Everyone likes a good optical illusion, but fewer understand them. Today we interview Katie Tregillus PhD about her research on color perception and adaptation. Katie takes us through the strange and complex world of color, from basic physiology up to conscious perception. How can different people looking at the same image 'see' totally different colors? How do colored lenses change our perception of the world of color? And what are some of the craziest visual illusions and perceptual adaptations known in the field today? All this and more today on MindMatters.

Running Time: 01:28:16

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Dr. Katie Tregillus: It's really hard to disentangle what is actually real, sometimes, in terms of color and what is actually being interpreted by our brain.

Harrison: Welcome back to MindMatters everyone. Today in the studio we've got Carolyn joining us again and Adam.

Adam: Hello.

Harrison: And we are interviewing Katie Tregillus, PhD. She is an expert on color adaptation, that is her field. We are going to be talking about all kinds of weird things about vision and how your perception of color changes in certain circumstances, and the long and short term adaptations to color perception and things of that sort, so looking forward to it and welcome Katie to the show.

Katie: Thank you so much for having me. I'm Katie, I'm currently a post-doc researcher at the University of Minnesota, and like you said I study color and adaptation to color. I do a little bit of work with FMRI - looking at the brain's responses to color. That's my current job.

Harrison: Well the way in which I found you was that a few of us here had engaged in a quite heated debate at times about one of those viral pictures. I think the first one was, I don't know if it was five, six years ago - 'the dress' - "is this dress blue and black or gold and white?" Shortly after that there was another one about the shoes - "are they teal and grey or pink and white?" So I searched around and found this paper of yours, we'll include a link to it and maybe others that you think might be of interest to our viewers and listeners.

This one is "Long Term Adaptation to Color" by you and Steven A. Engle. It's kind of like an overview of pretty much this kind of field and all the studies that have been done. And one of the things that stood out for me is that there hasn't actually been, it seems, a lot of research on these kinds of color adaptations.

I guess to start out with, could you explain to us what you mean by color adaptation - what is a specific example of the kind of adaptation you're talking about...

Katie: Actually this might be a good time for one of those slides I brought. I brought a couple of demos. Slide '4' might be a good one to start with.

(Picture of slide is shown)

This is an example of very short term adaptation effect. So if you could just stare at the center dot for a little bit and just leave that for a second, then when I switch over to the next slide you should see a pretty robust after effect, it works really well if you go back and forth a little bit. This is an example of what we call an 'after image' or an 'after effect'. This is really commonly seen for example when you take a picture with flash, and you end up seeing that large black spot in the center of your vision for a while. That's another example of an after effect.

Essentially what is happening is as you're looking at these colors, your brain is starting to adjust to those colors, and after you've adjusted for a little while your brain is now kind of in a little bit of altered state. So when you go back to a neutral world, the neutral page (picture on slide), you get these really robust after effects.

Harrison: That reminds me... I've seen those before. I've done 'after image' things like in books and I'm pretty sure I saw them various times when I was going to school, as a kid. But there's a few other effects like that that I'm sure a lot of our listeners have seen like the one with contrast where sometimes it will be on a checkerboard, like a chess board surface where one of the tiles looks grey but it's actually the same color as maybe one of the white and one of the black ones. But because of the shadow, your brain kind of corrects for the shading so ...

Carolyn: So it makes sense...

Harrison: So it makes sense, yeah, I'm not describing it very well but... Or am I? Is there a better way to describe that, Katie?

Katie: I think you're describing it exactly correct. So essentially, similar to what I just showed, your brain is constantly making these adjustments. So some of those adjustments happen across space in your vision, so you're kind of compensating for different effects and making these kinds of internal calculations about what might be happening in the scene. So for the example that you gave, where you might see something in shadow, your brain is now compensating for the fact that there appears to be a shadow in that location. So even though the color might be physically darker, you start to perceive it as lighter because you're kind of compensating for that shadow - you're getting this context effect.

Adaptation is kind of similar in that way but it happens across time. So as you start to see things, the more and more your brain starts to kind of adjust for what you're looking at and make some kind of compensations so that you can perceive something more accurately. I think the cool thing about a lot of these illusions is that, yes they are technically, you're not seeing what's actually there and that's what makes them an illusion, but the mechanism exists so that you can see things more accurately in the world.

I think you talked about 'the dress', the dress I think is a perfect example of this because a big part of why it happens is because some people are perceiving that dress to be kind of in shadow. So if you look at the image, essentially what's weird about it is that it's really low quality (laughs)... it was taken with a really bright flash. And in addition to that, in the very top corner of the dress, there's a really bright patch that people could perceive to be maybe a window. I think what it actually was, was a mirror that the flash is reflecting off of. So the people who perceive that to be kind of a mirror would say that this dress is really back lit and those people tend to say that it looks white and gold. But the people who had perceived, I guess correctly, that there was just a bright flash that's actually washing out the colors of the dress could perceive it to be blue and black.

So that's the kind of explanation that we have right now for the dress. As to why it's so 50/50, is really weird and what makes it such a unique thing. And it's such an exciting thing because - why was it so split? We still don't have a great answer on that.

Harrison: There was a paper I found after reading yours that was on that picture and it was really long, I think it was thirty pages or something, but what they found was that they could basically prime subjects to see it either as either front lit or back lit. So they could actually change the numbers of people that would see it in one way or the other. I can't remember if it was 50/50 to start out with but they could roughly shift it so that 75% of people would see it one way or the other way, just by giving cues that it was either in... I think the way they did it was they superimposed the dress on a wider scene where there's a woman wearing the dress where it's obviously in shadow, and one where it's obvious that the sun is shining directly on it. So again, seventy five percent or so of people would see it according to the context of the picture around it. But there were still some who weren't, which was interesting, and there were even some who saw different colors - it wasn't just those two sets of colors, there was a range and I think it was between 3 and 5 different colors for each one. I can't remember, I looked at the paper weeks ago, but one when I looked at it, I could not fathom that anyone could see one of the colors that was listed. It was a small percentage but it was very strange.

So that's one of the effects or phenomena that you talked about in the paper is that there are large individual differences in these types of phenomena. So could you maybe tell us a bit about that or give some examples, or just speak on it...

Katie: Sure. So the dress, I think is one of the best examples of individual differences for perceiving this kind of phenomenon. And there are other bi-stable allusions that are similar to that, not necessarily color ones, but I think everybody has probably seen the one with the ballerina that looks like she's turning one direction for some people and the opposite direction for the other people. It's difficult to explain why you get these individual differences. It could be because of certain factors, there are some people who have tried to correlate things like the dress with age, gender, time
spent on the internet - there are all kinds of different factors that could be contributing to why you might see it one way or the other.

Harrison: Is there a best guess so far or is everything kind of like up in the air still?

Katie: I think older people and women are more likely see it as white and gold, but I don't even think that's a very strong correlation. I'm not sure about the shoes. That's a little newer and I'm not sure if there's any kind of distinct purpose on that. The shoes I think are really interesting because a big part of why people thought the dress works so well is because it happens on along this daylight locus, so it happens in this blue to yellow region which is where most colors that we see in our daily life exist... And so we tend to confuse them a little bit more than we do with red and greens. The shoe doesn't quite fit that same narrative, so it kind of threw a wrench in some things, I think.

