Composite image with a drawing of a head with a universe inside it on the left and a drawing of a outstretched hand hiding a needle on the right

Unit 2: The science of implicit bias

Guided Learning


To truly outsmart implicit bias, we need to understand the science behind it. So what is implicit bias? Where does it come from?

The short answer is that we form associations in our minds, associations that we often don’t consciously know exist yet still impact our conscious thoughts, feelings, and behaviors.

The goal of this set of modules is to outline the history and science of implicit bias. Having this foundation should help you both appreciate the strength of the current scientific evidence and recognize how implicit bias can enter into decisions uninvited.

With this knowledge, we hope you will be able to understand and apply the principles of outsmarting implicit bias in life and at work.

40 years ago, researchers found that patients with amnesia could form new memories… implicitly. This sparked an ongoing revolution in research on the hidden mind.

Listen to the podcast


NARRATOR: We’re starting today’s podcast by talking about amnesia. Ask anyone what it means, and you’ll hear the same basic definition: the loss of memory.

Sometimes, the memories are old: things like who you are or what elementary school you went to. Sometimes, the memories are newer: what just happened? Who did you meet yesterday?

But the overall concept is the same: the things, people, and events you have amnesia for, you can no longer remember. But that’s not the whole story.

Around the turn of the 20th century, a peculiar report¬ was published: the Swiss neurologist Édouard Claparède wrote of hiding a small threading needle between his fingers and pricking the woman he shook hands with. The next day, he tried to shake her hand again, but this time she quickly pulled away.

Now, her reaction makes perfect sense… except for the fact that she had Korsakoff’s syndrome: a type of amnesia that kept her from forming new memories.

This woman had no idea what had happened the day before. She didn’t even recognize Claparéde, a man she saw every day. But some part of her mind – and this was a part that was hidden even from her – remembered what he had done.

Now, this was a different kind of memory than what we normally think of. It’s a memory that exists outside of conscious awareness. And amnesia or not, we all have it. So what exactly is it? How does our mind learn; what does it store? Perhaps more importantly, how does it shape our behavior? Today’s podcast is the first in a two-part series on the implicit revolution. Welcome to Outsmarting Human Minds.

MAHZARIN BANAJI: So think about this. If I ask you, “what did you eat for breakfast today?” Or if I say to you: “Remember when you were in fifth grade and you got lost?” and you have to remember that…

NARRATOR: This is Harvard psychologist Mahzarin Banaji.

MAHZARIN BANAJI: In any such act of remembering, you consciously go into your mind, and you try to pull something out, whether it was from a few hours ago or days ago or years ago. That kind of memory is a very conscious kind of memory. And the interesting result was that the people who were amnesiac patients, even though they had no conscious memory, they did seem to have some lingering sense of what had happened.

So in the experiment…

NARRATOR: This is a 1984 study conducted by Graf, Squire, and Mandler.

MAHZARIN BANAJI: …you could give them a list of words to learn, and say one of those words happened to be the word “motel”. M-O-T-E-L. Later you would say to them, you know, “Give me a word that starts with M-O-T.” Now, they could pick dozens of words.

NARRATOR: I tried this and pretty quickly came up with “motor”, “mother”, “motivate”, and “motion”.

MAHZARIN BANAJI: And yet they would be much more likely to generate “motel,” even though they had no recollection that they had even learned the word “motel” the day before. Something got saved in memory, and it came out when they were asked, even though they had no clue. That form of memory is what we call implicit memory.

NARRATOR: By the 1980s, the data was undeniable. These patients with amnesia – people who couldn’t tell you what they had eaten for breakfast or recognize the doctor they saw every day – they were remembering things. Not in a way that they could put into words, or even know that it was happening. But they were getting better at doing certain things with practice, even if they thought each time was the first time they were trying it. They were choosing words that they had learned in a previous task, even if they didn’t remember learning that word.

