so one of the things that I've read I don't know if you uh believe that this is true but um you know because everything turns out to be debatable among scientists uh just like everyone else but I've read that one of the things that shaped the evolution of our eyes is their shaping to be maximally visually evident to perceivers right we're unbelievably good at determining exactly where someone's eyes are pointed so even if someone is sitting across the room from you you can tell if they're looking at your eyes or at the tip of your
nose which is such a tiny fraction of of movement at the eye level or a fraction of angle that it's almost amazing it's amazing that you can detect it at all and that we have the white background and the colored iris and the black pupil partly because that maximizes the degree to which our eyes are Salient the hypothesis being that anyone in our evolutionary history whose eyes weren't Salient was Salient was someone who whose intentions were very difficult to determine and was much more likely to be misunderstood saying killed in consequence or much less likely
to to find a mate and so our faces have evolved at least at the level of of our perception of the eyes of others to ensure that we can understand intent and we do that by inferring attention by looking at eye gaze and you're making a strong case in your work for the relationship ship between perception color vision and emotion perception so we talked a little bit about cues of Health that might be associated with skin coloration and cues of fecundity but tell me about the emotional cues that are associated with differences in color so
you know the first thing I think people think about with with uh uh spectral skin signaling is blushes right and blanches and flushes but that's really just the beginning you know this barely touches the surface so uh you can imagine someone's angry and they can get red face which is very different from when somebody blushes and they get a with embarrassment and people actually if I'm in front of a stage and something happens is slightly embarrassing uh and the audience is over there and I'm looking this way um you actually blush more on the side
that's facing the audience your body right yeah this is known this is a Drummond some wow that's a very specific response right so this is these are strong arguments that these are signals uh not just automatic side effects of you know some kind of implicit side effect with no purpose well that's so complex too he because it opens up the question like first of all not everybody blushes and the issue is what does the blush signify and it it signifies something like self-conscious shame and then the question is well why would you want to Signal
self-conscious shame to people I mean because it's a shameful signal but it does indicate that you're the sort of one of the things it might indicate is that you're the sort of person who can't get away with what exactly violating the social Norm something like that right and it's and it's an honest signal because it's out of your control so yeah right honest honest signal just in this context is doesn't is a sort of a technical term of art so we we mean by Honest signal that you have no control over it and when and
it wears its meaning on its sleeve in some sense right right so it yeah that's right it's a signal of your intent beneath your conscious awareness La laughter genuine laughter seems to be a signal like that too and there's some evidence that genuine Smiles are like that too right because if you smile falsely your eyes don't smile although I think you can train yourself to do that but generally speaking someone is yeah it's hard if someone is manipulating with a smile they don't do it the same way they do when they smile spontaneously and so
those rapid onset implicit emotional displays are a signal about our genuine motivations and if those signals are obvious it's in principle easier for people to read us and therefore in principle easier for us for them to engage in trusting negotiations with us right because we wear our heart on Our Sleeve that's right and so I mean other predictions that come out of this by the way it should be the case that if this is true then um the primates with color vision as opposed to the primates that didn't have three three three color vision the
primates with color vision should have more naked spots they should have bare faces and in fact when you look the primates with with color vision are the ones with naked faces they often have naked rumps uh you know naked genitalia which because all of these sign things are signaling the ones without color vision are furry face like your typical bunny rabbit typical dog nakedness and color vision three color vision are opposite sides of the same coin okay okay okay does the theory that Tri chromate Vision evolved at least partly or perhaps in the main as
a Aid to emotion detection contradict the frugivore theory like is it possible that color vision also gave us an edge at least in some environments with regards to the detection of higher quality food sources it's it's certainly possible but it wouldn't have driven there's no reason to think that fruit would have driven those particular wavelength sensitivities of the middle and long wave wavelength sensitive cones you particularly given that they're so close together so that's the CR crucial is yeah and there's all kinds of things where we we we we leverage our color vision which is
peculiarly for empath kind of Health senses but we obviously use it for lots of things probably in nature beyond that um and in culture use all over the place uh but that doesn't mean that's a that that doesn't amount to an explanation for what drove well I mean part of the problem I guess that people have with evolutionary exp functional evolutionary explanations for the purpose of any given human attribute is that there's no reason ever to assume that any given attribute is singular in its function it's sort of like asking what the hand can do
what's the hand for well you know the hand is for a lot of things what's the is there a cardinal purpose to the hand that's a hard question to ask but there's no reason to assume that Evolution wouldn't operate so that a given biological phenomenon well here would be other than multi-purpose right well so the everything might be multi purpose but uh the odds of there being two competing or multiple competing deata that are determining the design that they're close to one another are going to be typically fairly rare typically one of them might be
10 times more important than the other you know or a thousand times more important usually in my experience it turns out that one of these is the principal drivers it can explain first order even second order properties of the thing and yeah there can be other third or fourth order stuff but that's that's slight mostly irrelevant so you can get away with explain so for example another another one why we have forward- facing eyes standard story and the fun thing all of these these these explanations whether it's pruny fingers still probably in the Wikipedia page
