The Origin and Properties of Flicker-Induced Geometric Phosphenes

A Model for the Origin and Properties of Flicker-Induced Geometric Phosphenes (PDF).

Many people see geometric patterns when looking at flickering lights. The patterns depend on the frequency, color, and intensity of the flickering. People report seeing similar shapes, which care common in visual hallucinations and are called “form constants”. Flicker hallucinations are best induced using a Ganzfeld (German for “entire field”), a totally immersive and uniform visual stimulation. This effect is capitalized on by the numerous sound-and-light machines sold for entertainment purposes.*

How do flickering lights cause geometric visual hallucinations ?

Basically, flickering lights confuse the eye and the brain, causing them to misinterpret what they’re seeing. One hypothesis is that the flickering interacts with natural ongoing oscillations in visual cortex, exciting a specific frequency of brain waves. This increases the activity in visual cortex. Activity can increase enough to overload the circuitry the brain uses for interpreting what it sees, causing you to see things that aren’t really there. Our model of visual hallucinations suggests that flickering lights can cause visual cortex to behave like a ‘reaction diffusion system’, which is a type of system that spontaneously forms patterns. The most famous examples of biological reacti
on-diffusion systems are the patterns in animal fur, like leopard spots and zebra stripes. For more information, including the mathematical details of the model, head over and check out the paper.

Much thanks to coauthor Matt Stoffregen and advisor Bard Ermentrout for making this possible, as well as the CNBC undergraduate training program.

*( I know of no scientific evidence suggesting that it is possible to alter the frequencies of neural oscillations with flickering lights, as most such devices claim. Instead, you might increase the amplitude of intrinsic oscillations in resonance with a flickering stimulus, to the point where geometric visual hallucinations can occur. )

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