What’s more, the research was showing that what we were seeing in patients with amnesia was also happening in everyone!

MAHZARIN BANAJI: You know, we think we’re so different from amnesiac patients. And we are; there is no question that we have more intact memories compared to them. The real question is: are we a little bit like amnesiac patients? Do we also have information that’s stored in our minds that’s there, that’s used, but that we don’t consciously remember? I mean there’s so many examples we might have in everyday life of this…

NARRATOR: Like when you see a face and you feel like you’ve seen them before – what is that? And then you don’t know if you’ve met them or what.

MAHZARIN BANAJI: You can’t tell what the source of that familiarity is. And that’s indeed exactly what Larry Jacoby capitalized on when he did these lovely experiments showing that you can take a name like Sebastian Weisdorf, some Joe Schmoe, and turn him into a famous person simply by exposing people to the name ‘Sebastian Weisdorf’ on day 1, and then later giving them a long list of names and asking them to identify the famous people on the list. Well, there were some real famous people there! You know, ex-presidents and athletes and movie stars. But the interesting question was: will they mistakenly identify Sebastian Weisdorf as famous, and he found indeed they did at a level much higher than they would have if they not seen the name the day before. You see the name Sebastian Weisdorf and it looks familiar. Why? It could be because that I saw name before, it could be because he’s a Canadian hockey player, who knows? That’s an example of all of us, ordinary human beings, with supposedly intact memories, also showing an effect that’s very similar.

NARRATOR: Another study by Tory Higgins and colleagues found that these implicit connections can influence how much we like another person: whether we find them to be adventurous rather than reckless; self-confident rather than conceited. This research showed that our impression of a person can be swayed by something we have no clue about.

All this tells us: we don’t know our minds.

MAHZARIN BANAJI: If you said to me, “Mahzarin, do you know what your pancreas is doing right now?” I would say, “I have no clue. Where is my pancreas really?”

But if you said to me, “Mahzarin, do you know what your mind is doing now?”, I’d say “sure! I know exactly what it’s doing. I know my mind. I can sense it, as it has thoughts and feelings.” But the point I want to make today is that there are significant parts of our minds that lie beyond the reach of conscious awareness. Those parts do exist. And they affect the things that we think and do. We just don’t know that’s what they’re doing.

NARRATOR: And that brings us to the second question of this podcast, which is: how? How are we all walking around, making these connections and memories without meaning to, or even being aware that we’re doing it?

Mahzarin tells me: it’s all about our experience.

MAHZARIN BANAJI: Let’s talk about a simple thing called “mental association”. Rats, chimpanzees, humans, we all have a fundamental ability to learn how to pair things that happen together in time and space.

Mother and father, bread and butter, salt and pepper, day and night. Sometimes they’re opposites, sometimes they’re just related. But thinking of the one will remind us of the other because the two have co-occurred over and over again in our experience.

NARRATOR: That’s it. It’s just experience. Listen to the same playlist again and again, and eventually when one song ends, you’ll immediately start hearing the next song in your mind. You’re not trying to make this connection – you just do.

That’s how powerful our minds are. Of course, the trouble with learning is that we can’t pick and choose what associations we make. They’re simply the thumbprint that culture and experience have left on our brains. Much like how Pavlov’s dogs couldn’t help the fact that their mouths startrf watering as soon as they heard the bell, we can’t help but respond to the implicit associations we’ve picked up throughout life.

So while our implicit memories allow us to do things like drive a car, tie our shoes, get back home after work effortlessly, we also have to ask: what else have we learned? What have we learned about people who are a different height, race, or sexuality? What gets activated when we hear an accent or see someone in a wheelchair? And then, there’s the bigger, looming question: what happens when the associations we’ve implicitly learned run counter to the things we consciously believe?

MAHZARIN BANAJI: We humans are unique in the animal kingdom in that we not only have a deep sense of morality, we have codified it in our mottos, credos, and most importantly in our laws.

