How Humans See Color: Eyes, Rods, Cones, Anatomy
This podcast explores the eyes as key sensory organs that convert visible light into signals for the brain to "build" the picture you see. It details eye anatomy, including the cornea, lens, retina, iris, pupil, and optic nerve, which work together to focus light and transmit information. A central focus is on photoreceptors within the retina: rods and cones.
Rods are highly sensitive, enabling low-light and night vision, primarily seeing in shades of gray and contributing to peripheral vision. Cones are responsible for color vision and perceiving fine details in bright light. Humans typically have three types of cones sensitive to red, green, and blue light. When light reflects off objects, it activates these cones, and the signals are sent via the optic nerve to the visual cortex in the brain, which decodes them to create our perception of color. The process allows humans to distinguish millions of colors, with some individuals potentially having tetrachromacy. The overview also touches on conditions like color blindness, which occurs when cones don't function properly. Maintaining eye health through regular exams and proper nutrition is also highlighted.
0.000000 6.000000 Welcome to everyday explained your daily 20-minute dive into the fascinating house and wise of the world around you.
6.000000 11.000000 I'm your host Chris and I'm excited to help you discover something new. Let's get started.
11.000000 13.000000 Welcome back to the Duck Dive.
13.000000 17.000000 Today we're zeroing in on something you use every waking second.
17.000000 24.000000 An absolutely incredible biological feat you probably will never stop to think about how you see the world.
24.000000 26.000000 It's not just about having eyes, you know.
26.000000 33.000000 It's the lightning fast partnership between those eyes and your brain that paints the picture you perceive.
33.000000 37.000000 Exactly. We've pulled together the sources you share to really dive into the mechanics.
37.000000 43.000000 How light gets captured, transformed, and then built into the vibrant detailed image you see.
43.000000 45.000000 It sounds like a complex dance.
45.000000 49.000000 It really is. A rapid, complex dance. And our goal today is to make sense of it.
49.000000 55.000000 Maybe uncover some surprising facts and perhaps give you a new appreciation for this everyday miracle.
55.000000 58.000000 Get ready for a few aha moments then as we impact this.
58.000000 61.000000 It truly is a marvel of biological engineering.
61.000000 62.000000 Okay, let's jump right in.
62.000000 67.000000 When we talk about seeing it obviously starts with your eyes, but they're not just simple windows, are they?
67.000000 68.000000 Not at all.
68.000000 76.000000 Think of them as incredibly sophisticated sensory organs designed specifically to grab information from the world around you
76.000000 79.000000 and that information is light and then send it along.
79.000000 83.000000 They do the crucial physical work of capturing that light.
83.000000 88.000000 And this is where it gets a bit weird, right? Your eyes don't actually see the final picture.
88.000000 93.000000 That's the slight mind bend. Yeah. They capture the raw data of the light and convert it into electrical signals.
93.000000 96.000000 They're like highly sensitive receivers.
96.000000 101.000000 Got it. That data then shoots off to your brain and that's where the real seeing happens.
101.000000 105.000000 Your brain takes those signals and actively builds the picture you perceive.
105.000000 107.000000 So vision is the whole package then.
107.000000 111.000000 Exactly. Eyes capturing data plus the brain processing and interpreting it.
111.000000 115.000000 It's definitely a team effort and having two eyes working together, that's a big part of it.
115.000000 117.000000 Oh, huge. It gives you that wide field of view.
117.000000 118.000000 Yes.
118.000000 121.000000 What is it? About 200 degrees side to side, 135 degrees up and down.
121.000000 122.000000 Something like that, yeah.
122.000000 129.000000 And that binocular vision is absolutely key for things like depth perception, that amazing 3D quality.
129.000000 132.000000 And, you know, assuming everything's working correctly, full color vision.
132.000000 136.000000 Okay, so how does the light actually get in and focus?
136.000000 142.000000 Right. The initial step is light entering the eye. It passes through a series of transparent parts right at the front.
142.000000 146.000000 The cornea that clear outer layer like the eye is protective dome.
146.000000 151.000000 Then the aqueous humor, which is a fluid, the lens, which is adjustable.
151.000000 152.000000 The focusing part.
152.000000 155.000000 Yeah, a key focusing part. And finally, the vitrious humor.
155.000000 158.000000 That's the gel that fills the main cavity of the eye.
158.000000 160.000000 And these aren't just passive windows.
160.000000 165.000000 No, no. They actively bend and focus the incoming light beams,
165.000000 168.000000 making sure they land precisely on the back of your eye.
