 Mae'r danediolaidd enghraifftrifeidd iddyn nhw ddweud am y hyd nun. Ac ament wedi gyd yn gwneud ein headset na hwnnw atordebوي rwrth comp converts yn ddiwrnod y rheoddiolproblemau am ydyn nhwydeg milion minell inhaladau f été pha nhw, os hwn i'r newid fel hwnnw hynod atjedw��. Mae el ride gwaith adehoseth i lloedd am y newid mewn gwneud hefyd. Felly sefyd olw되 sp الل dda ni eich examples, i ddefnyddio mynd. a bwyddo annu'r lloniad wrth ddedw, if it is look around, as you turn your head it looks as if you are looking in this apparently undersea world and it look like a three dimensional world that surround you. So my question for tonight is when you have that virtual reality experience and tonight I am just going to talk about visual experience, the visual experience with your eyes that you have. Although there are very interesting questions to be asked about gyda'r bakedlaethau mynd y gallain i fynd bryd? Gall Dawr canidogaeth nhw y bydd ar dangos maen poweranı gynnall pan dylindodol mewn med pickledol, nid ei t 마�un, dwi'n dilyn but sy'n mynd i nad一定要o gyda'r hey yn yr hyn. Ond rham, dwi seddu yли ynbiellol y bydd yr hyn di proprietary o gennych cynn curs o latioedd lokl-ier ac oed yngỷ? Mae'r troi symud i fynd goffreio gymryd that's what a good guy has, and they put in on the headset and it seems to me that there's a jellyfish in front of me. we know that there's not really a jellyfish in front of me. I've been in the lab in Glasgow and there aren't any jellyfish there just to reassure you. It's seems to me if there's a jellyfish there. You might think that my experience must be inaccurate in some sense it must be illusory or hallucinatory. On the other hand, some philosophers have recently posited that you are having an accurate experience That's not because you're seeing the world around you, but you're seeing either virtual or computational objects. After all if you're seeing a virtual world, then maybe you're seeing accurately the virtual objects that inhabit that world. So there's this little debate that's broken-out within philosophy circles about how should be think of the nature of that experience. Is it illusory or hallucinatory on the one hand, cos, after all, there's no jellyfish in the lab or is it an accurate experience, ond o dae dwy o blwych yn gweithio'r uned yn swyddfa trynd i fynd ffilm. A cynnaeth hynny i maen nhw'n eich hwn o hyffordd yn rhan, mae'r ysgolai ei wneud yn cael ei cyfnod o elwysiwn a gwych yn gwagwch siwr i ddweud hynny o ddydd arweithio'r gweithio'r byd, a'r gweithio'r holl mwy o'r hwn o gwych y tu'r llawer yn allu Wyddan a'r eich bod yn dweud hebiau'n mynd i ddod y Llywgr Ieithi'n bwysig o'r cyfrifau ffordd, ac mae'n ddiddordeb i'r ffordd ymlaen, ac rwy'n ddiddordeb i'r ffordd, ychydig i fynd i'r lleolau o llwyddiol i llwyddiolau i'r lleolau, ac rwy'n ddiddordeb i fynd i'r lleolau o'r cyfrifau ffordd. I'r ffordd, mae'n ddod i'r cyfrifau ffordd, mae'n ddiddordeb i'r plann ffyllt. A oedd y hyn, I Laws of AEMreckend. This very first thing you ever taught is about Descartes, one of the lovely things about Descartes is one of the reasons we teach it to our undergraduates is that he have a plan. He had this plan and carried out it and it seems notably a result. All seems intellectually exciting. Descartes said, how can I figures out what I really know is in the world around me? He said I am going to have this plan to figure that out. I'm going to doubt everything that I can possibly doubt and see if we end up with anything that we cannot doubt and as we famously know, the thing he thought that we could... Well, he thought we could doubt everything apart from the thought that I think therefore I exist, right? Cogito ergo sum is his famous phrase and then once he'd found that I think therefore I exist he tried to then build up from that back to the sort of everyday knowledge that we think that we have. Now, often people think that part of the plan didn't go so well but it seemed like the first part of the plan went really well he did all this doubting and then he found something he couldn't doubt and it's kind of misleading to teach undergraduates this bit of philosophy I think because Descartes was one of the few people who ever had a plan in philosophy like this and so when I started to think about virtual reality for the first moment in my career I felt like I was like a proper philosopher like Descartes because I had this plan I developed this theory of illusion and hallucination and now all I needed to do was apply it to virtual reality experience and to come up with the right answer so what I'm going to do is first of all tell you about the traditional accounts of illusion and hallucination tell you why I don't find them good enough and explain what my theory of illusion and hallucination is and then in the later part of the talk what we're going to do is apply that theory of illusion and hallucination to virtual reality experience and see what it tells us we should think about it so that's the plan for the talk so just to begin then someone actually came up right at the start of when I was hanging about here and said what exactly is vertical experience so a vertical experience is an experience that's accurate about the world around you so at the moment I'm having experience that represents lots of people sitting in the lecture theatre and I take it that there really are lots of people sitting in the lecture theatre in front of me so my experience is a vertical experience and in this case it's a perceptual experience so I really am picking up information about the world in perceiving you and we can contrast that with the illusory experience and so everyone's pretty much agreed that in the illusory experience you are seeing the world you're just seeing it inaccurately in one or more respects whereas in hallucination you have an experience in which it seems to you as if you're seeing the world or perceiving the world but it merely seems to you as if you're seeing the world you're not seeing or you're not perceiving the world in some respect okay philosophers usually think of a total hallucination so that everything you're seeing is hallucinated but we know that sometimes people hallucinate single objects within the world that they see okay so to begin then let me try and tell you a little bit about what the traditional accounts of illusion and hallucination are so here are the standard definitions so in traditional illusion you're supposed to perceive some worldly object and I say some worldly object here because some philosophers think that when you see there are really mental objects called sense data that you see so I'm not talking about any special weird philosophical mental object I'm talking about tables and chairs and people and cameras and computers and so on so according to the traditional definition of illusion you perceive some worldly object but you misperceive one or more of its properties so for example you might be looking at a blue car but there's funny street lighting lighting up your street and so you don't have an experience as of a blue car you maybe have an experience of a purple car so you're seeing the car but inaccurately so in some respect in this respect vis-a-vis its colour but of course you might be inaccurately seeing it on an occasion because you see it as mislocated maybe you see it as being shifted over here or maybe you see the shape as distorted in some way okay so here's a quote from a philosopher contemporary philosopher AD Smith he says illusion is any perceptual situation in which a physical object is actually perceived but in which that object perceptually appears other than it really is so this is just the standard account of illusion that everyone thus far really has bought into so in contrast to the case of illusion here's the traditional account of hallucination that people get so you have an experience as of an object and its properties but there really is no worldly object and there are no worldly properties that you're perceiving in virtue of having that experience so just to give you an example again so you might have an experience as of a blue car but you're not in virtue of having that experience seeing a blue car or indeed any other worldly object you're having this experience but you're not seeing a car now one thing that's really important to note is the case of what's called veridical hallucination so for the most part when people hallucinate their experiences are inaccurate right so when Macbeth hallucinated and he asked is this a dagger I see before me the question was no there's no dagger there right and that was sort of his clue to knowing that he was hallucinating sort of play a hideous trick on on Macbeth I might ask him what's this dagger like that you keep seeing and he might tell me about its nature and so on and I might go off and get one made that exactly replicated the one that he seems to see when he has these hallucinations and at the point when he says to me you know Fiona here I am hallucinating this dagger again I might run in with the dagger and place it right in front of him in the very spot where he seems to be hallucinating the dagger now in this weird situation he would be having a veridical hallucination he wouldn't be seeing the dagger but his experience would be representing the world accurately it would be representing the fact that there really was a dagger in front of him okay so we've got to note that special case of veridical hallucination okay so before we proceed it's important for me just to tell you a little bit about the standard philosophical account of perception now there are lots of