You can understand why this study lit up my twitter feed recently. It makes a remarkable claim: women — but not men — experience working memory declines after a sleepless night.
Why We Care
We have at least two powerful reasons to care about this study.
First, it makes strong claims about gender differences. According to lead author Rangtell (and 8 colleagues), women’s performance on a working memory task gets worse after a sleepless night.
On the other hand, men’s working memory performance remains just as good as when they had a cozy 8-hour sleep.
(I’ve written about gender differences before. You may recall that I’m often skeptical of specific claims, but do think that there are some important differences at the population level.)
So, this study plays an important role in the ongoing debate.
Second, Rangtell’s study focuses on working memory. And, working memory is really important in school.
What is working memory?
When a student works on a word problem in math, she first has to select the key information from the sentences. Then she holds that information in mind. Third, she reorganizes all that information into the correct formula. And finally she combines pieces of that formula appropriately: for example, she combines “7x+8x” into “15x.”
Whenever students select, hold, reorganize, and combine information, they’re using working memory.
And, our students do that all the time. They use working memory to conjugate a new Spanish verb. And, when they apply new terminology (“protagonist”) to a specific book (“Sethe is the protagonist of Beloved.”) And, when they balance chemical equations.
Basically, schools are shrines we build to honor successful working memory functioning.
If there truly is a gender difference in working memory function, that’s a really big deal.
Sleeplessness Harms Women More Than Men?
This study is, conceptually, very straigtforward.
Ask some people to do a working memory task after a full night’s sleep. Then, ask them to do the same task after they’ve been up all night. Is there a difference in their working memory performance?
Rangtell and her colleagues say: for men, “no”; for women, “yes.”
However, this study includes a very serious problem. The task that they use to measure working memory DOESN’T MEASURE WORKING MEMORY.
(You read that right.)
The researchers asked these people to listen to a list of numbers, and then type those numbers into the computer in the same order.
That’s simply not a test of working memory. After all, the participants didn’t have to reorganize or combine anything.
Instead, that’s a test of short-term memory.
Now, short-term memory is related to working memory. But, “related to” isn’t good enough.
Imagine, for instance, I claimed that sleeplessness makes people shorter. The way I determine your height is by measuring the length of your arm.
Of course: arm length and height are related. But, they’re not the same thing. Tall people can have short-ish arms. I can’t measure one thing and then make a claim about a related but different thing.
So too, Rangtell can’t measure short-term memory and then make claims about working memory. She didn’t measure working memory.
Does sleeplessness harm women’s working memory more than men’s? We just don’t know.
(By the way: I’ve reached out to the lead researcher to inquire about the working memory/short-term memory discrepancy. I’ll update this post if I hear back.)
