Field of Science

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)

4 comments:

S said...

Very interesting. I just did the experiment, and contrary to what is written in the explanation, I felt that my skill at the task improved over the course of the test, rather than diminishing. It seemed that as I began to recognize the objects and get used to them, they became easier to remember.

Even though I faithfully repeated "dog," and did not use a conscious verbal strategy, like naming the objects, I wonder how much you can really separate verbal from visual memory. To me it seems that you cannot isolate vision from language; they are both systems that compartmentalize fields of input into individualized, manageable components. When I was doing the memory test, it didn't seem much different from learning letters in an unknown language.

Anyway, thanks for the post; I really enjoy thinking about these things. It will be interesting to see the results of the experiment.

coglanglab said...

A actually agree that whether visual and verbal working memory can be separated is very much an active question! Some components probably cannot be separated, and some probably can -- which is which is of course the question.

As far as feeling like you got better during the task. You might have. Early data shows that some people do improve constantly through the task (typically those that ultimately get a high score). Others show a quick drop off and then level out. Others are in between. The nature of these differences is something I'm interested in understanding better.

Thanks again for participating in the experiment.

Anonymous said...

Is there a correlation between the results on a task like this and a person's IQ (especially performance IQ as measured by wais)?

Joshua Hartshorne said...

Anonymous: good question. It depends partly on what we mean by "IQ". IQ is meant to measure intelligence, but intelligence isn't necessarily all one thing (for instance, we usually distinguish between verbal and non-verbal intelligence, because they disassociate across individuals). There is a complex relationship between IQ and working memory capacity, and I believe some IQ tests include verbal working memory tests. That said, visual working memory is not nearly as well-studied, and what is true about verbal working memory and IQ may not be the same for visual working memory and IQ.

That about caches out what I know about IQ, unfortunately.