different accounts and particularly different philosophical accounts of perception and but for our purposes if we understand the standard account then we can use this to try and motivate my own theory of illusion and hallucination and do more than just back up certain intuitions that I'm going to try and elicit from you about various cases in which I'm going to ask you to say whether you think they're perception or illusion or hallucination okay so first of all according to the standard account of perception when we have perceptual experiences those are experiences that represent the world to be a certain way so at the moment if I were to describe my visual experience to you I would say well I'm seeing a lecture theatre and I'm seeing chairs and various people sitting in it and in so doing I'm describing what my perceptual experience represents the world to be about and you might think that and a lot of philosophers do think that there's not much more you could ever say to get across the nature of your experience other than say what it represented if I wanted to say in more detail what my experience might be like I might say well the chairs are blue and they're over there and they're this shape and so on and so forth but I'd just be saying more about what the experience represented perhaps one exception to that would be to talk about the modality of the experience was an experience of seeing or hearing or tasting or smelling and so on but apart from the modality really the way we get across information about what our experience is like is by saying what they represent what they're experiences of okay so this account seems quite intuitive because when we go to describe our experiences what we end up doing is describing what they represent what they're about now as well there's a kind of commitment to this idea that our perceptual experiences represent the world around us another kind of key constraint about what happens about what goes on when you perceive the world is that you consciously perceive the world if and only if you have some conscious perceptual experience that at least closely matches the way the world is in front of you and moreover that your experience is caused in the right way by the world now the reason for that extra clause goes back to thinking about the case of vertical hallucination just because you have an experience that matches the way the world is that doesn't tell you yet whether you're hallucinating or whether you're seeing the world because of course you could be in this strange situation where what you hallucinate just so happens to be walks out there in the world in front of you so people usually add this causal clause to make sure if you like that there's a connection between you and the world to make sure that it's because the world is the way it is that you're having the experience that you're having in other words your experience is sensitive to the world so that you can be truly said to be gathering information about the world and that's thought to be necessary for perception so the thought is there has to be this causal connection between yourself and the world and your experience has to at least closely match the way the world is in order for you to be said to perceive the world okay and on this account to say there's an experience that matches the world is just to say that your experience represents the world accurately or correctly another way of seeing that in philosophy and kind of technical jargon is to say that the content i.e. what your experience represents is correct and as i've just said you need to add into that correctness condition you need to add that there's a causal connection to the world so that you're genuinely picking up information about the way the world is okay so what i want to do is to show you that if you buy into this standard theory of perception then that standard theory will match up with what i take to be my accurate intuitions and what hope will be your intuitions too about how we should think about certain quite exotic cases of perception that might stray into cases of being illusion and hallucination okay so just to talk you through a sort of standard case of what of perception so imagine that there's a blue car and you're accurately seeing the blue car so you're seeing the color right you're seeing its location right you're seeing its shape right just a standard case of perception so according to the standard theory you would be perceiving the car if and only if you have an experience that matches the object and the properties in front of you and you can see up here that here's a cat in the world and here's my representation of your experience at the time you can see the experience if you like matches the way the world is and moreover we've got to say that the experience must be caused in the right way by the object that you're seeing okay so what is it for the experience to be caused in the right way good question well it turns out that there are lots and lots of different philosophical accounts of how we should describe that but sort of at base what most people agree is that the causal connection must be one of a kind so as to allow you to track objects and properties across a wide variety of perceptual situations such that if the car drove away and another car replaced it your experience would change and would update to reflect the nature of the car that was now in front of you so in other words what we want to do is to avoid that it's just luck making it the case your experience is accurately representing the world as was the case with Macbeth's dagger when I ran out and got this funny dagger made and ran in with it so that you're being sensitive to the way the world is in general okay so in a case of vertical perception where you're accurately seeing the world these conditions must hold you must have an accurate experience and have the right sort of causal connection to the world okay so that is the kind of standard account if you went to philosophy 101 and perception we'd tell you all this stuff in a bit more detail and think about objections and so on and so forth but why do I think that this account of illusion and hallucination that have given you thus far isn't correct well intuitively the idea is that I can set up a variety of strange cases of illusion and hallucination that first of all the traditional theory just would have nothing to say about them or second of all they would miss important differences between cases that our intuitions will say actually we need to mark those differences in other words this traditional theory just elides certain differences that we need to make sure are noted okay so just to get our intuitions up and running I want to start with a simple case so intuitively I think we can distinguish between cases of what I'm going to call property illusion from cases that I'm going to call property hallucination that are all taking place while we're actually perceiving an object now remember according to the standard account if you're perceiving an object and just getting one of its properties wrong all those cases should count as cases of illusion but what I'm saying is well some of those cases might be illusion but actually we should be classifying some of those cases as hallucination and not as illusion and that's why I think in part this is the first step in unpicking why the traditional theory gets things wrong and moreover we can back up that intuition with insights from this traditional causal theory of perception that I've just outlined to you so in other words what I'm going to introduce to you is a distinction between illusion and hallucination that the traditional theory just doesn't allow for okay so here's the kinds of cases that I want us to think about the intuitive contrast is between on the one hand a case in which you're sensitive to some property so that you can genuinely count as seeing that property but imperfectly so so that it's not just a case of accurate or veridical perception and on the other hand a case in which you're not sensitive to a property at all so that you don't really count as seeing it full stop so here's the example so imagine that you wear dark glasses right here you are looking at a light blue car and you stick on your dark glasses and you have an experience as of a car pretty much the right location the right shape but you see it as having a slightly darker color than it really has okay in this case you would experience an object and all of their visible properties accurately except for their color which you would experience as systematically skewed you would see everything as being a little bit darker than it really is because you've got the glasses on so I would say that this is a case where you're actually perceiving the color of the car but just in a systematically skewed or illusory manner why are you seeing it is because you're sensitive to the color that the car is if the car changed color your experience would change if it changed from blue to red your experience would change you would you would see it changing color you're sensitive to the way the colors are so intuitively I think this is a case of misperception and in addition the conditions on perception that we just discussed above are fulfilled so you're having a closely matching experience of a slightly darker car than the car that you're in front of one than than is really in front of you so you're having a closely matching experience and moreover the causal connection between the color of the car and your experience will allow you to track that color and other colors in a wide variety of scenes just