The door clicks shut on the soundproof booth in which I find myself, and I’m left alone in the dark. I’m sitting in an office chair, headphones on my head, as classical music begins to play.
What I am about to experience, I was told only moments ago, will be much more intense than anything I’ve encountered up to this point.
“We’re going to ease you into it,” Dr David Schwartzman, the researcher in whose lab I’m sitting at the University of Sussex, had said. “It’s really a journey through the experience.”
I keep my eyes pressed shut. A short distance in front of my face sits a dinner plate-sized strobe light which is about to begin flashing.
As the music builds, the light bursts into action. Except I don’t see the light. Instead, for the next 30 minutes I see a kaleidoscope of colours and patterns, washing over my internal field of view, perfectly in sync with the music.
Greens, reds and blues come in waves and ripples. As the music picks up pace, everything begins spinning into a point, until it bursts in an explosion of colour at the song’s zenith. By this point I’ve lost all sense of time. Have I been in here a minute? 10? Perhaps I’m nearing the end of the session – I have not a clue.
For more than 200 years, scientists, artists and those seeking something deeper have been flashing white lights at their eyes – at frequencies closely matching the brain’s natural rhythms – to produce vivid hallucinations of colour and geometric form.
The practice, known as stroboscopic light stimulation, ‘strobe’ or ‘flicker’ to those in the field, has accumulated a surprisingly rich scientific literature, a devoted counterculture following, and, more recently, the attention of serious neuroscientists.
Researchers now think strobe may offer something rare: a controllable window into the mind. Not merely into how it generates hallucinations, but into how the brain constructs conscious experience itself. And if simply flashing lights onto our closed eyes can reliably conjure entire inner worlds, what does that say about where our concept of reality really comes from?
My journey into strobe
My introduction to strobe came a few weeks before my visit to Sussex, when I was handed a small box containing the Nova mask from Lumenate.
A sleek consumer device that looks like a sleep mask, the Nova is endorsed by the likes of Rosamund Pike and Jennifer Aniston, and marketed for wellbeing, creativity and mental health.
I’ll confess that my initial reaction was mild scepticism. Having never heard of stroboscopic stimulation, and well aware that the wellness industry has a long history of charging a great deal of money for things that don’t work very well, I didn’t know what to expect.
The Nova pairs with an app that guides you through sessions from sleep preparation to creative exploration, all soundtracked by original music and, in many cases, narrated by Pike herself. You close your eyes, press play, and the mask begins to flash.
Within seconds, the darkness behind my eyelids is replaced by something considerably more interesting.
Geometric patterns bloom and collapse. Colours that don’t quite correspond to anything I’ve seen in ordinary life wash across my visual field in pulses roughly synchronised to the music. It is, not to put too fine a point on it, rather good.
I used it most evenings for the better part of two weeks, usually before bed. The experience varied considerably each time – sometimes vivid and almost dream-like, other times more subdued, a quiet wash of colour.
Occasionally, I caught glimpses of more complex hallucinations; scenes and faces, for the most part.
I found it reliably relaxing, occasionally genuinely absorbing. Family members who tried it reported widely different experiences: one saw her own eyes looking back at her; another saw little more than blobs of red.
The variation, as it turns out, is not a design flaw but a central feature. Much depends on your expectations going in and your brain’s state during the sessions.
Tom Galea, who co-founded Lumenate with his university friend Jay, came to strobe in a roundabout way. The pair had been working as engineers at a car company when they left to explore, as Galea puts it, “a vision to inspire people to live more fulfilling lives.”
Their journey eventually led them to the idea that accessible altered states of consciousness might be a practical tool for mental wellbeing, sitting somewhere between meditation apps (accessible but often underwhelming) and psychedelic therapy (transformative but expensive and, in most jurisdictions, illegal). Strobe, they concluded, occupied a useful middle ground.
“You wouldn’t do psychedelic therapy to help you fall asleep at night,” Galea tells me. “That’s where this softened middle ground can step in as a more regular practice – something people may do if they’ve had an argument, feel stressed from work, or are apprehensive about something coming up tomorrow.”
Having tried the consumer version, I wanted to understand what was actually happening inside my head. So I drove to Sussex.
