Human perception is imagination | Nadine Dijkstra

Summary

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Podcast Summary

Philosophy For Our Times

Episode: Human Perception is Imagination | Nadine Dijkstra
Date: May 12, 2026
Host: IAI (Interview by Ricky Williamson)
Guest: Nadine Dijkstra, Principal Investigator, Institute of Neurology, UCL

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Episode Overview

In this engaging interview, Nadine Dijkstra explores the intricate relationship between human perception, imagination, and reality. Delving into cognitive neuroscience, she discusses how the brain constructs our experience of the world, the distinction between perception and hallucination, the role of imagination (both automatic and creative), and the unresolved philosophical issues at the heart of neuroscience — most notably, consciousness. The conversation also touches on AI, the development of the brain, and the role of imagination in both children and adults.

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Key Discussion Points & Insights

1. Is Reality a ‘Controlled Hallucination’?

• Terminology Matters ([02:21])

  • Dijkstra pushes back on the emerging meme that reality is a “controlled hallucination,” arguing that “hallucination” implies dysfunction, whereas our imaginative processes are adaptive and efficient.
  • Quote:

    "Using the word hallucination is maybe a little bit… it's not helpful, I think, because it makes it sound like something is wrong."
    – Nadine Dijkstra, [02:21]

• How Reality is Constructed ([02:53])

  • The brain actively constructs reality, filling in information based on sensory input and prior knowledge.
  • Imagination, not hallucination, is a better framing for this process.
  • Quote:

    "As a neuroscientist, we know that the brain fills in what we perceive as reality. It kind of constructs our reality in an active way. We're not just passively perceiving reality like our eyes are camera."
    – Nadine Dijkstra, [02:21]

2. The Nature of Perception and ‘Reality’ ([03:30–04:13])

• Dijkstra refuses to speculate on the nature of “fundamental reality,” focusing instead on how we perceive reality, which is a blend of sensory input and interpretation.

• Our perception is always a constructed experience.

• Self-Reflexivity and Measuring Reality ([04:13])

  • She emphasizes a careful, scientific approach — measuring what happens in the brain when people make reality judgments, instead of speculating about reality itself.
  • Quote:

    "What I can do is measure what goes on in your brain when you decide whether something is real or not."
    – Nadine Dijkstra, [04:23]

3. What Does ‘Real’ Mean? Social & Subjective Definitions ([05:02])

• Dijkstra highlights the socially negotiated aspect of reality — shared perceptions become our collective ‘real’, while experiences diverging from consensus are seen as less real.

• Psychedelic experiences do not inherently access a “truer” reality, just an altered perception.

• Quote:

  "Reality in that sense exists a little bit on a spectrum... as you start to diverge more and more from what people agree on, it maybe becomes less and less real in that sense. But that's a social, a social definition of real."
  – Nadine Dijkstra, [05:21]

4. Materialism, Computers, and the Hard Problem of Consciousness

• Physicalist Leanings ([06:41])
  • Dijkstra acknowledges her implicit physicalism: she seeks physical correlates for subjective experiences but is open to other frameworks.
• Is the Brain a Computer? ([07:05])
  • The computer model is “useful, but not complete.”
  • Even with brain simulation, consciousness remains unresolved.
  • Quote:

    "If you simulate a rainstorm, it's not wet... I think that's where philosophy would come in for me."
    – Nadine Dijkstra, [07:17]

5. Neuroscience, AI, and the Future ([07:49–08:34])

• Neuroscience and AI are mutually inspiring fields: brain research influences AI models, and AI helps neuroscientists analyze and model brain functions.
• This interplay will accelerate discovery but may not resolve philosophical issues like consciousness.

6. Biggest Problems in Neuroscience ([08:39–09:05])

• The “hard problem” (consciousness) is currently more of a theoretical/philosophical issue than a tractable neuroscientific one.
• Even simulating the brain doesn’t solve consciousness.

7. Imagination: Definitions and Functions ([09:34])

• Imagination is crucial for both perception (filling in sensory gaps, e.g., the blind spot) and creativity (forming new associations).
• Both forms are essential for human development.

8. Imagination in Animals & Human Self-Consciousness ([10:30–11:09])

• Some animals show elements of imagination (e.g., rats simulating paths in a maze), but human imagination is broader and more creative.
• Self-consciousness seems linked to the ability to “decouple” perception from environment — a sophisticated form of “offline” processing.