it says it's a side effect of Osmosis or some bull crap right it's just it's still there to this day these old narratives and then for forward- facing eyes it's it's always has something to about about Predators want forward- facing eyes well except that every fish is a predator eating a smaller fish all the birds are predat they're all have sideways facing Eyes by our standards they're all sideways facing eyes um even even all all the carnivores the the paradigmatic you know mamalian meat eaters Predators have sideways facing eyes relative to us I mean they
still have forward- facing eyes in the terms of the big picture of things so there's a lot of variability and forward- facing eyess across the mammals and the question is why um is there this variability and so um there's been multiple kinds of one is uh is stereoscopy better stereoscopy yeah um but it's it's it you even get stereoscopy in a bunny rabbit bunny rabbit has a very thin binocular field and it can see stereoscopy within that thin binocular field but it also gets the benefit of seeing everything you can see directly behind it below
it above it so you've got this full panoramic Vision whereas we've chosen to lose right a lot half of our visual field or you know a lot of our visual field just to have better stereoscopy up in front now so one of the bad sorts of you have these two currencies like you know the standard arguments oh I've got this great wide stereoscopy field of better 3D Vision up front at the expense of losing into everything how do you balance those things what how is that an argument that I would want more of of you
know apples to have while getting less adverbs in the back they're not even obviously comparable things that I can trade trade off so my argument was like first of all stereoscopy is not it's like the the it's the least important 3D sense we have all of these there's there's many many three dimensional sense want is just what kinds of objects they are how far down uh towards the the towards the horizon are they how they overlap things yeah inclusions in front of other things if I just do this with one even with one eye I'm
getting amazing much better than stereoscopy all these things when you when you do if you're perception psychologists who create stimula with that have competing cues of two different kinds and they say which one's Trump um a stereoscopy loses always all of these other ones Trump they win if there's oh I see so that's a good way of testing what what's the most Cardinal element of the oh yeah and so none of serop be always Los and if you've played first person shooter video games you're you yeah you have both eyes open but you're being fed
one image on screen and these things are so immersive you never are confused as to where the guys are that you're shooting right they're always really unambiguously in one particular spot yet you're a cyclops right so um it it had occurred to me back then I said I don't think it has anything to do with stereoscopy whatsoever and it turns out it's all about one currency this is again to this idea of why why aren't there three two or three or more equivalent kinds of functions that are competing and then it's just some ugly mess
and it's not a good you know design hypothesis at all it be sort of ugly Cloe that happens to it's it's it's almost never a cluee and so in this case um the reason that we have forward- facing eyes and the more forward facing they are is is to see better and clutter and so what I mean by that animals that evolved with leaves all over the place when there's leaves if your eyes are more widely separated than the Clutter leaves let's say so for example if you if you you've played this game if you
just if I hold my finger up in front of you it's very thin and I look at you but not my finger I see two cop unless I've got a dominant eye but for those of you don't have a dominant eye you'll see two copies of your finger and each will be semi-transparent right all right now you're see you know what you can see through it right so what what one eye is being blocked with the other eye seeing the world beyond that and so your brain is evolved to just create two copies of it
and you're not confused like oh my god I've got two figures no you know what's going on it's just you you have this perception that combines them and creates semi-transparency um so that you can see beyond it now I can even my whole hand I'm almost missing nothing even with my whole hand in front of me you know there's a little bit of a core in the middle but there's but I'm I'm capturing most of it so for for objects that are less uh that objects that are not as big as this inter pupilary distance
the separation between my eyes then when you're an animal in that with those kinds of eyes in a forest with leaves that are typically smaller than that you actually get uh I call it x-ray you actually can see it's probalistic summation you actually can see much much more of the environment Beyond than when you're a cyclops so and in fact I noticed this playing video games back 20 something years ago when I would be you know because you're a cyclops and you're hiding in bushes and I'd be trying to snipe people and when you're in
a bush you can't see anything of course these are fake bushes I get it you can't see anything because you're just looking at the but where in real life you're in a bush you pretty much see the entire world outside of it you can you know peek from outside of your bush so you had to keep shaking to get different shots than someone shoots you because they see you wiggling in the bush in real life you're designed to be in these um cluttery environments and to see perfectly well beyond that without having to move too
without having to move and yes you're losing what's behind you but then you can start calculating how much of the environment can I see if I'm a forward- facing animal with this x-ray ability that is my eyes are bigger than the leaves versus a rabbit let's say uh effectively you know who has a full panoramic view yeah he can see he can see entirely behind him but he can't you can actually then calculate how much of the world outwards can you see he's actually I can see up to you if you think about it two
dimensionally I can see up to uh one two three three and a half s better than him if you think about as a two- dimensional grid but in fact it's more of a threedimensional grid then you have to sort of think about spheres sphere packing problem and so I can see only the front half of my little sphere and is but if the the little uh the world is sort of built out of these spheres of these little um uh surrounded by lots of clutter I can see the six spheres in front of me fully
and I can't see beyond that and only half of mes but I can see now six and a half times more of the there's like simple models that you can build of of simple models of forested kind of environments where you can show that now you're going to see uh really almost an order of magnitude more [Music]
