Speaker 1:	Hi, everybody. Welcome to second Tuesday, even though it's the first Tuesday. We realized we had a conflict next week, and so we moved things up, and actually next month we'll also meet on first Tuesday because second Tuesday is Spring Break. Then after Spring Break, we'll go back to second Tuesday. Anyway, Chris [Vessie 00:00:20], some of you probably don't know him, he's a visiting assistant professor in biology. He'll be with us for another couple years after this year. This year, he has the daunting task of teaching in place of Kathy Siwicki, and he's offering neurobiology, which is very, very popular with our students. Chris came back from a meeting and told me about this great story, and I think that's the story he's going to tell you about faces and how the brain recognizes faces. So, Chris? 
Chris Vecsey:	Let's see here. Cool. This is really fun. I'm really glad to get to speak to all of you. I really enjoyed this during the first semester in the audience, so it's cool to be able to talk a little bit about neuroscience. Although, as the flyer kind of said, this is not something that I study actively. I study fruit flies and sleep and circadian rhythms. This is a far cry from what I do in my lab. I went to a talk in November at this giant society for neuroscience meeting by this woman Doris Tsao, who's at Caltec. She studies face perception in Macaque monkeys. I'm going to tell you about her research mostly, with a little bit of other people's stuff mixed in. I think it's really fascinating to think about how something so complex as a face can be recognized in practically an instant by almost everybody in the world very easily. 
	Just a couple basics to get us started. The most basic unit of visual perception are these photoreceptors that live at the back of our eye, right, in this retinal layer. They're sort of tiled here. You've probably heard of rods and cones. Rods for dim light, and cones for color. What's interesting about these is that they sort of tile the back of the eye, and so light coming in from different directions will hit a different photoreceptor in your eye. That's sort of the smallest unit of visual perception. Physically, if a photon of light hits a photoreceptor, it will respond. It can only respond if that photon hits that one little spot. It has to come from right over there and come in and hit that one photoreceptor, and that one will respond, all right?
	That photoreceptor doesn't care whether that light was reflected off of a bright light from up here or off of somebody's shiny head. It doesn't care, right? As long as that light hits that photoreceptor, it will respond. How do we get from that, just little dots of light being sensed in the eye, to knowing that this complex shape is a face, and getting it right every time? Information is passed sort of piecemeal from the retina to the back of the brain, which is called visual cortex, or primary visual cortex. Already by the time information has gotten there, the cells have received and are pooling information from many photoreceptors. Instead of just responding to dots of light, cells that are back there are responding to bars of light, and edges, and things that are moving through space. We start to construct more and more complex representations of what we see as the information gets passed around the brain, and information gets integrated.
	Still, a bar of light is a far cry from a face, right? This information then starts getting passed in two different directions from the visual cortex. One direction is called the what pathway, which tells you what object you're seeing eventually. The other one tells you where in the visual field something is, and where it's moving, right? It starts processing movement as well. We would expect faces to be in the what pathway, since they're a thing, not necessarily moving, although there are some areas that respond to movement of faces. 
	That is exactly what we see. We see that actually this is with fMRI, right? We can record responses of swaths of the brain to visual stimulation. You can put in a picture of a face, a picture of house cat, a picture of a toaster, and you see what areas of the brain respond. It turns out that particular patches of the brain respond preferentially to faces relative to other things. In humans, the most famous area is called the fusiform face area, or the FFA. There's actually a disorder called prosopagnosia, where people don't recognize faces. Typically, they have brain damage in this fusiform face area.
	Let's go from humans to monkeys here. What's cool is that you can actually do fMRI recordings in monkeys. God bless the researchers who do these things. This is a picture looking up at the bottom of the brain. It's a little odd, but one hemisphere and the other hemisphere. Here's our fusiform face area, and a couple other areas of the human brain that respond preferentially to faces. Monkeys have these patches as well. They have different names, but a very similar kind of constellation of parts of the brain that respond to faces. 
	Unfortunately, doing these fMRI recordings doesn't tell you necessarily about individual neurons and how they're responding, right? What are these neurons picking up on in a face to tell you that it is a face? This researcher, Doris Tsao, and other people in her lab started doing experiments where they actually record from individual neurons in the brain. They'll have monkeys doing a task, viewing scenes or faces, and they will put an electrode down into these different patches of the brain that we just talked about. They'll target one at a time. They can do that very precisely anatomically. The electrical language of the brain can be read out, and you'll see these spikes. Each of these is what's called an action potential. The more action potentials a cell produces, the more it's excited, the more output it's producing. This neuron, if it's firing multiple action potentials, will be telling you something more strongly than if it only fired one or two. 
