Comprehensive Guide to Sensation and Perception in Psychology

All right, Hey folks today we are going to  be talking about sensation and perception!   um I'm gonna say up front, if you get the  opportunity to take an upper division level class   that focuses on sensation and perception, I think  it is essential that you uh you take that class um  

in the same way that I would say I would say the  same thing about a biological psychology class.   um We are uh um in my previous teaching  experience, I I I taught sensation and perception   as an upper division 15 week class. um And so  I'm keenly aware of how much is about to get  

left out over the course of this of this lecture.  There's so much more here that is so interesting   um and so uh just know we're going  to fly through some of this stuff and   um there is, again, like that class we spend  five weeks talking about Vision, right. And so  

um as you you know as you move on those  who who transfer and continue to study   psychology, uh Sensational perception is  a challenging class um and but um it will,   you know, I've talked previously about the idea  that like stats is you know and research methods  

is like a super-marketable skill. Sensation and  perception, genuinely, I think contains some of   the most interesting insights about what it  is to be like a person for you to just carry   with you into the future and so um this is a  topic that is near and dear to my heart and  

um I hope that that you share the same enthusiasm  when we're done here but just know there's just so   much more um and don't miss out on an opportunity  to explore it Okay so let's start with some basics   we have sensation which is the process of  receiving stimulus energies from the external  

environment doesn't that sound just so again  like uh like I mentioned in the Consciousness   lecture so new age um yeah we are uh um not  to blow anybody's mind but we we exist in   a reality uh right we are um uh surrounded by  objects and things and forces right like energy  

um you know like a little like you know kinetic  energy right um and uh by virtue of being a solid   physical object we're gonna run into a lot of  that right which is a very fancy way of me saying   sometimes you're going to touch stuff sometimes  you're going to see stuff sometimes you're going  

to hear stuff right Airwaves are going to move  through the air and reach your ears light is   going to to enter your eyes and before really be  funneled into your eyes and strike your retina   um you know you're gonna you're gonna touch  things and in you know you moving your hand  

right you're going to introduce energy into  your uh your touch receptors by something   moving into you it's transferring its energy  into into your touch receptors right and so   um uh with our chemical senses you know those  chemicals are going to come into direct contact  

with specialized neurons in our bodies right  Sensory neurons in our bodies and so just by   virtue of being here we are going to encounter  a lot of stuff and that stuff is sensation right   um when that stuff interacts with us in a way that  we are capable of receiving right so for instance  

um there is light that uh we can't see right for  instance uh we cannot see x-rays so that does not   um that might be stimulus energy that might be  in the environment but we don't see it we don't   experience it because we do not have uh body  parts designed to to take it in right so that's  

why we have to use machines to uh see x-rays  to see infrared right to see ultraviolet light   um so sensation just governs everything that  we are capable of receiving is there probably   a lot more absolutely right so from there and  that is all fundamentally physical right from  

there we have perception which is the process of  organizing and interpreting sensory information   because there's a lot of information a  lot of information all of the time and   so then a psychological process has to be  engaged which integrates all that sensory  

information into something coherent and if that  doesn't happen then then it's it's chaos right   um I look at any object in your room or wherever  you're listening to this or watching this right   now look at any object and think about all  of the details that make up that object right  

and at some level right if that object makes a  little bit of noise how that object feels in your   hands as you're looking at it what colors it is  what textures it seems to have or what textures   it has when you actually touch it all of that is  happening through separate processes Right Touch  

Vision maybe you smell the object you're holding  right at some point something has to happen that   tells you this is all one thing right that I'm  feeling right so the single object has a smell   of a single object has a texture the single object  has an appearance and it has a noise and it makes  

it all belongs to one thing that's a psychological  process that does not happen automatically right   um something somewhere between your hands and  your understanding of what you're touching also   your visual system is kicking  on being like ah this is what  

the thing I'm holding looks like and  this is a psychological process right the interplay between these is so strong um  that the only really way to think about that   in any kind of sophisticated way is that they  are one process sensation and perception are  

um are inseparable right there can be no ooh  I was gonna say there can be no perception   without Sensation that is not true because  hallucinations our perception without sensation   um however when it comes to thinking about a  normally functioning brain right um all perception  

comes from some kind of sensation right um and  then when there is perception without a sensation   which causes it we think about that as abnormal or  unusual right and so you know there are people who   lose their limbs who continue to feel that their  leg is there that's that is a hallucination right  

it's a special kind called Phantom limb um and so  uh that also should should tell you right that the   psychological plays a huge role in the process  of understanding the world right it's not just   what we perceive is what is in the environment  right our minds our psychology has to act on that  

information right before it becomes knowable  to us and if that's a little overwhelming   philosophically that's okay actually so we can  think of sensation and perception as also going   in two different directions bottom-up processing  which is initiated by sensory input we contrast  

that with top-down processing which is initiated  by cognitive processing so bottom up is the   outside world's influence on perception right you  see something right and the details of it coalesce   come together into uh something right like oh okay  it's got bark and it's really tall and cylindrical  

and it branches out and at the end of those  branches are many leaves oh it's a tree right   that's the bottom-up processing we take all the  details we put it together we get an understanding   right top down processing is uh is how our  internal mental World influences perception  

right so bottom up is the collection of all the  details top down is the identification process   right it is shaped strongly by  expectations and prior understanding right   um You cannot recognize something as a tree if  you have never been taught about a tree right  

