The 70-year Cognitive Puzzle That Still Divides The Sexes

in #steemstem6 years ago (edited)


Is this water puzzle the most solid experiment in the field of sex differences?
Source: qimono w/ CC0 Creative Commons license.

Curtain Open

It's called the WLT, short for Water-Level Task. I want to introduce it to you by asking you to attempt it.

And please don't look ahead to the answer!


Have you done it? Please do if you didn't, and show your answer in the comment section.

The Water-Level Task: Dividing the sexes since 1948


They had an argument over a glass of water.
Source: Pxhere w/ CC0 Public Domain license.

If the line you drew is anything other than horizontal, you answered wrongly. I won't go into the physics of why liquids follow gravity instead of the orientation of their container, as there are @steemSTEM authors who can do a better job of that. Thing is, if you can read, then you should have enough real-life experience to know that that's invariably what happens: you'd never be able to drink a glass of water by tilting the glass, if the water level followed the bottom of the glass like some jelly.

Females disproportionately give the wrong answer to this puzzle. In their efforts to level the results, researchers tried using photos instead of schematics, using a container with rounded sides so there will be less interference with a horizontal water line, having the water lines pre-drawn and just asking the participants which line looked correct, and just generally making it easier and easier. It didn't matter: after decades of variations to the puzzle, a significantly higher proportion of female adults and adolescents still draw a slanting line.

For fairness, I must mention that not all interventions are failures:

Thomas, Jamison, and Hummel (1973) demonstrated that when previously inaccurate college women are allowed to view the actual water level in a bottle tilted to the same angle as the test item, they copy accurately.[5]

Let's just move on.

The history


Source: Wikimedia commons w/ Public Domain license.

You won't learn a whole lot about the Water-Level Task from its wikipedia entry: it's shorter than this post's opening section. At least it mentions it was developed by Piaget (his colleague Inhelder's part in this was apparently consigned to oblivion).

Those of you who know him, know Piaget's work was primarily in child development. The WLT is no exception: he developed it in order to probe children's emerging spatial concepts and reasoning. It was by accident that a sharp sex division in the subjects' ability to complete the task was noticed (more on this in a bit).


Piaget distinguished 5 stages in the developing ability of children to solve the puzzle. The first stage is drawing squiggly lines — basically a big middle finger pointed in the direction of the researcher! Then the lines follow the bottom of the containers. In the third stage the line starts tilting as if trying to negotiate the gravity from the Earth with the gravity from the bottom of the container. In the fourth stage they figure it out in all cases where straight angles are involved, but get it wrong whenever the glass is tilted. In the fifth and final stage, they get it right.

The children reached the final stage by age 9, and there was nothing to indicate that adults would have any difficulty with the task.

That was until one Rebelsky, true to the Rebel part of her name, came along and disturbed the waters by reporting that some of her graduate and undergraduate students had great difficulty correctly completing the task. But most importantly:

In addition, Rebelsky reported that females were less accurate than males, a finding that has been replicated by virtually all subsequent researchers.[1]



Do boys have more experience with glasses of water?
Source: AxxLC w/ CC0 Creative Commons license.

A number of hypotheses have been proposed as to why women underperform men so much. My favorite is socialization. If you think that amounts to trying to explain why women have less experience with drinking glasses of water compared to men, you're right, that's what that means.

But in fact, the WLT is often used precisely to falsify the argument that large sex differences between the cognitive skills of men and women are always the result of greater experience or socialization that favors the men:

[The water-level] task exhibits large sex differences, despite the fact that every Western child, male or female, has daily experiences with fluids in transparent containers[2]

To be fair, there is clear evidence that boys and girls have different experiences, and that those experiences favor males. Here's some concrete examples relating to mathematics[6]:

  1. girls attribute success in math to their effort, boys attribute it to their ability

  2. girls attribute their failure in math to lack of ability, boys attribute it to lack of effort

  3. parents blame bad math scores of their sons on bad teachers, and attribute bad math scores of their daughters to lack of effort

  4. math teachers treat boys and girls differentially, and female math teachers even make self-deprecating remarks about their own abilities

So are girls and boys differentially exposed to mathematics and spatial-related training and expectations? Sure. Can mathematical and spatial abilities be influenced by experience, and do boys get more of that experience? Certainly.

