Flickering lights and pseudo-hallucinations: 5 Questions for psychologist Reshanne Reeder

Reeder discusses Ganzflicker and what it might tell us about psychedelic experiences.

Picture a red sports car. What do you see? Some people might see a vivid image in their mind’s eye: the car’s glossy paint job, its shiny rims. Others might only conjure the vague shape of a car, the details blurry. Still others see nothing at all — a condition scientists call aphantasia, or the inability to form mental pictures.

As a Ph.D. student, Reshanne Reeder became interested in people’s ability to generate mental images. What’s the relationship between, say, aphantasia and hallucinations, she wondered? She began studying ways to make people see things that weren’t really there. First, she tried inducing paredolia, or illusory faces. (If you’ve ever looked at a three-pronged electrical socket and seen two eyes and a mouth, you’ve experienced paredolia.) Reeder discovered she couldn’t consistently elicit the illusory faces effect in participants, so she began looking for other stimuli — and that’s how she discovered Ganzflicker, a rhythmic flickering light pattern that leads some people to experience psychedelic-like visual hallucinations. Reeder is continuing her Ganzlicker research as a senior lecturer in psychology at Edge Hill University in the United Kingdom. The Microdose spoke with her about how Ganzflicker works and what it might tell us about psychedelic experiences.

What is Ganzflicker?

Ganzflicker, or visual flicker, is a rhythmic flicker of light that induces very powerful, vivid, intense pseudo-hallucinations. I call them pseudo hallucinations, because even though they are very similar to real hallucinations, people know they're not actually there. Unlike real hallucinations, you can turn them off by just looking away from the screen.

It has been used for a very long time — Indigenous tribes have used flickering fire in rituals. You can also just wave your hand in front of your face repeatedly to produce that same effect. LEDs or a computer screen are extremely effective, too.

What’s the experience like?

The experience varies a lot between people. When I first stumbled upon Ganzflicker, I wasn't really seeing anything, just some spirals and geometric patterns. But my master's student, who was standing right next to me, goes, “Oh my goodness, I see a lighthouse, I see the beach, I see the waves rolling. And I see people swimming in the distance!” He saw an entire scene. There were people walking down the hall, so we called them in to participate. We showed them Ganzflicker and asked them what they saw. One woman gasped and said she saw faces.

What do we know about how and why Ganzflicker works?

That was investigated in the fifties and sixties when people were trying to develop mind reading techniques, but you can still glean some interesting information from those early papers. The takeaway is that everybody is prone to see geometric patterns and illusory colors, likely because the flickering light is interacting with natural brain rhythms and irritating the eyes, creating patterns. Those patterns are constrained by the visual cortex — seeing spirals or spiderweb patterns could be literally seeing veins through the eyes. 

So there are some pseudo-hallucinations that are somewhat physically constrained, but why do some people see really meaningful objects? That's where mental imagery comes in. 

In our first study, we found a group of people with aphantasia, that inability to form mental pictures, and asked them to watch Ganzflicker for 10 minutes. Half of them didn't see anything at all, and the other half saw geometric patterns, shapes and illusory colors — nothing meaningful or complex. Then we showed Ganzflicker to people with mental imagery, and 90% of them saw something, and about 30% of those saw complex, meaningful objects like faces, animals, even whole environments.

Ultimately, a lot of it is your imagination. Anecdotally I have found that people tend to see things that they've been thinking about recently. The master’s student who saw the lighthouse and the ocean said he had been swimming in the ocean the day before. It’s not under conscious control, but it seems to have an influence.

What could Ganzflicker teach us about psychedelics and perception?

Ganzflicker is also a tool that can normalize hallucinations and the experience of anomalous perceptions. Most people think, “Oh, you have to take drugs to experience this, or you have to be crazy,” but no, anybody can experience these pseudo-hallucinations. Perhaps there could be  future avenues for Ganzflicker as a hallucination simulator or a psychedelics simulator. 

I also think there are applications for research. Hallucinations notoriously cannot be controlled. For instance, if someone has schizophrenia and you want to bring them into the lab to investigate their brain activity while having hallucinations, you might bring them to an MRI machine — but because they can’t control the hallucinations, you can’t necessarily get them into the scanner at the right time. But you can control Ganzflicker, and it taps into some of the same phenomena present in people who pathologically experience complex hallucinations. There are also types of hallucinations that occur when you lose your vision, either through age-related macular degeneration — that's called Charles Bonnet syndrome — or with Parkinson’s disease. Perhaps people’s responses to Ganzflicker could be used to predict if someone develops hallucinations later on. 

You recently premiered a Ganzflicker exhibit at the Being Human Festival in Southport, where groups of people could experience Ganzflicker for themselves. Did that exhibit give you any new insights into the phenomenon?

After hearing people's experiences and talking to them about it, it drives home for me how similar Ganzflicker is to psychedelics. It's similar in terms of what people see, but also in how people feel: some people get this feeling that they're disembodied or floating off the ground, and they lose a sense of time perception. Others get very relaxed or meditative, almost like they’re hypnotized. 

I think it would be a cool future investigation to look at the parallel between what the same people experience under psychedelics versus Ganzflicker. Actually, a lot of people have asked me what would happen if someone took a psychedelic and then experienced Ganzflicker, but I don't think that using them together would tell us much. Rather, we could try to observe the overlap in effects if they experienced Ganzflicker and psychedelics separately. What do they see with Ganzflicker? And then if they take a psychedelic, what did they experience? 

This interview has been edited and condensed for clarity and length.

(Editor’s note: the UC Berkeley Center for the Science of Psychedelics is hiring for a Communications Director, and an Executive Assistant. Please share the roles with anyone you think might be interested.)