I've been told like oh hey yeah that's a tree  you can climb it if you want right until you've   had that experience you can't identify  something as a tree right all you get is details that are attached  by time or proximity right

and so these work together to form a unified  information processing system right we have we   use both all of the time right um a good example  of this is right now I'm sharing this office with   um my cat one of my cats who is sure to start  being she looks a little sleepy so maybe I'll  

be lucky but she's sure to start being annoying  at any moment and if I'm focused on giving you   all a lecture and I'm focus focus focused  and outside of my awareness she sneaks down   and starts rubbing past my leg right I'm gonna  probably use bottom-up processing to start I'm  

gonna go oh there's something on my leg right  which as somebody I'm very I'm like kind of   nervous around bugs and you know and stuff like  that and so I might immediately get oh there's   something rubbing on my leg oh my gosh what is  it right oh it's furry oh it's you know moving  

in that Slinky way right that cats do and or  it's moving in kind of a slinky way right and   then my top down processing is going to kick and  go oh that's my cat gnocchi okay never mind right   um we're we're okay right and they have to work  they work together right and so I don't need  

to take action to like brush something away from  my leg I just know my cat is kind of bidding for   attention right now that's fine right and so they  work together we go from details to understanding   right and our understanding shapes which details  we attend to right it goes in both directions

so sensation starts with sensory receptors these  are specialized cells that selectively detect and   transmit sensory information to the brain um so we  talked about neurons last week right most sensory   receptors are basically neurons in but instead of  dendrites which are there to receive information  

they have special structures designed to interact  with the environment so here I'll just talk about   vision for now because we're going to we're going  to touch on each of these a little bit but for   vision what you see is like down here there's  our cell body you can kind of see it right you  

can see the nucleus right and on top here we  have cone and here we have rod and though the   the cone structure here and the rod structure  here are actually designed to catch photons   and when enough the these structures are  filled with a special kind of chemical  

um which we do for unfortunately feel we don't  need to get into today but a special kind of   chemical that when a photon binds with that  chemical it breaks apart causes a chemical   reaction and when enough of that reaction is  happening in this Rod structure in this cone  

structure this neuron right this cell decides  to Fire and begin transmitting information   and that's how we see here taste smell and touch  stuff y'all that is how it works is we have a   special cell that is designed to catch energy or  catch a particular kind of chemical and when it  

catches enough of it it fires and that uh is how  we translate energy around us into what's called   like an a neural or a nerve impulse right and  that process is called we call that transduction   um we'll probably revisit that in a little  bit but that's the process of transduction  

where we have energy in the environment and  then we turn it into a neural signal right   and sensory receptors are responsible for  that transformation they catch stuff from   the environment when they catch enough of it  they fire an action potential initiates right  

huh and these signals move down  distinct neural Pathways so we   have a visual pathway an auditory pathway a  touch pathway right on and on and on foreign I'm gonna I'm gonna say something kind of funny  for a teacher to say about his life I want you to  

think about this one too hard um but we uh uh we  measure sensory acuity the sharpness of our senses   um uh on a couple different scales one of  the things we think about is something called   absolute threshold and this is how we measure  the strength of our senses as an organism right  

so if we want to compare human site to a dog's  site we are interested in absolute threshold   right which is the minimum amount of energy an  organism can detect 50 of the time right and   many of you if you're if you grew up um like me  like I was an animal kid growing up like I love  

to learn about you know you know different  animals like all the time and so you would   learn facts about like here's how a spider sees  or here's how a dog sees or whatever right and so   um what's interesting is that it wasn't until I  was a psychology student that I learned any of  

those vital statistics for people so for instance  our absolute threshold provision is a candle flame   at 30 miles on a dark clear night you can see that  about 50 of the time and that's you know when we   compare that Vision maybe to an owl we're probably  very inferior right hearing a ticking clock at 20  

feet under quiet conditions one drop of perfume  diffuse throughout three rooms for smell taste a   teaspoon of sugar and two gallons of water that's  super interesting I'd love to do an experiment   with that touch the wing of the fly falling  on your neck from a distance of one centimeter  

right so that's about the strength of our senses  a key thing to keep in mind right is that there's   going to be a bunch of things we experience that  are higher than that criteria most of the things   right the sound of a voice is way higher than  a ticking clock 20 feet under quiet conditions  

but there's a lot of things that are going to fall  outside of that threshold that we're never going   to notice or perceive which is why we have tools  like telescopes microscopes microphones right another thing we're interested in is difference  thresholds another way that we measure our sensory  

acuity right so how much stimulus change is  necessary for detection so this is we've got   a color wheel here where some for some folks they  might have a difficult time distinguishing between   um like a light purple and a lighter purple  right but we're very interested in something  

called just noticeable difference which is  what's the smallest amount I have to change   something before you notice there's been a  change and so we can think about this as two   light bulbs right and we can slightly dim one but  how far do we have to dim it before somebody goes  

oh that one is now duller than the other right  and that's just noticeable difference right just   notice just noticeable difference interestingly  enough gets gets bigger right with stimulus   magnitude so the brighter something is the more  we have to divot before you notice a difference  

one way that we study how our senses work is  is through signal detection right and Signal   detection theory is a increasingly  funny enough that you know this is   um uh still a part of the the basics like  one curriculum but um the signal detection  

is is getting to the point where we might start to  call outdated pretty soon just keep that in mind   um the the idea right is that uh we can we can  study or understand sensation and perception   through uh um understanding hits misses false  alarms and correct rejections right which is  

this idea that we show something right we play  a sound we show it uh you know we touch you in   a certain way we flash a light right so there  is a signal there is actually a light turned on   right and the Observer can either say yes I see it  right at which point they have a hit correct great  

good right this is our ideal situation it's here  and I notice it right this is one of two ideal   situations the second less ideal situation right a  signal is present and we don't stand we go no it's   not there even though we know it is there right  and Signal detection Theory actually comes out of  

um trying to understand uh whether radar  operators are going to reliably notice like   incoming planes right this comes out of like  I think post World War II um research and so   then there's nothing there right we didn't turn  anything on right and we say there's something  

there which is a false alarm also a problem  also not ideal right I already talked about   a miss the other ideal is a correct rejection  we say nothing nothing there when there is in   fact nothing there and so what signal detection  theory is all about is trying to understand how

strong a stimulus needs to be before we rely   reliably hits right so this is a  in part how do we how do we design   radar uh radar readouts so that when there's  something there people notice it right  

um and then how do we design radar readouts  too so to make sure that if there's nothing   there we don't get any like false like uh  we don't get any um you know we don't trick   our radar operators into being like is that a  DOT does that count right that kind of thing  

and so understanding the different thresholds at  which we get more hits than misses right at which   we get more more false alarms than correct  projections so what affects our perception   attention focusing Awareness on a narrowed aspect  of the environment right so the reason we have  