But that doesn't explain why at a certain age (before the hormones kick in) "girls are performing equal to or better than boys, in math in general"[6].

I also need to remind the reader at this point that we're still talking about glasses of water: that's glasses with water in them. Why then math and spatial abilities? Because those are the general areas in which the most data exists regarding socialization favoring boys. Is there any study showing that boys have more experience with glasses of water than girls do, or studies that show parents making disparaging comments when they catch their daughters drinking water? None that I'm aware of.


Is this where boys spend most of their childhood?
Source: niki_vogt w/ CC0 Creative Commons license.

Let's go the complete opposite of socialization, and consider a gene hypothesis of WLT sex differences:

a recessive gene on the X chromosome both facilitates acquisition of the horizontality principle and is more frequently expressed in men than in women[1]

A horizontality principle encoded in the genes? Get outta here! You can read more about it here if you want, but I'm moving on! (For the OCD among you, I got a footnote at the end of the post.)

A hypothesis that straddles biology and socialization says that:

different levels of exposure to sex-related hormones, such as androgen and estrogen, during the prenatal period cause the brains of males and females, including those areas that involve spatial ability, to develop differently[1]

Hormones affecting brains? Now you're talking!

The "bent twig" hypothesis, for instance, says that boys' biology (be it genes or hormones or both) bends the twig in a certain "pro-math" direction, but the growth itself is provided by socialization (hey, you can't learn math without schooling, after all).

If you've read my earlier posts, you'll see why I find this to be the most attractive hypothesis. If you haven't, wait for my next post, in which I'll talk about pubertal hormones: the last of John Money's critical elements of sex and gender.

Regarding the WLT, consider again a point I mentioned, that the sexes start more or less the same, but separate as they grow older:

The [WLT] sex differences are most pronounced in adult and adolescent samples, but do appear in younger samples as well[4]

That, to me, says it's the hormones that are doing the trick, since the sexes start on a more or less even footing on this task, and the differences appear only later. If that wasn't the case, Piaget himself (and his uncommemorated colleague) would've noticed it in their original study.

Curtain Close


Source: Wildfaces w/ CC0 Creative Commons license.

I haven't mentioned any numbers on how much the male performance differs from the female. It varies, but its significant. Females typically show from 2 to 3 times greater deviation from the horizontal compared to males. The studies, in toto, make the WLT one of the most robust in the history of the field. Despite the researchers' no doubt good intentions, they have been unable to eliminate the differences by altering the experiment.

So far, the exact causes of females' underperformance on the WLT remain a mystery. The task is simply too complex to be explained simply.[5] It's well known, however, that men perform better in mathematical and spatial areas, and so if you consider the WLT to be just an instance of those areas, as I do, then you don't need a separate mechanism to explain the differences in performance.

So how did you do on the WLT? Given how all of us here are either minnows, dolphins, or whales, I doubt any one of us will have issues with tasks involving water!

See you next time!


At most the data they gathered can be said to be consistent with their hypothesis. At worst they could be accused of some data-fitting by their introduction of a "misclassification error parameter" that makes the data just erroneous enough to fit the hypothesis. The error parameter implies that ~25% of the test subjects were misclassified.[5] They do argue however for the reasonableness of the introduction of this parameter. But still they needed to end their paper with a good word about studies that do not confirm their hypothesis: "It seems quite possible that the failure of recent studies to support the X-linked model reflects the inadequacy of certain statistical procedures rather than any absence of X-linked influences."[4] Sure.

Uncredited pics are by yours truly.