168.000000 170.000000 They also help maintain the eye's shape.
170.000000 174.000000 So sort of like a high-tech camera lens focusing light onto a sensor?
174.000000 178.000000 Exactly, but, well, infinitely more adaptable and dynamic.
178.000000 179.000000 Okay.
179.000000 181.000000 And that sensor at the back of your eye, that's the retina.
181.000000 182.000000 Ah, the retina.
182.000000 184.000000 Okay, tell us about the retina. What makes it so special?
184.000000 187.000000 Well, the retina is this thin layer lining the back of your eye.
187.000000 192.000000 And it's just packed with millions of highly specialized cells called photoreceptors.
192.000000 194.000000 Photoreceptors, light receivers.
194.000000 199.000000 Precisely. These are the cells that perform the real magic trick.
199.000000 204.000000 Converting light, which is energy, into electrical signals that your brain can actually understand.
204.000000 209.000000 And our sources tell us there are two main types of these photoreceptors, right?
209.000000 212.000000 Named pretty simply after what they look like, rods and cones.
212.000000 216.000000 That's right, rods and cones. And what's particularly fascinating is that these aren't just simple cells.
216.000000 218.000000 They are specialized nerve cells.
218.000000 221.000000 Nerve cells, like brain cells.
221.000000 225.000000 Kind of, yeah. They're extensions of your central nervous system directly connected to your brain.
225.000000 230.000000 Wow, so they're basically tiny bits of brain sitting in your eye, reacting to light.
230.000000 233.000000 Okay, let's talk about their distinct jobs. You mentioned rods first.
233.000000 237.000000 Yes, the rods. As you said, they're named for their cylindrical shape.
237.000000 241.000000 Their superpower is incredible sensitivity to light.
241.000000 242.000000 How sensitive.
242.000000 248.000000 Extremely. They can detect even minuscule amounts, making them absolutely essential for seeing in dim conditions
248.000000 252.000000 that's your low light or night vision. Sometimes called scotopic vision.
252.000000 255.000000 They're the night owls of the system. And there are lens of them, right?
255.000000 259.000000 Oh, millions. Over a hundred million in each eye.
259.000000 263.000000 They are far, far more numerous than their counterparts, the cones.
263.000000 264.000000 That there's a catch.
264.000000 265.000000 There's a trade-off, yes.
265.000000 272.000000 Rods only see in shades of gray, they give you brightness, information, luminance, but no color whatsoever.
272.000000 273.000000 Okay.
273.000000 277.000000 They're also crucial for your peripheral vision, helping you detect movement on the corner of your eye.
277.000000 280.000000 So, gray for finding the bathroom door in a dark room, maybe.
280.000000 281.000000 Exactly.
281.000000 284.000000 And not so much for appreciating the colors of a twilight's guy.
284.000000 291.000000 Precisely. For that, you need the other type, the cones, named predictably for their conical shape.
291.000000 292.000000 The color crew.
292.000000 298.000000 Yes, the color crew. Unlike rods, cones need significantly more light to get going.
298.000000 300.000000 They really shine in brighter conditions.
300.000000 306.000000 But when they are active, they are responsible for your ability to see all those vibrant colors and also find details.
300.000000 300.000000 Okay.
306.000000 308.000000 And how many of these color specialists do we have?
308.000000 310.000000 Fewer than rods, you said.
310.000000 312.000000 Way fewer, about six million per eye.
312.000000 315.000000 And interestingly, they're not evenly distributed across the retina.
315.000000 317.000000 Oh, where are they concentrated?
317.000000 321.000000 Most of your cones are clustered in a small area right at the center of your retina.
321.000000 322.000000 Called the macula.
322.000000 323.000000 The macula.
323.000000 324.000000 Right.
324.000000 330.000000 This high concentration of cones there is why your sharpest, most detailed vision.
330.000000 338.000000 The vision you use for reading, recognizing faces, spotting that specific item on a shelf is also where you see color best.
338.000000 339.000000 Right in the center.
339.000000 345.000000 So, cones are the ones that let you pick out the rightest apple at the market or figure out if your socks clash.
345.000000 347.000000 Totally essential for everyday life.
347.000000 348.000000 Absolutely.
348.000000 354.000000 And that brings us naturally to the big question, how do these cones actually let us see color?
354.000000 358.000000 It's not as simple as, you know, each cone being a tiny pixel of red, green, or blue.
358.000000 359.000000 Right.
359.000000 360.000000 That seems, yeah, too simple.