attention the reason we have that singular kind  of like band of when I'm attending to something   I'm attending to one thing um the reason we have  that is it's adaptive because it aids in our uh   perception paying attention to something makes  us notice changes about it more reliably right

so selective attention right is uh this this  process uh by which which we talked about a little   bit during the Consciousness um lecture is this  idea that um you are not always paying attention   to everything all the time right and so attention  is selective it Narrows on to particular things  

um we talked about the cocktail party effect in  the last lecture as well so the gist is right   um that uh in some cases our attention is grabbed   right and it's grabbed by things that we weren't  necessarily paying attention to beforehand right  

um the uh another example of uh and we talked  about cocktail party effects I don't want to go   into too much detail um make sure you review  the electron Consciousness for that um the   Stroop effect is an example of what's called the  failure selection the Stroop effect is basically  

um uh I'll I'm gonna link you all to a demo  of this um uh in the in the course canvas but   the gist of this is if I give you a task of  I want you to read a series of color words   right when I change the font of those color words  like the word yellow if I write the word yellow in  

the color red right so the word yellow is written  out but the letters themselves are the color   red that disrupts your ability right to reliably  identify color of the wording right because you're   either attending to what color are the words  written in or what word is written here right  

and again that will become so Crystal Clear once  you do that once you do that demo so if right now   in this moment you're like what I want to strongly  encourage you to go to the canvas and and follow   the the link to the the Stroop effect or the  Stroop test um that'll be uh part of this module  

so things that affect our our attention are  going to be novelty how new how different is   it how big is it right um or if it's unusually  small right um it's color how much it's moving   right what our emotions are in a given moment  right you'll notice that when you're feeling  

very sad all the songs on the radio seem to  be about you and your problems right that's   because you're feeling sad and a lot of songs are  sad and so you start to notice those more right um we can miss things because we are feeling a  particular motion when we're sad we're better at  

noticing sad things when we're happy we are better  at noticing good things right and happy things and   so we'll miss possibly important details depending  on how we are feeling right and in many cases we   experience something called unintentional  blindness unintentional blindness so this  

is where because we are attending to one thing we  might we might miss something very obvious right   um uh a good example of this is um I'll link  you to I'll link you to another example of this   um uh as well and so definitely check the  canvas for some good uh for uh for honestly  

check the canvas for a good time because both  the strip the Stroop effect is fun to mess with   um and I'll give you an example of an  intentional unintentional blindness as   well I'm in touch I'm making a note  to myself an intentional blindness

and swoop okay yeah I'll have a good time with  that so factors that also affect our perception   we have what is called a perceptual set we as  it says here our predisposition our Readiness   to perceive something in a particular way um  this super cliched image of a woman holding  

up the Leaning Tower of Pisa right it's the it's  the like classic like wow what a boring tourist   um thing to do uh but it's a fun gimmick because  yeah based on perceptual set how we tend to see   things we'll look at this we'll go oh whoa for a  split second we'll have the thought she's holding  

that up she's not doing a I guess she's doing  a pretty good job with this actually but the   perspective Clues quickly help us understand  oh she's not actually holding this up but   um the illusion is there for a brief moment  because we have a predisposition to use other  

kinds of cues like her positioning see her hand  is like a is like really it's like this really   well positioned to create this illusion but then  details like Shadows her size the other like where   the the lines of the Horizon and the environment  go we know oh she's not she's not holding this up  

but other cues suggest that maybe she is  so we have a split second of like what   foreign aptation right is a change in  responsiveness of the sensory system   this is actually the sensory adaptation is  happening all of the time all of the time  

um and this is uh this is um as it says a change  in responsiveness of the sensory system and so   what that means is and to put it really simply  um when you walk out of a movie theater and the   light is really bright it's because your eyes  adapted to the dark right that's all it is right  

um if you are hearing a really loud noise for  a really long period of time eventually you're   uh you're going to be able to tune that out  because again your sensory system is adapting   um some might argue that it is fatiguing it's  getting too tired to keep sending the same  

information whatever either way it's adaptive  and useful because as you become adapted to   a dark room or a room that's really bright or a  noise that's really loud as you become adapted to   those things other stimuli start to stand out more  so if you're in a room with a lot of loud noise  

and a lot of like maybe persistent rhythmic loud  noise it's easy to tune out right what happens is   you become better able to notice other sounds  that are going on in the environment so even   if it is fatigue right causing the sensation of  adaptation it's still really useful right and so  

it's based on the level of surrounding stimulation  dark room red Outdoors right we adapt foreign I'm gonna fly through this super quickly um  extra sensory perception like perception beyond   our senses you know that thing where you're like  oh I dreamed about them and then they died right  

um you know oh I knew what they were thinking  right um there is no just there is no scientific   evidence for you know psychic powers you know  perception Beyond you know beyond the physical um   and anything that that appears like convincing in  that way is one of two things right it's carefully  

constructed like fraud right um like somebody  who does like cold readings um uh you're most   of you listen to this are probably too young  to remember um I think this guy's name is Jon   Stewart he shared a name with um I think either  way um he would do cold readings and like pretend  

to be talking to people's dead relatives and  you know he would know things that he couldn't   possibly know it's a it's a careful skill you can  craft and the other thing the other piece of it is   is neglecting the fact that our brains are really  good pattern finding machines they just are right  

um and so um you know oftentimes we'll we'll  we'll reach conclusions or or have guesses   about what's going to happen next that um  that are totally logical but we don't have   access to the logic that brought them about so  um you know not to burst anybody's bubble but  

um you know extra sensory perception there's no  evidence that suggests that there's there's that   it's there um and um in the instances where  it seems like maybe it's happening um the the   explanations are probably far more mundane but  the thing that I want to say because I don't want  

to I don't want to be a total Downer here and I  genuinely do believe this what I'm about to say is   um the other thing to keep in mind about  extra sensor extra sensory perception of   this idea of like again perception of the world  independent of like our our natural senses is  

belief in these things belittles or ignores  the like incredible um Power of our bodies   right um you know to look at the amazing things  that our minds can do and chalk it up to Magic is   it really diminishes um the reality which is that  we have the the the brain and the mind that it  

