Keep Cognitive Psychology WEIRD

Back in 2010, Joe Henrich, Steve Heine, and Ara Norenzayan dropped a bomb[1] on psychology with their paper “The WEIRDest people in the world?” They argued that most psychology studies rely on Western, Educated, Industrial, Rich, Democratic (WEIRD) populations. These samples, they warned, are about as representative of humanity as Walter Sobchak is of a calm, reasonable human being. I should mention that I deeply respect all three scholars and even consider them friends.

Since then, their critique has dominated psychology. Every editor, reviewer, and funding agency now fixates on sample composition. It's become the go-to critique that even first-year undergrads can confidently make: "But professor, isn't that sample just WEIRD?"

But here's where it gets interesting. What if relying on WEIRD samples isn't always a problem? What if, for some areas of psychology, it doesn't matter much at all?

I'm more open to this idea after reading a brilliant new paper by Dorsa Amir and Chaz Firestone that made the rounds on Twitter a few months back. Before getting into it, I want to encourage you all to read this truly excellent paper. It represents scientific critique in its Platonic form: thorough, charitable, nuanced, and completely devastating.

Remember the Müller-Lyer illusion from Psych 101? Two lines of equal length that appear different depending on which direction the arrowheads at their ends point? Here's a refresher from Amir and Firestone’s paper:

Despite what your eyes tell you, both lines are the same length. Measure if you don't believe me.

For decades, psychologists explained this illusion as a universal feature of human visual processing. Our brain misinterprets the arrowheads as depth cues: inward arrows make a line look closer and therefore longer, while outward arrows signal distance, making the line seem shorter.

Then the WEIRD paper flipped this on its head. Henrich and colleagues argued the Müller-Lyer illusion wasn't universal at all but culturally specific. They pointed to decades-old cross-cultural research by Marshall Segall and colleagues from the 1960s claiming people who grew up in so-called carpentered environments (say in Western cities with lots of right angles) experience the illusion strongly, while people from non-carpentered environments (like foragers in the Kalahari Desert) barely experience it.

If this interpretation of the Müller-Lyer illusion is correct, it would be huge. The illusion isn't just how human vision works; it's a WEIRD illusion created by our boxy Western world. If even basic visual perception is shaped by culture, we'd need to rethink everything.

The only problem? In the words of Amir and Firestone, this idea is "almost certainly false."

Ouch.

The evidence they present is compelling. To start, they found serious methodological issues in the original cross-cultural studies. But even setting those reproducibility concerns aside, the case against culture shaping this illusion is overwhelming.

To start with, the illusion works with curved lines, not just straight ones—if it depended on Western right angles, curved versions shouldn't fool us, but they do. And you can even feel the illusion with your fingertips while blindfolded. Most convincingly, people born blind who later gain sight experience the Müller-Lyer illusion immediately, despite having zero previous exposure to Western architecture. These people see the illusion just as strongly as those who've had vision their whole lives. So much for the carpentered world hypothesis.

But the most mind-blowing evidence? Fish experience the Müller-Lyer illusion too. In a clever experiment, researchers trained guppies to swim toward longer lines for food rewards. When shown the Müller-Lyer illusion, these fish chose the line with inward-facing arrows, exactly like humans do. The same pattern shows up in parakeets, capuchins, and even ants and flies. None of these animals live in carpentered environments or Western culture, yet they all fall for the same visual trick.

If this illusion depends on exposure to Western carpentry, how the hell do guppies living in transparent tanks lined with gravel perceive it? How do flies, operating at a completely different scale from human architecture, experience the same effect?

Sure, these animals were raised in Western labs, but if flies buzzing around at millimeter scales are somehow influenced by human architecture, then “culture” has become so broad it explains everything and therefore nothing. The fact that animals across the evolutionary spectrum perceive this illusion suggests it comes from fundamental visual processing we share across species. This illusion, in other words, cannot be a product of exposure to one culture or another.