So there's not a great way to figure out which people might see these bi-stable illusions one way or which people might see them in another way. But what's cool about individual differences is you can actually use them to understand the mechanisms that underlie those things, so you can actually analyze the amount of variance and the number of ways that people vary with these different illusions and start to understand - ''well, are we consistently getting variation along this certain dimension of stimulus space?" - and that can kind of give us a hint as to how many different ways this could be interpreted, and how many different mechanisms might underlie that particular perception.

Carolyn: One thing that I wanted to ask, was when you were talking about speed of adaptation in your paper, when you would park somebody in with yellow lenses or red lenses, and one thing I thought is that it was really kind of sad that the sample groups were so small but I guess it's really hard to persuade a large number of number to let you like - "can I screw with your vision for like the next month?"

Katie: Why don't people want to do that? (laughter)

Carolyn: But I sort of had this fleeting idea that it would be interesting to maybe run your cohorts through a big 5 personality, because we actually were talking about this earlier today that there were sort of two hypotheses of who adapted the quickest and we could have gone with either the really conservative rigid personality would want to snap their world back to what they are used to really quickly, because changes is like 'ick'. So whatever the red lenses, or whatever, that they would swing back to their proper world view. Or, the other equally possible thing in my mind would be that that open personality would just go "hey, cool", and go with it. So it would be interesting to see should you ever be able to round up enough of the sample group to make it worth doing something like that.

Katie: Yeah, it's a really interesting idea. I will say that part of the reason I love studying vision science in particular is because I think personalities like in these other kinds of 'top down' psychologies are really difficult. It's hard to explain a lot of the variables that go into what helps someone develop those kind of executive function personality, decision making... I have so much respect for the people who study that, but it's always confounded me because it's so many kinds of things that you have to try to explain all at once. That said, I will say a lot of the time when we do these studies we try our best to kind of trick people so that they're not using as much of their 'top down' influence, especially with things like our lenses. We try our best to kind of put them in an environment where it's hard to make a choice that's not just totally based on their perception. It's obviously very hard to do that kind of thing but... especially with the lenses, like you were talking about - we try to put them in a position where they have to really rely on their senses and not on whatever kind of decision making process they're going through.

I definitely think there's a big gap in the research. They're trying to connect these things with like how you perceive things and your personality and things like that. I know that that's a big part of what the internet likes to say - "are you right brained or left brained?" - that's how you see 'the dress', they don't think there's a lot of support for that kind of thing so when you see that you can kind of say that's not really how it works. But there is probably something going on to how people are perceiving this dress that's a little more complicated.

Harrison: One comment on that, just on the sneaker, the shoe picture. I couldn't find any papers on it, maybe there is and I just didn't search hard enough, but I was trying to find statistics on it and the closest thing I could find was just an online poll on some news article from back when it came out. The poll's been going for five years or something but according to that poll it was more of a... I think it was a three to one split. So around 75 percent, it was around two thirds or three fourths of people that saw blue and grey, as opposed to white and pink. So what I was thinking about that one is that with the dress photo it's easier to create a context where I can infer or hypothesize that the light source is coming from the back. It's easier for me to figure out with my mind because there are the clues in the picture itself. With the shoe photo, it's almost as if it's in an environment with a blue light on it. I'm one of the kind of blue/grey people, but after I learned about it I was like "no that actually looks pink now", and now I see it as blue and pink. (laughter)

Katie: Yeah I think I had a similar perception where I think I saw it as blue and pink, and that wasn't one of the options and I thought "well... okay". But I did find one paper that talks a little bit about the shoe and the dress, but there's not as much work that's been done on the shoe yet. But I think they show something similar that it's not as much of an equal distribution between the two options, and then also they did some kind of priming experiments, kind of like what you talked about with the dress where they kind of blocked out certain parts of the picture to try to give people more contexts. I think they blocked out certain colors to try to prime what the lighting might be, and they were able to kind of adjust what people saw, if I remember correctly. I can find the paper and send a link to it. Similar to the dress, you can kind of change how people see it by giving them cues as to what the lighting might be.

Harrison: This might be a good segue to get into some of the experiments and the research you do because for me that picture is as if I'm looking at that picture through light blue lenses... right? I think we've got a couple of stories about our experiences. Well Adam, do you want to give yours first?

Adam: Yeah, I'll just give mine. So we out back and we were doing some target practice and I had some safety goggles on and they had a light yellow tint. We were out there for maybe an hour or something like that, and we were walking back to the house and I completely forgot that I was wearing them. And then all of a sudden, I'm like "wait", why are these things on my face?

Harrison: You were looking at your car, right? Which is white.

Adam: Yeah, which is white, and realized that I was still wearing them, I was like "oh, why am I wearing them?" so I took them off. And all of a sudden everything looked extremely blue. It was fine. I knew that there was something not quite right when I was wearing the glasses but I couldn't really tell what it was. And then when I took them off, yeah, everything just seemed super blue... which was really weird.

Katie: Yeah, people experience that a lot too. Swimmers can get that because a lot of times swim goggles have a little bit of a tint, skiers experience a lot, again with a similar thing - they have a little bit of a yellowish tint usually in ski goggles. It's really fascinating how your brain can adjust to that kind of thing.

So we have an experiment going on right now using these kinds of bright red lenses that are really intense, and generally people don't completely notice that they're gone. They're maybe a little too intense to completely adapt all the way which is kind of like in itself really interesting to us because -- what are the limits of this adjustment that you can make?

I published a paper a few years back using yellow lenses and people did kind of generally completely adapt to yellow - like you described - where you just couldn't really tell that anything was different anymore. Interesting, though, for that paper we didn't find that people had very much of an after effect, so they didn't really see the world as being too blue. We think it could be because they spent so much time in the dark room doing measurements before they walked out into the world, so maybe it was just enough time to reset.

But yeah, the after effect part, I think is still something a little bit mysterious to me and how that after effect works - if it could last as long as potentially it takes for you to make that adjustment in the first place.

Carolyn: I'm sort of curious because it wasn't addressed in your paper and maybe it didn't even apply. But just as a matter of curiosity, why is it that the adaptation - when you remove it - for the after image is a complementary color? I'm sure you've seen that one where it's an American flag but it's actually green and black stripes and orange for wherever they needed blue, and I always kind of wondered why is it just this very rigid correlation, it seems?

Katie: So this is another... good thing I have slides (chuckles). We can talk about this, so we can actually go to the first slide at this time...

Harrison: Oh cool...

Katie: Maybe you all know but sometimes people don't. The way our color vision works is we have three different types of color receptors in our eyes. We have all these things in our eye that can pick up light and the color receptors are sensitive at different parts of the spectrum. So in this graph, what you see along the bottom, that's essentially the rainbow. So starting at the lower end at about 400, that's going to be pretty purplely, and then at the top around 700 is going to be really reddish and you have these three different cones that are sensitive at different parts of that spectrum. And then, right next to that, what you see is a kind of a little simplified diagram of how our brain interprets - what's coming from those cones. So essentially what's happening is your cones are combining - we call this opponency - so essentially for the blue/yellow signal, your brain is looking for the difference between the short wave length cones and then the combination of the medium and long wave cones. So essentially, what is the difference between the blue and the yellowish colors in the world. And then for red and green, your brain is looking at what is the difference between the middle wave length, then the long wave length, which is essentially what is the difference between the greenish and the reddish colors. And then for lighting, for darkness or brightness, you see the long minus the middle wave lengths so just a magnitude of how much they're firing.