generates is an incredible tool right um and so  keep that in mind too that if that if you're if   you're if you're looking for Wonder in the world  there is plenty of it to find uh through science   um uh because this is uh because yeah um so  just just kind of keep that in mind that um  

but there's there's plenty  of Wonder here to find so   let's let's pivot let's let's get away from  Magic I don't want to talk about magic anymore   unfortunately the slides are not going to  bring up magic anymore so we're good so  

um we are going to start by talking  about vision and to start by whenever we   start a conversation about the senses and our  perception we have to talk about what creates   those perceptions right which we need to start  with light light has uh some properties to it  

um uh light is a is a is a wave-like particle  that um is is made of photons which uh most of   the light we experience is uh are photons  that are being uh uh ejected from the sun   right the light the sun gives off we're being  bathed in its photons all of the time right  

um everything we see those photons also bounce  off other objects and when those photons bounce   off objects they bounce right into our eyes and  that's how we see other objects right the light   that bounces off of things around us is what our  eyes capture and how we begin to make sense of the  

world visually so let's talk about the properties  of light because we we need to understand how   how we see so light has a wavelength right let's  start even further back light behaves like a wave   it goes up and down right it oscillates back and  forth right and so the wavelength is the distance  

between the peaks of those waves some of these  wavelengths are Beyond human sensation the ones   we can see get perceived as cube or that's the  color of the light right and so red wavelengths of   light are sh are long excuse me are long as we get  toward blue and purple which are not pictured here  

those get shorter right amplitude is the height  of a wave this is where we get brightness right   so really bright red really bright pink really  bright light is light with really high waves purity refers to how many how um how mixed  together the wavelengths we're seeing are  

right and we perceive this as saturation right how  colory are the colors right and if you can again   go into your phone and and open up your camera app  and edit your uh edit your colors to increase or   decrease saturation you'll quickly see what this  is referring to so there are these waves right  

they are everywhere they're coming directly to  us from the sun don't look directly at the Sun   you'll hurt yourself um but those photons are  coming down hitting objects and bouncing off of   those objects and going in every direction and in  our case for us when we're interested in Vision we  

want to talk about the photons that are bouncing  off objects and going into our eye this is a side   view of our eye it's got a couple of different  components up front here we have the iris   right that is what gives your eye its  color it's also a muscle that squeezes and  

that squeezes and stretches this structure  here which is the lens right by squeezing   right and relaxing this lens right we can focus or  bring out a focus what we are seeing right now on   the outside is the cornea the cornea is is like a  lens as well it is responsible for about 80 of the  

focusing that we get the lens does the other 20  gets us to where the to make the image sharp the   cornea just makes sure that the light gets bent  and then projected onto the back here right and so   the cornea is the hard shell on the outside of our  eyeball right it focuses light along with the lens  

right the lens is is is is squished and put into  position by the iris now the pupil is not really   a structure at all it's a gap it's a hole here  right and so the pupil the thing that dilates   opens and closes right right the iris governs  that and light will pass through the pupil and  

eventually it gets to the retina now the retina is  this kind of this purple area here that's all over   the back of the eye right it is a it is a film you  can think about it a lot like a projector screen   um but it is much more special than a projector  screen because it's not passive right so light  

gets projected onto this structure here the  retina and inside the retina are a bunch of cells   who love light and those photons get directed   and projected on to the retina and then the  cells and the retina eat up that light and  

wherever that light is landing whatever kind of  light it is those cells get very very excited   the sclera is the sort of structure on the outside  of the eye it's not it's not important to us right   now um the thing the other things to know the  fovea is when you are looking at something when  

you're reading something right and like reading  words on a page the fovea is the main focal points   where they've got the highest density of cells it  gives you the sharpest division so when you look   directly at something you're getting the crispest  clearest most accurate version of that image

nearby is a area that's not labeled  here but it's called the blind spot   right uh the blind spot is where you have no  rods and cones no cells there's a gap in your   retina you don't see anything there and the  reason you don't perceive your blind spot is  

there are two reasons the first reason that  you don't see your blind spot is because you   have two eyes and they compensate for each other's  blind spots right the second reason is much cooler   um your brain right as part of processing visual  information uses information from the edges  

of your blind spot to make a guess about how  to fill in the blind spot so um many of you   who've used Photoshop are aware of like what is  a Content aware fill where you can kind of just   like Scribble over an area and Photoshop will be  like I think this is what's supposed to go here  

yeah your brain was doing that millions of years  before Photoshop did um and so basically again   as your brain is building the image of what it's  seeing out of all the information from cells in   the retina it pays special attention to the cells  right here on the very edge and makes something up  

um sometimes it's wrong most of the time it works  just fine and the reason that we have a blind spot   at all is to make room for the optic nerve this  is where all the neurons that make up the retina   their axons bundle together and make one thick  optic nerve that runs all the way to the brain

so let's let's zoom in on the retina so the retina  the retina is made up of photoreceptor cells one   type of which are rods these are sensitive to dim  light but not color this is because of the way   they are networked with each other there's nothing  special about an individual Rod that makes it more  

um uh more sensitive in dim light it is the way  they are connected to each other that changes   their sensitivity so they function well in low  illumination we have about 120 million rods   cones respond to color right they operate best  under high illumination we have about six million  

cones most of them are around the fovea right  and so our color vision is kind of bad along our   peripherals right and again the reason that cones  respond best under high illumination is because   they are they're the the way they are connected  to each other is different right then uh for rods

so yeah the fovea is densely popular with cones  and is vital to many visual tasks right when   you're looking directly at something  right your phobia is working overtime   so the way that your retina works is light  comes in right and this is correct right  

light comes in it goes all the way through  our retina where it reaches the rods and cones   and then that information Works its way back out   all right I'll do that with my uh Mouse  pointer here a little slowly so go light  

comes all the way in stimulates the rods  and cones and then it works its way back out   and through our optic nerve so we have first our  rods and cones which are networked to bipolar   cells these bipolar cells are attached to rods  and cones and then attached to ganglion cells  

the ganglion cells are a little bit like the glial  cells we talked about a couple weeks ago which is   basically like they're they're the support cells  they're the structural support but they also are   the ones who are receiving visual information and  finally passing the message along to the brain  

