Of course vision system then begins with actually the light or the imagery project through the eye. And then from here the eye will transfuse those signals into electro signal, and then this information is encoded and then by the spectrum, right? The different the extra potential. And then the information will be transferred to the brain here is the LGN, light, [FOREIGN], okay? And then this is a relay center, [FOREIGN] will flares are go to the visual contacts [FOREIGN]. Now this is the process, right? So, we'll first begin with what happened in the eye, okay? Let's talk about its detection. So, the eye is actually very similar to an artificial, okay CCDs [FOREIGN]. Maybe more as a camera, right? Yeah, so what's the difference between the eye and the camera or was it the common thing or the difference between these two? [FOREIGN] the difference is one of these is the focusing, right? In the camera you move with a lens [FOREIGN]. >> [FOREIGN] >> [FOREIGN]. >> [FOREIGN]. >> [FOREIGN] Okay lets take a look here. [FOREIGN] the focusing [FOREIGN] sensitivity unit. [FOREIGN] sensitivity [FOREIGN] to the neuron. [FOREIGN] now just we know that the sensory system. They came dynamically changes again over the sensitivity, okay? [FOREIGN] if the light is too strong for a camera. What will you do? [FOREIGN] yes. For human then, for eye what will happen to the eye? >> [INAUDIBLE] >> Good. [FOREIGN] if we feel the light is too strong, then the brain will make the action. The action is actually to get a smaller pupil. [FOREIGN] only one side feel that the light is very strong. And then both eyes will have a small pupil. Okay, now [FOREIGN] detect them [FOREIGN] you cannot [FOREIGN]. So, they means actually, this important a protection [FOREIGN] try to protect you. That is actually [FOREIGN], okay? [FOREIGN] the effect is rest more at the most it only can reduce about 16 of the same 15 fold of the 19 intensity. [FOREIGN] okay? [FOREIGN] okay? [FOREIGN] how can we deal this system right now? The light intensity is so huge arranged. Now, your total arrange, [FOREIGN] not 15, not 100, not 1,000, not 10,000. [FOREIGN] to make arrange [FOREIGN]. Essentially, we never actually have the problem actually in the [FOREIGN] the eye, the pupil. [FOREIGN], so we have a neurosister. [FOREIGN] focal for example, even the single neuron [FOREIGN]. What kind of mechanism can they use to change this again over the system? For example, we have the adaptation. Adaptation is actually if you have a strong light coming and then the neuron can perceive this light. And then make a change of the signaling pathway [FOREIGN] sensitivity [FOREIGN]. Okay, so this is the main difference. [FOREIGN] what is the [FOREIGN] how will you design an experiment to examine the sensitivity of our eyes. [FOREIGN] take a light. Light is a photon, right? [FOREIGN] so you do a question [FOREIGN] what's the minimal photons needed to trigger a visual perception? [FOREIGN] this is 1942. A psychophysical study. Psychophysical [FOREIGN] human as a subject. [FOREIGN], okay? [FOREIGN] you have I guess everybody has this experience. When you are sitting in a dark room. Then your visual system will actually get more sensitive, right? [FOREIGN] sensitivity [FOREIGN], okay? Now, here is actually in the complete darkness. [FOREIGN] after half an hour [FOREIGN]. So, I guess this which would not go to the details but if you are interested you can look at this paper. Okay, this is a very classic sensory neurobiological paper. [FOREIGN] okay? [FOREIGN]. Now [FOREIGN] photon 9. The photons 9 [FOREIGN] six photons per flash. [FOREIGN]. So, because this flash cover about 500 photoreceptor. [FOREIGN] visual field [FOREIGN] calculation. Very simple. A calculation is actually what's the probability of one single photoreceptor to detect more than two photons under this condition? Okay, let me repeat again. Six photos were flashed and this flash covers 500 rod photoreceptors. So the question is, what's the chance of lens single photoreceptor to hit by two photons or more than two photons. [FOREIGN] there are six photons okay. [FOREIGN] now take a probability [FOREIGN], okay? [FOREIGN] why single neuron is unlikely to hit by two photons. [FOREIGN] okay? Now what it mean? What it means is that the six photons are detected by six different neurons. You agree? >> [INAUDIBLE] >> Okay, another way to say this, actually, one single neuron Six single neurons respond to these six different photons. Each of these six different photons. And that means actually, one single neuron is so sensitive to detect one single photon, right? [FOREIGN] You know actually under these conditions that information already goes to your brain. You can make the perception. >> [FOREIGN] perception. [FOREIGN] how can the eye achieve this feature?