  1. Vasta, R. and Liben, L. (1996). The Water-Level Task: An intriguing puzzle. Current Directions in Psychological Science, [online] 5(6), pp.171-177. Available at:

  2. Mealey, L. (2000). Sex Differences: Developmental and Evolutionary Strategies. 1st ed. Academic Press. Available online at:

  3. Wikipedia contributors, "Water-level task," Wikipedia, The Free Encyclopedia, (accessed July 2, 2018).

  4. Thomas, H. and Jamison, W. (1981). A test of the X-linked genetic hypothesis for sex differences on Piaget's water-level task. Developmental Review, [online] 1(3), pp.274-283. Available at:

  5. Allen, M., Wittig, M. and Butler, K. (1981). Comments on Thomas and Jamison's “a test of the X-linked genetic hypothesis for sex differences on Piaget's water-level task”. Developmental Review, [online] 1(3), pp.284-288. Available at:

  6. Baenninger, M. and Newcombe, N. (1995). Environmental input to the development of sex-related differences in spatial and mathematical ability. Learning and Individual Differences, [online] 7(4), pp.363-379. Available at:

Earlier Sex Differences episodes:

8: Do Transsexual Persons Have An Opposite-Sex Brain?

7: Do Parents Stereotype Their Children's Gender?

6: Sex Differences: Do females and males have different brains? Addendum

5: Sex Differences: Do females and males have different brains? Pt 3

4: Sex Differences: Do females and males have different brains? Pt 2

3: Sex Differences: Do females and males have different brains?

2: Sex Differences: Check out the gonads on that one!

1: Sex Differences: Does the Chromosome Maketh the Man?

steemSTEM is the go-to place for science on Steemit. Check it out at @steemstem or browse the #steemSTEM tag or chat live on discord


As usual, an interesting post. While as a group one gender may outperform or under-perform another in a specific area, that information is meaningless when it comes to an individual. As soon as policy or judgment is formulated based on perceived group metrics, mistakes are going to be made. To make it personal (as ruth-girl did, I'll follow her lead): I have very poor spatial visualization skills. Not for a guy, or girl--but for anyone. However, I had a natural talent for geometry in high school. The proofs were self-evident to me. I actually corrected the text book. Given my very poor spatial visualization skills, no one ever would have predicted this.

As an individual, I surprise. That's my point about gender neutrality. Whatever distinctions may be perceived between groups, how does that advance our understanding of the individual? What does this tell us that we can use, in a practical sense? Making predictions about behavior based on gender imposes expectations on individuals. That doesn't work to the advantage of the individual or society. Forget about gender. It won't help you to know anything about me, that's for sure.

Again, an interesting post got me looking up articles on the relationship between geometry and spatial visualization. Yep--there is supposed to be a relationship. Go figure.

I'm one of those people who value research for its own sake. Often called 'basic research', you never know what practical benefit might come out of it. I give an example of how a gender difference might be helpful in this post, in the 'Blood and Brains' section (the relevant paragraph starts with "The fact that estrogen levels influence female brains, and all that this implies, would create unfair treatment if left unacknowledged.", but the whole section must be read to be understood.)

Personally, I don't want anyone compensating for a possible deficit due to hormone fluctuations that may or may not occur. I think women's cycles have been over-studied because these cycles are so conspicuous. There are long-standing religious taboos associated with these cycles, because some of the physical effects can be intrusive. But, as a woman who doesn't want special consideration for anything, I ask everyone, please ignore hormone fluctuations. We all have issues unique to our lives that we have to deal with. Men have cycles too, but we don't know much about them because there isn't a long history of socioreligious significance associated with these fluctuations. And they're not highly visible (although men's behavior may be affected by them).

I love to know about the brain and hormones. I like to understand myself and the people around me, because understanding is good and it does help us to deal with each other. What I don't think is helpful is any sort of compensatory treatment, assessment, evaluation, etc. based on hormone fluctuations, for men or women.

As I became a productive member of society (that is, I went to work), one of the things I noticed that divided me from my male colleagues was their perception that I would somehow receive special consideration. I had to work hard to prove that I neither expected nor would accept any sort of accommodation because of my gender. This was a physically challenging work environment, but my attitude was, if I can't do the job, I don't belong in it. This was the only way for me to be considered "equal" by my colleagues.

What I did notice was that drawing attention to my gender compromised acceptance.

