot do this. They seem to guess randomly.

Here is another odd example. It's been known for many decades that three-year-olds do not understand false beliefs. One version of the task looks something like this. There are two boxes, one red and one green. They watch Elmo hide some candy in the red box and then leave. Cookie Monster comes by and takes the candy and moves it from the red box to the green box. Then Elmo returns. "Where," you ask the child, "is Elmo going to look for his candy?"

"In the green box," the child will reply. This has been taken as evidence that young children don't yet understand that other people have beliefs that can contradict reality. (Here's a related, more recent finding.)

However, Kristine Onishi and Renee Baillargeon showed in 2005 that 15-month-old infants can predict where Elmo will look, but instead of a verbal or pointing task, they just measured infant surprise (again, in terms of looking time). (Strictly speaking, they did not use "Elmo," but this isn't a major point.)

So why do infants succeed at these tasks -- and many others -- when you measure where they look, while toddlers are unable to perform verbal and pointing tasks that rely on the very same information?

One possibility is that toddlers lose an ability that they had as infants, though this seems bizarre and unlikely.

Another possibility I've heard is that the verbal and pointing tasks put greater demands on memory, executive functioning and other "difficult" processes that aren't required in the infant tasks. One piece of evidence is that the toddlers fail on the ball task described above even if you let them watch the ball go down the ramp, hit the wall and stop and then lower the curtain with two doors and make them "guess" which door the ball is behind.

A third possibility is something very similar to Marc Hauser's proposal for non-human primate thought. Children are born with many different cognitive systems, but only during development do they begin to link up, allowing the child to use information from one system in another system. This makes some intuitive sense, since we all know that even as adults, we can't always use all the information we have available. For instance, you may know perfectly well that if you don't put your keys in the same place every day, you won't be able to find them, put you still lose your keys anyway. Or you may know how to act at that fancy reception, but still goof up and make a fool of yourself.

Of course, as you can see from my examples, this last hypothesis may be hard to distinguish from the memory hypothesis. Thoughts?

Visual memory -- does it even exist?

Researchers at Rochester recently reported that short-term memory for sign language words is more limited than for spoken words. In some sense, this is surprising. We've known for a long time now that sign languages recruit the same brain areas as spoken languages, so it stands to reason that many of the properties of sign languages would be similar to those of spoken languages, despite the obvious differences.

On the other hand, short-term visual memory is severely limited. If you give somebody a list of 7 spoken words, they can typically remember all of them. If you show somebody 7 objects, they cannot remember them. The textbooks say that you can only remember about 4 visual objects, but that turns out only to be true for very simple objects. In a series of experiments I ran (some of them online), the average person could remember only about 2 objects.

Even more striking is that visual short-term memory cannot be trained like verbal memory can be. A few people have learned to extend their verbal memory so that they could remember dozens of words at a time. However, nobody has been able to significantly improve their visual short-term memory (see a research report here).

Visual short-term memory is so incredibly limited that some vision scientists have wondered if it, in some sense, really exists. That is, they think that it may just be a biproduct of some other system (like our ability to imagine visual scenes), rather than a memory system in its own right. There is some sense to this. After all, what do you need short-term visual memory for? With verbal memory, it's obvious. You need to be able to remember the first part of a sentence while reading/hearing the rest of it. But why would you need to remember what you see over very short intervals?

Those who do not want to read a plug for my ongoing research should stop reading here.

I've been really fascinated by the limitations of short-term visual memory. I have run several experiments, one of which is still continuing. You can participate in it here.

What is the relationship between short-term and long-term memory?

In a textbook, you may see a description of memory in terms of stages. The first stage is iconic memory, which lasts just a few seconds, during which you can to some degree revive the perceptual experience you are trying to remember. Think of this almost like the afterglow of a bright flash of light.

Then comes short-term memory, which may or may not be also described as working memory (they aren't necessarily the same thing), which allows you to remember something for a short period of time by actively maintaining it. Anteriograde amnesics (like the guy in Memento) have intact short-term memory. What they don't have is long-term memory, which is basically recalling to mind something you haven't thought about in a while.

There are many aspects of the relationship between short-term memory and long-term memory that are still not clear. Over the last several months, Tal Makovski and I have been running a study trying to clarify part of this relationship.

We thought we had concluded it last week. I took the experiment offline, analyzed the results, wrote up a report and sent it to Tal. He wrote back with conclusions based on the data completely different from those that I had. Bascially, the results of two conditions are numerically different, but statistically there is no difference. He believes that if we had more participants, the difference would become statistically significant. I don't.

It's up to you, dear readers, to prove one of us wrong. The experiment is back online (click here for info; here to go straight to the test). It involves a quick visual short-term memory test, then you watch a video, after which you'll be quizzed on your memory for the video. It's by far the most entertaining of the experiments I've put online, mainly because the video is fantastic. It is Bill et John: Episode II, which was profiled in Slate. I've watched it easily a hundred times in the course of designing this study, and it's still fall-out-of-your-chair funny. Which is good, because it's nearly 10 minutes long, making the entire experiment take about 15 minutes.

Once again, you can find the experiment here. Once the results are available, I will post them on this blog and on the website.