because you're wearing dark glasses it doesn't stop me seeing the colors of things so that would be a case of property illusion so contrast that case with the following case which I think is a case of property hallucination so imagine that you experience objects as colored but which object sorry but which color you experience the object is having is completely random and why is that because we imagine that some evil scientist is zapping area v4 of your visual cortex which we know is responsible for you experiencing color so here you are strapped up to the evil scientist chair and you're looking at a light blue car and on this occasion let's say you experience it as being purple why do you experience it as being purple because evil scientist is doing what he's doing to your visual cortex so in this case you're not responsive to which object so to which color objects have so for example in this condition if the car changed color you would continue to experience it as being purple because the evil scientist is doing what he's doing you're not sensitive to the color that the car has so in these circumstances you look at car you experience it accurately except for the fact that you experience it as being purple when it is in fact blue and you're not though tracking colors in your environment in any sense but you are tracking everything else that's standardly visible so I would say that you're seeing the car you're seeing its location you're seeing its shape but in no sense at all are you seeing its color that the color you experience it is having is completely dependent on what the evil scientist is up to and not what the colors of objects are in the world so I would say that this is a case of object perception but property hallucination and that's just a case that the standard theory of illusion and hallucination can't accommodate so the conclusion thus far is that intuitively there's this distinction between property illusion on the one hand and property hallucination on the other hand that happen in nonetheless in cases where you really are perceiving an object and that's just a distinction that the traditional account of illusion and hallucination elides and so it's not a good account okay and moreover what I've shown you is you can back up that intuition using material from a standard causal theory of perception you can explain why we should think that way now at this point you might have a worry in about what I've been saying so you might sort of ask me look you know what's the criterion at play for saying that there's a closely matching experience after all in the kind of case I gave you of closely matching you were wearing sunglasses and there's a light blue car you put on your sunglasses you saw it as dark blue well intuitively that is closely matching but what does it take for something to be closely matching how close does this matching have to be and what exactly does closely matching consistant so one answer you might try to give here is that the experiences you have when you wear the sunglasses is phenomenally quite similar with respect to the experience that you would have if you didn't have the sunglasses on and you were seeing the car accurately so you might think well you've just got to look at the experiences and judge is the experience similar or not but I don't think that's a very good answer so it still doesn't answer well how similar what if you saw the car as purple what if you saw it as red what if you saw it as looking like a bird at what point do you say well that's not close enough matching and sure maybe we want to allow for some cases of illusion where the illusion might be really quite radical so there's a case where the philosophers think about a lot imagine you had a pair of inverting color lenses such that when you put them on you saw everything is having this sort of complementary color than the color really has so for example you wouldn't see the sky is blue but it's being yellow you wouldn't see red flowers as being red but being green so for every sort of color in the color view you would see the opposite one a lot of people think well you would still be tracking the colors it would just be that it was quite a radical or quite a big illusion that was taking place and if we went for something like well the experience has got to seem quite similar to you you wouldn't be able you wouldn't get to count that case as a case of illusion so I hold that what's required for there to be a closely matching experience is that there's a suitable causal relationship between the experience and the environment and moreover that you would be able to form some correct judgments about the property in question on the basis of taking the set of the the illusory experiences that you would have in the particular illusory condition like waning the sunglasses which you would have and if you took those experiences at face value you would be able to make some true judgments about the property in question so in the case of looking at a light blue car and waning the dark sunglasses you'd be able to make the following accurate judgments and if you just took your experiences as telling you accurately about the world the car is blue the car is darker in color than my car sitting beside yours that car is more similar in color to my car than it is to your car and so on so waning the sunglasses you'd still be able to make lots of true judgments about properties and for me that would count therefore as close enough and matching to count this case as illusion so this kind of thing would allow there to be large systematic kinds of illusion and I think that that's a good feature of the account but now on the other hand you might think well maybe I've gone kind of too far the other way maybe my definition is now too liberal and would count too many cases as being cases of illusion cases that we would would want to say they don't even count as seeing the world at all they should really be cases of hallucination so in other words perhaps this account that I've given you entails that too many cases of systematic mismatch would count as cases of illusion when we really shouldn't count them as such even cases that intuitively would not be so I want you to imagine the following strange circumstance suppose that whenever you look at a patch of color instead of seeing the color you had some kind of smell experience right some olfactory experience okay now suppose that when you were faced with different colors you would have systematically different smell experiences one smell experience corresponding to each color you might think intuitively that there's no way in this world that we should ever count an olfactory experience as being one that closely matches a color experience after all I chose this example to be as about as different as as we could possibly get but of course my definition would rule that some such cases are cases of illusion as long as you could make some true judgments about the world on the basis of those experiences so suppose when faced with red and then orange and then yellow you had systematically when faced with red a very strongly fruity smell and then when faced with orange you had immediately fruity smell experience and then when faced with yellow you had a very mild fruity olfactory experience this would obviously be a rather strange kind of situation in this case you'd have a systematic mismatch between the smell experiences and the color experiences but you would be able to make some true judgments about the world if you took your olfactory experiences at face value judgments of the form a is more similar to b than it is to c well of course red is more similar to orange than it is to yellow so as a result the worry is that my definition is going to count too many cases as being cases of illusion cases which you might think you know you can't count the c in colors in virtue of having an olfactory experience so what should i say in response to this well i think the first thing to know is that being of a close match admits of degree so whether my experience matches the world well there can be more similar ones and there can be less similar ones and in different cases there are going to be more or fewer accurate judgments that you can make about the world on the basis of taking your experiences at face value thus i think exactly where someone wants to draw the line and say okay you need to be able to make the this number of true judgments about the world in order to count with the best perception and where someone says well yeah that's not enough true judgments that you can make here that should count as perception i'm quite happy to think that people might vary as to where they want to draw that line in other words i think that the distinction between illusion and hallucination is really one of degree and i'm proposing that we put the line at a certain point if you can make some true judgment let's count that as seeing but i can understand why people might say yeah actually you need to be able to make more true judgments than that but i predict and in fact empirical research amongst philosophers suggests that actually people's intuitions vary about this color smell case some people say no no that could be a way of of perceiving the world by having these systematic smell experiences in response to color and i think that that kind of case is really on the cusp between illusion and hallucination because the number of true judgments that you can make about the environment based on taking your experience at face value are incredibly limited they're limited only to relative judgments you know a is