How good is your memory?

January 13, 2009 by coglanglab

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)