What Happens in a Mind That Can't 'See' Mental Images
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Welcome to the Quanta Science Podcast. Each episode, we bring you stories about developments in science and mathematics. I'm Susan Vallett. Neuroscience research into people with aphantasia who don't experience mental imagery is revealing how imagination works and demonstrating the sweeping variety in our subjective experiences. That's next. ♪

It's season three of The Joy of Why, and I still have a lot of questions. Like, what is this thing we call time? Why does altruism exist? And where is Jan Eleven? I'm here, astrophysicist and co-host, ready for anything. That's right. I'm bringing in the A-team. So brace yourselves. Get ready to learn. I'm Jan Eleven. I'm Steve Strogatz. And this is... Quantum Magazine's podcast, The Joy of Why. New episodes drop every other Thursday. ♪

A couple of years ago, Sarah Shomstein realized she didn't have a mind's eye. The vision scientist was sitting in a seminar room, listening to a scientific talk, when the presenter asked the audience to use their imagination. Imagine an apple, close your eyes, and then report in terms of vividness how vivid is your image. And I closed my eyes.

And I imagined an apple, just like I know that I can imagine things. And I was like, I imagined an apple. That was great, but it was completely black. But I imagined an apple. I can tell you everything about it, right? Schamstein was confused. How come she didn't actually see an apple? Most of her colleagues reacted differently. They reported actually seeing an apple, some vividly and some faintly, floating like a hologram in front of them.

In that moment, Shomstein, who's spent years researching perception at George Washington University, realized she experienced the world differently than others. I see black. I mentalize, but I don't visualize.

So that was how I discovered that I had aphantasia. Schamstein is part of a subset of people, thought to be about 1% to 4% of the general population, who lack mental imagery, the phenomenon known as aphantasia. Though it was described more than 140 years ago, the term aphantasia was coined only in 2015. It immediately drew the attention of anyone interested in how the imagination works.

That included neuroscientists. So far, they're finding that aphantasia is not a disorder. It's just a different way of experiencing the world. Early studies have suggested that differences in the connections between brain regions involved in vision, memory, and decision-making could explain variations in people's ability to form mental images.

Because many people with aphantasia dream in images and can recognize objects and faces, it seems likely that their minds store visual information. They just can't access it voluntarily or can't use it to generate the experience of imagery. That's just one explanation for aphantasia. In reality, people's subjective experiences vary dramatically, and it's possible that different subsets of people with the condition have their own neural explanations.

You've got aphantasia, and then you have hyperphantasia, the opposite phenomenon in which people report mental imagery as vivid as reality. They're two ends of a spectrum, sandwiching an infinite range of internal experiences between them.

Nadine Dykstra is a postdoctoral researcher at University College London who studies perception. We think we know what we mean when we talk about what mental imagery is, but then when you really dig into it, everybody experiences something wildly different. That makes studying aphantasia, hyperphantasia and other internal experiences difficult.

But far from unimaginable. Dijkstra says, think about it this way. So the idea is that when you perceive the outside world, light falls on the retina and then that's being sent first to the back of your brain, which is the primary visual cortex. And then activation kind of spreads forwards to more high level visual regions. And this is how your brain kind of perceives the outside world.

And high-level regions extract the meaning of your input. So you go from an image to what you are looking at. That's how visual perception works. And then the idea with imagery is that it's the other way around. So you start with an idea, like a cat, a concept, and then you generate a mental image in a reversed order.

So you start from high-level visual regions and then you slowly fill in the details. But that's only a working model of visual imagination. There's still so much we don't know about the process, such as where mental imagery begins and the exact role of the visual cortex. These processes were even less defined in 2003, when a man with an interesting problem walked into Adam Zeman's office.

Zeman is a neurologist at the Universities of Edinburgh and Exeter who studies visual imagery. He listened to the patient recount how he lost the ability to conjure mental images. And I thought this was a really intriguing symptom. I'd never come across it before.