So this kind of makes up the dimensions of our color space - we kind of think of our color vision happening in three dimensions which are roughly blue, yellow, red/green and light and dark. So if you actually could go maybe down to slide six...

So this part is a little bit of an animation that a friend of mine made - name is Sunny Lee - but essentially how it works is you would have... Your brain is seeing white, and that looks neutral, then the magenta frog pops on and your brain correctly interprets the frog to be magenta. But over time, kind of like I explained, your brain starts to adjust to that magenta and it kind of starts to go away. So it's a similar mechanism to what you described when you were wearing your yellow lenses - after a while you kind of stopped noticing that yellow was even there.

So your brain has now shifted the entire red/green mechanism so that the magenta looks more neutral. So when I take away the magenta, and what you see is a neutral white, it actually appears to be more green because your brain has started to adjust itself in such a way that you now have this green perception where it should just look neutral white... if that kind of makes sense. It's all based on this opponent way that your brain is encoding color.

Harrison: That whole phenomenon strikes me as completely crazy. I don't know if it's just the way it's described because to get this perception of a color, we're going to take these photo receptors and we're going to take that signal in and then we're going to subtract it from this one, we're going to add them together, then we're going to... it just seems like a crazy calculation to do just to perceive a color. Am I crazy for thinking that or... (chuckles)

Katie: No, I think it makes sense. But if you think about how else could you perceive so many different colors, let's say for example that you're an animal who has a bunch of different cone types. We know these exist - mantis shrimp have something like 25 to 40 different kinds of separate cones - and some people think they're doing some kind of insane multi-dimensional calculation to compare all of these different signals. But more likely, what they're doing is that they're just saying 'okay, this cone likes that color best, and so therefore that color is red - that's my red cone so this is red'. But because we only have these three, and that makes sense from an evolutionary perspective to give us really nice acuity, you want fewer cone types so that you can make direct comparisons across more of same types - if that makes sense? You want a lot of these really tightly packed luminous sensitive trunk cones -- the 'L' and 'M' cones -- so that you can make these judgments about luminous edges, brightness and darkness, so you can do things like read text and see fine details.

Therefore, what that means is that we can't have forty six different cone types to tell us all these different colors. So your brain can make do with what it has - which is just these three. But just these three gives us this entire spectrum, we can discriminate really really finely across the entire spectrum of visible light.

Harrison: I want to hear your thoughts on this because one of the ideas I had when I was thinking about cones... Well actually, after this let's talk a bit about color blindness because you mentioned the red/green in your description of the cones. So I want to get back to that. But first, on this subject of, let's say animals with a whole bunch of different types of cones...

So our vision, our three types of receptors, have a certain range... what did you say, 400 to 700 or something?

Katie: A little sub 400 and a little over 700.

Harrison: So hypothetically, if we were to gain another two types of cones that would go into the infrared and ultraviolet regions, would you think that we would actually see more colors or do you think that the colors would be the same spectrum of colors that we see would be distributed over just a wider range? Do you have any thoughts on that?

Katie: That's a great question. I will say that our cones are positioned in a very nice location. So there are some animals that can see into the infrared, but they're generally cold blooded. So if we saw infrared we would kind of be blinded by the heat of our own body, if that makes sense, because you're essentially seeing heat... (laughter from all)

Harrison: I didn't think about that...

Katie: And then on the other end, there are animals that can see ultraviolet - bees, mice I think can see ultraviolet, humming birds can see ultraviolet - but the thing is, is that ultraviolet light is really damaging so our eyes are kind of built in this way that we filter out a lot of ultraviolet light. That's to keep our cones safe, so they're not damaged by the sun. So if we could see ultraviolet light, our body might try to even just filter it out just so it doesn't actually damage the cones.

Adam: Or potentially, it wouldn't be for very long before it just got to damaged... okay.

Katie: Yeah, the animals that can see ultraviolet just tend to live shorter lives so they don't have to deal with the long term repercussions of that. So there's a reason why we sit in that particular range, and why a lot of animals sit in that particular range. And then to your second question - if we added more cones: there are some people that have an extra cone, so this is pretty interesting.

The way you get some color blind people is that there is something called anomalous trichromacy, which is where you have three types of cones, but two of them are just slight genetic variations of each other. I showed you 'L', 'M', and an 'S' cone, but let's say for example you only had 'L' cones and 'S' cones. But then some people have 'L' cones and then a slightly 'off' 'L' cone, we sometimes call this an 'L' and a 'L prime'. And those two 'L' cones are both just normal variations of 'L' cones that live in the population, but this person just so happened to get one type of 'L' cone from their mom and one type of 'L' cone from their dad. So now they have color blindness because they don't have that middle sensitive cone, but they can see some red/green because they have a little bit of difference between their 'L' and their 'L prime' cone... does that kind of make sense? So that anomalous trichromacy is actually the most common type of color blindness, if you know somebody who's color blind they probably have anomalous trichromacy.

So the way you get a person with four cone types is actually women, or people with two X chromosomes, can have both of those genetic variations. So they could potentially have an 'L', an 'L prime', an 'M', and an 'S'. We call those people tetrochromats. It's rare and it's controversial (laughs) because it's not clear that the people who are tetrochromats can actually use that fourth cone. There are some people who have been genetically confirmed that they're tetrochromats and they do seem to perform slightly differently on very specific tasks. And so we think that they may be are using their fourth cone. What it looks like, we're not sure of. And also, what they may be using it for, we're a little unclear on too because it might just be that they're better at discriminating reds than other people?

Carolyn: I read in the article about tetrachromats - and this is strictly self reporting - but apparently it was her assertion that she was able to see much finer gradations of hue and tone, and of course she had no idea that nobody else could. So she would be arguing with somebody over three shades of peach, which to her were like completely distinct colors, and somebody else would be going 'ahh, they're all peach'. But it is a self report, so what do you do...

Katie: The person you're probably talking about is there's an artist in southern California who works with somebody a lot at UC Irvine (University of California, Irvine campus) and she paints these kind of surrealist paintings that have a lot of color - they're really beautiful - and I think she's a fascinating person because she does have now this combination of... yes she does actually have genetically better color vision than other people, and she has all this training because she's an artist that can discriminate colors generally better. So artists get better just because they're doing that all the time - discriminating colors.

So it's a little bit of a confound because she already has that training that she's so good at it. But yes, I think there are tests that show that she is genetically better at color vision (chuckles) than other people. So yeah, it's one of those questions - 'if I put my brain into your head, would it really look any different to me?' - it's unclear. But she definitely has a little bit of a super power, I would say.

Harrison: One thing we wanted to ask about is on the subject of color blindness. There are those glasses that have been developed that are supposed to help people with color blindness to be able to perceive those differences in color - how does that work?