so it goes rods and cones then bipolar cells  then ganglion and then on to the brain and   this bundling of the ganglion axons is called the  optic nerve we talked about the blind spot already so an interesting fact about our visual field  that that is just kind of an interesting fact  

we don't need to spend too much time thinking  about it or talking about it is that our visual   processing is actually um a little bit inverted  which is the same our left visual field is dealt   with for the most part in the right side of the  brain and our right visual field is dealt with  

mostly in the the left the left part of our  brain incidentally and interestingly enough   um there is some overlap there and so the  way that things work is the information   leaves your optic nerve where it goes to the  thalamus on one side of the brain or the other

um in the thalamus it reaches something called  the lateral geniculate nucleus right which is   the part of the thalamus responsible for vision  all you that's all you need to know the lgn right   is part of the thalamus and it's about routing  information for vision right from there that  

information goes to the visual cortex all  right and so again information in your   right visual field goes to the left information  in your left visual field goes to the right Okay so when we think about uh color vision um  there are a couple different theories about how um  

color vision comes about the first is the  trichromatic theory very straightforward it   just says look there's three types of cones cones  that like green cones that like blue and Cones   are like red when they fire we get a good idea of  um what color we're looking at right and then you  

know if blue and red are firing together it means  we got purple right really straightforward um and   then what's nice about this theory is it explains  colorblindness really well which is this idea that when a person is colorblind one or more of  those cones isn't working right and if you are  

having trouble reading some of the numbers um  in either of these uh um circles here or you're   going there's numbers there I need you to talk  to your doctor um uh or go see an optometrist so   that's the trichromatic theory just different  cones like you're among all your rods and  

cones just three different types they  respond to different colors of light so time passes and you know historically  after the trichromatic theory and then   um we start to wonder about some other weird  phenomena of vision so for instance we see an  

after image when we look at a thing for a really  long time and then take it away we kind of see   it linger in our vision and trigramatic Theory  doesn't have an answer for that so out comes   opponent process Theory which basically says that  we have receptors right a little further along in  

um not necessarily in our retina but a little  further along the process closer to the   um visual cortex that get really excited by  one color and really inhibited by the other   right and so if it's a if it's a red excited  neuron it's going to see red and go yeah awesome  

amazing and then if it sees green it's going  to go oh I don't care about that I'm going to   fire really slow all right and so whoops  and so the way that this works is the way   that the reason this explains after images  is if I show you red for a really long time  

your red excited neurons are going to go yeah red  red red red and they're gonna keep chanting as   long as I'm showing them red they're going to  go red red red red they're super stoked super   excited and then you know what's going to happen  is I'm going to take that right away and they're  

going to go and as they're exhaling as they're  tired as they're fatigued they're gonna slow down   in the same exact way they would have slowed down  if I showed them green right and so that slowing   gets interpreted by fur uh by further along in  your visual system as oh those neurons are slow  

and we're seeing green show them green right and  that's where that green after images comes from   is your your red excited neurons are fatigued and  so once the red is gone they slow that slow that   slowed firing gets interpreted as seeing green  same with the you know the blue and yellow here  

okay so foreign I kid you not when um when I  teach sensation and perception the last couple   of slides that we've been going through starting  with the the stuff about light wavelengths that's   about four weeks plus so there's a lot more there  right you'll notice there are a couple of things  

I just sort of mentioned it didn't elaborate on  um just know that there's a there's a lot more   um to this uh especially on the biological side  that's super super interesting so please take a   sensation and perception class when you get  a chance so moving outside of the sort of  

cellular um and biological level right we also  need to think about how we organize the like   basically we've talked about up to this  point we'll start to give you an idea of   how we might organize our understanding of like  a particular object or like a single color right  

um we also need to start thinking about well  how do we put how do we come to understand the   environment we're seeing how do we put  all of this visual information together   in a coherent under into a coherent  understanding of our environment so  

part of that is we we interpret objects along  these different dimensions what is the shape of   the object how far is it how deep is it right so  is it far away and is it like a big round object   is it flat is it moving and how still is it is it  staying in one place right so one of the ways we  

think about organizing this information was put  forward by the Gestalt psychologists right which   suggests that perceptions are naturally  organized according to certain patterns they go on to say this idea that they lean  on a lot which is the whole is different  

from the sum of its parts which is to  say again looking at this picture right   um if you look at this new immediately go that's  corn right and you look at this and you go that's   rows of corn those rows belong together right  there's a there's a sense of wholeness to these  

rows as you look at them right and then even  further in the back here and with the Gestalt   psychologist for a reaction to was this was this  idea that like oh well vision is just you know   you know one visual cell is seeing a little yellow  another visual cells seeing a little bit of black  

and yellow and other visual cells seeing yellow  and we sort of like you know you basically with   pixels create an image like a social psychologists  are like no that's not really how perception works   it's not just like like pixel like pixels and  they wouldn't have known the word pixel at the  

time but it's easy to think about um what they  were objecting to by saying like our Vision Works   just like a TV does right um and the Gestalt  psychologists were like no it can't be that way   because when we look at things like meaning Beyond  what is present visually gets added automatically  

right you look at this and you automatically see  rows right you interpret these individual pixels   as forming a shape greater than just like you  know black next to Green right you see rows right   um and so the other way to think about this I  think is clear for some people is if if I come  

to you and I say um uh you're listening to your  favorite song and I say to you hey you know this   song is just a series of notes right you're going  to look at them and go well yeah you're right but   not really right because a song also has a melody  that doesn't exist until many notes are together  

right and so the gestational psychologists are  arguing that our perception of the world is   much more similar to the generation of a Melody  rather than just a series of notes put together   right and so some gestap principles are  the figure ground relationship this is  

the perception of like what is you know what is  an object versus what is the background right   um uh the the control principle of  closure is this idea that we we tend to   um depending on like the shape of um here we  go I have some examples for you this is an  

example of figure ground you can either  see a vase or two faces looking at each   other depending on what you're perceiving in  a given moment either the vases figure or the   faces our figure and then whatever is not there  is just the background right so this is a white  

vase with purple negative space or this is  two purple faces with white negative space   so closure here is this idea that even though this  triangle is not complete it still is very triangly   right same with the square same with this horse  right that's had its you know body basically like  

divided up we still look at this and we think  of it as one object even though it is many it   is objectively speaking what is drawn there is  many different objects and then we introduce   through our perception we introduce the shape  of the horse to this but it's automatic right  

proximity the same deal right this is a four by  four grid that we basically automatically see   as four lines right because of the principle of  proximity right there's this distance here that's   not here this way and so we see four vertical  lines similarity is the same thing we have we have  