Science is wonderful. Knowledge is important. But in the real world, emphasizing the difference between men and women as a group just makes things harder for women. At least that's my experience. And I bring that to your discussion.

I can see that drawing attention to gender differences could lead to more discrimination against women in the workplace. Spatial ability is relatively easy to conceptualize and measure, which can help to create super clear results like in the water level experiment. It’s much more difficult to assess more subjective skills that woman might be better at, like some aspects of communication.
From what I’ve read, spatial skills are likely to get less and less important in the workplace, as more and more physical work gets automated.

I agree, some important qualities cannot be measured as easily as spatial visualization. Resilience, for example, is a trait women overall tend to have in greater abundance (or so the studies seem to show) than men. While this has been considered with reference to longevity, it is a quality that affects adaptation in all environments. That's just one example of something unquantifiable that can affect performance in everyday life. I think the brain is a new frontier...we're just on the threshold of understanding its complexity. I look to the work of pioneer neuroscientists such as Thomas Insel to lead the way toward understanding the relationship between the brain and behavior. Fascinating subject. That's why I keep reading and commenting :)

Don't know if this relates to resilience per se, but men do commit suicide 4-5 times more than women. I think they might just generally take things to heart more easily/deeply (unlike the stereotype would have it), and have extreme reactions, e.g. violence, be it against others or against oneself.

Never thought of it that way... certainly could be a reflection of resilience. Men also don't handle loss as well as women--death of a long-time partner and break-up of long-term relationships. May be another reflection of resilience (statistically).

Yup, I know that first-hand!

You know I'll be looking up articles on the fluctuation of male hormones... :)

It's true, there's even a best time of the day to exercise (for men)! Around 4 or 5 PM I think.

You have an amazingly balanced keeps me reading. Thanks :)

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Thank you for appreciating my comment. I joined Utopian-io on discord but don't code, so can't contribute much. I've been reading posts, because much of it is interesting.

I will go to the website. If I can contribute I will. My science information is mostly driven by curiosity and persistent research. It is gratifying to be acknowledged by your community. Makes me want to work harder. Thank you, again.

I don't recommend reading this article if you have a glass of water near you, you might get tempted to do something stupid and spill the water all over your desk...

This, of course, DID NOT happen to me 😎

I tried doing the experiment in my mouth. Almost drowned myself 🤕😳

I wish i read this comment earlier .......

Bad news, but both men and women are wrong about this one. It turns out water's strong adhesion gives it a meniscus so its actually a curved line :P

Alright I'm just messing around. This is a genuinely surprising difference between males and females.

Haha I love this, good job for winning the comment feed =D


A-ha! I feel so stupid that I read and wrote about that experiment and never once did this basic scientific fact cross my mind!

Maybe you just drew the line wrong and you're trying to come up with excuses :D

FYI I got the test right :P

Well, the hormone hypothesis is something I strongly believe to mess with one's perception of space. At least in my case, if I may share some personal information that could be of help, one or two days before menstruation I cannot park my car. I find it very difficult to calculate the right angles and park in less than 3-5 moves (that I usually take when I have enough space). Funny, isn't it?

I drew a horizontal line too.

I 'd never believe you'd get it wrong anyway 😘


one or two days before menstruation I cannot park my car

For some reason the way you put it is hilarious 😂

Well, though I never in my life hit another car while driving (thus far), I did scratch my car (on walls and tree branches) a few times while parking. So I'm probably male-menstruating 24/7 :D

male-menstruating 24/7?!?!

Those are minor "accidents" don't worry! (I get those every once in a while with the silly bars they put to protect trees by the sidewalk, they are so low you can't see them, once I almost tear my front bumper off 😖)

I decided to try and quit smoking cigarettes when I was about 24. I was so discombobulated that I went to Blockbuster and scratched a car as I was pulling out of my parking spot. It was like I was on drugs.

I think I got it.

Schrodingers Water.png

Almost. But the apostrophe’s all wrong. Let me fix it.


There. Now it looks okay.

For the OCD among you, I got a footnote at the end of the post.