more similar to b and so on but that's what you're limited to there's no further true judgments you could make in that case on the basis of your experience but i actually think it's a strength of my theory that it kind of predicts and explains why people's intuitions about this case will be kind of mixed why some people say yeah that counts as perception and why not and so i kind of like this account and if we want to sort of argue about exactly where to draw the line i'm quite comfortable with thinking that there's room for argument there but i think that the general framework is exactly right and nothing i say really turns on putting the line just exactly there as long as you're happy with the general methodology of putting the line somewhere based on how close of a match is your experience to the way the world is so in philosophy as soon as you discover a new case my sort of technique for thinking further about things is to try and start drawing up tables and trying to think about well what other weird cases might be out there so up here we have this table where we have basically what this represents is an experiences as of objects all having certain properties and you can see here that here we have a standard veritical accurate experience of the world where you veritably perceive an object and you veritably perceive one of that object's properties experienced is belonging to that object in questions that's just a standard case that we've seen in the world accurately and then here's the traditional illusion case where you're veritably perceiving the object where you're having a loosening perception of one of the object's properties experienced is belonging to that object and what we've done in thus far is to say well actually we need a box here that we can put a tick in where you're perceiving an object but just having a hallucination of one of its properties the case where the most scientist is exactly your point then and then we find that traditional hallucination lives in a box over here where you're hallucinating an object and you're hallucinating and a property is belonging to that object but immediately this opens up this kind of logical space here well could you have cases where you hallucinate an object and you have veritical or a hallucinating perception of one of that hallucinated object's properties experienced as belonging to it now most philosophers were thinking that's been the most bizarre how could you ever do up a case like that and how could you talk about accurate property perception of a hallucinated object that just seems bizarre okay so interesting cases to think about and then also we've got veritical perception of an object and a hallucinatory experience of an object could you ever have the illusory perception of an object well I want to conventionally connect ticks in all of these boxes and to start I want to start about talking about cases of how you could have cases of a illusory perception of an object this is just a set of cases that the traditional accounts of veritical illusory or hallucinatory perception just don't ever mention or everything could exist and I want to try and persuade you that they could exist at this point you might be starting to think it's gone on along a lot about weird cases in philosophy and I am going on a lot about weird cases in philosophy but we'll see that there's a really nice payoff when it comes to thinking about virtual reality we'll see that some of these kind of bizarre cases that seem why are we bothering thinking about those we'll see that actually when it comes to virtual reality experience we're going to discover that virtual reality experience is like a lot of these weird cases that we're discovering that we're discussing just now so how could we think of what an illusory experience of an object would be well my account of veritical and illusory object perception turned on the idea that in both cases there's got to be this suitable causal relationship between your experience and the environment the difference is that in veritical perception you form holy accurate judgments about the way the world is if you took your experience at face value whereas in the case of illusion at least some of the judgments you make will be false about the way the world is okay now you can apply that idea to object perception so here's how I do it think of someone or a detector or a machine or a person who could who was an object detector if you're an object detector you could be a better or worse object detector you could be really accurately checking the presence of objects or you could be really very bad at detecting the presence of objects okay if I'm a perfect object detector I will detect objects when and only when there are objects present and of course people aren't perfect object detectors we make some mistakes like when we hallucinate we think there are objects in front of us when but consider someone who had some form of systematically skewed object perception for example suppose that they systematically experienced two objects as being present for every one object that really was present so imagine that they have a kind of form of double vision okay now most of us have double vision if you take your finger and you look at it and you stare at it and you pull it up really close to your eye there's a point at which it suddenly seems as if there's two semi-transparent fingers floating in front of your face and so we're kind of familiar with a form of double vision but in this kind of situation we're not really tempted to think that there are two objects there basically because you know what's going on and both fingers look semi-transparent they don't look like you'll solid fingers in front of you okay but imagine an idealised version of double vision in which the two objects that you experienced were opaque just like your normal experience of a finger and each seemed so imagine that I'm looking at one finger here but I experience let's say one finger one inch on either side of where the actual finger is okay so you might think that experience of one of these fingers amounts to seeing the finger that's really there and the other one doesn't maybe it's a hallucination of that finger or something like that that's a possibility but the problem of that view would be to choose which one's the hallucination and which one's the real deal which one's really perceiving that finger especially if each one was you know an inch on either side of the finger and each one in other respects looked exactly like the finger in front of you so I think in this kind in these kinds of cases it's more plausible to say that the experience of each object the two apparent fingers amounts to perception of the object what's going on is that you're seeing your finger twice in virtue of having these apparently experience of two fingers each one amounts to seeing an object and that's a view that the philosopher E.J. Lowe advocated and I think that I think that this is right I think this is a good account of this kind of double vision so in double vision there's going to be a suitable causal relationship between your experience and the environment that leads to systematic skewing for every one object present you'll see too okay so there's going to be you're going to be tracking objects just in a systematically incorrect way you see for two for every one that's there taking your experience at face value of course you'll form many incorrect judgments about what's out there in the world right so if I'm holding up this number of fingers and if I do my experience at face value and I had double vision I would say well there are six fingers there and obviously that's going to be false right but I will be able to make lots of correct judgments such as there are twice as many objects here as there are here right so in this kind of case where there's a systematic skewing of your experience of objects in this case double vision I would say this is a case of object illusion you're seeing the object but in an illusory fashion you're seeing two objects for everyone that's there and again this is a case that the standard theory of illusion just doesn't account for it doesn't even think exists okay so I think that we can put a tick in this box there are cases of illusory perception on object and of course there will be cases where you've veritably perceived some of the properties of that object so if you're having double vision of the finger you might perceive the color of the finger right you might have illusory perception of one of its properties so for example you might be wearing dark glasses and see the color in a systematically skewed way and of course you could be having a hallucination of the color of the finger when you're seeing it in this double vision form because some evil scientist is zapping your brain and causing you to experience the finger as purple in some way that's unrelated to the color that the finger really has okay so I think we can put ticks in all of these boxes and now we come to think about well what's going on here well before I tell you about what's going on here I have to tell you about another weird case philosopher's life from weird cases okay so that's why we talked about veritical perception of one of an object's properties experience as belonging to the object now why are there being stress in that well that's because you can imagine cases where you can have veritical perception of another object's property experienced as belonging to a first object okay so let me try and explain that kind of case to you before we get on to these hallucinatory cases so suppose the