9. How the Brain Distinguishes Reality from Imagination ([11:29–12:27])

• The brain can sometimes confuse vivid imagination with reality, even in healthy individuals.
• Dysfunctional versions of this mechanism can manifest in psychosis or schizophrenia:
  Quote:

  "If that goes wrong is people can develop things like psychosis or schizophrenia where they start to really decouple from the consensus of reality."
  – Nadine Dijkstra, [12:08]

10. Why Do Children Imagine More? ([12:35])

• The “reality monitoring” function (rooted in the prefrontal cortex) develops late; children’s brains don’t fully distinguish between imagined and actual experiences.
• Quote:

  "Maybe kids just don't have a reality monitor yet. So for them, whether they are making it up or whether it's really there is kind of the same."
  – Nadine Dijkstra, [12:53]

11. Is More Imagination in Adults Desirable? ([13:15])

• Retaining “better” imagination as adults would likely be dysfunctional, leading to confusion between fantasy and reality.
• The key is a balanced imagination — rich, but anchored enough for consensus reality.

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Notable Quotes and Memorable Moments

• On the illusory nature of perception:

  "We're not just passively perceiving reality like our eyes are camera."
  – Nadine Dijkstra, [02:24]

• On the future of neuroscience and AI:

  "There's a virtuous cycle. It's not only that the brain inspires AI, but AI can inspire the way the brain works as well."
  – Nadine Dijkstra, [08:05]

• On consciousness as the biggest challenge:

  "There was this really big project where neuroscientists wanted to just replicate the brain... But even if you’ve built a brain in a computer, you still have not solved the problem of consciousness."
  – Nadine Dijkstra, [08:46]

• On imagination and functioning society:

  "The imagination that's most useful is pretty good. But not too good. I think that's what we need."
  – Nadine Dijkstra, [13:52]

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Important Segment Timestamps

• [02:21] Dijkstra on “controlled hallucination” vs. imagination
• [03:53] Discussion on how we never contact “fundamental reality”
• [05:21] Reality as a social/consensus spectrum
• [06:41] Dijkstra’s working physicalism and the “hard problem”
• [07:05] Brain-as-computer analogy and its limits
• [08:05] Neuroscience and AI as mutually inspiring
• [09:34] The dual definition and role of imagination
• [11:29] How the brain can confuse imagination and reality
• [12:35] Why children imagine more than adults
• [13:15] Why more imagination isn’t always better for adults

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Tone and Style

The conversation is reflective, measured, and rigorous, with Nadine Dijkstra careful to distinguish scientific knowledge from philosophical speculation. She often clarifies the scope of neuroscience and resists sweeping metaphysical claims, grounding complex ideas in concrete research and relatable metaphors.

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Summary Takeaway

Nadine Dijkstra provides a nuanced picture of human perception, arguing that our brains continually construct reality using imagination and prior knowledge, but this is an adaptive, functional process — not a “hallucination.” The challenge of distinguishing imagination from reality is ongoing, especially in developing brains, and when this goes awry, it can lead to dysfunction. The mystery of consciousness remains unresolved, and while AI and neuroscience will continue to co-evolve, bridging the explanatory gap will require both scientific and philosophical advances. The ideal imagination is rich, but tempered — allowing us to function, create, and build shared realities.

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Transcript

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[Nadina Dykstra]

One hypothesis that we've been entertaining is that this reality monitoring. So deciding whether something is real or imagined is a function that your brain needs to develop. And we think it's something that relies on your prefrontal cortex, which is kind of the latest brain areas to develop. Maybe kids just don't have a reality monitor yet. So for them, whether they are making it up or whether it's really there is kind of the same because we know the brain processes those things similarly. But just in adults we have this add on solution that makes sure we don't confuse the two. But maybe in children that actual function of reality monitor just doesn't work that well yet that's our current hypothesis.

[Daniel]

Hello and welcome to Philosophy for Our Times, bringing you the world's leading thinkers on today's biggest ideas. I'm Daniel.

