dog ghosts facts

hey vsauce i'm jake and in the chroniclesof riddick series, one of riddick's unique features is his ability to see in the dark.of course, this is due to a fictional operation called a shine job that creates somethingsimilar to what a lot of animals are born with, a tapetum lucidum. the tapetum is a reflective membrane in theanimal's eye, behind the retina, that acts as a mirror, re-sending the photons back outfor another chance to be collected. if you've ever taken a photo of your dog or cat witha flash on, the glowing eye effect is the light being bounced back from the tapetum.it is also what fueled the old tales of glowing eyes in the dark.

unfortunately we don't have shine jobs ortapetums to give us enhanced night vision, but when it's dark, when all the lights areoff, there are still things that we see...or are there? what exactly do we see in the dark? our retinas, the layer of cells in the backof our eyes have two main light receptors, the rods and cones. each eye has about 6.5million cones, they allow us to see colors and shapes but require a lot of light. theyare also mainly located in the fovea, the most sensitive part of the retina and thearea with the highest density of cones. the further we get away from the center ofour retina, the more rods we find and the less cones there are. rods are incrediblylight sensitive but they are also color blind.

you can test this by taking something withcolor and holding it out so its in your peripheral vision, you'll be able to see it but you won'tbe able to tell what color it is. when we are in the dark, we use our rods tosee, but it isn't immediate. it takes at least 30 minutes for our eyes to fully adjust. that'swhy when you go from a room with light to one without, it feels completely dark, completelyalone. it's speculated that the eyepatch that pirateswore was for when they would go below deck, where there wasn't much light, they'd haveone eye that was already adapted to the dark. cutting out the time needed to wait. but if you do wait, if you do just sit inthe dark you might start to see things, things

that aren't really there...phosphenes. whenyou close your eyes or lay in bed at night, you sometimes seestrange patterns or soft white lights. you can actually experience it right now by closingyour eyes tightly and *gently* pressing on the center of your eyeballs with your indexand middle finger. this phenomenon is also referred to as theprisoner's cinema, and has been reported by astronauts, pilots and of course prisonersafter spending prolonged amounts of time in complete darkness. with the prisoner's cinemathough, people start to see colors shifting and dancing and, occasionally, forming humanshapes.

but what can we truly see in the dark? wellthat depends on where you're looking. in a room with hardly any illumination you arecompletely blind in the center of your retina, where the fovea is. since it is entirely cones,there is nothing for them to pick up. averted vision. it's a technique astronomersdo, where they see using their peripheral vision. next time you're in your room in thedark, take a piece of white paper and stare directly at it. you probably won't see iteven though it is right in front of you, but if you avert your eyes to one side a bit,you'll suddenly be able to. we might not have shine jobs or tapetums togive us more light, but what we do have are our minds. they show us things even when wecan't see, they remind us that we aren't alone.

we just need to keep looking...even if itis in the dark. and as always, thanks for watching.