following suppose every time you see an object at the center of the left hand side of your visual field you perceive it accurately except for its color suppose that the color you experience that object is having depends on the color of the object that's really at the center of the right hand side of your visual field okay so imagine here I am and in the center of the left hand side of my visual field is a car and let's suppose I perceive that accurately in all respects except for the fact that I misperceive its color what color do I experience the car is having let's suppose that that's the term by what's over here in this case a red tomato so I experience the car as being red in this case you're suitably causally sensitive to the left hand object and all of its visible properties except for its color so you're suitably sensitive to its shape and its location and so on and you're suitably sensitive to the color of the right hand object the color of the tomato it's just that you incorrectly attribute the color of the tomato to the car you incorrectly attribute the color of the right hand object to the left hand object creating a non-vedical experience you experience the car as being red when it's not well you might think as we've said thus far you know surely you've kind of left the planet now Fiona right I mean you know this is such a bizarre case that you're describing why do we need to think about this case well actually we know that there are real-life cases like this that psychologists discover in the laboratory so there's a very famous case called cases of failures of binding which are just like this so if I showed you a red square next to a green circle but I showed you that for a very short period of time you're highly likely to report to me seeing a green square next to a red circle and so what's going on is that you're detecting the colors and you're detecting the shapes nobody suddenly reports seeing a blue triangle right you're detecting the shapes you're detecting the colors but you're sticking them together if you like in the wrong way well that kind of case is exactly the sort of case I'm describing and what I like about this is that based on philosophical exploration of what's the logical space of all the possible cases you could find you actually find a real-life case like this it's non-phyridical perception it's illusory but the standard theory of illusion and hallucination doesn't account for this case at all and I think that that's why my theory is good because it allows us to account for these unusual cases if you want to read more about failures of binding and the standard references and treesmen and colleagues okay so what we've done then is put a tick in this box here where you were politically perceiving an object and in this case the car and you were experiencing and perceiving another object's colour as belonging to that first object okay so can we put a tick in this box here could you have a case of hallucinating an object but perceiving an object's property is belonging to that hallucinated object I think we can so again suppose that at times you randomly visually hallucinate an object at the centre of your visual field and let's suppose at other times you experience nothing and imagine that when you so hallucinate none of the properties that you experience the hallucinated object is having are dependent on the way that the objects are in front of you in the world except one let's suppose that the colour of the object that you hallucinate is actually determined by the colour of the object that really is in front of you in the centre of your visual field so let's suppose that there's some evil scientist that zaps your brain from time to time that causes you to randomly hallucinate some object in this case a pick but let's suppose that in those conditions for whatever reason that we care to elaborate on the object that really is at the centre of your visual field in this case a green house is such that you detect its colour but you attribute the colour of the house to the pig so that you experience a green pig okay I would say that what's going on here is that your hallucination of the pig is not counterfactually sensitive to whether there's an object in front of you because you have experiences of these objects at random based on what the evil scientist is doing to your brain but your experience matches perfectly and is counterfactually sensitive to the colour of the object that's at the centre of your visual field in this case the green house thus you hallucinate an object but you viridly perceive the colour in front of you and you inaccurately attribute it to the hallucinated object and that is the exactly this case here so now we've got this case in question and ready to try and talk you through these rather the most bizarre cases of all if you like thus far so suppose at certain times you randomly viridly hallucinate an object at the centre of your visual field and at other times you experience nothing and imagine that when you so hallucinate like the last case none of the properties that you experience the object is having are dependent on the objects in front of you in the environment except one let's suppose again that the colour of the object that you hallucinate is determined by the colour of the surface that's really in front of you but imagine that it just so happens that when the evil scientist zaps your brain and you hallucinate at random let's suppose you hallucinate Michael Antelos David let's suppose Antelos David in this occasion that was in front of you in the world and that you experience the whiteness of the marble and you attributed that colour to Michael Antelos David this would be a case where you're hallucinating an object but you're viridly perceiving a property of that object experienced as belonging to the hallucinated object okay so we can put a take in this box and of course you could imagine a similar case where you perceive the colour of the object but just in a systematically skewed way because for example you were meeting dark glasses now I'll let you fill in this box for yourselves and then we know the general way of the time to find these faces I'll leave that one to you but actually our table is hiding a whole bunch of other exotic cases because here I've been discussing viridical perception of another object's property experienced as belonging to an object but of course basically you could have viridical illusory or hallucinatory perception of one of an object's properties experienced as belonging viridically or illusory or hallucinatory to another object so there's a whole bunch of cases that you can pack in there as well right so far so good that was the the the theory that I came up with about various kinds of illusion and hallucination that the standard theory didn't account for and now the question is suppose you take that that account and you now turn to look at virtual reality experience what does that account tell you about what's going on in virtual reality experience so are the sorts of current visual experiences that we have in virtual reality while using devices like the Oculus Rift or the HTC Vive other devices makes are available and are they on the one hand illusory or hallucinatory or are the viridical perceptual experiences of virtual or computational objects well discussion in the contemporary philosophical literature makes it seem like the answer is one or the other that either the viridical of these virtual objects or their illusory or hallucinatory because you know there aren't jellyfish in my office when I put on the VR headset so here's someone just a very famous philosopher some of you may have heard of him David Chambers he's written a paper recently in 2017 called the virtual in the real he says the most common view is that virtual reality is a sort of fictional or illusory reality and the what goes on in virtual reality is not truly real this view naturally goes along with the view that experiences in virtual reality are illusory okay and the opposite view virtual reality is a sort of genuine reality virtual objects are real objects and what goes on in virtual reality is truly real and experiences in virtual reality are non illusory in other words they're viridical experiences of virtual objects so there's the debate set up for you okay now I think that this conception of the debate doesn't for a start take a proper account of the way the contemporary technology works and secondly I think it has a really metaphysically impoverished conception of illusion and hallucination because it has the traditional account in mind and so I think that once we apply my more complex view we'll see that things are far more complicated than are traditionally thought therefore the standard conception of the debate presents us with a false dichotomy it's either all vertical or virtual objects or it's all illusory or illusory because those objects are merely virtual thus I think that the modern debate really fails to understand and appreciate the complexity of virtual reality experience so why do I think that it doesn't take proper account of the way that the contemporary technology works well virtual reality experience when you put the headset on and you experience that you're under the world sorry under the water looking at jellyfish and so on and it doesn't just involve an experience of a virtual world it also involves perceiving the two screens that are mounted on the inside of the headset so when you look at one of these headsets close up there's a screen here there's a screen here and when you put it up against your face your left