Katie: There's a few different variations of this. So if you want to cheat a color test, there are a few ways you can actually do it and one of them is that any kind of colored lens could actually help you cheat a color test. That's because color tests are designed specifically with the spectral properties of color blind people in mind, and so if you put on any kind of colored filter you're going to shift the entire space in such a way that now the color test is not actually testing on that dimension that you're really bad at, if that kind of makes sense.

These specific lenses though, that I think you're talking about, are EnChroma lenses, which is the brand name. They're interesting because they have what's called 'the notched filter'. So if you look at the light that comes in through just a pair of sunglasses, you're going to see all the same light on a spectrum but it's just decreased by a little bit. But their lenses are specifically filtering out light at certain parts of the spectrum, so they're essentially just filtering the blue and the yellow part of the spectrum so that the people who are wearing the glasses see a lot more of red/green in comparison to the blue/yellow. So what that does is it makes them, in the same way we were just talking about context - the red/green now appears to be much more enhanced. Again, this would only really work for people with that anomalous trichromacy. If you're a dichromat, there's really nothing there to enhance, dichromacy meaning you just have the two kinds of cones. So that's the way that these work.

There's a recent study that came out in current biology that showed that wearing them actually could help you long term, to kind of learn to see these colors better. It's a little controversial...

Carolyn: Like a form of brain training, you're messing with the wiring now.

Katie: Right, and it's kind of like what I was saying about the artist who got really good at discriminating colors, in a similar way these people maybe could have been training themselves to see red and green more their whole lives, but maybe they're not doing that until they get these glasses and now these colors are really obvious and apparent, so now they get better at it over time.

It's a little controversial because you might actually predict an opposite effect. So if you are exposing yourself to a lot of this red and green, in the same way that you were exposing yourself to a lot of red with the red glasses, those colors might start to fade over time. And so when you're not wearing the glasses anymore, you might see less red and green.

Carolyn: Actually that was exactly my question... My question was, if you were to, for some awful reason - long term - would you in essence decommission the cones or the rods or the wave length? I was sort of thinking of this analogy - when you have too much dopamine or too much whatever, you actually down regulate your receptors. So, if you're over loading one aspect of your perception mechanism, let's say the red cones - will they wear out, shut down, quit working... can you attenuate their function?

Katie: That's a great question. And yeah, I would have expected, I was really shocked when I thought... I would have expected what you said where maybe you actually get worse at red/green when you're not wearing them. But the data are the data, so they showed that people did seem to improve when they were being tested without the glasses. And I think they tested people for eleven days, and people into the first three days showed this improvement, and that improvement remained pretty stable across the entire rest of the session, with a lot of variability. People who have studied anomalous trichromats know that they're a very heterogeneous population, both genetically and behaviourally.

Carolyn: I'm talking about a normal sighted person, like somebody that would have rounded up your study. I'm not saying there's potential for damage, but is that something you would expect when you sort of take one... I don't know, are you over loading with input with red glasses or are you just sort of subtracting that... I was just curious, are those studies possible, or what?

Katie: That's a fantastic question, and the short answer is we're pretty sure that it's not going to permanently change anything just because your cones actually are kind of always shutting pigments really quickly - the part that's responsible for absorbing light. So in the short term, we wouldn't expect any kind of physical damage to your actual cones. But like we've talked about, your brain is so involved in all of these processes so that whether or not your brain is now doing some kind of tricky thing to permanently change how you see red, we can't really know.

I will say one thing that we're working on right now, that in our lab with these red lenses is - can your brain kind of switch modes when you put these glasses on and off. So it's like when you get a pair of new glasses, they cause kind of a headache for a little while, your optometrist will tell you that you just have to get used to them. But what you might notice then is after a week, when you put them on in the morning, you don't have to get used to them all over again - right? So now you spent some time without them and you put them back on, your brain just instantly is okay with it. So we've been wondering with these red glasses - could we simulate something like that? Could you put on these red glasses and kind of jump back to where you left off, in your adaptation state?

We have some promising evidence to show that that's kind of what happens - is that when you have the context of feeling the frames on your face, seeing the red, all of that combined to allow your brain to develop these different visual modes, that you might be able to switch back and forth. And I'm working with a grad student, Yen Gen Lee about a paper about this, and I can send you that.

Harrison: Something you just said, and then something you said previously, just reminded me of a paragraph under the 'natural experiment' setting in your paper. I'll read the whole because I don't trust myself not to leave out something important, so:
Natural experiments provide additional evidence of long lasting adaptation to changes in seeing color.
So this is what made me think of it is because we were talking about wearing these glasses and then having almost like a permanent effect - right? So I guess that closest thing in that research would be - long term adaptation - in relation to that.

So as people age, the lens of the eye yellows, shifting the spectrum of the light reaching the retina. Neutral settings in older observers do not show a corresponding shift however, indicating that the long term adaptation occurs. When the yellowed lenses replaced as treatment for cataract surgery, the long term adaptation is evident as a negative after effect. Because the more yellow scene has become neutral, the unfiltered world appears bluish. Remarkably - now this is the part that I was thinking of - this after effect takes months to fade.

So this would be after years of, you know, your vision getting...

Katie: Yeah, slowly adjusting.

Carolyn: Very gradually.

Katie: Exactly, so then you suddenly take away that yellow, everything looks really blue. It takes months for a lot of those cataract patients to return back to the setting that they had before the lens was removed, which is really interesting.

Harrison: That would make me think that... Well I'd think there wouldn't be any kind of like long term danger of totally adapting your vision to something else and then not being able to fix it - right? Because I'm reminded of a couple of things; one is the experiment that they've been doing for, I think like over a hundred years, of inverting your vision using prisms, or mirrors, so essentially I learned about this in psychology in university - basically create some goggles that flip your world upside down so when you look through the goggles, the world is actually upside down. So in these experiments, these guys will wear them for days and days and days, or weeks, and what they find is, and there's some videos on you tube you can find if you search for them - spilling their tea and they can't do anything, and they're trying to ride bikes, falling all over the place, because literally your arm is moving in the opposite direction that you think it is. But then after time they get used to it, to the point where they're totally adapted to it - they can ride their bike, they can pour their tea, they can go about their lives totally ordinarily. Then after that they take the goggles off for the first time and all of a sudden - boom - they're back in this upside down world even though they're not wearing the goggles anymore. But it takes less time to adapt back to normal.

So the two things that strike me as very interesting about that are first of all that you adapt in the first place, but it's not that strange considering that apparently we all do that as babies because our vision is upside down and our mind makes senses of it by aligning it with the movements we actually make so that everything makes sense. But still, it's weird.

And then, the second thing that is interesting is that, well I'm still marvelling over that first one, but the second one I think is that adaptation time - that there is pretty much a permanent adaptation while you're wearing it, then afterwards... I guess no one's done an experiment where they've done it for years at a time, because that would be quite awkward. But I wonder if... Well do you have any thoughts about that? What's the relation to the adaptation time, it takes a long time to adapt the first time and then it's short afterwards.