Columns of circles and squares and rows of circles  and squares here right and we interpret the sense   of togetherness because they're the same shape  right and again there's nothing like in physics   right that says that the these things like  belong together in this way again other  

than their you know our perception  of them being close to one another um there we go so we use um binocular cues to understand uh

3D right and so the sense of disparity  right differences between how objects   appear to each eye and then convergence  the sense that the what we're seeing is   is converging toward one eye more than the  other gives us the sense of three dimensions  

uh those are our binocular cues that we need  two eyes for right you've all probably heard the   idea that if you lose an eye you get your depth  perception becomes worse and that's because you   lose these binocular cues but not you don't lose  your depth perception completely because there are  

monocular cues single IQs and so um things like  familiar size and overlap we know that children   are bigger than paint brushes so when we look  at this we see oh well these paint brushes must   be small because they overlap over the girl and  they're bigger than her and those things together  

are immediately processed as understanding  like oh these are small paint brushes in the   foreground the blurring helps too but uh we also  use like shading right differences in in Shadow   to to tell and if you're an artist you know the  the pain of trying to recreate this all too well  

um but ultimately we use Shadow and shading  and the location of light to help us understand   we also use a linear perspective or height in  the field here's the horizon line and this this   trainer God only knows what this is a picture  of actually [Music] um uh kind of going into  

the distance right tells us that well I I said  I caught me off guard and I said it goes into   the distance right we immediately perceive  this as like as a creating a sense of depth okay texture gradients as well again this  creates the sense of a singular plane that  

sort of goes off into the distance because of the  changing in shape of the elements of this texture so we have uh this is again a one we talk  about motion for an entire an entire week   um in sensation and perception we have specialized  motion detectors right our retinas and cells and  

the you know the the the the cells that make up  our visual cortex are designed to uh perceived   motion right there are specialized cells that are  designed to help us understand motion um Sometimes   some things create a parent movement right like  if you look at this it tends to seem to move on  

its own because it really seems to wrinkle those  uh those motion detectors so another thing that   we're interested in is constancy right perceptual  constancy so recognition that objects do not   physically change despite changes in vantage point  and viewing conditions this is very easy to it's  

a perfect example of this here's this woman she's  looking right out she's got this big old hair big   old smile right she's looking right at us and then  she turns to the side at no point does anybody   think this is a different person right this is  also why it's really hard for computers to uh  

um get really good at recognizing objects  is because people turn their heads a lot   right objects get viewed from many different  angles and so um we are able to perceive and   understand that this this is the this is the  same woman as the one in the picture up here

and so what happens when this woman is looking  at us and then looks to the side right it's   very interesting um her image on the retina is  going to change right this shape is different   than this these are two different images right  and so they're gonna appear on the retina in two  

different ways but at the perceptual level the  psychological level we understand that nothing   has changed right and so this is again one of  the interplay between stimulus and perception   right between sensation and perception right  objectively speaking the physics what is happening  

to our retina is dramatically different in these  two pictures but we know right psychologically   is the same person right and we do this with size  shape and color constances right um so consistency   and shape right like you know big hair in in  the front is big hair on the side right it all  

makes sense she's the same color right she's  kind of got these little Rosy Cheeks going   um it's kind of got a similar smile going  on right lip you know lips eyes everything's   the same color right she doesn't grow right  um and so the the ways that the that is how  

psychologically we understand like oh this is the  same woman in both pictures okay so I'll say this   um now might be a good time to take a little  break if you want you can hit pause on this   um because we've got a we've got a  few more senses to go through here  

um but uh um yeah let's hopefully pause and take  taking a break Let's uh let's come back and work   on sound so uh we hear sound because of sound  waves which are propagated through the air right   um that is how we get sound um so wavelength is  the distance between peaks of those sound waves  

higher and lower wavelengths determine  a frequency right which we perceive as   pitch so high frequency right um or really  short wavelengths right make higher sounds   so the whimpering of a dog for instance  is going to suggest hi frequencies right  

some wavelengths cannot be perceived just like  with light amplitude is the height of the wave   if amplitude for light represented brightness  I bet you can guess what amplitude is for sound   it is indeed perceived as loudness and then  we when we get a mixture of wavelengths we  

get complex sounds we perceive this as Timber  or tone saturation now some of you are going   to be like what could that be and this is super  easy actually um well once I give you an example   it'll be super easy it's okay to be confused  right now but this is very straightforward  

um if I play an a note on a saxophone  it is distinct from an a note on a piano   or a violin or a singer singing an a  note right and that's Timber the fact   that you can recognize the an a note out of a  saxophone or you know any brass instrument right  

versus an a note out of a piano  means that you understand Timber   all right let's talk about the ear look at  this look at this old image wired headphones   couldn't be me absolutely could be me love wired  headphones um this this wire wired uh wireless  

headphone trend is is the worst um so anyway we've  got these these old these are these are what the   original iPhone headphones look like this is an  old image fortunately the structure of our ear   hasn't changed terribly much over the years so we  have on the outer ear a couple of things we have  

the pinna that's your ear right that's the thing  that we the you know when you're an artist and   it's really the thing that's really hard to draw  that's the pinna so that the wrinkly floppy weird   thing on the side of your head that's the that's  the year it acts as a funnel to funnel sound in

here in the outer ear still is the auditory canal   uh the auditory canal you would think is just  like this is just the hole that sound goes down   but the auditory canal is designed such a way to  amplify sounds of certain wavelengths particularly  

the wavelengths we must associate with human  speech interestingly enough thanks Evolution okay   so sound goes to the auditory canal resonates  or doesn't with the uh the auditory canal and   then it reaches the eardrum which is the end  of the outer ear right that those waves hit  