eye sees one screen and your right eye sees the other screen okay and I think it's really useful in thinking of virtual reality experience to start by comparing and contrasting it to a series of far more familiar experiences that we're all far more used to having so think about seeing a picture or watching a film of a real world event right so imagine that you're watching the blue planet and David Attenborough has filmed a jellyfish migration and there you are sitting at home watching the jellyfish migration on television a really commonplace event this is a perfect model of indirect perception you see the jellyfish migration that David Attenborough filmed in virtue of seeing something else in virtue of seeing your television screen okay as was mentioned I'm a partic thistle fan occasionally I get to see partic thistle playing a football match on television I get to see the game in virtue of watching my television screen so I see one thing in virtue of seeing another thing okay in this case where David Attenborough's filming the jellyfish you indirectly see the jellyfish in virtue of directly seeing your television screen and what's true of that kind of case of indirect perception is that if you weren't seeing the screen you wouldn't be seeing the jellies it turns out that if you're a jellyfish expert you call jellyfish jellies and not jellyfish because jellyfish aren't fish that's my little bit of jellyfish trivia for you so now consider what happens when you see a 3d movie or a 3d image basically it consists of what's called a stereogram or in the case of a movie or a film lots of stereograms in quick succession which basically is two offset two dimensional images one displayed to each eye of the viewer and there are lots of ways to do this if like me you're a child of the 70s you will remember this wonderful device the view master right so is a card that you slot in and basically opposite sides of the card there are two images that are very similar to each other one's just offset a little bit from the other and you look through and you don't see you know one eye is looking at one image and one eye is looking at the other image we don't see two images you have an experience of one three-dimensional world okay so it's like one eye sees this one eye sees this that you see a three-dimensional jellyfish and many of you will have been to 3d movies at the cinema the way that works in is that they basically put a kind of blueish image and the red image of the same object overlade on each other and then you get these very sexy glasses to wear one has a blue filter that makes it such that the blue image doesn't reach this eye one has a red filter which makes it such that the red image doesn't see reach this eye so the each eye sees a different image but of course you don't appreciate that you're seeing the each eye is looking at two images rather you just have this one experience of a three-dimensional jellyfish so clearly in these kinds of cases you don't have an experience that represents two two-dimensional objects you have an experience of one three-dimensional object of course information from those two two-dimensional objects is being picked up by your eyes and your brain right if you weren't picking up information about the images on the screen you wouldn't be seeing what you were seeing so what's going on is that systematically your experience represents one scene in front of you one jellyfish in front of you when really two are present now you should be thinking this is the reverse of double vision vision for every two objects present you see one so as your experience is counterfactually sensitive to the images in front of you we have good grounds for saying that you're seeing those images but quality objects of perception you're seeing those objects in an illusory fashion you're seeing half the number present than are really present so that's thinking about object perception but what's going on with the property perception in these kinds of stereogram cases are there any features that are experienced actively well what about the shape of the jellies well arguably yes the outline shape of the of the jellyfish in the two two-dimensional models gets transferred and becomes the outline shape of the one three-dimensional jellyfish that you apparently experience so the outline shape of the jellies is accurately perceived your counterfactually sensitive to it if it changes your experience will change too so this is a case of vertical perception of an object's property in this case its shape experienced is belonging to an object that's illusorily perceived because you have this kind of half vision qua objects so in other words we can put a tick in this box it's illusory perception because it's half vision but you're accurately perceiving the shape of the object and are there any features that are experienced inaccurately well yes the location of the images is inaccurately experienced there's one image here and there's one image here where you see a three-dimensional jellyfish here in front of you okay so this would be a case of illusory perception of one of an object's properties experienced as belonging to an illusorily perceived object so here we get to put a tick in this box vis-a-vis the objects on the screen that are in front of you now suppose these images were generated by David Attenborough filming a real world event of a jellyfish swimming under the Pacific Ocean you would thereby be seeing I suppose it's a movie rather than a still photo you would thereby be seeing the event of the jellyfish swimming in this indirect fashion in virtue of seeing the two images that are each shown to each eye so this is a case of indirect perception you're seeing the real world event of the jelly swimming in virtue of seeing the succession of two images that are shown to each eye in this case your experience is counterfactually sensitive to an accurate about many features of the jellyfish we could set things up so that you see the shape of the jellyfish accurately by seeing the tv you see its colour accurately and so on but of course it's going to be inaccurate about its location so when you sit and watch the tv it looks like the jellyfish is right there in front of you but of course the jellyfish that you're seeing was swimming away on this Pacific Ocean which might be over there somewhere so you're going to be inaccurate about the location of the object you're going to be inaccurate about the time of the object swimming it was filmed three months ago and here you are today sitting and watching the jellyfish so but you're going to be right about the temporal order so you know the jellyfish swims like this and you're seeing the right you know the order in which it's swan and the order in which it moved its jellyfish bits and I never thought I would be imitating a jellyfish standing up here okay so you get the you get the idea so there's going to be um you're going to be viridly perceiving the object the jellyfish qua object there was one jellyfish and you're experiencing one jellyfish and then you're going to have a mixture of viridical perception of its property say it's shaping its colour illusory perception of its property say the location of the object and the order of the timing and some of of the properties will just be illusory like the time of occurrence of the swimming so you can see here that we've got this quite complicated picture vis-à-vis the objects of the screen we've got these boxes picked vis-à-vis the jellyfish swimming under the sea we've got this object and we've got these boxes picked moreover we've got a case of indirect perception so you're seeing or experiencing certain of the jellyfish's properties in virtue of perceiving the properties of the object on the screen so basically you have viridical and illusory perception of another object's properties the screen experienced as belonging either in the viridical illusory or hallucinatory fashion and belonging to the jellyfish so basically we get to put a tick in this box and this now explains the indirect perception now if the images that you are seeing were generated by a computer rather than being generated by a filming of the jellyfish under the water then the options that are cited in the literature for what you're experiencing are either some non-existent illusory or hallucinated jelly or a viridical experience of a virtual or digital jelly okay so here's what David Chammer says about that second option that's the option that he likes he says what you see are digital objects to a first approximation they can be regarded as data structures located in the computer okay so here's Chammer's view the data structures perceived are the ones that produce the experiences of the objects in VR so the the idea is something like this suppose you put the headset on and you're experiencing the jellyfish the idea is that there will be a data structure in the computer corresponding if you like one on one T to the jellyfish and to the extent you're experiencing the virtual jellyfish you're just experiencing according to Chammer these data structures in the computer according to my account what should we say about this about what's going on here well i would say that we would viridically perceive the data structures qua objects if the right sort of tracking exists if there's a kind of one-to-one correspondence between the number of jellyfish or objects easy in virtual reality and the number of data structures that are producing those objects and of course in some computational setups you could ensure that that was happening okay it needn't happen VR needn't be set