360.000000 363.000000 Our sources dig into this and it's really quite clever, isn't it?
363.000000 364.000000 It is very clever.
364.000000 367.000000 For most people with normal color vision, you have three main types of cones.
367.000000 368.000000 Three types.
368.000000 369.000000 Yeah.
369.000000 371.000000 Each type is most sensitive to different wavelengths of light.
371.000000 380.000000 Think of them as broadly specializing in red-ish wavelengths, long greenish wavelengths, medium and bluish wavelengths short.
380.000000 382.000000 This is known as trichromacy.
382.000000 383.000000 Trichromacy.
383.000000 386.000000 Vision based on three colors essentially.
386.000000 388.000000 You got three channels of color information.
388.000000 397.000000 So when light bounces off an object, say, a flower and enters your eye, it hits these cones and activates them based on the mix of wavelengths present in that light.
397.000000 398.000000 Exactly.
398.000000 400.000000 Let's use that example from the sources.
400.000000 402.000000 Seeing a yellow flower.
402.000000 407.000000 When light hits the flower, it absorbs some wavelengths and reflects others.
407.000000 414.000000 The light reflected off a yellow flower contains wavelengths that happen to strongly activate both your red sensitive cones and your green sensitive cones.
414.000000 418.000000 Okay, so the red cones are firing, the green cones are firing.
418.000000 421.000000 But you see yellow, how does the brain figure that out?
421.000000 424.000000 Ah, this is where the brain steps in again as the interpreter.
424.000000 428.000000 The signals from these activated cones travel up the optic nerve.
428.000000 435.000000 Your brain receives these signals and compares the relative strength of the input from all three cone types red, green and blue.
435.000000 436.000000 It compares them.
436.000000 438.000000 It compares the pattern of activation.
438.000000 443.000000 Based on that comparison, it decodes and interprets the specific color you perceive.
443.000000 453.000000 So if the red and green cones are activated strongly and the blue cones may be less so, your brain essentially calculates, ah, that specific ratio means yellow.
453.000000 454.000000 That's incredible.
454.000000 457.000000 It's like a complex calculation happening instantly.
457.000000 459.000000 The mask doesn't even begin to cover it.
459.000000 460.000000 Seriously fast.
459.000000 459.000000 Yes.
460.000000 466.000000 Our sources mentioned this process of comparison and decoding happens in as little as 13 milliseconds.
466.000000 467.000000 13 milliseconds.
467.000000 471.000000 Yeah, which is what about 16 times faster than the blink of an eye?
471.000000 480.000000 And with this system, just comparing the activity levels of those three cone types, your brain can distinguish somewhere between 1 and 10 million different colors.
471.000000 471.000000 Wow.
480.000000 485.000000 It's taking relatively simple input and creating this incredibly rich visual world.
485.000000 491.000000 And the brain even tries to keep colors looking consistent even if the lighting changes right?
491.000000 495.000000 That whole thing with a lemon still looking yellow indoors or outdoors.
495.000000 497.000000 That's color constancy at work.
497.000000 502.000000 Your brain makes these sophisticated adjustments based on context to maintain consistent perception.
502.000000 506.000000 It's constantly processing and refining without you even being aware of it.
506.000000 507.000000 Amazing.
507.000000 517.000000 So after the rods and cones do their work converting light into these electrical signals, what's the next step in building that final picture in the brain?
517.000000 522.000000 Okay, so those electrical signals travel out the back of the eye through the optic nerve.
522.000000 529.000000 You can think of the optic nerve as the main high speed data cable, carrying all this visual information directly to the visual cortex.
529.000000 533.000000 That's the part of your brain located way in the back of your head, specialized for vision.
533.000000 535.000000 And that's where the final assembly happens.
535.000000 536.000000 The picture gets built.
536.000000 537.000000 Pretty much, yeah.
537.000000 542.000000 Your brain receives these coded signals and processes them almost instantaneously.
542.000000 553.000000 It's piecing together information about light intensity from the rods, details and colors from the cones, information about shapes, movements, all at once, integrating it all.
553.000000 556.000000 But it doesn't stop there.
556.000000 566.000000 Your brain then layers on meaning, it uses your past experiences, your knowledge of the world, input from other senses to actually understand what you're seeing.
566.000000 568.000000 Ah, so it's not just showing an image.
568.000000 570.000000 No, it's telling you what it is.
570.000000 571.000000 Yeah.
571.000000 577.000000 That yellow shape is a flower and maybe it reminds you of the scent or the feeling of warmth if you've seen one like it in the sun before.