Amir and Firestone’s paper is a big deal. New information has come to light, man.

This isn't just about one cute illusion; similar claims of cultural variation have been made for other illusions. Yet when these claims are carefully re-examined, the cross-cultural differences appear overstated. The real significance of this paper lies deeper.

If culture can truly penetrate low-level perception—the most basic way we see the world—it would require a fundamental rethinking of how the human mind works. This is why so many researchers have argued urgently for incorporating non-WEIRD samples in our experiments. But if culture does not shape basic cognition, perhaps the WEIRD problem isn't quite as urgent as we’ve been told.

Don't misunderstand me. Cultural variation clearly matters for higher-level cognition, especially in domains like social psychology, moral reasoning, and decision-making. Henrich's groundbreaking research with the Machiguenga of Peru demonstrated just how dramatically economic behaviours can vary across cultures.

But—because I’m me—I can't help wondering if our fixation on non-WEIRD samples has been overblown for more basic cognitive processes. Recent evidence backs this up. A landmark replication of 12 tasks supposedly showing East-West cognitive differences found half showed no cultural differences at all, with some showing the opposite patterns from what was originally claimed. Another large replication failed to find evidence of cross-cultural variability in yet other visual cognition tasks.

Even more compelling is evidence from non-human animals. The Stroop effect, in which conflicting information slows processing? Honeybees show similar interference patterns when navigating contradictory visual cues to find food. Something remarkably like cognitive dissonance appears in rats, ants, and grasshoppers. Perhaps most astonishing, cuttlefish, invertebrates with entirely different brain structures than humans, perform surprisingly well on the marshmallow test, waiting patiently for preferred prey rather than settling for immediate but less desirable food.

When the same cognitive processes appear in species as evolutionarily distant from us as cuttlefish, grasshoppers, and bees, it suggests these mechanisms emerged long before the cultural variations that define WEIRD populations. I can’t help but think this diminishes concerns about WEIRD sampling biases for numerous cognitive capacities.

None of this means culture doesn't matter. It absolutely does. But we need to be more precise about where culture has its strongest influence. Here's the uncomfortable truth: running studies with diverse, non-WEIRD samples is expensive and time-consuming. If Mississippi undergrads process visual illusions the same way as Kalahari foragers, why fly to Botswana to prove it? Those resources could be used to fund studies on questions where cultural variation actually matters or to replicate the shaky findings that desperately need it. The WEIRD critique has become so reflexive that we've lost sight of when it applies versus when we're just checking a box.

To be clear, I'm not arguing we should never study non-WEIRD populations. The animal studies and cross-cultural replications that debunk the carpentered world hypothesis were essential to establish universality. But once we've shown that guppies and humans process the Müller-Lyer illusion identically, we don't need to keep proving it with every new visual perception study[2].

Cultural differences show up most in domains involving social norms, values, self-concept, and higher-level reasoning—how we think about ourselves in relation to others, our moral intuitions, how we make meaning of the world.

But the further we get from social processes and the closer we get to basic cognitive mechanisms, the more universal human psychology may be. This suggests that for many questions in cognitive psychology—how attention works, how we perceive visual stimuli, how we encode memory, how we resolve cognitive conflict—WEIRD samples might be perfectly adequate.

So, the next time an undergrad (or a reviewer) asks, “But professor, isn't that sample just WEIRD?” maybe you can respond: “That's just, like, your opinion, man.”

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[1] The paper is possibly the most influential social science paper in the 21^st century, cited over 17,000 times as of this writing. For context, the paper that made the case that psychology was in the midst of a replication crisis, the Psychology Reproducibility Project published by the Open Science Collaboration, has been cited just over 10,000 times

[2] Special thanks to Chaz Firestone and Dorsa Amir for reading and commenting on an earlier draft of this post, including helping me see when testing cognitive studies in non-WEIRD samples is vital.