[Zeb]

And I'm Zeb. Today's episode is Human Perception is Imagination, an interview with Medina Dykstra about her research in imaging neuroscience. Nadina is a principal investigator at the Institute of Neurology at UCL where she investigates how the brain generates mental images and differentiates them from actual perception. In this interview, you'll hear her speak about everything from the difference between imagination and hallucination to whether brains are computers, to the biggest problems facing neuroscience today.

[Daniel]

This interview is conducted by Ricky Williamson from the IAI editorial team and was held at our how the Light Gets in festival in early 2025. So without further ado, I'll hand it over to Ricky.

[Ricky Williamson]

Nadina Dykstra, welcome to how the Light Gets In.

[Nadina Dykstra]

Thank you. Thank you for having me.

[Ricky Williamson]

So you are a cognitive neuroscientist and you lead Imagine Reality Lab. So many people these days like to argue that reality is a controlled hallucination created by the brain. What do you make of that view?

[Nadina Dykstra]

So I think using the word hallucination is maybe a little bit. It's not helpful, I think, because it makes it sound like it's like something is wrong. And it's something you have to do something about. So in that sense, I think that word itself is not helpful. But I do, you know, I do. As a neuroscientist, we know that the brain fills in what we perceive as reality. It kind of constructs our reality in an active way. We're not just passively perceiving reality like our eyes are camera. So in that sense, yes, we are imagining our reality. But I wouldn't use the word hallucination, imagining.

[Ricky Williamson]

So what's the difference between imagination and hallucinating? Sorry. So hallucinating suggests something's wrong, you say?

[Nadina Dykstra]

I think that's what it is. So it suggests something is wrong. And the way that we imagine our reality is usually very efficient and it's adaptive. Our brain has developed this way because it's a very efficient way of processing the information that's out there in the world. So we don't have to start from scratch every time we get signals into our eyes. But we can use our prior knowledge to kind of fill in the gaps. And it's, it's, usually it works well and usually it goes right.

[Ricky Williamson]

So, okay, so is all of reality imagined then or is just parts of it?

[Nadina Dykstra]

Well, as a neuroscientist, I don't say anything about what reality is. I just say how we perceive reality. The way we perceive reality is a combination by what comes into our senses, which is based on, you know, things that are actually out there in the world. But then how we interpret and perceive it is then also influenced by our prior knowledge and expectations.

[Ricky Williamson]

So at no point we come in contact with reality.

[Nadina Dykstra]

I mean, our senses get signals from reality.

[Ricky Williamson]

Yes, but is that kind of fundamental reality or is that the reality that we perceive is created?

[Nadina Dykstra]

Well, again, as a neuroscientist, I don't say what fundamental reality is. I don't know what fundamental reality is. I don't know what that question means. But I do know that the way we perceive reality is something that's constructed by our brain.

[Ricky Williamson]

Okay. And so just is there a kind of self reflexive problem there? Because isn't that thought itself a creation of your brain? And therefore.

[Nadina Dykstra]

Exactly. That's why I'm very careful to say if I could say anything about what reality is. What I can do is measure what goes on in your brain when you decide whether something is real or not. For example. So we've done experiments where we ask people to imagine things and then sometimes if they imagine something really, really vividly, they say it's real. Well, we know Nothing is out there in the world. So we know that in that case that's, that is a hallucination because it's incorrect. But we can really look at what happens in your brain when you decide whether or not something is real. And that's what I am interested in. Not about whether it's real or not, but about how your brain decides whether something is real.

[Ricky Williamson]

Okay, and by, what does real mean? Real means kind of confirmed by other people.

[Nadina Dykstra]

It's what it feels like for you. Right. So how do you decide whether something is real? It's because it feels real.

[Ricky Williamson]

Right, but, but you, you're saying something. If something isn't there, it's not real. But can there be phenomena that appear only to my mind or to someone's mind.

[Nadina Dykstra]

Yeah, others. Yeah, I guess that's a good point. And I think reality in that sense exists a little bit on a spectrum where what we now see, we can kind of agree on that. That's blue, black, and like what I'm wearing is orange and all of those things. But then there's this, there's a spectrum where as you start to diverge more and more from what people agree on, it maybe becomes less and less real in that sense. But that's a social, a social definition of real. Right, which is.

[Ricky Williamson]

Yeah, because lots of people who have hallucinations on psychedelics, for example, kind of think that they're more real or more true than the reality that we see. What do you make of that?