Thank you very much Alexander. You are very thoughtful 😌

I took this test to my whatsapp status and I did not get any reply from my female contacts sadly while the males that responded got it right.

Oh that was a good idea!

Yeah I think the only people who respond are the ones who get it right 😄

I'm not sure if anyone has mentioned this yet, but it seems to be a test of basic spatial recognition. Males have been demonstrably shown to be more adept at these tasks, while women excel at social comprehension. This is why there is a strong divide between men and women in social sciences vs. hard sciences. Depending on the magnitude of the effect shown here versus the magnitude of the difference between such processing skills, this effect may simply be down to differing evolutionary roles. Men had to learn spaces and mechanics in order to hunt and design weaponry/tools. Women had to learn to teach children and socialize.

What you're saying is most probably, from what we know, part of the picture, but it's not the whole picture. For example women aren't just going to social fields cos they're more inclined, but also because someone (society) inclines them. As the short section where I wrote about math demonstrates, women are disencouraged from going into scientific fields, whereas men are encouraged. There are women who are leaps and bounds above me specifically at math, so encouraging a woman like that to go to the social sciences, while encouraging me to go to the sciences, would do a disservice both to her and to me and to our fields. We should do as much as we can to probe the specific talents of individuals rather than groups. But we shouldn't be blind to biology either.

Before drawing the line, the only thing I could think of was whether the water level would be higher or lower than it was originally. I concluded that it had to be higher. You can imagine my surprise when I realized that the test was about whether the water level was horizontal or not.

Another conclusion from the test might be that women perceive the definition of water line different form men. Maybe they thought the water line was the wet line left on the glass indicating where the water had previously been. I'm not sure this is a reasonable assumption with water, but if the glass contained hot chocolate...

When I did the test, I wasn't thinking about height, if I recall. But I was thinking about it when I drew it for this post: I became aware some may concentrate on the height, and now you verified it.

There's researchers who suggested something similar to what you said. For example, they suggested females might draw a slanting line to indicate the water level in transition, before it reaches its new equilibrium. Thing is, if you try this live using a bottle or glass of water, you'll see the disturbance is minimal: in other words, tilting the bottle barely makes a difference to the water line, so that even if you drew it the way it was while tilting, still you'd basically draw a horizontal line. Plus, the water line goes back and forth, so it would make sense to draw the average, which would be the horizontal. So if there's some explanation regarding how women may interpret the instructions, it's probably based on a visual illusion that makes us think the water line is less horizontal when it's inside a tilted container.

Or... What if women perceive the world different when tilting their head, than men, so when they see a tilted glass drawing, they might not consider the glass as tilted, but rather the drawing as tilted, which causes them to perceve the gravity in the draiwng as tilted as well.

It would be interesing to see a similar study comparing how women and men read text which is tlted 90 degrees: If they rotate their head, or if they simply read it the way it is presented.

Well that's a bit 'out there' :D

I got the typically male result, and I'm a transgender man. Hahahahaha. 😁
Fwiw, I've always struggled with math, in a does-not-compute kind of way; I never could memorize multiplication tables, I would completely drop numbers doing any advanced math in school where we had to show work, I have NO concept of time. In adulthood, someone said to me that I probably have dyscalculia. They sent me to a site about it and the symptoms list was like, yep, yep, yep, yep, ...nope. The hard no being spatial difficulties. I get random compliments about spatial skills because of how I can Tetris any storage, shopping bag, suitcase, closet, bookshelf, etc. This is true for math, too: show me physics with a visual and I understand; show me an equation and I have no bloody idea what you're talking about. BriefER History of Time (no equations, pictures instead), yes. Brief History of Time = ??! I do not know why I am like this, but I am!

Memorizing the multiplication table was one of the most dreadful memories I have as a child. I know it's silly, but at the time it did cause me a lot of stress. Now I understand math is quite easy, compared to almost all other subjects!

I sometimes forget how old I am and twice I forgot whether I was born on the 26th or the 24th!

because of how I can Tetris any storage, shopping bag, suitcase, closet, bookshelf, etc.

Awesome sentence! :D

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