| 00:00 | this is the third section of the and we're starting with the visual |
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| 00:04 | we will do over the next few as we will understand the anatomical |
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| 00:11 | functions of different cells along the visual all the way from the retina into |
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| 00:18 | primary visual cortex. And we'll end even understanding how neurons in the primary |
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| 00:25 | cortex in the occipital lobe are capable forming what is called the primal sketch |
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| 00:31 | the outside visual world, the sensor that's coming in the form of |
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| 00:37 | Now there's this term in german that quite specific in Germany and quite specific |
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| 00:44 | psychology but it is also very much to visual system and understanding what we |
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| 00:51 | a complete picture. German term gets , its configuration reform. It's a |
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| 00:58 | picture that we see, what we represents properties of objects and organization of |
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| 01:05 | by the brain. There's an outside that we're seeing and the outside world |
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| 01:11 | interacting with the cells and with the and the certain organization within our |
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| 01:20 | A lot of times we assume three experiences or we assume that things are |
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| 01:27 | dimensional but we're really looking at two items. So for example, if |
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| 01:35 | were to make a quick drawing that something like this. Okay, what |
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| 01:47 | this? And most of you would ? Well it's some sort of a |
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| 01:50 | is some sort of a cube as sort of a rectangle. You would |
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| 01:55 | . It's a three dimensional structure. , it's nothing but two dimensional lines |
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| 02:03 | a piece of paper that are joined a certain way. That makes you |
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| 02:08 | things in a certain way. So certain things that we learned and then |
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| 02:13 | we learn, we perceive them within certain pattern. And that pattern can |
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| 02:18 | stable to go stall pattern. A pattern is constant despite the variations and |
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| 02:26 | information perceived. So I could even this piece of paper in different |
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| 02:32 | And you'd still say it's still a . It's still a cube. It's |
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| 02:35 | a cube. I could bring it and you wouldn't say like, my |
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| 02:38 | , it's so massive that it has over dr Z's desk and everything are |
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| 02:44 | bringing back and say it's so tiny cuba disappeared. I can't see. |
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| 02:48 | with a microscope, where is So we know that the change of |
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| 02:52 | hasn't changed. It remains constant. learned these things. The variation happens |
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| 02:57 | the environment, in the sensory uh coming in. So the brain makes |
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| 03:05 | assumptions about what is to be seen the world. And these are expectations |
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| 03:11 | these are perceptions that derive in part experience what is out there. And |
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| 03:15 | from built in neural wiring provision which will understand we have a lot of |
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| 03:23 | ability in our visual system to to group things together. So for example |
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| 03:31 | top and a we have an ambiguous . Then just circles you look and |
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| 03:40 | I will say, what are you most of you will say, well |
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| 03:44 | seeing here on top, I'm seeing uh or is all vertical yellow and |
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| 03:55 | blue in here. I'm seeing horizontal and horizontal blue and that similarity. |
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| 04:03 | we tend to group yellow together and blew together and say that these uh |
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| 04:09 | these must be columns and these must rose of blue and rows of |
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| 04:17 | If things are closer to each our vision does what it's called, |
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| 04:23 | , principle of proximity. So if put things slightly closer, the same |
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| 04:29 | object, the circle slightly closer you'll say, well, wait a |
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| 04:33 | . These are columns and and this configuration. These arose because they're closer |
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| 04:42 | in this way. But in reality don't know that in reality we don't |
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| 04:48 | whether the intent is to have columns rows, whether the intent of whatever |
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| 04:54 | being communicated from the outside world is us to say that it's yellow, |
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| 05:00 | and blue rose rather than say that blue and yellow and blue and yellow |
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| 05:08 | . But a lot of times we abide by the similarity and proximity visual |
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| 05:15 | that guide us. So the same as visual illusion. If you were |
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| 05:20 | take these blue lines out. Although arrow, the line for the arrow |
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| 05:27 | the arrowheads in the same length. I were to take these blue lines |
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| 05:32 | , you would think that the second at the bottom is longer because the |
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| 05:37 | are pointing outward. So these are and we have a lot of very |
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| 05:44 | illusions, visual illusions have been Uh And okay, you have |
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| 05:55 | So you will say this line is but in reality it's not. And |