The mechanics of strobe
Schwartzman’s lab is the kind of place that makes you feel that real science is happening: monitors, cables, equipment that looks purposeful rather than decorative, and a soundproof booth with a professional-grade strobe light that makes the Nova mask look, by comparison, like a head torch.
During our discussions, he explains that the hallucinations produced by strobe begin in the visual cortex – the part of the brain at the back of the head that processes what we see.
When a bright, rhythmic light drives this area at certain frequencies, particularly around 8 to 12 Hertz (known as the alpha range, close to the brain’s natural visual rhythm), large groups of neurons synchronise and begin to amplify their own internally generated patterns.
The signals aren’t coming from the eyes any more – or rather, they are, but they’re not carrying anything meaningful from the outside world. The brain, unable to do nothing, starts interpreting its own activity.
“In some sense,” Schwartzman says, “stroboscopic hallucinations reflect the brain momentarily seeing itself. The patterns you experience – the spirals, the grids, all of that – are specific to you. They’re based on the wiring, the tracks of neurons in your visual cortex. So that hallucination is in some sense a representation of the structure of your own brain.”
This also explains the colours. The alpha range is thought to stimulate the colour-sensitive regions of the visual cortex directly rather than through the normal route from the retina. People regularly report colours they feel they’ve never quite seen in ordinary life.
The effect is, in this sense, not adding something foreign to the mind. It’s revealing hidden features the brain is capable of experiencing, but which are usually drowned out by light data streaming in from the outside world.
The precise neural mechanism is not yet settled. There are at least four competing (or complementary) theoretical frameworks, according to a recently published review paper co-authored by Schwartzman and colleagues at Sussex and research centres in Berlin.
The short version is that multiple things are probably happening simultaneously, which is why the experience varies so much between individuals, and why the same session on different days can produce entirely different results. How tired you are, how caffeinated, what mood you are in when you sit down: all of these appear to shape what the brain produces.
That variability was also part of what initially drew researchers to strobe as a scientific tool. It can be induced reliably in most people, switched on and off in seconds, and the differences studied under controlled laboratory conditions without any of the limitations that make psychedelic research so fraught.
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The origins of strobe
Humans have probably been stumbling across strobe for as long as there have been flickering lights to look at. The Czech physiologist Jan Purkinje first documented the phenomenon in 1819, having waved his hands in front of a candle with his eyes closed and observed geometric patterns emerging behind his eyelids.
In the 1950s it was rediscovered by the neuroscientist William Grey Walter, who was using strobe lights to study brainwave activity.
The artist Brion Gysin encountered it around the same time and invented the Dreamachine – a cylinder of cut card that spun around a light bulb – which he introduced to Kurt Cobain, Paul McCartney, Brian Jones and Allen Ginsberg, among others.
It’s easy to imagine people making the same discovery for millenia, perhaps sitting around a prehistoric fire, the flames flickering at just the right frequency through half-closed eyes.
A window into the conscious mind
Anil Seth is the director of the Sussex Centre for Consciousness Science, in which Schwartzman’s group sits. He has been thinking about hallucinations for a long time, and he doesn’t think about them the way most people do.
The conventional understanding treats hallucinations as things the brain does when it malfunctions, whether through psychosis, drug use or neurological disease. Seth’s view is rather different, and it’s worth sitting with because it changes how you think about something as ordinary as looking at a table.
“All kinds of perceptual experience arise from the same underlying process and principle,” he tells me, sitting in his sunlit office overlooking the busy Sussex campus on the outskirts of Brighton.
“The brain makes predictions about the causes of sensory signals and uses sensory signals to calibrate and update these predictions. It’s just that there’s a sort of sliding scale where the brain’s predictions can start to overwhelm the sensory data.”
Normal perception, in other words, is not a passive recording of external reality. It’s the brain’s best guess, continuously updated.
Most of the time these guesses are very good, because the sensory data coming in is rich and the brain has millions of years of evolutionary refinement to draw on. But the guesses are guesses nonetheless.
“When we agree about our hallucinations,” Seth said in his 2017 TED talk, “we call that reality.”
Faces in clouds are a familiar version of the sliding scale he describes. There are no faces in clouds, yet something face-like is genuinely perceived. The brain is pattern-matching with its predictions and finding more grip than it should.