And at the best of times, we do act in accordance with our values and beliefs. We try to do the right thing. But there are also times when our decisions are influenced not by what we believe, but by what we have learned. And that’s where we see disparities.

NARRATOR: Consider healthcare for example: Dr. Monika Goyal and her colleagues looked at cases of appendicitis in the ER between 2003 and 2010, and they found that black children presenting with the same level of pain as white children were 80% less likely to receive opioid painkillers. Another study by Fowler and colleagues shows that older women receive fewer life-saving interventions than older men. Now, no doctor is going to say that these kinds of things are okay – but the data show that it’s happening. So we have to ask: what’s going on in the doctor’s mind at the moment of decision-making? Is something implicit shaping that decision?

And if so: how do we know?

Okay, so when I make a mistake, I try to catch it and fix it. But my question is, how do you catch something that you don’t know exists?

MAHZARIN BANAJI: You can’t. So the first step is to know what exists. You need a device.

NARRATOR: Almost a century after Claparède’s first report on amnesiac memory, mind scientists began creating these devices. These were tools, paradigms, tests that were all designed to reveal the kinds of associations that were getting stored in our minds, and how they influence our behavior. And in Part 2 of this podcast, we’ll explore one of these: the Implicit Association Test, and how psychologists Tony Greenwald, Mahzarin Banaji, and Brian Nosek harnessed the birth of the internet to share this device with the public.

Outsmarting Human Minds is a program founded by Mahzarin Banaji, devoted to improving decision-making using insights from psychological science. Support for Outsmarting Human Minds was provided by PwC and Harvard University. This episode was developed by Olivia Kang and Mahzarin Banaji. Sound editing and mixing was done by Evan Younger. Music was composed by Miracles of Modern Science. For references and related materials, go to



Key takeaways from this module

Learn the story of a small group of scientists, the test they developed to reveal implicit processes of the mind, and how they shared it with the world.

Listen to the podcast


NARRATOR: We are captivated by the idea of mind-reading. Movies like X-Men, TV shows like Star Trek – these all portray worlds where it’s possible to look inside another person’s brain and know what’s happening in their mind.

SPOCK [from STAR TREK]: “Our minds are merging, doctor. Our minds are one. I feel what you feel. I know what you know.”

NARRATOR: Now, much of this is the fantastic stuff of science fiction… but in some ways, it’s just the stuff of science.

In today’s podcast, Part 2 of the Implicit Revolution, we’re exploring the story of a small group of scientists, the device they developed to reveal implicit processes of the mind, and how they harnessed the birth of the internet to share it with the world. Welcome to Outsmarting Human Minds.

MAHZARIN BANAJI: Imagine this: you are asked to shuffle a deck of cards with hearts and diamonds to the left, and with clubs and spades to the right. This is not hard. It takes me under 20 seconds to do this.

NARRATOR: This is Professor Mahzarin Banaji. She’s describing the task that would eventually inspire the IAT – the Implicit Association Test. Visualize it, and you’ll immediately realize what makes it so easy. Hearts and diamonds are red. Clubs and spades are black. You could sort them perfectly without ever looking at the shapes at all.

MAHZARIN BANAJI: Now imagine that I have to sort clubs and hearts to the left, and spades and diamonds to the right. Not hard in the bigger scheme of things, but much harder than the previous sorting. The previous sorting relied on an association between hearts and diamonds: their redness. And I don’t have that prop anymore.

NARRATOR: You can still do the task. But now it’s harder; now color is working against you, and you really have to think about what you’re doing. This was the “aha” moment for psychologist Tony Greenwald and his colleagues. Because thinking deliberately will ensure that you’re sorting the cards correctly… but it’s also going to slow you down. And that means that one way to measure the mind is to measure time.

The IAT came out of this realization. Instead of just shapes, it asks people to sort things or concepts or people, and uses time to calculate how strong different associations are. The faster the sorting, the stronger the implicit association.