He was a great research participant. He was a very articulate, bright man in his mid-60s. He'd lost the ability to visualize after a cardiac procedure. We studied him in detail and essentially it was very difficult to find any correlate for the very convincing complaint he gave of the change in his experience. So he said, you know, previously I could visualize faces of friends and family to get to sleep. Can't do that anymore. Previously, when I read a novel he loved reading, I would enter a visual world. That doesn't happen. Previously, I dreamt visually. I now dream without images.

Previously, if I lost something, I could visualize where I'd put it. I can't do that. Basically, after his procedure, his mental stage was empty. At the time, evidence was accumulating that the visual cortex activates when people imagine or perceive something. Zeman wondered whether his patient's visual cortex had become somehow deactivated.

He had the patient, Jim Campbell, lie down in a functional magnetic resonance imaging machine. He then measured blood flow in the brain as a proxy for neural activity. Zeman showed Campbell pictures and then asked him to imagine them. Whereas when you and I, if you have imagery, visualize famous faces, familiar faces, we activate our visual cortex. He did not.

even though when he looked at famous faces, he activated his visual cortex quite normally. In a 2010 case study, Zeman described him as having "blind imagination,"

Discover magazine covered Zeman's case study of Campbell. And then people began getting in touch over the next few years, initially just a trickle of people saying, I'm just like this guy, but I always have been. I've always realized that I'm a little bit different in this respect. Zeman heard from an additional 20 or so people who had never had the ability to visualize images in their minds.

Apparently, this was a somewhat common experience. In 2015, Zeman decided this condition needed a name. There were some terms in the neurological literature, but they were very unwieldy ones like defective revisualization and visual irreminiscence. I have an old friend who studied classics at university, so I had tea with him and asked him if he had any ideas for what we might call this. And he suggested that we borrow Aristotle's term for the mind's eye, which is fantasia, and tag an A on it. So the term aphantasia was born.

Soon after Zeman's team reported the shiny new term, the New York Times published a story about aphantasia, triggering a fresh flood of interest.

Zeman has now received more than 17,000 emails from people wanting to learn more about their vivid mind's eye, or lack thereof. So creating the terms turned out to be an unexpectedly good trick. It attracted a lot of interest and revealed quite a large appetite among people who lack imagery or have very vivid imagery but had lacked a term with which to describe this. And we're really rather pleased that a bit of light was being shone on this slightly unusual aspect of their psychological makeup.

I mean, one of the big surprises really, particularly initially, was a lot of gratitude. People saying, this is fantastic. It really explains a lot of things that have puzzled me about myself. At dinner tables across the world, friends and family discussed whether they could imagine an apple. Philosophers used aphantasia as an excuse to probe explanations for the mind. Art exhibitions displayed works created by people with these extremes in visualization.

and scientists dreamed up new ways to study aphantasia as a window into how imagination works. Studying aphantasia wasn't easy. How do you measure someone else's inner reality?

Sarah Schamstein, the vision scientist who has aphantasia, says the research she's seen hasn't been satisfying. Right now it's focused on showing that the condition exists, that it's real. To me, I don't need to be convinced of that because I haven't. I'm sitting next to a woman who's like, that's just, that's bogus. They're making it up. And I'm like, you know, right here.

Early studies relied on reports from participants, and they still do. The most famous test is called the Vividness of Visual Imagery Questionnaire, created in 1973 to study the strength of mental imagery, long before aphantasia was named. However, such tests rely on introspection and self-reported experience, which made some neuroscientists doubt that aphantasia was real.

Could reported differences in visual imagery be a language disconnect, given the ambiguity in how we describe our inner worlds?