	What you'll hear, I'm going to show a handful of videos, when you see these videos you're going to see what the monkey are looking at, and then you're going to hear this chattering in the background. Those sounds are actual action potentials recorded from a single neuron, one at a time, from the areas of the brain that we just talked about. This is sort of a representation of this, with an electrode in this first major area that they were able to record from, and the monkey sort of looking at this face on the screen. They train the monkeys so they're always staring right at the front.
Speaker 1:	Are they looking at human faces or monkey faces?
Chris:	Everything you'll see here today, they don't have monkey faces in there. People have studied preference for monkey faces versus human faces, and there's some interesting stuff there. Everything here is with humans. I'll give away the punch line before we show the video, which is that basically 100% of the cells in this area responded preferentially to faces relative to other things. Let's see if this works. 
Speaker 3:	Of what we heard, on the very first day of recording from this face patch. You're going to see what the monkey saw, and you'll also hear these clicks, which represent the electrical signals generated by this single neuron. Here's the very first cell.
Chris:	You'll see that it's extremely rapid. 
Speaker 3:	I hope you notice the cells have spiked at very specific subset of stimuli. 
Chris:	The thing that's important is relative number of spikes, so you'll see some that are firing at rest, but then that rate goes up, right? 
Speaker 3:	Next cell. Do you notice a pattern? Around cell four, we noticed a pattern. It seemed like every cell we encountered responded more to the faces than to other objects.
Chris:	What's cool about this is that you're talking about the electrical activity of one cell. You could basically just listen to that one cell as an animal was moving around the world, and you'd know every time it saw a face, right? Pretty reliably. Just that one cell is doing well. They have probably 50, 100, 1,000 at least cells just in that one tiny patch. Probably way more than that. What's cool, let's see, let's go back here. This is a graph of this, all right, where you have all these cells that they recorded from. Here's 130 cells. The faces that they gave are over here. Basically, you can see the red, the bright red, is high firing rates. All these other objects and things that they showed, including other parts of animals, bodies and things like that, very few cells are responding to those at all. Pretty dramatic.
	What's cool, and what you might be wondering, is if every cell here is just responding to any face, how do you ever recognize a particular face? They started looking in more detail, because here they're just looking at do they respond to faces relative to other things. It turns out that a lot of them are in fact tuned to specific face characteristics. I'll show you an example of that. Actually a couple. 
Speaker 3:	The presence of hair. 
Chris:	They're using stylized things. 
Speaker 3:	Here's a different cell that's detecting the presence of irises.
Chris:	Not just eyes, but irises. Pretty wild, right? You'll notice that there's some noise in there, right? Sometimes they're not firing exactly the same way. This is where you start needing more than just one neuron. You need to have a bunch to actually reliably detect these different features, right? You can imagine that these neurons are pooling together to tell you not only are you seeing a face, but it's got these different characteristics. Not just does it have them, but what are their qualities? In this video, if this will work, they're actually varying the size of the eye. It's a little hard to pick up, but basically what's happening is that whenever the eye is small, the cell is responding much more than if the eye is large. 
	That black dot is just showing the gaze of the monkey, just showing that it's looking at the screen. What's cool here is that the face is going to disappear. It's not just responding to circles, right? It's not a simple response. There has to be a face on top of those eyes. That means that this cell is receiving input from those first cells that say, "Hey, you're looking at a face. Now, tell us something about the face." It says, "Oh, well this is a face with small eyes." Now let's feed that back into the system, and now you're starting to recognize features of the face. 
	Going back to that one where there's the hair detector, you might wonder why do monkeys care what hairstyle these little things have. Who cares that it has, what is that, a bob? I don't know. It actually turns out that this is what a monkey looks like. These are what these Macaques look like. They basically look like they have sort of a ring of fur, hair, around the outside of their face. Obviously, being able to recognize and pick out faces is going to be really important for monkeys in their social networks as well. That's a feature that would probably be pretty salient for them. 
	It turns out that this was all within that one region, that first big region. They started recording from other regions as well, and they all have some slightly different properties. In one of these regions, they actually started to find cells that were selective for particular faces. In this particular video that you're going to see, this cell only respond to one face out of many faces that the cell will see. Probably, that cell, if you gave it enough faces, would respond to a subset, not just ... There's this idea of the grandmother cell, right? The one cell that responds to your grandma but nobody else. That probably doesn't exist. 
	Probably, there's sort of a set of 20 or 30 faces out there that you'd see that this would respond to out of a thousand, or something like that. Oh, and the other thing here, some cells in some areas, as I mentioned, they have different attributes. Some will respond to faces only when they're looking right at you, others when they're looking down, up, sideways, things like that, whether the face is profile, et cetera. This one is completely independent of that. 
Speaker 3:	The monkey didn't know this person, the same way you probably don't know him. 