Here’s an example. The first IAT simply asked people to sort pictures of flowers and insects with either good words:

MAHZARIN BANAJI: Words like sunshine and love and peace and joy and things like that…

NARRATOR: …or bad words:

MAHZARIN BANAJI: evil, bomb, war, vomit…

NARRATOR: One pairing is a lot easier than the other. I probably don’t even have to tell you which one; just ask yourself: which one is easier to sort with ‘vomit’ – tulip, or cockroach?

That pairing will be faster – maybe just by a few milliseconds, maybe by a few hundred. Just how much faster reveals how strong the association is.

And once they had the test, the questions were endless.

MAHZARIN BANAJI: Every day, we’d come up with new ideas for new experiments we could try out on ourselves. We’d say, “I wonder how it will come out if I take a test for lobster versus anchovy.”

NARRATOR: And then, just like that, you could go from testing innocent preferences for anchovies or sports teams to discovering hidden biases for things like age, weight, and race.

MAHZARIN BANAJI: The first test I ever took was the race test. For half the trials, the light-skinned faces and good words were associated while dark skinned faces and bad words were associated. And I did that one first, and I did that one flawlessly. And I knew that the opposite pairing would be equally easy for me: white and bad, black and good – why should that be any different than the one before?

So I was quite stunned when my fingers almost couldn’t find their way on the keyboard. When I couldn’t keep in mind which had to go where. I made many more mistakes. I took one and a half times as long to do it. And as you can imagine, by the end of this three-minute experience, I was in a sweat. And my first thought was “something is screwed up with this test, because it can’t be me. I know my mind.”

NARRATOR: But it wasn’t the test. Mahzarin and Tony tested themselves again and again – each time getting the same result . They shared it with friends and family, the students in their labs, fellow scientists at conferences. The results were clear: somehow, the IAT was able to bypass conscious belief and reveal implicit associations they didn’t even know they had. Mahzarin and Tony began joking:

MAHZARIN BANAJI: These effects are so big, you could even pick it up on the Internet.

NARRATOR: In 1998, the internet was this barren, unknown thing – teeming with potential, but something that few people knew how to navigate. It was Brian Nosek, then a graduate student in Mahzarin’s lab, who turned joke into reality.

MAHZARIN BANAJI: He had come with a joint degree in Computer Science and Women’s Studies. And he just said, “this can be done.”

NARRATOR: Here’s Brian, now a Professor of Psychology at the University of Virginia, and Executive Director of the Center for Open Science:

BRIAN NOSEK: Mahzarin was convinced earlier, but she knew Tony needed to be convinced too, and he doesn’t convince easily. But the way he told me that he was convinced was he sent me a note saying, “Okay, I’ve scheduled a press conference for six weeks from now. Go get it done.”

It was terrifying because I had been saying, ‘Oh, I can build this, I can build this, I was a computer engineer, I know I could build something for the Internet.’ I had never made anything for the internet prior to that, I had never written in Java, I had very little experience with HTML, for goodness sake, which is the basics of making webpages. So you know, I was talking big, and he called me on it, and so I just stopped sleeping, and I started right then just building this website as fast as I could.

NARRATOR: Between Mahzarin and Brian, there are a flurry of anecdotes: stories about sweating in the un-air-conditioned basement of the Yale Psychology building, about eating pizza with one hand while programming with the other, of sleepless nights and countless bugs – but suffice it to say:

MAHZARIN BANAJI: We made the deadline.

BRIAN NOSEK: It got done, like, the day we were going to the airport to fly to Seattle for the press conference. I don’t even remember the details anymore, other than the terror that it inflicted on me.

MAHZARIN BANAJI: We had talked about what the response would be. And given what the web was at the time, it seemed to us an extravagant prediction that in a year, we would have 500 people take the test. We thought, “wouldn’t that be amazing.”

BRIAN NOSEK: I had it set it up where I could watch the tests come in. And I probably sat there for two hours watching them come in, just coming to the realization of “Th- This is big.”