Rebecca Keogh is a research fellow in cognitive neuroscience at Macquarie University in Sydney, Australia. Say we all imagine an apple. Maybe I say, oh, when I see, I imagine the apple, it's really, really strong. It's almost like seeing it. I can see the red and everything. And someone else might say, oh, I only have, you know, a grey apple. I don't really see it very well. Someone might say they don't have an image. But it could be the case that we're all actually experiencing the exact same apple. We're just describing it differently. In 2015, when Zeman coined Avantasia...

Keough was finishing her doctorate under Joel Pearson, a professor of cognitive neuroscience at the University of New South Wales. They were intrigued. The group designed a few tests to confirm aphantasia's existence. One probed the mind's ability to hold a visual image. The other measured sweat and pupil responses to mental pictures.

Keogh says their pupil study was based on a previous study. When you see a dark image, your pupil dilates. When you see a bright image, your pupil constricts. And they found that when people imagine dark things, the same sort of thing happens. So your pupil's larger when you imagine dark images and smaller when you imagine light images. And we found...

that we could replicate this with a group of people who said that they have imagery. But when we compared people who report not having imagery, you don't get this kind of suggesting that it's not just that they're reporting a difference. There seems to be some sort of difference in their experience. To Cornelia McCormick, a memory researcher at the University of Bonn in Germany, the idea that some people don't have mental images was hard to accept.

But then she became curious. Most of those vivid memories that we have come with images. So we see the event in front of our mind's eye. And then I heard about aphantasia and I thought, how on earth do those people remember their own lives when they don't have those rich images? To test this, she and her team scanned the brains of people with and without aphantasia while they recalled personal memories.

They found that people with aphantasia indeed tended to have weaker autobiographical memories and less activity in the hippocampus, which helps encode and retrieve such memories. But to their surprise, the visual cortex had stronger activity among those individuals than in people with more typical visual imagination.

McCormack speculates on what might be happening. One idea is that this heightened activity prohibits the small signals that you need for mental imagery to exceed the signal-to-noise ratio.

So if you would dampen the activity in the visual cortex, also those mental images would come over this noise level and could be seen in your mind's eye. A growing number of papers have also found that people with the condition have activity in their visual cortex as they imagine something. Paolo Bartolomeo is a neurologist at the Paris Brain Institute.

He says maybe they have access to the visual information. Is this functional disconnection a sign that congenital aphantasics, they do have access to the visual information, but somehow they cannot integrate this information in a subjective experience? This hypothesis meshes with the fact that people with aphantasia can recognize objects and faces, and most can see images as they drift off to sleep and in their dreams.

Here's neurologist Adam Zeman. Many people with visual aphantasia dream visually. So they know what imagery is like from their dreams, even though they can't visualize to order during the day. But for some reason, they have trouble accessing this visual information voluntarily. Zeman wondered what was happening in their brains.

A few years ago, Zeman scanned the brains of volunteers as they rested in an fMRI machine. The scan suggested that, at rest, people with aphantasia have weaker connections between the prefrontal cortex, which houses the brain's higher-level control centers, and the visual cortex, compared to those with hyperphantasia. The findings were broadly supported by a recent study from Bartolomeo's lab, which is currently under peer review.

Bartolomeo and his team had participants lie in brain scanners and actively imagine shapes, faces, and places. In people with aphantasia and without, similar areas of the brain activated. But aphantasics showed disconnections between the prefrontal cortex and the fusiform imagery node, a region involved in higher-level visual processing. Bartolomeo had identified that region in 2020.

Taken together, the findings suggest that in people with aphantasia, the connections between visual centers and other integrative brain regions differ from those in people without aphantasia.

Benza Nane is a professor of philosophical psychology at the University of Antwerp who researches mental imagery. Just statistically, it seems like there's more aphantasia where you have mental imagery, just you don't have control over it, then not. And in those cases, the connectivity between the hippocampus and the visual areas is as good as yours or mine. The issue is elsewhere. This is a good claim for some subset of aphantasia. But Nane says chances are there are other neural explanations as well.