Mother Teresa appearing in a cinnamon bun is another. These are not signs that something is wrong. They are demonstrations of the same underlying process, dialled up slightly.
Strobe takes this considerably further. With eyes closed, the brain is not expecting any interesting visual input. There is nothing for its predictions to latch onto as an interpretation of the external world.
And yet something is happening – bright, rhythmic activity in the visual cortex – and the brain, always trying to make sense of things, begins making interpretations.
Because the early parts of the visual cortex are wired up to detect lines, shapes and colours of things, this might be why colourful geometric shapes are the most common features to arise in stroboscopic hallucinations.
Normally, the brain’s edge- and pattern-detecting machinery is invisible to us, Seth explains. The eyes take in a collection of lines, textures and colours. Our brains turn this into a finished product – a face, a table, a room – without any awareness of the processing that produced it.
Strobe disrupts this. With eyes closed and no coherent visual input to resolve, the brain can’t deliver a finished product. Instead, the raw machinery starts showing through – and those edges, grids and geometric forms could be what it looks like from the inside.
That, in miniature, is the question at the heart of consciousness research: how the brain generates subjective experience from physical processes. And while Seth is careful not to overstate what this means for our understanding of consciousness, he believes the science is picking up pace.
Thirty years ago, consciousness was regarded by many scientists as essentially off-limits as a topic of empirical enquiry. Now there are competing theories, experimental methods to test them and a growing body of data. Strobe is one part of that.
That reliance on the brain’s internal wiring is also why strobe is unusual as a scientific tool. It’s not adding anything chemical to the brain. It offers no sustained pharmacological effect. And the experience ends the moment the light goes off.
“We have a way of inducing altered experiential states,” Seth says. “They’re not equivalent to psychedelic states at all, but they nonetheless kick you out of your normal way of experiencing the world. But we don’t use any pharmacological intervention.”
There is also a therapeutic dimension, still early but worth watching. Schwartzman is currently running a Medical Research Council-funded trial investigating whether strobe light sessions can reduce symptoms of depression.
The working hypothesis draws on the parallel with psychedelic therapy, specifically, the accumulating evidence that it’s the quality of the altered experience itself, rather than any purely pharmacological effect, that drives therapeutic benefit.
If that is correct, then strobe – which induces a related if less dramatic alteration of experience, without any of the legal or logistical complexity of controlled substances – might offer something clinically useful.
“So far we’ve found quite significant improvements in people’s depressive symptoms following a four week intervention,” Schwartzman says. The technique is still in its infancy, with work focused primarily on establishing safety and tolerability in people with depression before any larger claims are made. But the early signs, he says, are encouraging.
What flashing lights in my eyes has taught me
Sitting in the soundproofed booth in Schwartzman’s lab at the end of my session, I tried to articulate what the experience had been like.
This turns out to be surprisingly difficult. The contrast between the intensity of what you see and how little it took to produce it – just light, darkness and your own brain – is pretty mind boggling.
It’s not like watching a film or listening to music. The experience is entirely internal, and yet entirely involuntary. You’re not imagining it. Something is happening.
What strikes me most, thinking about it now, isn’t the geometry or the colours, but the implication.
Strobe is not adding anything to the mind. There are no chemicals crossing synapses that would not otherwise be there. The light is simply providing a rhythm, and the brain is doing the rest.
Those inner worlds – the spirals, the blooms of colour, even the faces – were already there, hanging out in the structure of my visual cortex, waiting for something to call them into being.
As Seth puts it: “the less you take things for granted, the more wonderful they become”.
Take the fact that someone can have an out-of-body experience, for example, and feel convincingly that they have left their physical body. Accepting that the brain is always doing this kind of thing is not a reason to dismiss the experience.
It’s a reason to find everyday perception considerably more astonishing than it usually seems.
As for the Nova mask, I plan to continue using it. As a practical relaxation tool it works well, and the experience before sleep is, I find, a useful way to reflect on each day. But I’m also now returning to it with slightly different intentions.
It’s less a wellness gadget and more a reminder of something Seth said about walking around in the world: “Just think, ‘this is amazing’. The fact that I have this first-person experience that feels like a first-person experience.”
The line between ordinary perception and the strange worlds the brain can generate turns out to be much thinner than it looks. And strobe just makes it briefly visible.
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