[Nadina Dykstra]

I don't see why that would be the case. It's still their brain interpreting signals coming into their senses. I don't, I don't, I don't see any argument of why their brain on psychedelics would interpret those senses as more real than a non psychedelic brain.

[Ricky Williamson]

And so does this rely on kind of a physicalist notion of consciousness, do you think? And if so, what's your kind of answer to the hard problem of consciousness?

[Nadina Dykstra]

What's my answer to the hard problem of consciousness? That's your question.

[Ricky Williamson]

I mean, it seems kind of embedded a little bit because you're saying kind of reality, we perceive just electrical signals in the brain or perception just is with electrical signals in the brain. Yeah, but that seems to be going, that seems to have.

[Nadina Dykstra]

So I think I do have an implicit physicalist or materialist philosophy, but it's not something that I would, I would, I would defend until the end. It's just something that I, as a working assumption. So I look for physical correlates of subjective experiences. That's.

[Ricky Williamson]

Yeah, so Obviously, AI is very big right now. Is the brain a computer in your view, or is something non computational about the brain?

[Nadina Dykstra]

Yeah, I think thinking about the brain as a computer is useful. I think it allows us to solve some problems and see what might go wrong when people have symptoms that are bothering them. So I think it's a useful model of the brain. I don't know if it's a complete model or a completely accurate model. I also don't know that if we would simulate the brain in a computer, if that simulation would be conscious, it's kind of like if you simulate a rainstorm, it's not wet. Right. So I think that's, that's where philosophy would come in for me. But I do think it's a useful model. Yeah.

[Ricky Williamson]

What does the future of neuroscience look like with AI embedded? Obviously, kind of musk has this neuralink going on. I mean, what's the future of neuroscience and the AI connection with that?

[Nadina Dykstra]

So I think always neuroscience and AI have been super intimately linked. So AI kind of was inspired by neuroscience, by cognitive science. Back in the day when we couldn't measure brains, we just thought about how thinking would work, and then that led to inspiration of neural networks. And I think now we're at the stage where there's a virtuous cycle. It's not only that the brain inspires AI, but AI can inspire the way the brain works as well. So we can run AI simulations to get inspiration of how specific kind of functions might be implemented in brains. And I think that's going to continue. It's going to be a mutually inspiring

[Daniel]

field,

[Nadina Dykstra]

and I think it's also going to make some problems more efficient to solve. We can use AI to generate more efficient analysis. So. Yeah.

[Ricky Williamson]

What would you say are the biggest problems facing neuroscience today?

[Nadina Dykstra]

Well, the consciousness one is a pretty big one, but I don't know if that's a neuroscience problem at the moment or if that's a philosophical problem at the moment. It seems like a theory problem at the moment because neuroscientists. There was this really big project where neuroscientists wanted to just replicate the brain. They wanted to build the brain in a computer. But even if you've built a brain in a computer, you still have not solved the problem of consciousness. So I think those are. Yeah, it's a hard one, but that's, I think that's one of the, one of the interesting ones.

[Ricky Williamson]

Yeah. Do you think that's coming kind of being able to build a brain in a computer? Maybe it won't be conscious. But could it do all the other things that brains do?

[Nadina Dykstra]

Maybe, yeah. I mean, I just went to Anders Sandberg's talk and we are getting closer to at least emulating some of the functions of brains in computers. I don't see any natural limit to that. And then the second question of whether that simulation would be conscious, that's an independent question, I think.

[Ricky Williamson]

Okay. Returning to imagination, how crucial is imagination to human beings?

[Nadina Dykstra]

So there's, I guess there's different definitions of imagination. The imagination that when I talk about when what your reality is imagined as the kind of automatic filling in. Like you have this blind spot in your eye right where your nerve leaves your eyeball and that you shouldn't see anything there. But we always, we don't have a, have a gap in our perception. That's imagination, that's part is imagined. And I think that's really crucial because that's essential to how we perceive the world. And then you have the more creative imagination of being able to create new associations and new and new concepts and new ways of thinking. And I think that's crucial for more kind of development in a more broad sense of the word.

[Ricky Williamson]

Is that kind of something special about human beings or can animals do that? And how crucial is it to kind of self consciousness in human beings, that act of imagination?