Chris:	Right. This isn't a matter of familiarity. It wasn't that the monkey had seen this face before and so it was picking up on that. These were all new, or actually they were probably all familiar to this monkey at this point. They test the monkeys for as long as they possibly can. At this point, we've got some cells that are actually telling you something about not just that there is a face, but who that face belongs to. Just in the last section here, I'll just talk about an idea of instead of just recording from these cells, what if you actually stimulate these? Would you make them see a face? Could you change their perception of a face by stimulating the cells while they're viewing other things? 
	The verdict on whether you can make a monkey see a face where this is no face is pretty murky. It seems like that's pretty tough to make a monkey do. That's probably because you'd have to stimulate all of those face patches at once to actually get the right response. What you can do is actually manipulate their perception of an existing face. They did this experiment in monkeys where they show them a face, and then they wait a little while and they show them either the same face or a different face, and the monkey has to respond if it's the same face. Then they either do nothing to them or they stimulate with an electrode in one of these face patches while they're viewing the second face. They've already seen one, they know that face. Now you're trying to see do they say it's the same face or a different face more often. 
	It turns out that almost every time the monkey says that they don't recognize that face anymore. I.E. by electrically stimulating in this region, you're adding some extra attributes, or manipulating the attributes that the monkey should be seeing based on that image. You're sort of warping it, or changing it. We can't ask the monkey necessarily about what it's seeing, right? We can't exactly ethically do these studies most often with humans. What do we do? How do we figure out if this actually would happen in people? Well, there was a recent paper that came out that was able to actually duplicate this experiment in a person. They way they were able to do that is that there are people who have intractable epilepsy. Basically, nothing else, no drug treatments, are working for them. It's debilitating to them, and so they go into the hospital and they have electrodes implanted in their brain to try to find out where the locus of their seizures are.
	While they're in that situation, lying in the hospital bed with these electrodes in, every researcher in the world wants to work with them, because it's the only time when you can ever do this experiment with a person. They are booked solid for their time in the hospital. It turned out that some of the electrodes in this one particular fellow happened to be put into the fusiform face area, and actually one other area as well. They were able to stimulate through those electrodes while he was viewing faces. 
Speaker 4:	Just look at my face, and tell me what happens when I do this, all right?
Speaker 5:	Okay. 
Chris:	The first one is going to be nothing. It will say sham.
Speaker 4:	One, two, three. 
Chris:	In the next one, they're actually going to stimulate with some current, electrical current.
Speaker 4:	I'm going to do it one more time. Look at my face. One, two, three. 
Speaker 5:	You just turned into somebody else.
Speaker 4:	Tell me about it.
Speaker 5:	Your face metamorphosed. Your nose got saggy, went to the left. You also looked like somebody I've seen before, but somebody different. That was a trip. 
Chris:	This is pretty wild, that just from this one electrode stimulating in this area, you change his perception. It's very specific for faces. He says I could still see your coat, your tie. I knew that it was a doctor I was speaking to because you were all dressed that way, but just your face changed its perception. That's it for this. Just in conclusion, I think that it's fascinating how these different parts of the brain work together to make a cohesive perception of something as complex as a face. Clearly, this is really of high importance to humans as well as monkeys, and probably explains why we're always seeing Jesus's face in various foods, and rocks, and things like that. We're very, very good at picking out features that remind us of faces, even if they're not real faces. The middle one is amazing, right? I'm pretty sure that one was drawn on there. Thanks, thanks a lot. 
Speaker 1:	I'm sure if you have questions, he'd be happy to answer them.
Chris:	Yeah, yeah. Yeah? 
Speaker 6:	Lots of times I'll be lying in bed in the morning, and I'm looking out at a lot of the leaves. All of a sudden, there's a cow there. You'll see something in just the shadows and everything. Is that sort of the same thing?
Chris:	Yeah, clearly faces hold some really high importance. We'll find all sorts of outlines of things that remind us of actual objects, right? We can draw sort of just a stick outline of a rhinoceros, and we know it's a rhinoceros. We can pick that out very easily.
Speaker 6:	I mean, I look at it and I think I need a pencil and paper here because could I really draw that? Because if I tried to do it without looking at something, I couldn't. I feel like [inaudible 00:22:48] bed and it's absolutely there. [inaudible 00:22:51] cow's head is perfect. It's just in leaves.
Chris:	No, we are definitely good at synthesizing those pieces of information. I forget the number, maybe I have an example of it. They do these vision experiments where there's high background and just a few pixels are popping out. This can go down to something like three percent different than background, and you'll still know 100% of the time that's a face. We're really good at picking out faces, even from very dark backgrounds or murky backgrounds.