MAHZARIN BANAJI: We had 45,000 completed tests in the first month. I think we crashed the Yale site, like, several times in the first week.

BRIAN NOSEK: And we’re thinking, “Oh my – oh my gosh! What just happened?”

NARRATOR: The IAT went viral. Mahzarin knew this after a flight she was on, where a pig farmer she was sitting next to heard she was a psychologist, put his fingers on an imaginary keyboard, and asked her:

MAHZARIN BANAJI: “Left-right, black-white – do you know that test?”

NARRATOR: The link to the site had been sent to him by another pig farmer.

MAHZARIN BANAJI: And that’s when I knew that this was out of our hands, that there was something about this that was intriguing enough, depressing enough, challenging enough, but ultimately something that people were going to keep going back to, because they wanted to be the good people that they thought they were.

I have been really humbled by people’s responses, because I don’t believe that I would have dealt with it as well as many people have. I know I didn’t deal with it well when I showed race bias. I’m usually amazed at the people who get it right away.

NARRATOR: What Mahzarin means by “getting it right away” is understanding that our culture and our experience shape what we implicitly learn. And that this learning has consequences.

Over 20 million tests have been completed since the IAT launched, and the data show us some incredible things. For instance, a 2009 study led by Brian found that if you look at how much an entire country implicitly associates “science” with “male” rather than “female” – this average predicts sex differences in 8th grade science and math achievement nationwide. The following year, Matthew Nock and his colleagues measured implicit associations of “self” with “death” and “suicide” in over 100 people seeking treatment at a psychiatric emergency department. They found that the strength of this association predicted whether a high-risk individual would attempt suicide in the next 6 months better than known clinical risk factors such as depression or previous history of suicide attempt.

The data also tell us that we as a society are changing:

MAHZARIN BANAJI: Our attitudes are elastic. They can stretch and accommodate new information that will change them – change our feelings about groups of people other than our own.

If you look at the data over the last ten years or so, we’re seeing a 37% decrease in implicit bias towards gay people. We’re heading towards neutrality. We see this too for race – that bias has gone down by about 13%. We’ve never seen this before. We’ve never seen strong, clear evidence that our implicit attitudes are changing.

NARRATOR: Of course, this doesn’t mean that listening to one 10-minute podcast or going to a single seminar is going to get rid of associations that have been reinforced for decades. Our minds are smarter than that.

MAHZARIN BANAJI: Instead, what we should be thinking about is “how do I change my daily environment so that the props in it routinely allow me to have the thoughts and activate the beliefs that I know are the right ones, that I know are in the interest of my society and me, are in the interest of the students that I teach?”

The outside does get inside, and what we’re observing in these data on change gives me great optimism, because it says that as our world changes, we and our minds will reflect that change.

NARRATOR: Change isn’t necessarily fast; and creating lasting change isn’t easy. But if we are motivated, we can learn to unlearn our biases – the ones that we ourselves don’t want. And that is something worth working towards.

Outsmarting Human Minds is a program founded by Mahzarin Banaji, devoted to improving decision-making using insights from psychological science. Support for this episode was provided by PwC and Harvard University. This episode was developed by Olivia Kang and Mahzarin Banaji, and featured Professors Mahzarin Banaji and Brian Nosek. Sound editing and mixing was done by Evan Younger. Music was composed by Miracles of Modern Science. You can take the Implicit Association Test at For references and related materials, go to



Key takeaways from this module

Can implicit associations be measured? How do they compare to self-reported attitudes and beliefs? Take the IAT to find out!

Each test will take about 5 minutes.

What You've Learned

As we move through our lives, we have experiences that create new mental associations and shape the ones we already have. These implicit associations can impact our behavior without us consciously knowing it.

Now, these associations aren’t always bad! They can create a bias favoring our own group that may even be beneficial. Just think about how our love of our family, a favorite sports team, and even where we work positively shapes our behavior – we are kind, caring, and loyal to our group.