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| 06:01 | you also have understanding that the person is sitting down the hallway, it's |
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| 06:08 | much smaller because of your visual It's actually not a really small |
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| 06:14 | So if you were to bring this , this person wouldn't be this tiny |
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| 06:18 | . This person of course is smaller they're further away. This is all |
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| 06:25 | built in some classical optical illusions to or a vase. Yellow fish or |
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| 06:38 | frogs. Some of the optical illusions difficult to recognize. The interesting thing |
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| 06:47 | optical illusions. Individual circuits at once recognize once you see the faces and |
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| 06:52 | days want to see the frogs and fish, you'll always see both. |
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| 06:59 | it's it's it's quite interesting. um how does that happen? Of |
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| 07:11 | . There is light that we process has its own properties. It's electromagnetic |
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| 07:18 | that comes in a certain wavelength That wavelength becomes in the frequency of |
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| 07:24 | light. And the human visible light is from 400 here on the left |
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| 07:32 | 700 nanometers. If you remember Roy biv Okay, Roy G. |
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| 07:41 | Death is red, orange, green, blue, indigo violet. |
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| 07:53 | below violet, you have ultraviolet rays you have X rays and below x |
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| 07:59 | . You have gamma rays and above nanometer wavelength red you have infrared |
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| 08:08 | And then radar broadcast broadcast bands. . C circuits, radios A. |
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| 08:13 | circuits. This is the visible wavelengths 700 will appear as red And 400 |
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| 08:24 | violent. The light strikes that I strikes the objects. It can be |
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| 08:30 | from the object. The light can absorbed by the objects and by different |
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| 08:39 | . The light can be refracted which the rays of light can bend as |
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| 08:47 | crosses from one medium air into another of water. You have refraction and |
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| 08:57 | when the light hits the pupil and into the pupil gets refracted. This |
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| 09:03 | the iris. This is the Here and in the back of the |
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| 09:10 | you have the optic nerve and the is being held and controlled by extra |
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| 09:16 | muscles that are in part mostly controlled ocular motor cranial learns. And this |
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| 09:25 | only the beginning. The information from eye travels into the thalamus of the |
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| 09:31 | gesticulate nucleus. So from the sensory retina it gets processed there. The |
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| 09:40 | gets converted into an electrochemical signal and potentials from the optic nerve an optic |
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| 09:47 | enter into the lateral gene Nicollet nucleus the thalamus and from the thalamus these |
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| 09:54 | go into the primary visual cortex or , the one in the primary visual |
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| 10:02 | . So in the next three lectures will understand the whole pathway from the |
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| 10:06 | into the primary visual cortex what the in these structures process and how the |
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| 10:12 | visual cortical cells create the primal sketch the outside world from the primary visual |
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| 10:19 | . What we have is we have divergence of the pathways. One pathway |
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| 10:25 | dorsal parietal or posterior parietal pathway that to posterior parietal cortex. That visual |
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| 10:33 | pathway is the inferior temporal cortical pathway ventral inferior temporal pathway, which basically |
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| 10:41 | that mps have come into the Some of them, as you can |
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| 10:46 | , are primarily concerned with processing color , depth and form and others are |
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| 10:54 | concerned with processing motion and is closely with somatic sensory and motor cortical |
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| 11:06 | So these are the primary cortical areas if you want. V. two |
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| 11:09 | a secondary cortical area before the coordinate cortical area. And then in these |
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| 11:17 | when it travels further away from this visual cortical area it becomes. We're |
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| 11:23 | with other sensory modalities and information such it's amount of sensory and uh auditor |
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| 11:36 | in the temporal cortex association areas in parts of the brain. Mhm. |
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| 11:44 | let's understand the i as the icons through the pupil you have these suspense |
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| 11:53 | ligaments that are holding the lens. is the lands and you can can |
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| 12:01 | and relax these ligaments and as you that uh Lance can get thicker or |
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| 12:10 | can get thinner in front here you a quiz humor which is full of |
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| 12:20 | in front of the pupil and the of the eyeball is maintained by sort |
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| 12:26 | a vitreous humor. That's a gel solution that forgives the eyeball its |
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| 12:33 | And in the back of the you retina here and retina form accents of |
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| 12:41 | optic nerve that exits out in the of the eye. Yeah. What |
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| 12:52 | some other important components here cornea canal tear drainage here? Yes, Clara |