Speaker 7:	Just fascinating. Two questions. Last set of results, would that lead us to infer that normally there's some kind of innovation going on as you [inaudible 00:23:47] familiar faces so that there's less activation in that area?
Chris:	I think just when you stimulate with this electrode, you don't have the precision over which cells should be activated relative to what should be by what they're seeing. You're kind of tacking on these extra neuronal activities that are aberrant. That's why you're just warping that perception of the nose, right?
Speaker 7:	That leads to my second question, which is in the earlier studies where the monkey was recognizing a particular face due to that nerve being activated, how the heck do you find that nerve? 
Chris:	Right, exactly, because there are infinite numbers of possible combinations that would make up faces, right? How do they happen to hit that one cell? That's where it comes in that I think that each of those cells probably responds to a subset. One out of a hundred, or 200, or something like that.
Speaker 7:	Still, that's incredible.
Chris:	Yes. They actually found a bunch of them, but they spent a lot of time with these monkeys too. Yeah?
Speaker 8:	I remember hearing that the humans and monkeys also have a pretty amazing ability to see basically organic movement [crosstalk 00:25:03] see something [crosstalk 00:25:04] you know whether that's-
Chris:	Alive.
Speaker 8:	[crosstalk 00:25:08] or a leaf or something like that. I'm wondering if that is a completely different part of the brain that is making that very quick snap judgment [inaudible 00:25:23] seeing?
Chris:	I think probably something similar is going on there, but not in these areas of the brain most likely. Once you're talking about movement of things, that's probably going to be in that more dorsal, towards the top of the brain pathway. That's going to be probably a whole different set of cells. You know, obviously at some point you've got to put the head on the body, right? That's the whole person. At some point, that all gets integrated together. They're not going to be completely separate, but I think it's probably different cells but the same kind of thing. You have an arm, you have an arm, you put those together, and yeah. Go ahead.
Speaker 9:	Do you think you could put it into context of other research? Kind of recognition and stimuli in general. This is pretty unusual for [inaudible 00:26:13].
Chris:	Right. There are parts of the brain that respond to objects. Some of them are actually mixed in here, but they're very low frequency in these areas. Clearly, we can recognize, and learn to recognize, thousands and thousands of different objects, and recognize them pretty accurately too. There are populations of the brain that respond to those different objects too. 
Speaker 9:	In terms of what we have already studied, is this [inaudible 00:26:46]? What aspects of this is sort of like [crosstalk 00:26:51]
Chris:	I don't know if any of it is. I mean honestly, people discovered the fusiform face area in the 80s or something like that, 70s, 80s I think. Is that about right? Yeah. That research has been around for a while. It's not super surprising. As they start to be able to target these areas more precisely, and record from individual cells, that aspect of it has been pretty new over the last ten years. All of this research is from 2006 to now. Just in terms of other connections with things, autism is a really interesting connection with face perception. It turns out that they actually have often reduced activity in the fusiform face area when viewing faces, and also in emotional parts of the brain that also respond to faces. Something called the amygdala also has reduced responses. 
Speaker 1:	Chris, I was amazed at when you were showing the faces and the monkeys response to them. I mean, I guess I'm slower than a monkey, but I was amazed at how quick. There was no delay. In my brain, at least by the time I thought about it, or realized I had thought about it, I was a second behind. The response time is kind of amazing.
Chris:	The neuron knows you've seen a face before you do, right? 
Speaker 1:	I feel a little better.
Chris:	Because that readout from the neuron that says it's a face is going to have to go through a few more pathways, a few more steps, before you really have that picture and you realize it. It's incredibly fast. Yeah? Sure.
Speaker 11:	I know that you have examples of people who don't have the facial recognition [inaudible 00:28:49] an example [inaudible 00:28:51] for instance who won't recognize his own face in the mirror. Is that usually the case where if you have the condition where you're not recognizing, you're not going to recognize your own face, or you're not going to recognize any very familiar face? Is there a sliding scale that can happen?
Chris:	I think there's definitely a sliding scale. I'm not an expert on those disorders, but my understanding of prosopagnosia is that it is usually because of some sort of trauma, like brain damage. Obviously, that can be totally different from one example to the next. How much of the area is disturbed will determine how poor you are at recognizing faces. There's also a sort of other variance of those disorders. One's called Capgras syndrome, where people know that they're seeing a face, but they don't assign any emotional connection to it. They'll see somebody who might be their sister, and they'll know that it's their sister, they'll know that it's a face, and that it belongs to their sister, but they don't feel any emotional connection. They actually think that this person has been replaced with some double that they don't really know. It makes a very weird feeling for these people not to have that emotional connection. Different parts of the brain go wrong, and you get different aspects of the process gone awry. Cool.
Speaker 1:	Chris, thank you very much.
Chris:	Thanks, thanks.