Katie: Right. So it's a little complicated I think. We know that there are kind of these critical periods of development, so when you're really young your brain is wiring all these different ways. And so for example, there are people who have done studies where they rear kittens in worlds that don't have horizontal edges, and then for the rest of their lives those kittens aren't able to see those horizontal edges because their brains were never really able to make those connections. Similarly, there are people who lost their sight when they were incredibly young, and then as they got older some new medical treatment came along and they were able to gain their sight back, but there were certain things they were never able to redevelop. There's something called "face plainness" or Prosopagnosia, so all of them have this Prosopagnosia because you can't really learn to recognize faces as well once you're an adult.

But the lines of these so called critical periods are a little blurry, because it does seem like there are some things that you can develop when you're a little older. Some of those things are in the visual system. And there are also people who lets say, have a stroke or some other kind of brain damage as an adult but then they're kind of able to recover some of that function - in theory by recruiting other brain areas to take over that function.

So that's a little bit of why I say what I study because a lot of the time people think of the visual system is being really hard wired from the time you're really young, but we know that you can adjust in these different ways - you can learn these different modes of being - but what are the limits of that? What are the limits of how much your brain can readjust over a relatively short periods of time?

Carolyn: I have an adjustment story. About ten years ago I had an episode of Central Serous Chorioetinopathy which is... oh you know what that is, yay...

Katie: I know Retinopathy, I know the last part...

Carolyn: Okay. What it means is that behind the retina, and mercifully not directly in front of the optical nerve, the different layers separated and they started to fill with fluid. And I didn't even know this, but the net effect is like having a sunglass lens at the back of your eye. It was kind of accidental that I even noticed it, I was just playing with my vision - cover one eye, cover the other eye, and I noticed there was this big circular dark area. Then I got on the internet and scared myself to death, "I'll need an operation" blah blah. So I walked to the ophthalmologist, and apparently it's not uncommon but it can be a vision problem because the more fluid, the less light reception, but like I said it's like having a sunglass. It is treatable and I ended up having laser surgery to kind of cauterize the point of the leak and then the eye reabsorbed, I would say, 95 percent of the fluid. However, there was a permanent distortion in the back of the eye, so if I only look through that one eye, verticals aren't vertical - they're kind of curved, there is a little less light coming in so my perception is that if I'm only looking through that one eye, it's not as bright. However, with two eyes - I can't tell. It's like somewhere in the back of the brain it takes both inputs and mixes it into something that looks perfectly normal - that just astounds me. Just about every day that there is so... if I hadn't been actually playing around with 'one eye, then the other eye', I never would have noticed because the perceptual mixing was being done so well that 'who knew'?

Katie: And we all actually have an example of this. So do you know about the blind spot? So yeah, you actually are completely lacking photoreceptors right where all the paths goes back into your optic nerve so anybody can kind of see it if you cover an eye and move your thumb at about arms length away, you might see the tip of your thumb disappear for a second. And that's an example we were talking about where we were calling it filling in - where your other eye is now compensating for that little lack of vision in that one part of your eye.

That's really interesting, so are you good now? (laughter)

Carolyn: It's as good as it's going to get. For a while it was down like twenty seven 'D', which is terrible because I used to have really good eyes. But the amount of light coming in is as good as it's going to get, in fact I tested with certain stars - if I can see certain stars, I know that it's really good. And if I'm starting to have trouble, it's actually an interesting barometer of stress - if it starts to get a little more dim then I know I need to back off and settle down...

But okay, so the work you're doing is that you're staying at the mechanical side, I don't want to use the word mechanical but the word sort of... the start of the whole chain of perception you're looking at?

Katie: A little bit, yeah. I mean I will say there are people who are little bit lower level than me who setting mostly in the eye and the retina, and I'm at least in the early part of the brain, (laughter) where the input is first coming in, but not much beyond that (laughter). Yeah, that's about where I sit in the hierarchy of people who study psychology (laughter)... Close to the bottom.

Harrison: So are you at the part in the brain where the 'Photoshop editors' are that are doing all this stuff, you know, to ... Where's the 'Photoshop editor'?

Katie: I mean it's hard to say, so when we were talking context effects, probably a lot of those happen pretty early. A lot of them happen probably in early visual cortex -- we call it V1 - but then there are certain parts of our color perception that we think happen a little bit higher, so probably part of the reason you are so surprised when I talked about these opponent mechanisms is because that's not really the way we think about color normally. If I said -- what's the opposite of red? You might say green but it also might not be that intuitive to even think about colors having opposites. And especially if I go kind of off kilter like - what's the opposite of orange? Somebody with art training might get close to it, but it's still hard to think about.

We generally think of colors as these discrete categories, so you have these different bunches of colors that are red, green, turquoise, orange, whatever you may have it. And that happens a little higher up in the brain, probably more close to how we think about objects and language and things like that. So that's a little bit intermixed with what I think about as well.

Harrison: Well speaking of orange, we haven't talked about orange yet have we? Just really quick, this is one thing I wanted to mention earlier on when we were talking about just the basic visual illusions and things like that. I'll give the link in the show description to a video, the channel... Technology Connections. He did this video on 'brown', and the conclusion which blew my mind was that brown is really just dark orange. But like I said - blew my mind - when I saw this. (laughter) And I'm not the only one, I can proudly say I'm not the only one...

Carolyn: There was much yelling in the room... (laughter)

Harrison: Yes! (laughter) There actually was... (laughter) Because, well let's put up a slide, one of the screen shots. Okay, what color is that? That looks like brown to me. We might have to fix it in post production but now let's go to the other one. We'll have to do it in post production because it looks the same to me.

Adam: I think that was something that he was talking about that... because we have all of the extra context that it's not going to give it the stark contrast that it needs in order to really...

Carolyn: Because we did it right. We turned the lights off, we did the whole thing and it was...

Harrison: But basically so, what we just saw was the context, the light, the relative lightness of the scene, which was essentially just a black or white background, will affect how we perceive the square in the center. There are all kinds of reasons for that he goes through, he has a very handy way of doing it. He uses the color, what's it called when you put the hue circle or something, where you have a triangle in the middle with hue brightness and saturation. So basically you lightened the... You're basically in the orange section of the spectrum and then you basically go...

Carolyn: Head down towards black...

Harrison: Head down towards black, so you've got a dark orange. And when you're looking at the triangle that's showing all the shades of orange, it looks black and then there are all these orange, and there's a dark orange but then when you click on it and you choose that color and you start drawing with it - it's brown. So it's one of those automatic strange things about color perception. And his point was that, aside from the fact that brown is his favorite color, really it's just a shade of orange that we've come up with a name for... Well one reason but, do you have any strong opinions one way or another on orange and brown?

Katie: Yeah, I think that orange/brown stuff is very cool. So a lot of this work has been done by a guy named Steven Buck, who's at the University of Washington and may be retired now. His grad students who worked on this are Delawyer and Stinson, I think did most of it. But it's very cool so brown is what they call a context color, meaning you need to have some amount of contrast in order to see it at all. So people will probably see with the demo, if you just see brown on black with no context than anything brighter it will still look kind of orangey or honey comb. I think it's so funny that when he was doing these experiments he would ask people to draw the honey comb line, which is where that border between orange and brown or yellow and brown kind of sits.