the eardrum and then we move to the middle  ear right where that eardrum right hits   what are called the stapes right which are these  three bones the three smallest bones in the body   and so that eardrum gets hit boom and then the  ant the hammer hits the Anvil pushes the stir up  

right and what we get here right is we get the  wide eardrum and the impact of the white eardrum   being narrowed down to a thinner point right  and the inner inner point is going to knock   on what is called the cochlea which is the  snail-shaped spiral shaped structure here now

the the impact of the Stirrup here on the  cochlea is going to send a wave through the   interior of this cochlea which is going  to tickle a bunch of hair cells inside   the cochlea right these are not the ear hairs  that are going to start growing on your ears  

somehow right on your 30th birthday these are  much smaller hair cells on the inside of the   cochlea right the semicircular canals are here to  help with like balance and stuff like that and so the hair cells inside the cochlea get stimulated  they get stimulated in a certain way that is going  

to send a signal down our auditory nerve and then  we start to make sense of what we are hearing so a couple of different theories of hearing the  first is the place theory of pitch perception uh   now that I put that up let's go back here uh to  explain the place theory of pitch perception so  

the idea is that different frequencies of sound  are going to maximally stimulate different areas   on the cochlea in particular depending on the  frequency it's going to change how far in the   cochlea is maximally stimulated The Sounds  usually going to get the whole way through but  

if it's pretty low frequency sound we might  find ourselves getting maximally stimulated   right here where a higher frequency might  make it further in that kind of thing and   So based on where the cochlea is being maximally  stimulated we explain our our sense of pitch this  

only works for high frequencies so instead we  look at the frequency theory of pitch perception   right which is this idea it's very interesting  idea that you know sound is coming in waves   right each Little Wave causes a new round of  nerve firing is the idea and so a really high  

frequency sound is going to cause firing rights to  go like right and a low frequency sound is going   to cause the neurons to be firing at a slower  Pace boom boom boom boom and that pace of firing   gives us our interpretation of frequency  right the issue with this is neurons can  

we fire so quickly neurons have something  called and we didn't talk about this in   um uh in our Biology lecture but that's okay  neurons have something called a refractory   period which is that after a neuron fires  that there's time before it can fire again  

we explain this away by something called the  volley principle in which neurons fire like   um if you think back to if you think back to the  Revolutionary War where one round of Musketeers   would fire step back and reload but another group  that was already reloaded would step forward and  

fire again you would get these waves of fire  like boom boom boom boom because you'd have   three or four rows of people who are constantly  in different stages of reloading firing so you   could get consistent volleys off right and there's  the idea that neurons would work like that where  

one group would fire rest while another group  fired right and this way these different clusters   of cells sending different volleys could beat  the firing rate imposed by a refractory period the way that auditory information moves through  the brain as it goes to the cochlea the auditory  

nerve from there to the brain stem up to the  thalamus and then into the temporal lobe right   again we have a crossing of information across  hemispheres right where we go again from the   cochlea to the auditory nerve and then um based  on how it is relayed the temporal lobe then helps  

us develop uh helps us organize the sound and  then really there's another step where this goes   to the frontal lobe where we get to the place  of recognition and decision making around what   we hear so we use intensity which tells us about  distance and sound Shadows when localizing sound  

now sound Shadow is really straightforward um  you know how you can if you listen to music uh   you're walking let's say you're walking by like a  club and you can kind of hear the I wonder I hope   that's going through the audio but that muted bass  right that is you experiencing a sound Shadow and  

you immediately understand oh that's because music  is coming from deeper inside this building and   only the bass is reaching me then you step inside  and boom there's all the music all the treble all   the other instrumentals all that and so the sound  Shadows when an object blocks or interferes with  

the sound waves it's going to mess up the  intensity of what you're hearing so far away   sound sound behind an object timing also right  timing also is going to give us information about   where sound is now what's interesting is that  many of you probably um have taken a little  

bit of trigonometry at one point or another and  um if you're like me maybe your memories of it   aren't particularly fond but the good news is that  your ears do a bunch of trigonometry all the time   um your ears your ma your brain uses information  about how quickly Sound reaches each ear because  

remember sound compared to light travels  relatively slowly and your brain is actually   able to parse the difference between when a  sound in your environment reaches each ear   and uses that information to help you  pinpoint where a sense coming from

so let's talk about the other senses let's get  to our cutaneous senses starting with touch   so those receptors for touch receptors we have  about four different types of tetracceptors that   deal with different kinds of touch and that's not  even including receptors for temperature um uh  

and other kinds of uh input but we have our touch  receptors that connect to the spinal cord that go   up to the thalamus and then they make their way  to the somatosensory cortex in the parietal lobe   right um to help us understand what we are feeling  right we have thermoreceptors who respond to warm  

and cold interestingly enough simultaneous  warm and cold gets perceived as hot [Music] when it comes to pain we have different kinds  of pain receptors mechanical heat and chemical   receptors beyond that these receptors then also  have responses along fast and slow pain pathways  

your fast pathways are about getting you away  from that so if you touch something in the oven   and it's hot your hand is back before anything  and then there's that moment right you all know   what I'm talking about any of you who've ever  cooked or ever burned yourselves right there's  

that moment where you touch something  and you immediately withdraw your hand   and then there's that beat you get a second  you get some time to go oh this is gonna hurt   and then the slow pathway kicks in right and  you're like oh that hurts right and you have  

to go put your hand under some water and hold it  there for a while and hope you have somebody else   to take the lasagna out of the oven right and  that's that slow pain pathway and you I don't   hope but I'm betting many l of you have this kind  of experiences stubbing your toes the same deal  

there's that initial stub and then your your  spine kicks and it's like oh get your toe out   of there right and you immediately with trap  with withdraw and then there's that slow pain   pathway that's where you're cursing up a storm  the fast paying Pathways where you go ow and  

you're not even sure if you really hurt yet  then that slow pain pathway that's when you   start cursing start yelling and then your wife  comes in like what's wrong and then you're like   I stub my toe and then you know that whole that  whole song and dance that's the slow pain pathway

um we release our natural opiates called  endorphins when we experience pain to sort of help   us um get over it enough to ideally get ourselves  to safety right this is why in some cases   um with really severe injury um with the  help of adrenaline endorphins help us  