up in that way but let's be kind of kind to Chammer's and let's suppose that it is set up in this way because it's only if things are set up in this way you could get any sort of tracking of virtual objects so do we viridically perceive the properties of those data structures well obviously not right when you put on the virtual reality you need know nothing about computers and data structures and what's going on and so on you experience pink jelly shaped objects in the space in front of you and there are no pink jelly shaped objects in front of you answering to something that's in the computer those are simply properties that data structures lack and of course likely those properties of the jellyfish being pink being here having the shape will correspond to properties of the data structures right that's it is these properties here that will be driving the display of different properties on the screen so that will be counter factually sensitive to properties of the data structures but we won't be accurately representing those properties we'll be representing really quite different properties pinkness in the shape of jellyfish and so on and so forth now could we form correct judgments about the properties of the data structures on the basis of taking our experiences of the jellyfish at face value well at best you could form comparative judgments you might be able to form judgments of the form this jellyfish is more similar to this jellyfish than is that jellyfish therefore if you took your experience of face value you might say well you know really what you're judging is that this data structure is more similar to this data structure than is to that data structure so at best you would be doing these kinds of judgments is more similar to be that it is to see at best you could be getting those kinds of judgments correct about the data structures and as we saw previously whether that is enough to count this is a case of perception and a case of illusion or whether we should think of that as a case of illusion if you remember that was right on the cusp it's like that kind of case divides people so it's kind of hard to say whether it's illusion or hallucination but it definitely is illusion and hallucination you're not accurately seeing the properties of the data structures okay so what what are we seeing these are the the properties of the data structures well if you're tracking those data structures accurately because there's a one-to-one correspondence between them and what's on the screen you're having a vertical perception of those objects qua objects but you'll either be having a illusory or hallucinatory perception of the properties of those objects you're not having a vertical perception of the properties of those objects so that's why we should put two ticks in the box here qua computational structures of course qua the objects on the screen we know that we should be putting the boxes in here and of course again we've got this nice explanation of indirect perception the reason that you are experiencing illusory or hallucinatory in an illusory or in an hallucinatory way the properties of the data structures is that you're doing so in virtue of perceiving either accurately or in an illusory fashion the properties of all the objects on the screen so we get to put a nice tick in this indirect perception box and of course suppose that you're looking at a screen and thereby seeing data structures and thereby that's actually recorded a real wide event of seeing a jellyfish swimming then you're getting this doubly indirect perception you're seeing the jellyfish in virtue of detecting the computational structure in virtue of detecting the properties on the screen so you get this hugely complex of three lots of objects being perceived in these fashions and of course you've got this double indirect perception rule on the top of that as well so the conclusion is that virtual reality experience involves a real wide variety of veridigol illusory and hallucinatory elements if you're interested in illusions I would like to point you towards the illusions index which we run and if you're interested in practical VR applications we are developing virtual reality applications for teaching at the University of Glasgow please go to this website and you can see details of those projects there thank you very much so like everything there are different ways to define counterfactuals but the standard the kind of standard thing is supposed to be something like this suppose I'm looking at the glass okay what what we want to ask as they actually are in other words if we were in a counterfactual situation in some way other than the way things are what we're asking is would my experience update depending on what the counterfactual was so if we replaced the glass by a pen with my experience update and now represent the pen as opposed to representing the glass that's that's the gist of it does that satisfy you in the audience not just myself but for my son I want to go back to the very beginning and challenge your assertion that the car is really blue when seen under a sodium light isn't this concept really blue completely smooth over the fact that the whole matter of colour is an interaction between substances that are on the surface of the object and the way things are light that are falling upon it and really using the word really it seems to me you are just implicitly assume that normal total spectrum of sunlight is what makes for real colour very fair comment I couldn't agree with you more so for the purposes of this talk I made a huge simplify explanation which were the properties that we're talking about like shape and colour and location are really properties of objects and they can be accidentally or inaccurately picking up on them and of course the case of colour is one of the hardest cases to actually make out that that's true not only because of the different variation in lights but because of the huge variation in perceptual systems so some people are colour blind as you go older the macula of your eye gets more yellow and you will make different very subtly different colour judgments we start looking at the animal kingdom we start to see teachers with many more types of eyes in the sectors and so on and even when we look at human perception as well as people who are being colour blind that are looked as if they're like super perceivers who are tetrachermats who can detect more colours and things so absolutely and I was making this huge simplifying assumption that obviously we do have colours and we can pick them up or not what's really interesting about thinking about colour in this more accurate and complicated way that we just are now is there's a real question about whether you can hang on to any sense of predictability in whilst taking account of different viewing conditions and different perceptual systems and there are some ways that people do that so for example some people think that objects just have multiple colours at the same time so this pen is both red and this in sodium light it looked pink let's say this pen is both red and pink and it's just that on one occasion we're picking up on one colour property of it accurately so in another viewing condition we're seeing another colour property of it but accurately so and similarly you can relativise that to perceptual systems so maybe someone who's colour blind and someone who's normal trachematic vision are just picking up on different but nonetheless accurate colour properties of objects so yes you're exactly right i skipped over all that but my system can nicely account for that because we can ask are there any properties that you're really tracking out there or not you might have to get quite confused at what those properties are i'll go back in a little bit thank you very much for your colour blind quite a lot anyway yes i have a house for this one is so blind you cannot tell the difference between the electric cable which is on and the grass which is cutting cutting so he doesn't use a pen he doesn't use an electric one having said that i also very luckily have a granddaughter Ada who is in three we told does she have visual perception of a 3d thing and the answer is probably not because she has to touch it and what has not been in the lecture this the other senses touch smell taste so we we see things in 3d we don't see 3d in television because television is flat absolutely our vision there's 180 degrees i can't remember what the vertical degrees are but it's 180 degrees and we see things in 3d because we've touched them and we experience it so if you were to show me a virtual reality of jellyfish unless i'd actually see the jellyfish for real i am looking at it from what it feels like other can give me a bad smell you can go for it but i don't know if they're red ones very good absolutely so of course there's lots and lots of topics that have not covered in this lecture in this lecture so i haven't talked about the development of vision and there are super interesting questions about to what extent in order to see do you have to match up your experience your visual experience with experiences and other modalities so very famously there was moll and news question if a man-born line were made to see would he be able to judge just by sight the difference between a sphere and a cube and moll and you thought probably not you'd have to have a good you'd have to probably have a good fuel first of all and there's now some good empirical research that suggests indeed more or less that's right so i haven't talked about how it is that we come to perceive in 3d one