That would mean that there's more than one type of aphantasia, and indeed a whole spectrum of internal visualization across different people. People with aphantasia report a variety of experiences. Some can hear in their minds, while others can't imagine either vision or hearing. Some have excellent autobiographical memory, while many don't. Some have involuntary flashes of mental imagery.

Most dream in images, but some can't. Most are born with aphantasia, although a small minority acquire it after injury. Here's Nani again. Aphantasia is not a monolithic phenomenon. It's a kind of a term that's used for a lot of things that in terms of neuroanatomy look very different. Hyperphantasia isn't monolithic either. People with hyperphantasia see mental images that seem to them as real as the things they actually see.

The images that hyperphantasics see aren't the same as hallucinations because they know, at the time, that they're not real. But that doesn't mean they don't feel real. There's a subset of people with extremely vivid imaginations who are known as maladaptive daydreamers.

Post-doctoral researcher Nadine Dykstra says some choose to live in their imagination rather than in real life. It's fascinating. These people, they just like they sit down on the couch. They don't leave their house. They don't go to school. They don't see friends. They don't go to work. They just imagine their whole life just the way they want it, because for them it feels as real as reality. They have some kind of insight that it's not real.

but it feels as real to them. Despite all of these differences, scientists all agree on one thing. Ephantasia and hyperphantasia are not disorders. People at either extreme of the spectrum don't have problems navigating the world. Neurologist Paolo Bartolomeo says aphantasics are often fine at describing things. And when you ask them, but how could you answer this question if you have no mental images? They say, I just know.

It is not normal, it is just one end of a spectrum. And people with aphantasia are absolutely not people with a pathological condition.

Not having mental imagery could even have advantages, says Ben Sanani. You might think that aphantasia is this terrible thing that, oh my god, it must be a very impoverished mental life. I really think that if

If you have aphantasia, you actually have something to be happy about. Because if you have aphantasia, you're much less likely to have any kind of mental health problems. Nane says that's because imagery is often deeply tied with mental health. On the other hand, if you have hyperphantasia, then you're very much at risk. And a lack of mental imagery doesn't imply a lack of imagination. Neurologist Adam Zeman has heard from many artists who self-describe as having aphantasia.

Sarah Shomstein, the vision scientist whom we heard from who has aphantasia, considers herself a creative and imaginative person. Successful people, including novelist Mark Lawrence and software engineer Blake Ross, a co-creator of the Firefox web browser, have revealed they have aphantasia. Ross wrote in a 2016 Facebook post that all his life he had thought counting sheep was a metaphor.

For many people, it can be jarring to find out that they see the world differently than others. Shomstein still can't believe that other people, with their eyes wide open, can imagine an apricot against the backdrop of the real world. She wonders how that wouldn't interfere with your everyday life. Shomstein says she thinks they're weird, while at the same time, they think she's weird. The world, as we see it, smell it, hear it, think about it, is reconstructed.

And reality is what is reconstructed by our brain for us from the environment. The environment is extremely rich with all sorts of information that our brain does not reconstruct. UV rays and other smells and sounds that we cannot hear. Students tell me like, oh yeah, yeah. You know, like I always knew that, well, dogs can hear different frequencies or, you know, some animals can do this, but they didn't understand that.

what the neural machinery is like, right? And what reconstruction actually means. It's just a bunch of neurons firing in a coordinated fashion that gives you a sense of this rich visual environment that we're in. Even a single shared experience, a thought, a memory, or a simple image of an apple can look and feel shockingly different on the mind stage. So what do you see when you imagine an apple? ♪

Arlene Santana helped with this episode. I'm Susan Vallett. For more on this story, read Yasmin Saplakoulou's full article, What Happens in a Mind That Can't See Mental Images, on our website, quantummagazine.org. Just a little note, this is our last podcast for 2024 because our next release date falls on Christmas Day. So we're giving everyone a holiday break. The podcast will pick back up again January 8th, 2025.

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