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| 13:01 | people. These are all great label questions. When the light comes in |
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| 13:06 | the pupil, the light actually the amount of light strike zone called the |
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| 13:12 | . In the back of the retina is very centrally located directly in front |
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| 13:18 | the pupil. Anchovy is responsible for highest security or for the highest resolution |
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| 13:25 | that we see primarily mediated by the photoreceptors. But what this shows is |
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| 13:31 | the light enters through the cornea through lens and is directed. Its focus |
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| 13:39 | lens focuses the light on the retina in the retina you have a circuit |
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| 13:46 | cells that are ganglion cells, bipolar and photo receptor cells and photo receptor |
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| 13:54 | are located in the very back of retina and these photos are suffer salts |
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| 13:59 | the ones that are going to trans or convert if you may the photons |
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| 14:05 | light into synaptic potential to the bipolar or bipolar salsa into synaptic potential retinal |
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| 14:13 | south retinal ganglion cells will then send first action potentials out of the retina |
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| 14:21 | the lateral lenticular nucleus of the And here you have picking in the |
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| 14:26 | here in the in the back of photo receptors. So this is the |
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| 14:32 | of light. The light comes in actually crosses these cellular structures before It |
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| 14:39 | on two types of the photo receptors have calm and rod photoreceptors, cone |
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| 14:47 | are further subdivided into blue, red green photo receptors. These voter receptors |
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| 14:55 | communicate the information to bipolar cells. bipolar cells will communicate the information to |
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| 15:02 | ganglion or retinal ganglion cells. And ganglion cells will produce action potentials and |
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| 15:08 | form the fibers of the optic And retinal ganglion cell fibers are the |
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| 15:14 | output that is coming out of the . Okay so the transaction happens photo |
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| 15:24 | but the only output and the only potentials are produced by the retinal ganglion |
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| 15:31 | fibers. Now this shows that the can accommodate and that means that when |
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| 15:38 | object moves in and out, you always have to move your head with |
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| 15:43 | object in order to see the same of the object instead. What you |
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| 15:48 | is you use these uh suspense our and you shape the lands and as |
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| 15:54 | shape the lines you can refocus, same beam of light directly indirectly where |
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| 15:59 | far away. If it comes closer make the lines thicker and the projection |
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| 16:04 | stays directly onto the right now. is a good exam question. This |
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| 16:11 | normal vision which is referred to as vitro pia. And then you can |
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| 16:16 | high propia or my oh pia. in high propia, what you have |
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| 16:24 | you have a reflection uh the outside that is not focused properly on the |
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| 16:33 | but rather the focused object is focused distance beyond the retina basically. You're |
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| 16:48 | , are you giving This was gonna my question for the exam. So |
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| 16:56 | let's everybody can look it up. you would use this come vax lands |
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| 17:06 | France. So if you put this slants in front glasses or for for |
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| 17:15 | in front then what you do is refocus the object directly onto the rightness |
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| 17:21 | now it's in focus. So you use glasses, you can use lenses |
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| 17:28 | in my Appiah it's the opposite in . The lands focuses it in |
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| 17:36 | What would be a little bit before retina also making an object blurry. |
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| 17:44 | then you would put these concave shape or gloss and it would refocus your |
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| 17:56 | and the image on the proper distance we'll keep it and focus on the |
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| 18:05 | mm hmm. And of course you also do adjustments with the laser surgery |
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| 18:12 | the lens itself that can help we and shape the lens in a way |
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| 18:20 | will help focus objects where they need be on the back of the |
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| 18:27 | So we have this world, this world that we perceive. And if |
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| 18:35 | were to close one eye, You have 150° That you can see with |
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| 18:44 | eye, it's about 90 because this be 90. I actually can see |
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| 18:49 | 60° or so. So it's 150°. if you were to put a pencil |
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| 18:57 | a pen at a certain distance it may be occupying Or a different |
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| 19:03 | here. It's on buying 100° It's occupying 20° here is occupying the |
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| 19:11 | away my object is away from The last Here I am occupying more |
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| 19:18 | your degrees. Now I'm occupying less your degrees. A lot more of |
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| 19:22 | degrees. A lot less of your of 150 space. So let's say |
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| 19:28 | know the distance to the moon in sky. And if you were to |