Yeah, I think it's really great, and there's a lot of... I can try to find some but there are a few different illusions that then can interact with brown and yellow so that different context illusions that work with lightness and brightness will also work with brown and yellow, which is really cool.

Harrison: Cool. Speaking of yellow, if we move on from brown unless anyone else has any more thoughts on brown... Okay, speaking of yellow, I want to talk a bit more about the actual experiments that you do and that you talk about in this paper because the thing that blows my mind the most about this kind of research is... Adam gave his story, his adaptation wearing these slightly tinted yellow lenses and I've got another similar story - not to do with lenses - that I'll tell, but the thing that really blows my mind is the fact that you can be looking at an object through a colored lens so, I'd say objectively, whatever that means, there is a certain wave length of light, a certain color that you should be perceiving. But the way the adaptation actually works is that the range of that color will actually change, so you will start seeing essentially what might be a yellow tinted white - as white. So you're not actually seeing the yellow anymore, which blows my mind.

But before I ask the question, I want to talk about this software that he used - Flux - I don't know if you heard of it. It's one of those computer programs that take out the blue... As the sun goes down it takes out the blue light in your monitor to kind of relax your brain, so you're not getting blue light in the evening. Same as with Blue Block or lenses, but it's just a screen version. So I've been using it for years so it goes on automatically as the sun goes down, to the point where sometimes I can realize it's on because I know it's on, but most of the time when it's on I don't realize that it's on. And when you turn it off, then all of a sudden it's like stepping into a new bright room where everything is a lot brighter. But when I'm looking at it - it's the same as what Adam said - I can't tell it's on and I'll be able to say 'okay that's white', even though I'm pretty sure it's not white. But the thing about that is that because it is taking out the blue, sometimes I might be watching a video where I know there should be something blue there, but I can't see it and it's only after a while that I realize 'okay, wait a second, why can't I see the blue thing?' Well it's because I haven't been seeing blue for hours, there's no blue that's actually there. But, one of the questions that you ask in the paper about color adaptation is - does the world seen through colored glasses ever appear completely normal? And you talk a bit about the difference between weaker lenses and stronger lenses. So this is what I wanted to get into because on the one hand it seems like, let's say with a weaker lens, it seems like you should be able to adjust and see all the colors. But in the example of, let's say, looking at something under a monochromatic light; let's say you get thrown into an environment where you've just got this one light color, and I don't know if you have seen videos or pictures of it. You might be looking at Rubik's Cube and you put it under monochromatic light and then all of a sudden you can't see the difference between all these squares - they just look all the same, right?

Maybe that can be a launching off point for what kind of adaptations we actually see, and then what you think the limits of that might be. Are there ways that you absolutely wouldn't be able to adapt to? In a monochromatic light environment, would you be able to see a certain color that just seems to not be there when you're looking at it?

Katie: It's a great question and it's something I've struggle with a little bit with the really bright red lenses we're using now, because after wearing them for a few days or even if you just wear them for a few hours at a time, things definitely look green but I don't know for sure that I'm actually getting anything into my eye that is green - if that makes sense? But I definitely can tell when something is green because green, through the red lenses, is physically very grey. So it's essentially a neutral to my cones, but it looks really green maybe because I've just learned that that's what green is.

So that's a great question, and again it kind of goes back to what we were talking about with people who have very yellow lenses when they're older, they probably aren't seeing blue and haven't actually seen blue for a long time. A lot of that is just completely cut off. But yet they're still seeing blue, they still know when things are blue because they just kind of learned statistically what blue should look like. There's a guy named Karl Gegenfurtner who has done a lot of work on something called Color Memory, which is essentially when you see something that has a very strong color association and it looks like it has color, even when it doesn't. So he does these experiments where he shows people a banana, and he asks them to make the banana grey by adding different colors to it, so it will start off as a really blue banana and they have to add yellow until it looks neutral. What he's found is that people have to add too much blue because they're seeing the banana as just a little bit yellow, and he's kind of repeated this with several different objects that have these really strong color associations.

And you can experience this in real life, a lot of science museums and things have sodium lamp rooms, and sodium lamps are, they only have a very narrow band of light that they project. So everything is technically monochromatic - they can only really give you different shades of this kind of orangey color, that's the only light that they emit, so that's the only light your eye can reflect, that you can pick up. But when you go into these rooms, sometimes they'll have something like a Pepsi can that has a very strong color association and it looks blue, it looks like a blue can even though it's physically not - you cannot see blue there. And sometimes people can even take it a step further and they'll paint the Pepsi can green and it will still look blue, and then you take it outside and it's actually a green can.

So there are these things where our brain has really learned what colors are, learned about the distribution of colors in our world. And so it's really hard to disentangle what is actually real sometimes, in terms of color and what is actually being interpreted by our brain.

Adam: I had some of the similar thoughts that you were having, and when you were trying to come at the question of what's happening at that level. It's like the mind, or the brain, knows on some level what this is supposed to look like. And so it's giving you an interpretation of the thing based on a memory. It's like it knows what you consciously see without you consciously telling it what you're seeing, which I think is just kind of like...

Carolyn: But it's busy Photoshopping it, so you're happy.

Katie: Right. Anybody can experience this too at a certain light level. Those cone photoreceptors aren't sensitive enough to pick up any light, so we have this other set of photoreceptors called rods that are responsible for night vision. So during the day they're inactive because everything is too bright so they just max out and essentially we call them bleached, and they can't do anything. But when you go to bed and you turn off all your lights, you only have rods, and rods are color blind - they're just one singular unit that they're all sensitive to the same wave length so they can't make any comparisons.

So everyone is color blind at a certain light level, but almost no one's aware of it. (laughter) And so that's something you can try out - turn off all the lights and just have maybe a tiny little light source like a really dim candle or something. In theory, you're color blind in that condition but you might still think that you can see colors.

I was talking about the sodium lamps, now they're really pretty rare and you can also only find them in these science museums and things like that. But they used to be used for street lights, and it was a big problem for this reason because people who witnessed something or were looking for somebody, perceived colors - at least three colors - under these lights when there weren't any. And so they would be like 'I am pretty sure it was a red car' - well, you had no idea what the color of the car was because you literally couldn't see it. (laughter) So they no longer have sodium lights as street lights.

Carolyn: Wonder how long it took them to figure that out? I mean from a witness point of view, it would be a problem.

You said really interesting and I just wanted to fly back to it for just a second. The eye seems to be very efficient at maintaining itself. I knew a cornea replaces itself every three days but the rods do to? I mean all the cones are constantly bringing themselves... wow.

Katie: Yeah, you essentially have these discs that are absorbing light and they're constantly shutting and replacing themselves because they kind of... Yeah, they have to in order to keep absorbing new protons.

Carolyn: That's amazing, wow!

Harrison: I want to bring up one of the diagrams, one of the figures from the paper... Adam can you go to figure 2? I'll read the description of it. This is a sample of long term adaptation effects, data are plotted from an observer after dawning red glasses: unique yellow shifted towards redder color coordinates, and slowly returned to its prior values after the glasses were removed. Okay, so we got the picture up there. Could you maybe just walk us through this and explain what this experiment is and what we're seeing on this graph?

