Look at me being topical and making a Kanye West title joke!
Anyway, one of you asked me a great question a few weeks ago during my Monster Marathon:
Why do your eyes take so long to adjust to the dark but adjust so quickly to the light?
Great question! If anyone’s ever seen a matinee movie in a theater and come out into the sun, you know that you’re blinded by the light at first, but eventually get used to it. Similarly, I’m sure you’ve all tried to navigate a dark room–when you first turn out the lights, you’re absolutely blind! But after a long time, you’re able to see rather well in the dark, at least enough to see the monsters in your closet. So why does this happen? Why does our night-vision adjust so slowly while our day vision adjusts so rapidly? Well, let’s discuss the most hardcore sounding psychological theory (and great rock band name): Dark Adaptation Theory.
First off, let me break down the eye for you: It’s a magnificent organ that’s wonderfully efficient. It allows us to see, and despite what Daredevil may think, sight is by far our most dominant sense. In fact, 60% of your brain is involved in one way or the other with visual processing. So, let’s follow the path of photons as they travel through the magical world of your eyeball.
First, light travels through your Cornea. The cornea is actually extended past your eyeball, and this allows you to have peripheral vision. Some people’s corneas extend further than others- allowing for better peripheral vision. In fact, your cornea allows (most of) you to see behind your eye! Don’t believe me? Take your pointer finger, hold it behind your head and next to your head. Now start wagging it and slowly moving it forward. Stop moving it when you see it just out of the corner of your eye–it’ll most likely be behind your actual eyeball. The cornea bends 80% of all the light that enters your eye and is very easily scratched. Some people with permanently scarred or damaged corneas can actually get corneal implants–they’re quick, clean, and rarely cause rejection (there’s no blood in the cornea). Why not do whole eye transplants, like in The Eye?. Well, First, off, the blood in the eye would put it at a much higher risk of rejection. And secondly, there are about 1 million nerves going from your eyeball to your visual cortex which would all have to be connected by hand. It’d actually be easier to do a whole head transplant.
Light then travels through your pupil, a small hole in your iris. Your iris is the colored part of your eye, and it’s actually a muscle that controls the size of your pupil. Your pupil changes size for two reasons: to change the amount of light let in (bigger for dark environments, smaller for light environments) and in response to emotions (bigger for pleasant emotions, smaller for negative emotions). It’s actually this second reason why candle-lit dinners are romantic: your body misinterprets your increased pupilary size for attraction, and we also see people with larger pupils as more attractive. Believe it or not, your pupil size changes in about 2 seconds, so dark adaptation has little to do with it.
The light then goes through the lens, where it is finely focused and (unless you’re near-sighted or far-sighted) bent onto the back of your eye–the retina. On the retina are a whole bunch of photoreceptors called rods and cones. These are responsible for sending signals when light hits them and are the reason you’re able to see. Also on the retina is a dark pigment called Rhodopsin, and this is where dark adaptation occurs. In animals that operate during the day-time, the retina is coated in Rhodopsin. It’s dark, so that stray light that doesn’t hit photoreceptors is absorbed.
In nocturnal animals (such as dogs, cats, and owls), they don’t have Rhodopisn, instead they have a light blue-green pigment known as Tapetum. This is the reason why dogs/cats have what looks like laser-eyes when you take a picture of them with the flash on.
Tapetum reflects stray light, which bounces around the retina until it hits a photoreceptor. This gives the animal much better night-vision, albeit at the cost of visual acuity. Nocturnal animals can’t really see clearly–it’s why you have to point out the ball you threw to your dog five times before they actually pick it up.
Rhodopsin is made of two chemicals: Retinal and Opsin. When light shines on your retina, your Rhodopsin breaks apart–the Retinal and Opsin separate and you can’t see in the dark. It actually takes quite a while for the two to rejoin once the lights go out. Because there’s fewer cones on your retina, they repair much quicker (in ten minutes or so), but since they kind of suck at seeing at night anyway, your eyes still aren’t adjusted. It’s only until about 30 minutes in the dark that your rods gradually adjust to your maximum sensitivity.