um do the things we need to do to get to safety um  and so a lot of people who have suffered injuries   in combat will talk about the pain not really  settling in until they even realize they've   been injured or you know didn't really settle in  until we were you know we were in the you know  

we were being evacuated right and that's the  help of endorphins and then perception plays   a huge role our cognition plays a huge role in our  experience of pain um being distracted lowers our   experience of pain being told that what's about  to happen will not be particularly painful helps  

um listening to soothing music helps being  in a good mood helps um knowing that the pain   you're going through does it like understanding  that the injury you've sustained isn't going to   um cause life lifelong harm being like Oh yeah you  lost your finger but you know you'll be able to  

reattach it hurts less than an injury that you're  you know not sure you'll ever recover from foreign touch and visioneral energy senses they rely on  energy in the environment either in the form of   photons sound waves or direct like somebody  touching you right or an object coming into  

contact with you and transferring some energy  to you or taking some away in the case of cold   um our chemical senses are smell and taste  and they are all about specific receptors   designed to bind with the kinds of chemicals  we'd experience in the environment so um

yikes um give me one moment I deleted that image what a shame all right nice that should be

sorry about that folks there so we have receptors  on the uh on our tongue called uh uh papillae   um they uh respond to sweet sour bitter salty  and then um uh also uh the the flavor of uh   Umami Umami is a recently discovered um uh taste  um that is sort of responsible for the kind of  

savory meatiness there's a cultural influence here  where um Western culture did not have a culinary   culture of cultivating the flavor of umani um now  we do um an example of this that's kind of fun   um uh that I like I like to cook it was a one  of my um uh hobby I cultivated over the pandemic  

um uh some recipes um call for the use of fish  sauce which is a traditionally like more Eastern   condiment called the use of fish sauce in  Bolognese which is a an Italian meat sauce   they'll call for the use of fish sauce  um if you use fish sauce you do not have  

to cook the food you don't have to cook  your sauces long to cultivate the sort of   umami flavor that you generally get from  stewing meat for a really long time for instance   um so I don't know just a fun fact about the fact  that um uh there are you know there are more uh  

senses and tastes probably than we're aware of  and um we cultivate our understanding of these   things by coming into contact with other cultures  right it's why um to me this is a very clear-cut   example of why um uh inviting many perspectives  into um into your spaces is super super important  

because it doesn't matter how open-minded you are  if you are not from a particular culture it's you   know it's going to take you a lot longer  to become aware of the the wholeness of uh   a human experience right because we literally  like when I was in when I was in elementary  

school was not taught about Umami right because  if it's a relatively recent uh realization so   um uh again like there's there's a cultural  influence on on taste for smell um uh uh our   olfactory epithelium is uh this the structure kind  of above our sinuses that is there to kind of like  

we we breathe in and then it is it is picking  up the materials that we uh that we breathe in   um so yes when you smell something no matter  what that thing is that means that there are   um uh particles of it um now in your nose so  um have fun uh with that piece of knowledge  

um from there this runs to through the  temporal lobe and the limbic system and uh uh from there we we begin to process stuff  related to like recognition right again getting   into the the from there to the frontal lobe  right um people talk about a lot the relationship  

between smell and memory um where it's like oh I  smelled that and it took me it it takes me back   um uh that connection is still being um is still  being understood um the truth for for taste   and smell is that um taste and smell are both  senses that are incredibly well interconnected  

um an example of this is uh tasterversion right um  all it takes is one bad food poisoning experience   um to cultivate in some cases to develop in some  cases a lifelong aversion to a particular flavor   um I have a personal example of this I was in  college um my roommate at the time was getting  

really into cooking he made these pork chops with  this like hollandaise like sort of horseradishy   sauce and I got food poisoning for three days  from them um and so now um there's a it was   I mean it was they were delicious um but that  particular flavor profile still makes me queasy  

um I remember it very vividly um and so um many of  you probably have similar experiences with other   Foods you know anytime you've consume something  that eventually made you vomit or get sick   um you are likely to give it a second thought  before you consume it again and uh so that  

connection between like the chemical senses  and like and memory is probably really strongly   adaptive right of like is lucky that I survive  right thinking about um you know when you get   diarrhea or get food poisoning or any kind of  vomiting um if you are an environment where  

water and other food is scarce though that kind of  illness can be a death sentence right so thinking   about to our earliest ancestors and so it's very  adaptive to be like hey if you survived getting   sick from a food you need to never eat that food  again because it's you got lucky right and so it  

makes sense that we would have those built in um  systems to help us remember well the tastes and   smells around us that are significant so that  we can avoid or approach them in the future   foreign so we have other senses there's more  than five senses five senses was just a number  

Aristotle made up like you know 2500 years  ago um that number's not exact but um and so   we have more senses we have a kinesthetic sense  which is about movement posture and orientation   understanding where your body is in relation to  the rest of your body and in space and your sense  

of balance all of those things right so that's  the appropriate step to feedback is understanding   like kind of like where your body is relative to  the other parts of it right our vestibular sense   governs balance actually so it's another another  extra sense um our balance and acceleration our  

sense of movement those semicircular canals  in your ears really impact that um and so um   yeah I mean that's that those are um kind of  a again today's lecture this conversation uh   has expands out very easily right when I when I  teach Sensational perception I still have a hard  

time fitting everything in the 15 weeks let alone  this you know hour and change that that I've been   talking to you folks about this and so um there  is there are a lot of a lot of details that that   we've glossed over again make sure you do your  reading about this uh of this chapter and then  

when you get the opportunity take Sensational  perception it's like a it's a foundational topic   within psychology it's wild to me that it would  be considered to be optional in some cases and   so make sure when your upper division classes for  psych is bio make sure one of your upper division  

psych classes is sensation and perception  and then after that go ham have fun focus   on whatever you want but sensation perception  is absolutely foundational to understanding how like physically our minds relate to the  outside world right and if you feel like  

the picture of that is still fuzzy that  makes sense because there's many more   details for us to touch on so again I want  to thank you for your attention and effort   um and work this week um and I  will talk to you all very soon