Katie: Sure. I've talked a little bit about how we make these measurements, but really what people do is essentially show you something and they ask you to make some kind of judgement about it. So in this situation, what they were doing was they were showing people a light, a very narrow band of light - in this case it's kind of in the yellowish range - and they were asking people to adjust it until it appeared to have nothing but yellow, so no red no green, it was just the purest yellow. This is a really nice judgement to me because in theory that yellow is a little bit special, because where your 'L' and your 'M' cones may be kind of neutralized - it's a little bit of a debate.

But that's kind of the idea behind making this kind of judgement - is that you can adjust a color until it looks pure yellow to you. So what that means, is because that yellow is based on the combination of those 'L' and 'M' cones. If I give you these red glasses, the red glasses are going to be specifically affecting all of the 'L' cones. And so when you wear these red glasses, now your 'L' cones are adjusting to that red and kind of eliminating it - they're getting exhausted by the red and they're starting to tone down their signal a little bit because of that red. So then what that means is now when you take off the lenses and you make this kind of judgement, everything looks a little too green so you have to add more red back in, in order to compensate for that adaptation that you just went through.

So essentially what this is showing is the way that setting changes over time. So before they put on the glasses, their yellow point is sitting between 576 and 578. And then when they're wearing the glasses they now have to add a lot more red in order to cancel out, in order to compensate for those exhausted red cones - they've just been doing too much for so long. So you get this shift that lasts for a while and then when you stop wearing the red glasses, you get this slow shift back to neutral.

Harrison: So basically you're wearing these glasses and then you put them on... Well throughout this whole thing, all those points, all those data points on this graph are basically; this is what yellow looks like. So the exact same perceived color, perceived shade of yellow is actually appearing now in different frequencies - a difference of like 6 nanometers - that's what 'nm' means right?

Katie: That's what 'nm' means yeah.

Harrison: And then for like ten days afterwards, it takes ten days for that normally yellow to actually get back the perception of yellow to get back to where it should be. So this is the crazy thing, is that this whole time you're seeing the same shade of yellow but what you're actually looking at is a different frequency of light, this whole time.

Katie: Yeah, exactly. And this is kind of what we were talking about a little bit when we're trying to fool people, because the important part about this study is that they go into a dark room and all they can see is that light. So if they had the chance to see everything else in the room, they might be able to figure out that everything statistically is different. Everything looks a little bit too green because the 'L' cones are tamped down. So if we ask them to make this judgement in a fully lit room, they might actually give us the exact same answer as they did before they wore the lenses. But because they did this in a dark room where all you can see is this little light coming out of this machine, now you can actually see how the cones are changing over time in the data.

Harrison: Well wouldn't that also apply... So let's say you're wearing tinted glasses and you're wearing them for weeks, and if you're looking at an apple or a Coca Cola can, it should be a particular shade of red, or whatever - any object, any different color - what am I trying to say? It would change in the same way, wouldn't it? Wouldn't everything change - like basically you are perceiving things on a range of frequencies that is shifted from all those... All those frequencies are shifted from they should be without those glasses, right? So it's basically like a translation so it's like 'here is where it should be, here's where it is now' and your perception actually shifts to seeing different frequencies, a different set of frequencies, a different range of frequencies, as the previous set which is totally different -- which is crazy. (laughter)

Katie: Yeah.

Carolyn: It's like an overturned window -- you just moved everything... how many nanometers one way or the other. And if you're looking at it contextually, that's where you stop saying 'oh how strange', because everything is moved together.

Katie: It is a little controversial but potentially you're kind of adapting to the green world now, because everything is too green and so now your brain is adjusting to the green lens. How does that work? (chuckles) That's where I'm at -- how do you adjust to the after effect too? I think it's a great question.

Harrison: One other really cool thing that I didn't even think about was that in the same section on natural experiments where you talk about basically natural environments that will affect your adaptation. For example just living in a green... in the summer when there's all kinds of green, that will actually affect your color perception - your vision will compensate for that extra amount of green in your visual field - which is also very cool. Is there anything you can say about that?

Katie: People might have experienced this already if you move to another region. I went to grad school in Reno which is very 'deserty' and brown, and then I moved to Minnesota in the Midwest, and I got here in the summer and it was like 'wow, this is so much green!' (laughter) But after a period of time it kind of went back to normal, and the same thing happened when I was in Reno - I didn't... obviously I knew it was brown and I was aware of the lack of color, but I didn't think of it as that unusual after being there for a while. So those long term effects you can really experience if you think about it when you move to a new location or when the seasons change, or anything like that.

Carolyn: Well I went the other way. I went from Upstate New York, like trees forever, to Southern Nevada and I remember getting off the plane and it was just brown, everywhere. And it took a long time before you could start to see the gradations of the color of the foliage and plants. But yeah, it was quite a shock.

It would be interesting to do work, perhaps, with Inuit people - so much white.

Katie: Yeah, my graduate advisor used to spend a lot of time in India which is a very colorful culture in general, but also they have these huge changes in color across the events because where he was at in India, they had a rainy season and an arid season. And so he used to do some color naming experiments with the people who lived there. And yeah, that would be a really fun thing to do (laughter), it's like 'I'm just going to go to this country and figure out how people are seeing colors there'.

Harrison: Katie did you want to show us anymore of your slides, is there anything else that was in there?

Katie: What you might find fun is the Lilac chaser illusion; I like that one a lot. If you stare at the cross in the center you will start to notice that you see a green circle going around.

Carolyn: Oh my god!

Katie: So the green circle is actually not there, the green circle is an after effect. And the other cool thing is if you stare at it for even longer, all the purple disappears. And then all you're left with is this green, and the green is not real, which I think is fantastic.

Carolyn: Oh that is bizarre.

Harrison: It's like green Pac Man eating these pink dots. (laughter)

Carolyn: And then they're all gone...

Katie: Yeah, so I like this one a lot because I think it kind of demonstrates why adaptation is so important, and why I love it so much is because it's what our visual system really needs to care about in any given moment is what's changing in a scene. So everything that's very stable is not really important to you, you don't need to perform any kind of actions on it immediately, if that makes sense. And so something that your visual system does is called fading, which is where you can have these things. It mostly happens on the periphery where you have what are called bigger receptive fields, so you can kind of pool information in their areas together. And so you see these things kind of disappear right in front of you. I think this is especially cool - there are some animals that have stabilized eyes, so they don't have eye movements, they only move by moving their heads...

Harrison: Like Batman...

Katie: And potentially (laughter)...

Carolyn: Owls...

Katie: Owls, yeah. Potentially some people think the reason that might be is so that they can sit very still and have the entire world just fade away and only see something as it moves, which might be a very efficient way to be a predator. So that's the Lilac chaser illusion.

Harrison: That's crazy; I had not seen that one before. It's mind blowing.

Katie: And then the next one is not a video - the Spanish Castle illusion - so it's just a fun one that I like a lot. It's another color after image, so this time again you just want to stare at the dot for a little bit, and essentially this is a negative image of the original. So now when you go to the next slide, this is actually a black and white image...

(Everyone is amazed)

Carolyn: And it just faded... Wow!