Now, this gradual change over 30-40 minutes is one of the coolest things you’ll learn about the eye from a movie website today. It’s extremely advantageous (and probably evolutionary selected) because guess what also takes 30-40 minutes? Sunsets.
In caveman times, there weren’t any sort of artificial lights. The only time it got dark was when the sun went down, and you wouldn’t want your night-vision to immediately adjust the instant it got totally dark, or you’d be screwed at twilight. Now, the converse is not true. Your Rhodopsin only takes a few minutes to bleach completely and adjust to the light. Why no gradual change over time? Sunrise also takes 30-40 minutes–but people don’t gradually wake up over 30-40 minutes (except on Monday mornings). In caveman times, people would wake up suddenly and exposed to light. Any asshole who had to wait 30-40 minutes to completely adjust to daylight wound up dead. As to why it hurts your eyes? CHEMICALS IN YOUR EYEBALL ARE BREAKING APART AND BEING BLEACHED.
Now, also on the subject of light, I want to talk about another awesome band name: Photic Driving.
Let me regale you with a story from the 1990’s about the Pokemans.
In 1997, an episode of the popular Children’s show Pokemon called “Electric Solider Porygon” aired in Japan. One scene involved rapid flashes of light that supposedly lead to over 600 Japanese kids being rushed to the hospital with seizures. It’s kind of become lore over the years, and a lot of it has been distorted, but the basic facts remain true. It wasn’t 600, it was more like 30. And it wasn’t all kids, it was largely adults that had these–but these people had mild photosensitive epileptic seizures. So just what the hell is up with Pokemon? Did the Japanese develop a weapon? Possible (the US Military was trying to develop a seizure gun in the early 2000’s), but improbable. The real culprit is a phenomenon known as Photic Driving.
A lot of people have heard the term Brainwave before, even without knowing just what it is. Brainwaves are simply neural electrical oscillations that happen in your brain, and we’ve correlated different patterns of wavelengths/amplitudes/frequencies with various states. One of those types of waves is referred to as “Alpha Waves.” Alpha waves have 7-10 cycles per second (Hz) and are associated with restful relaxation.
Photic Driving is when your brainwaves sync up with a pulsating stimulus. Any change in this stimulus can alter the frequency of your brainwaves–and this can cause some serious shit. Photic driving, even when the stimulus stays at the same frequency, causes eye-strain and headaches. And god forbid the frequency of the stimulus changes, this can cause severe headaches and even epileptic seizures–even in people who don’t clinically have epilepsy. You’d be surprised at the kind of stimuli that can cause this. Obviously flashing lights or strobes at the discotech, but even a ceiling fan that’s rotating in the 7-12 cycles per second range can cause this.
Pictured: horrific torture device
Ever been driving through the woods at dusk/twilight and the sun shines through the trees? This pulsating light can cause photic driving if your speed matches up with the range of your alpha waves, it can be nauseating, disorienting, and if you speed up or slow down significantly–debilitating.
So, what can be done about this? Well, if you’re epileptic, I’m sorry to say that you’re genetically predisposed to get seizures easily from photic driving, and from other stimuli, and that there is no current cure (though it can be controlled using medications in 70% of patients). For people without epilepsy, don’t stare into strobelights at clubs. Be careful about flashing/pulsating/flickering lights. If you feel like crap around them, be careful and leave. Also, companies–FOR GOD’S SAKE AVOID ANYTHING WITHIN THIS 7-12HZ RANGE! This is the easiest thing to do, and the good news is that marketing perceptual psychologists have done a lot of research and most companies are aware of this problem. So it isn’t nearly as common as it was in years past.
Moral of the story, light is really important and can do some crazy things, and Electric Soldier Porygon is a stone cold killer who will melt your brain.
He will burn everything you are and everything you will ever be…
Anyway, join me next week as I talk about the military and how media handles it. Also known as the good, the bad, and the DARPA.
And be sure to check out my other column, where I review action films on Mondays: Mindless Action Mondays
Have a science-related question? Ask it! Also send me fan/hate mail!
If I don’t know the answer, I’ll find someone who does.