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| 19:34 | in the moon when it's risen it's half a degree of this visual Angle |
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| 19:42 | 150°. And that have a degree. moon Would project about 140 Micro m |
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| 19:53 | space on the retina. You're focused the moon, 140 Micro m of |
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| 20:01 | Ratna which is centimeters would be occupied this 0.5. So the fall would |
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| 20:11 | 150 of course just a fraction of at 140 μm. But depending on |
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| 20:18 | how far the object is and we the visual angle. We can then |
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| 20:27 | the amount of the retina right now . It would be active. You |
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| 20:36 | put a little star next to I would be like .1° and that |
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| 20:41 | be 14 micrometers of space and you barely see it. Um that's probably |
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| 20:49 | the best resolution you can get to .1°. Again important points as photo receptors |
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| 20:59 | the back of the right now the light sensitive cells ganglion cells is the |
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| 21:05 | output from the retinal ganglion from the the right and left. And you |
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| 21:12 | these horizontal and mclean cells and these um A green cells, inhibitory neurons |
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| 21:20 | they're going to control the communication between and bipolar cells. For bipolar cells |
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| 21:26 | ganglion cells. And there's several different visual representations that are half of the |
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| 21:36 | for you. And the retina in is subdivided into the outer nuclear layer |
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| 21:44 | have the nuclei of the photo cone and rod. The outer flights |
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| 21:50 | form layer which is the synopsis between receptors and bipolar salsa. And as |
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| 21:57 | can see photo receptors or horizontal cells have inner nuclear layer where you have |
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| 22:04 | nuclei of a McQueen bipolar horizontal selves the perplexing form layer, the connectivity |
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| 22:14 | bipolar ganglion as well as um a cells. And then you have the |
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| 22:20 | cell layer which is the output layer is the retinal ganglion cell selma's. |
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| 22:31 | you have a laminar organization of the . It's organized in layers. You |
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| 22:37 | this first layer of photo receptors which really the last layer. The middle |
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| 22:43 | . It's another presentation out of Out of flex, a form in |
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| 22:47 | nuclear in a flex a form and cellar with axons coming out so you |
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| 22:54 | see of course the blood vessels that be innovating the eye and eyeballs that |
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| 23:01 | coming through this spot too. And spot would also be a blind |
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| 23:05 | That would be a small space in eye where we have a blind |
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| 23:10 | But we account for it with another . And with perceptive learning photo |
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| 23:19 | They have the outer segments, the segments and the synaptic terminals. But |
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| 23:24 | outer segments. The rod photoreceptors that this free floating discs inside. And |
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| 23:31 | photoreceptors have these indentations or imaginations and plasma membrane. And the reason for |
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| 23:39 | these member Ernest disks or member and is to increase the surface area for |
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| 23:47 | for the photo pigment. And obviously more uh the photo pigment you have |
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| 23:55 | more sensitive the cell is going to so rod cells are more sensitive than |
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| 24:00 | cells. Again it's showing these free discs in the rod cells and the |
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| 24:07 | segments and these folding membranes and the photo receptors. The synaptic terminal of |
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| 24:19 | , is where the contact of the cells or bipolar cells happens. The |
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| 24:25 | difference between rods and cones is that highly sensitive to lighten. A specialist |
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| 24:33 | night vision. They have a lot photo pigment because they have more surface |
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| 24:39 | due to three free floating discs and capture mall. Are it so ross |
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| 24:46 | high amplification. They can detect single of light but they have low temporal |
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| 24:53 | . That means that they have a response and long integration time. There |
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| 24:59 | also more sensitive to scattered rays of , scattered, meaning not direct ways |
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| 25:07 | life but scattered or weak rays of rock system. By that virtues lower |
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| 25:14 | . It's not present in the central ross system. If you look at |
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| 25:20 | of these diagrams have highly convergent retinal and it's a chromatic. There's only |
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| 25:28 | type of raw the pigment. So can say that rock but the receptors |
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| 25:34 | responsible for gray scale vision, if make what I mean by that grayscale |
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| 25:41 | and the rod activation is a perfect is walking into a dark room or |
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| 25:46 | movie theater and at first for a or two everything looks the same dark |
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| 25:52 | seconds later you see darker shades, can start seeing where people are sitting |
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| 26:00 | longer time goes, you can recognize lighter coat and their face maybe. |