[Nadina Dykstra]

So I think some human, some non human animals can also generate offline perceptions. So they can, they can like simulate, for example, there's rats running in a maze and they can simulate alternative paths to the ones that they've just taken. You could say that's a form of imagination. I guess the, the, the, the extent of the creativity of that is probably less than in humans. Self consciousness, as in being aware that you are a self or self consciousness, as in having a subjective experience.

[Ricky Williamson]

Self consciousness in that you are aware that you're aware, you're aware that you're aware, then you have an idea of identity of yourself.

[Nadina Dykstra]

So I guess in order to have an awareness of your, of you as a, as a being, you need to kind of be able to decouple your perception from the immediate environment. You should not just be like a response output thing. You need some kind of offline processing. You could call that imagination. Sure. And then. Yes, that's. But we're stretching the concept a little bit here, I think. Yeah.

[Ricky Williamson]

And so in your research looks at how the brain distinguishes between reality and imagination and as I understand it can't, sometimes can't.

[Nadina Dykstra]

Yes. Yeah.

[Ricky Williamson]

What consequences do that have?

[Nadina Dykstra]

Well, I mean, I guess if it goes wrong too often. So what we've studied, we've studied in healthy brains, people who are otherwise completely functioning. There's no diagnosed disorder or anything. And then on a very specific circumstances, we show that we can get them to confuse their mental imagery for perception. But I think that's because we're pushing the right circumstances. And that's, that's because we're showing that that's the way the system works. But it works well. Like it usually this is a function that works well. Usually. I guess the problem is that if that goes wrong is people can develop things like psychosis or schizophrenia where they start to really decouple from the consensus of reality. And then I guess that behavior becomes dysfunctional and it can't function in our society anymore. That's the extreme end of that.

[Ricky Williamson]

Yeah, obviously. Well, maybe not obviously actually, but children seem to imagine more than adults. Why is that? Why do we lose that?

[Nadina Dykstra]

That's a really good question. So we've been thinking about this quite a lot and one hypothesis that we've been entertaining is that this reality monitoring, so deciding whether something is real or imagined is a function that your brain needs to develop. And we think it's something that relies on your prefrontal cortex, which is kind of the latest brain areas to develop. Maybe kids just don't have a reality to monitor yet. So for them, whether they are making it up or, or whether it's really there is kind of the same because we know the brain processes those things similarly. But just in adults we have this add on solution that makes sure we don't confuse the two. But maybe in children that actual function, the reality monitor, just doesn't work that well yet. That's our current hypothesis.

[Ricky Williamson]

Would the world be a better place if we could imagine better as adults, as we do as children?

[Nadina Dykstra]

If we could imagine better? No, I think that would lead to a lot of dysfunction because we won't be able to keep it apart from reality. Right. So I think we need as a functioning society to kind of diverge on or like to get at a shared reality that we can agree with in order to, you know, to live functionally.

[Ricky Williamson]

Isn't imagination kind of crucial to any possible future though? You know, we can't build a future of our first imagining.

[Nadina Dykstra]

I guess that's true. Yeah. Yeah, that's true. I think that's true. But I think there's a difference between having extremely good imagination and having imagination that's useful. I think the imagination that's most useful is pretty good. But not too good. I think that's what we need.

[Ricky Williamson]

Wonderful. Nadina, wonderful to meet you and thank you for coming to Hallelujah.

[Nadina Dykstra]

Thank you.

[Daniel]

Thank you for listening to philosophy for our times. What do you think? Is consciousness the biggest problem facing neuroscience today? What do you think, Seb?

[Zeb]

Well, I'm no neuroscientist, but if you head over to our YouTube channel, you can watch the first episode of our new video series Ideas for Our Time, where I talk through the consciousness problem with scientist Bridget Queenan. She presents an exciting perspective on the problem that taking inspiration from music could provide new ways of thinking about how the brain works.

[Daniel]

Yeah, if you're interested in consciousness, I definitely recommend checking that out. Well, we would love to hear what you think. Please write to us using the email in the show notes below.

[Zeb]

Do like and subscribe for more. You can also head over to our website IAI TV for thousands more brilliant debates, talks and interviews from the world's leading thinkers.

[Daniel]

Bye bye.

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