577.000000 578.000000 It adds context.
578.000000 583.000000 It's like your brain is constantly narrating and adding context to the visual stream.
583.000000 585.000000 So much more than just seeing pixels.
585.000000 586.000000 Absolutely.
586.000000 597.000000 Which, you know, given how intricate this whole system is, built on millions of tiny specialized cells in this rapid fire brain processing, it's probably not surprising that sometimes things don't work perfectly.
597.000000 598.000000 Right.
598.000000 600.000000 What happens when this complex system hits a snag?
600.000000 601.000000 What kind of issues can come up?
601.000000 605.000000 Well, some issues are directly related to those photoreceptors, the rods and cones themselves.
605.000000 606.000000 Okay.
606.000000 611.000000 A common one involving cones is color blindness or more accurately color vision deficiency.
611.000000 612.000000 Right.
612.000000 614.000000 Not usually seeing in black and white.
614.000000 615.000000 Exactly.
615.000000 616.000000 That's very rare.
616.000000 622.000000 Usually it means one or more types of cones aren't functioning correctly or might be less sensitive to certain wavelengths.
622.000000 626.000000 So people still see colors just differently.
626.000000 628.000000 Red, green color blindness is the most prevalent form.
628.000000 632.000000 And if the rods aren't working right, the night owls.
632.000000 633.000000 That can lead to night blindness.
633.000000 635.000000 The medical term is nictalopia.
635.000000 636.000000 Right.
636.000000 639.000000 It makes it very difficult to see in dim light or after dark.
639.000000 643.000000 And what about conditions affecting that central sharp vision area you mentioned, the macula?
643.000000 648.000000 Yeah, conditions like macular degeneration directly affect the macula that cone rich area.
648.000000 658.000000 Damage there causes a loss of sharp central vision, which impacts the ability to read clearly, recognize faces easily, or see fine details.
658.000000 665.000000 It's also fascinating our sources mentioned that vision problems can sometimes be a sign of issues happening elsewhere in the body, not just the eyes.
665.000000 667.000000 That's a really crucial point.
667.000000 668.000000 Yeah.
668.000000 671.000000 Sometimes vision changes are the first clue to underlying health conditions.
671.000000 677.000000 Things like diabetes can affect blood vessels in the eyes, neurological events like strokes can impact vision pathways.
677.000000 683.000000 Even something like the yellowing of the whites of the eyes can indicate liver issues like jaundice.
683.000000 687.000000 There's a definite medical truth to the idea of eyes being a window.
687.000000 691.000000 Maybe not to the soul, but certainly sometimes to your brain and overall health.
691.000000 697.000000 So if you notice any significant changes in your vision, it sounds like it's really important to get it checked out, not just ignore it.
697.000000 704.000000 Absolutely, don't delay. And eye care specialist has a whole range of tests way beyond just checking if you need glasses.
704.000000 705.000000 Like what?
705.000000 711.000000 Well, comprehensive exams using dilation to get a good look at the back of the eye, the retina and optic nerve.
711.000000 718.000000 Specialized tests like visually-voked potentials, which actually measure the electrical signals traveling from your eye to your brain.
718.000000 720.000000 They can get a really full picture of what's going on.
720.000000 723.000000 Which brings us nicely to some practical steps.
723.000000 726.000000 How can we help take care of these incredible complex systems?
726.000000 727.000000 What can we actually do?
727.000000 729.000000 Well, prevention is key, right?
729.000000 732.000000 Well, we can't guarantee perfect vision forever.
732.000000 737.000000 There are several simple, yet powerful things you can do according to our sources.
737.000000 740.000000 Number one has to be regular eye exams, doesn't it?
740.000000 742.000000 Even if your vision feels totally fine.
742.000000 746.000000 Definitely. Think of it like a routine check up for your eyes. Same as a physical.
746.000000 752.000000 An eye specialist can detect many conditions early, sometimes way before you even notice symptoms yourself.
752.000000 755.000000 An early detection is key.
755.000000 757.000000 Critical for preventing long-term damage.
757.000000 761.000000 Most recommendations suggest a comprehensive exam every one to two years.
761.000000 766.000000 And something so simple, but maybe easily overlooked, where I protect you.
766.000000 767.000000 No, absolutely.
767.000000 774.000000 Safety glasses or goggles when you're doing anything that might send stuff, flying workshop, yard work, certain sports, it seems obvious.
774.000000 779.000000 But it can save you from a really painful injury and potential permanent vision loss.
779.000000 783.000000 Avoiding tobaccos and other big one, right? Smoking, vaping.