Katie: Yeah, so you kind of have to blink, maybe move your eyes around a little bit before you can tell that it's not real colors, but it's very convincing - that you just saw a full color image.
I like this one a lot because it demonstrates...

Harrison: So what does it demonstrate?

Katie: It demonstrates the way that color interacts with luminescence. So essentially, what I was talking about before, the reasons why we have so many 'L' and 'M' cones in our eyes are also so that we can see luminous edges. And those are kind of what our visual system is really based on seeing, so color is amazing and it's obviously my favorite. But really what's important to us are distinguishing edges and distinguishing objects from backgrounds, and things like that. And so color tends to fill in toward these edges and so these after image demonstrations work a whole lot better when you can combine them with something spatial.

I did want to mention the McCollough effect because it's my favorite. If anybody wants to go do some reading, the McCollough effect is this really interesting after image that is semi permanent. So what we were talking about before, that most of the time when you do these after effects demonstrations, are really short term. But the McCollough effect is really interesting because for some mysterious reason, if you look at the demonstration for five to ten minutes you can have an after effect that lasts for months or years. So if you want to try it, you absolutely can, there are demonstrations on you tube. Essentially the way it works is that the adapting stimuli are two sets of gradings - one is vertical, one is horizontal, and they're switching back and forth. And one grading is very colorful, probably something like red, and then the other grading is very colorful green. So when you switch back and forth from these two things for a while, and then you look at a black and white grading, now the vertical grading will have the after image from the vertical colors so the vertical green will look green, and horizontal green will have the after image from the horizontal color - it will look red. And it's really cool because, number one; it essentially means that you're storing two different after images in your brain at the same time, in the same location, which is kind of weird and - how does that work? I don't know.

And the other very cool thing about it is, like I said - it lasts for a really long time and we don't really know why you would have something in your brain that was so nearly permanent, because then for months, whenever you see a black and white grading at about that same frequency, it will look colorful to you.

Adam: Wait, so it's almost like it's stored for that specific pattern, like it's that one particular image... wow.

Katie: And it's like you really need these high contrast edges, like a black and bright color is the way it works best. And you need to have this kind of switching for some reason - there's all these parts of it that need to really come together to make it work. Then you get this weirdly permanent after image, and it's my favorite because there are hardly any other examples of something like this, and people still don't have great explanations of why it lasts so long. So that's what I'm studying right now, is the McCollough effect.

Harrison: That's cool. Almost as amazing as the actual effect is the fact that someone actually discovered it - this McCollough guy.

Katie: Yeah, her name is Celeste McCollough and she's kind of a personal hero of mine because another cool thing she did is she wore colored lenses for sixty plus days - just to see what would happen. (laughter) It speaks to me, it speaks to my heart... (laughter)

Harrison: That's actually something I wanted to ask you is if you've tried wearing colored lenses and what's the longest you've gone with them.

Katie: I think I've done like ten days when I did the yellow lens project I did, about ten days in a row. I've worn these red ones quite a bit, but not as much as the grad student who I work with. She's probably done a lot more than me. And there are people who wear these colored lenses kind of semi permanently - some people think that they're good treatment for certain visual disorders. I'm not totally familiar with the research on that, but some people are prescribed colored lenses for certain visual disorders. And some people just wear them for fun - like gamers have yellow lenses that sometimes they'll get them as a prescription, or they'll just wear them all the time. So there are a number of people who do it, not for science, but just for fun.

But I have exposed myself to the McCollough effect, maybe as much as anybody else in the entire world - basically I've done it for hours and hours. (laughter)

Adam: And it doesn't affect your vision in any other way other than when you just go back to look at it again, you're just like 'this is so cool'.

Carolyn: I think I had a brief glance at his paper because you do have it...

Harrison: Her paper?

Carolyn: Oh I'm sorry, her paper. Nobody ever puts their pronouns in their sites, could thing we do.

Katie: Well it is from 1965, yeah so another reason why Celeste McCollough is one of my heroes, because she was actually doing this work in a time when very few women did that work and she was, I think, the first female faculty in the sciences at Overland College or something, but a pioneering person as well.

Carolyn: Was she... I skimmed through a lot of the references trying to familiarize myself... Did she discuss the issue of early computer programmers seeing...? Because it was, and I grew up on the black screen with the green lettering and when you spent days and days and weeks and months, that when you took your eyes off the screen you sort of permanently saw white paper with pink lines.

Katie: Yes. I don't think that's the reason why she did this study, but shortly after this came out, I think that like five years later people finally got really excited about it. And part of why was because of that exact reason, because people were complaining that when they helped their kids with home work, and they had lined paper, it looked really pink.

Carolyn: So kind of an unintended effect because they were just looking for readability because those early screens were just... they were bad. But it was sort of like the best compromise you could make for just utility. Thank god for 'ginormous' screens today, we love them.

Katie: But I'm sure it's still like people who program all the time that experience that stuff? I'm not sure.

Yeah, so the McCollough effect is another great one. And finally, just a quick aside - adaptation happens in the visual domain and in any number of dimensions. So you can experience these after effects with things like faces, blur, orientation, there's all kinds of different ways that you can experience these after effects. And so we bring those out because they're unlimited and fun.

Harrison: Could you describe how it would apply to faces?

Katie: Yeah, so essentially what you could do is... actually if you want to pull out the last slide that I have... Well essentially what people do is the manipulating of faces in Photoshop in any number of ways. So for this example they basically take the center of the face and they just squish it so that it looks like they have a very pinched nose and kind of close set eyes. And if you stare at that for a while, at first it looks really odd and then after a few seconds, up to a minute, it looks like almost a completely normal face. And then when you go back and look at the original face, it looks really big, it looks like his nose is too big and his eyes are too far apart. And you can do that with a number of facial dimensions, so people do it with gender so you can take a male face and a female face and kind of morph them together. And after you stare at the female face for a long time, when you look at the morphed faced it looks really male, and if you look at the male face for a long time and then look at the morphed face it looks really female. So it can (?), it works with all these different facial things and dimensions. So, some other fun things...

Adam: Entertainment for the next two weeks. (laughter)

Katie: Do you all know about the illusion of the ear contest?

Harrison: No...

Katie: Yeah, so it's a web site that you can go to. Every year they - mostly vision scientists, but sometimes just people from the community - make illusion demos and upload the videos. So you can go there and find all the winners, I think they've been doing it for like fifteen years or something. That's endless entertainment, it's fantastic... (laughter)

Carolyn: You can garner the best of it and send them to us. (laughter)

Harrison: That's great. I'll find the link for that and I'll include that into the description too because I'm sure everyone will enjoy it.

Well, I think that's good Katie, unless - were there any other points you wanted to make, or things you wanted to mention, or cool things that come to mind?

Katie: I think that's it for me but I could talk about this forever. But thank you so much for having me and inviting me...

Harrison: Yeah, thank you for coming, it was a blast. It's just such an interesting topic and even the things that you as just a normal like lay person looking at internet memes, you could only come across so much of the good information. So I'm glad we got to talk to you and find out the nitty gritty and see some really cool stuff, that I've never seen before.

Katie: It was great to meet you all.

Harrison: Okay, well, take care and thanks again.