It’s when implicit bias gets in the way of us making the best choices for ourselves and our organizations that we need to pay attention. Does implicit bias lead us to favor a member of our own group to our disadvantage, or lead us to act in ways counter to our own values of fairness and equality? A manager shouldn’t select a family member for a job over a better candidate who is not a family member. A doctor shouldn’t deny a working-class patient an appropriate medical treatment that they would offer to a wealthy patient. These are the errors in our decisions that we can only correct if they are revealed.

The first step in making our actions align with our beliefs is to know what our implicit biases are. Of course, taking an IAT will not by itself alter or “fix” our bias any more than taking a cholesterol test will cure us of heart disease. The best use of the IAT is to use it to learn more about the contents of our minds of which we are unaware. Once we do this, we are ready to shape our behavior in the direction we choose.

We can get the most reliable data about ourselves by taking an IAT multiple times. Think about it this way – if you wanted to know how good a batter was, you wouldn’t toss them a single ball once and then decide if they’re the next Babe Ruth or not! To get an accurate measure of your implicit bias, take the same test a few different times and consider the average of your scores to be the best indicator of your score.

The important takeaway is this: Only if we know our implicit biases can we actively work to outsmart them.

Test Your Knowledge

  1. The concept of implicit bias was developed by
  2. Implicit bias refers to (select all that apply)
  3. IAT stands for
  4. The IAT assumes that when two things have been repeatedly paired in our experience,


Question 1

Taking an Implicit Association Test and reflecting on it can be a pivotal moment. It certainly was for the co-developers of the IAT. At first, we were puzzled about how the test could show us to be biased when we “felt” no bias at all. But thinking about the IAT and asking deeper questions about what our test result meant allowed us to recognize where bias comes from and how it gets inside us; this knowledge has given us a more accurate and even more humble view of ourselves.

If you have taken one or more IATs, please write about the experience of taking them in the box below. Here are some questions to help guide your reflection:

  • Which tests did you take?
  • How did you think you might perform on the test before you took it?
  • How did you feel or what did you sense as you were taking the test? Were some associations easier to make than others?
  • Were you surprised by your test result?
  • What do you think the test result means? Think about your own biology and temperament, your upbringing and culture, and your current station in life. How might these have shaped you?
  • Do you feel your test results align with the values you hold?

What you write in this box is just for you. You will have a chance to download your response, but it will not be stored on our servers.

Your response:

Our thoughts:

Some people “feel” the conflict between their stated values of fairness and the implicit bias the test reveals. Others do not experience any conflict and are surprised by their IAT result.

But we all want our values to dictate how we behave. The IAT experience is often memorable because it can challenge your sense of yourself.

If you show no bias on a particular test, take another! We hope that your IAT experience can be a catalyst for your own thinking and growth.

Congratulations! You have completed Unit 2: The science of implicit bias.

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Dive deeper

Extra materials if you want to learn more

“[W]here did this idea of implicit bias come from? How can we measure biases that people don’t know they have, or at least are unwilling to endorse openly?” Hear the conversation between psychologists Andy Lutrell and Mahzarin Banaji at Opinion Science.

“Is there a part of ourselves that we don’t acknowledge, that we don’t even have access to and that might make us ashamed if we encounter it?” NPR’s Invisibilia discusses the implicit revolution further in their episode “The Culture Inside”.

Explore the lab websites of Professors Anthony G. Greenwald and Brian Nosek to learn more about their research on the implicit processes of the mind.

“We provide the first report of long-term change in both implicit and explicit attitudes — measured from the same individual — towards multiple social groups,” Charlesworth said … “implicit attitudes appear, in fact, to be capable of long-term durable change.” From Stephen Johnson’s Big Think article “Americans have become less biased — explicitly and implicitly — since 2004

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Unit 2: The science of implicit bias