Why Netflix Warns Flashing, Fast Edits Can Trigger Seizures

Bright, dazzling, or rapidly changing lights are a common cause of reflex seizures.

Source: Public Domain / Pixabay

Have you noticed the increasing number of Netflix programs that begin with a warning: “Some scenes have a strobing effect that may affect photosensitive viewers.” What are they talking about? And in what way can a video “affect” its viewer?

Screen images that flash or change rapidly can trigger stimulus–sensitive seizures, a variety of so-called “reflex epilepsy.” It is a curious phenomenon in which highly particular actions—some physical, others mental—precipitate a convulsion. The most common culprit is the flashing and flickering illumination common to today’s ubiquitous screens. It almost sounds like science fiction. Except it is all too real.

Seizures can be elicited by looking at specific visual patterns, especially geometric ones of stripes, bars, and contrasting alterations of light and dark, especially ones that change direction. One continuous series of stripes is printed text, so it should be no surprise that “reading epilepsy” constitutes one of the varieties of reflex seizures. Eating and even thinking along certain lines are less common triggers.

Geometric patterns, especially ones that cause apparent motion, are also common triggers.

Source: David Zydd / Pixabay

Famously, a Pokémon television episode broadcast in Japan sent 700 children to emergency rooms suffering from seizures, nausea, and vomiting. The offending incident turned out to be flashing lights—the bright red and blue ones that dominated the episode’s battle scenes. For many of the affected children, it was the first time they had been diagnosed with any kind of seizure disorder.

Epilepsy, in general, is a condition characterized by recurrent physical convulsions. For multiple reasons (e.g., read about kindling), groups of neurons suddenly begin to fire without having any countervailing force to halt their proliferation. Uncontrolled electrical impulses spread throughout the brain, ending in an epileptic convulsion. The key to understanding responsible triggers is the degree of synchrony achieved among the population of firing cells: anything that boosts their unison can incite a convulsive fit in susceptible individuals.

Lights that flash about five to 20 times per second easily synchronize nerve cells in the visual cortex. They recruit other neurons to beget a massively synchronous discharge. Red and green light is the most provocative. But brightness is also problematic given the brilliance of today’s TV and smartphone screens. Brightness and glare cause headache, nausea, and dizziness in many individuals who do not have seizures. However, between the ages of five and 24, more than one in 4,000 individuals do suffer from photosensitive epilepsy.

Not many years ago, strobe and disco lights set off reflex seizures as the main instigators. Besides flickering televisions, other common causes are dappled sunlight, shimmering water, the alternation of light-and-dark when driving past regularly spaced telephone poles or a stand of trees, even waving one’s hand in front of the eyes. Today, screen flicker and rapidly changing edits in video games are significant reflex instigators of seizures.

Even dappled sunlight can affect sensitive individuals.

Source: Isabel 780 / Pixabay

Three-quarters of individuals who have reflex seizures have more than one trigger: doing mathematical calculations, reading, playing cards or board games, doing crossword puzzles, making a decision, even knitting.

Many people are unaware of their sensitivity to flickering lights or visual patterns until they have a seizure. They may develop generalized epilepsy or have seizures triggered only by certain conditions of illumination. Photosensitive epilepsy typically responds well to medication used to treat conventional seizure disorders.

Cover one eye and turn away from the offending source if you are suddenly exposed to a trigger. Closing both eyes or looking in another direction will not help. Wear polarized sunglasses to reduce screen glare from phones, tablets, televisions, and monitors. Take frequent breaks from your phone and computer. Be mindful that tiredness, stress, and excitement all increase photosensitive risk.

Beware::

• Video games or TV broadcasts that contain rapid flashes of alternating patterns of contrasts or colors.

• Strobe lights such as those used in visual fire alarms.

• Sunlight flickering through trees, shimmering off water, or through the slats of Venetian blinds.

• Stripes of contrasting colors or any light-and-dark pattern that moves or changes direction.

• Any effect that occupies your whole field of vision (e.g., being positioned close to a screen).

Intelligence Essential Reads

What Primitive, Ancient Animals Can Teach Us About Being Human

Unveiling the Secrets of Intelligence and Giftedness

Kindly address Dr. Cytowic via the author portal or ask for a free copy of Digital Distractions: Your Brain on Screens.