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| 26:06 | this is slow response long integration time very little light is necessary but you |
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| 26:14 | don't see much color. So it's chromatic Collins. On the other |
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| 26:20 | cones are packed in the zone of phobia which is immediately located right |
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| 26:29 | So cones will have very high density direct rays of light will come in |
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| 26:35 | this is where cones are most They're low sensitivity photo receptors. So |
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| 26:42 | for day vision they have less photo because they have less surface area, |
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| 26:48 | amplification very fast. So they have temporal resolution with short integration time and |
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| 26:57 | they are most sensitive to a lot light. Cone system is high acuity |
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| 27:04 | because they are concentrated in a phobia I showed you and they have dispersed |
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| 27:09 | pathways furthermore, unlike a chromatic cones are chromatic and they come in |
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| 27:17 | types of cones three times of Each with a distinct pigment that is |
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| 27:24 | sensitive to a different part of the light spectrum. That means that pigment |
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| 27:30 | going to be most sensitive to certain to three different separate wavelengths. |
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| 27:39 | rod system walk in the dark movie , slow low level of light that's |
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| 27:47 | it works. Cohen system, lots light, high Q division telling you |
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| 27:52 | color and highest resolution that I can using my eyes. This is we |
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| 28:01 | to look at the distance across from central retina, which is in a |
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| 28:08 | and the types of the photo receptors expressed. You will see that the |
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| 28:11 | photo receptor expression peaks in the various retina and a phobia. And that |
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| 28:18 | photoreceptors are flanked and that they peak and are highly expressed in the peripheral |
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| 28:25 | and the size of the retina. you make the blind spot, there's |
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| 28:30 | expressed here because this is the optic fibers or retinal ganglion fibers that are |
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| 28:36 | out informing the optic nerve. So you have peripheral retina that is dominated |
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| 28:43 | rod photoreceptors. Central retina that's dominated cone photoreceptors and nasal, peripheral |
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| 28:54 | temporal versus nasal. Again is dominated rod photoreceptors. So in a way |
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| 29:03 | where your acrobatic night vision is. central retinas, where your high acuity |
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| 29:11 | resolution. Right here in a phobia have even an indentation, a physical |
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| 29:19 | indentation and the circuit of the retinal making a little crater that would direct |
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| 29:26 | light directly into that little crater in phobia in the back of the retina |
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| 29:31 | the cone photoreceptors for the fast high color vision. The three counts blue |
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| 29:42 | and red. So the blue cone be maximally activated 100%. With a |
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| 29:50 | wavelength of light which is 420 440 groups. The red is going to |
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| 30:03 | most sensitive. The peak of that be closer to the red spectrum and |
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| 30:08 | green will be closer to the How do you get blue? So |
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| 30:15 | if you have 400 nanometer light, you have a light that's green, |
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| 30:22 | 480 nm, it will activate some the blue cones, some of the |
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| 30:27 | cones and majority of the green And the combination of activation of varied |
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| 30:35 | of these different photo receptors will result the color perception. Yellow colour will |
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| 30:45 | 550 nm and you have activation of and red cone photoreceptors in order to |
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| 30:54 | the yellow color. So Red color perceived blue, no activation, |
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| 31:04 | activation, blue cones, 100 colour green, 31% activation of green, |
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| 31:13 | activation, 31 of red, 36 blue and 67% of green cones. |
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| 31:26 | you know what? It's actually quite . But the chickens can see more |
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| 31:31 | than we can more huge, You perceive more hues than we can. |
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| 31:38 | when you eat that chicken, next thinking about how colorful chicken's life really |
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| 31:43 | compared to ours. But we do a lot of colors and we do |
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| 31:48 | a lot of colors because we have you would call mixing color mixing or |
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| 31:56 | lines of life that affect different These wavelengths of light Renecting different |
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| 32:06 | different amount of activation of three types cones. So if you have |
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| 32:12 | blue and red overlapping, you get . And so from this you have |
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| 32:22 | of the colors that we can proceed white to black or from red. |
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| 32:27 | violent. Uh huh. And this really happening at the level of the |
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| 32:35 | and the light one that comes in it activates these photo receptors, it |
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| 32:41 | transducer, it gets transformed. If make it make it gets converted into |
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| 32:48 | electrochemical |
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