of the interesting things about virtual reality compared to tv is that you have three dimensional experience and indeed there has been a case of a man who had only two dimensional experience he was a neuroscientist in Canada and he went us to a 3d movie and he put the glasses on thinking this isn't going to work for me and he actually had an experience of 3d vision for the first time and actually persisted once he took off the glasses and left the theatre and he wrote quite a substantial article about how going to see a 3d movie had cured his 2d vision and given him 3d vision for the first time so you know there are a hundred interesting questions that you're asking that i didn't talk about and stand here all night and talk to you about it and we'll go get a glass of wine i'm very happy to talk to you about all of this. Okay, over there, a black jumper. Do you think analysis is easier to handle if you started off by defining hallucinations as a perception which cannot be shared as a purely private and the reality which you had a perception which could be shared which can be and not be shared between people but can be consensually validated that then needs you with the illusion can be shared which cannot be consensually validated if you received three starting definitions perhaps it might not be quite as complicated but you know i'll have that reaction. So i don't think that's a good starting point. Two very different notions of privacy that we might have in mind when we ask the kind of questions that you're asking and i think it's really important to keep them apart. So in one sense there's the thought that what goes on in my mind is utterly private to me and that you can't know really what's good on in my mind. I mean i can tell you but i can be lying right and that there's something very private and special about my own experience. Now in that sense in neither the case of hallucination nor in the case of accurately perceiving a world is can we share experiences each of our experiences is private to ourselves but now there's another sense of private in which you were trying to sort of say something like well a hallucination is private because you would just be having the hallucination and other people wouldn't verify it they wouldn't be undergoing your hallucination but with virtual reality that's not the case. In virtual reality i have a 15 person lab where i can get the virtual headset on 15 people and give them all exactly the same visual experience right at the same time where it's not accurate and easy to be wired. So in another sense of could you be having the same experience could two people be having the same experience at the same time and to be hallucinating the answer is yes. So i don't think that that's a good way of telling the private person and the definition of it doesn't help you cannot discuss what is really out of there bring down what nobody knows what it's really about so you get the first definition of your first and you set it up. No so on the first definition what i was saying was what goes on in your own mind is is utterly private and can't be shared all that sense. Now it was a separate question of given that we have our own subjective experience can we ever know the nature of the world and so on that's a that's a different question and i haven't i've been assuming that we can perceive the world i haven't been tackling the sceptical question of do we ever have a right to think that we don't accurately perceive one. Okay we have a question over here. Professor in the context of this lecture how do you describe dreams? So it's a great question so in the case of dreaming you at least seem to have a perceptual experience that what one thing that's strange about dreams is that when you're in the dream and having the perceptual experience you don't realize that often A the content's quite weird and that B the content is usually quite diminished in comparison to the typical everyday waking experience often once you wake up and you realize that your experience was A quite bizarre and that you didn't notice that at the time and B was actually quite diminished in in in comparison to your standard everyday waking experience. Now you're shaking your head lots of people have lucid dreams and very very vivid dreams and it's true that people can have those and i'm certainly not denying that but there's usually there's often a diminishment in content that you don't notice at the time that you do notice when you wake up so i would think of dreams as hallucinations of a forum of a very special forum and it kind of depends i mean there are very various different theories of what hallucinations are so some people think that hallucinations are just your own imagination that's mistaken for perception so that would be one account and there's lots to say about that and whether it's any good i myself think that there's a distinction at least of degree to be made of typical imagery and typical hallucination and i would say that dream experiences are are basically like hallucinations albeit sometimes distorted and weird and odd and one thing that's unusual is that you don't notice the oddness why you are dreaming but you do remember it when you wake up. We had a discussion last weekend about the erigite illusion and hallucinity however i feel that we in agreement with this gentleman that we've missed the real point of the lecture and that is the definition of virtual you talked about virtual reality in terms of seeing jellyfish and they've got the the things on and i expected to come along and have it more focused on the virtual aspect of it whereas i think the problem with the data comparison and mr challenge is that we are comparing a virtual creation a data creation with an actual experience and we really should have defined virtual before we started all the other definitions thank you um i guess one thing that i wanted to do was kind of leave that question deliberately open because my question was in advance about the nature of the virtual sport i said the virtual is merely virtual it's not real at all then i couldn't say that our experience was accurate these and the it because if it's not really it doesn't really exist we're not the question of accuracy doesn't even arise if i had said the virtual is really real and of course we're seeing virtual reality i would have taken a stance and said well we really are accurately seeing these virtual objects and that was precisely the question that i wanted to leave open now when we looked at the chammers quotes that i put up what he showed us was that the view that the virtual is real goes hand in hand with the view that you're really accurately seeing something and the view that the virtual is not real goes hand in hand with it's just an illusion not a hallucination and the point of my talk was to say it's not just one or the other it's a really deep and complex mix of those things and so i would say that in a way the the virtual is a really complex mix of the really virtual and the real i'm just following on well really just following on from the dream question and so how would memory or imaginational perceptual experiences fit into your screen because they're not they're things that we do all the time they're not very lucrative and weird circumstances so i'd like to see a lot of features that you were talking about in some ways on the same track you could capture the same criteria to capture yeah so typically when people have at least sensory imagery and sensory imagination then you have an experience that as david human said is less vivid and less lively than a perceptual experience now what is really meant by those terms is a hugely interesting question and something i think that has really been under explored but people recognise that there's a similarity in imagery and memory experiences and the perceptual experiences and then there's a question of well if your perceptual experience gives you typically knowledge of the way the world is what does memory experience give you well if it's accurate it gives you knowledge of the way the world was in the past and then what does imagination give you and philosophers have often said imagination can give you knowledge what's possible right if i visually imagine a golden mountain mean there isn't a golden mountain at least in my knowledge there wasn't one in the past but what i'm doing is creating something that i know could exist right you get a lot of gold and make it into a mountain so there's interesting questions about whether imagination can give you actual knowledge of the present so for example if i lifted up my computer and i held it i could probably imagine that i could get it through the door there just fine and so maybe your imagination can tell you about how things about how things are vis-a-vis certain of their properties like their shape and the fact that you could be able to get the computer through the door okay we're going to stop there just before i think your next lecture i'll just remind you that the next lecture is on the thought of a march and it's on an electronic scheme that's real or virtually interesting and the refreshments are available i'll just now send you the audience and i'd also like to thank you very much for doing what's really quite a complicated topic when i came i thought i knew what reality was there are certain things i hope weren't real for it well done now um you're not so sure i'm not so sure about illusions and hallucinations and i think that's what you're trying to prompt us to think that it isn't as straightforward as you are so on so join me please and thank you very