783.000000 787.000000 Huge. Tobacco products damage the tiny, delicate blood gussles throughout your body.
787.000000 791.000000 And that absolutely includes those that nourish your eyes.
791.000000 795.000000 It significantly increases the risk of several serious eye conditions over time.
795.000000 798.000000 And does diet play a role? Eating your carrots?
798.000000 801.000000 Well, carrots have vitamin A, which is important.
801.000000 807.000000 But, yes, more broadly, eating a balanced diet rich in various vitamins and minerals,
807.000000 815.000000 things like antioxidants, omega-3 fatty acids, supports overall eye health, and the function of those photo receptors.
815.000000 819.000000 Maintaining a healthy weight is also mentioned, as overall health is linked to eye health.
819.000000 823.000000 Exactly. It's all connected. And again, that point about not ignoring symptoms.
823.000000 828.000000 If something seems off with your vision, just get it checked out. It's always better to be cautious.
828.000000 836.000000 And the sources highlight some specific symptoms that require really prompt medical attention. These aren't subtle changes.
836.000000 838.000000 No, these are the big red flags.
838.000000 842.000000 Things like sudden loss of vision, even in one eye, seeing sudden bright flashes of light,
842.000000 846.000000 a sudden increase in floaters, those little specks drifting around.
846.000000 848.000000 That's special if it goes with flashes, yeah.
848.000000 853.000000 Or a sudden loss of part of your field of vision that looks like a dark curtain or wall coming across.
853.000000 855.000000 Definitely seek immediate attention for that.
855.000000 862.000000 Also, any significant eye injury burns or symptoms like sudden double vision or significant unexplained eye pain.
862.000000 869.000000 Right. Any sudden dramatic change in your vision is worth getting checked out quickly by a professional.
869.000000 870.000000 Don't wait.
870.000000 878.000000 So, when you really stop and think about it, that incredible, high definition, full-color world you experience every single day,
878.000000 884.000000 it's built piece by piece by this amazing partnership between your eyes and your brain.
884.000000 890.000000 Relying on those tiny specialized rods and cones, capturing light and sending signals at just, well, lightning speed.
890.000000 896.000000 It really does make you pause and to think objects in the world don't inherently have color.
896.000000 905.000000 Color is something your brain actively creates, interpreting the pattern of light wavelengths based on the signals it gets from just those three types of cones.
896.000000 896.000000 Right.
905.000000 907.000000 Your brain is constantly doing this complex decoding.
907.000000 913.000000 It truly gives you a new appreciation for just how much work your eyes and brain are doing behind the scenes.
913.000000 915.000000 Every single millisecond you're seeing something.
915.000000 916.000000 It does.
916.000000 919.000000 And here's something maybe to leave you with, something that always makes me wonder.
919.000000 920.000000 Okay.
920.000000 924.000000 We've talked about how most of us have three types of cones, letting us see millions of tellers.
924.000000 927.000000 But we know the animal kingdom has much more variation.
927.000000 928.000000 Oh, yeah.
928.000000 937.000000 Many animals think some birds, fish, insects, they have more cone types than us, or cones sensitive to different parts of the light spectrum entirely.
937.000000 938.000000 Like what?
938.000000 945.000000 Some can see ultraviolet light, for instance, which is completely invulgable to our human eyes simply because we lack the right photoreceptors.
945.000000 954.000000 And our sources mention that incredibly rare instances in humans, just due to a genetic variation, can result in a fourth type of cone.
954.000000 955.000000 Exactly.
955.000000 957.000000 Tetrochromacy, it's cone.
957.000000 965.000000 Potentially allowing those individuals to perceive maybe up to 100 million colors, vastly more than the one to 10 million, the rest of us perceive.
965.000000 967.000000 Wow, 100 million colors.
967.000000 974.000000 So it just makes you wonder, what incredible colors, what amazing nuances of light and shadow, what whole parts of the visual world
974.000000 982.000000 are happening all around us right now, but are completely invisible to our eyes just because our biological equipment isn't designed to capture them.
982.000000 987.000000 Something to ponder the next time you look at something familiar, like a flower or butterfly, maybe.
987.000000 988.000000 What else is really there?
988.000000 991.000000 And that wraps up today's episode of Everyday Explained.
991.000000 994.000000 We love making sense of the world around you, five days a week.
994.000000 999.000000 If you enjoyed today's deep dive, consider subscribing so you don't miss out on our next discovery.
999.000000 1002.000000 I'm Chris, and I'll catch you in the next one.