S&P exam 3 - ch 9 , 10 , 15

Color

Why do we need color perception?

·      Perceptual grouping

o   How things go together to organize and group features together

o   Powerful visual cue & grabs your attention

o   Helps to quickly understand and identify an object

§  Example: The result was that observers recognized the appropriately colored objects more rapidly and accurately. Thus, knowing the colors of familiar objects helps us to recognize these objects.

o   color also helps us recognize natural scenes and rapidly perceive the gist of scenes.

·      Aquatic animals are monochromatic

o   Dolphins only have one type of chrome cells

·      Most animals are dichromatic

o   Dogs and bears etc. Have two types of chrome cells

·      Animals like humans and monkeys are trichromatic

o   Have three types of chrome cells

Light spectrum

·      Color is a mental response

o   We have evolved to respond to the color wavelengths

o   Different wavelength patterns can lead to the same color perception

·      Starts with a light source

o   White light is made up of all the frequency’s at the same levels

o   Selective reflection: All frequency’s hit the apple, the apple absorbs most of the color frequency’s and then reflects the color red and doesn’t absorb it

§  Reflectance curves: shows how much is being reflected

§  Achromatic color: doesn’t map onto any of the hues from the light spectrum

·      Something like white, grey, black

·      Reflectance curve is a flat line because it’s equally reflecting all the different parts and colors from the light spectrum

·      More or less dependent on how dark or light the grey is

o   Selective transmission: light passing through something

§  Absorbing all parts of the spectrum that don’t look blue but it isn’t bouncing off and hitting your eye but its passing through things like glass

o   Subtractive color mixing: Each components is subtracting out the spectrum of light but is leaving behind the little bit that isn’t being taken away

§  Mixing colors together ; paints

§  End up with black

o   Additive color mixing: adding not subtracting color light

§  Mixing lights together

§  End up with white

How do we distinguish colors?

Dimensions of color

·      Hue: what makes green look different than blue etc.

·      Saturation: how intense and how pure is that color

·      Lightness (value): adding in different shades of grey to make them lighter or darker shades

Dimensions of color:

Color theory

Trichromatic theory of color

·      The theory that color perception is based on the combination of three independent colors

o   Red, green, and blue

o   Additive color theory (adding lights together)

·      Young-Hemoltz theory of color vision

o   Color matching studies

§  Give someone a reference color and then give them control over different colors of lights and they try to recreate the standard color you gave them with adjusting the lights

§  If you give them three colors then they could match any color, compared to if you gave them two or more than three, they wouldn’t be able to recreate a color

o   S-cones (short) (blue)

o   M-cones (medium) (green/yellow)

o   L-cones (long) (yellow/red)

§  Refers to the wavelengths of lights

§  One cone on its own can’t tell you anything about what color you’re perceiving, you need 3 different cones that vary in brightness

§  Proportion of responses from different cone types

§  Perception: When cones are hitting at the yellow, there is an equal firing response from L and M cones because it is hitting the same level of sensitivity

§  Metamers: When you have different wavelengths of light that lead to the same color perception

·      Red, green, and blue are metamers of white

Color deficiencies

·      Total color blindness or color deficiency: partial color blindness

o   occur at birth because of the genetic absence of one or more types of cone receptors

Monochromatism

·      Aka color blindness

·      Can’t distinguish color from any other color

·      Can only see darkness

·      Very rare

·      Can make out shapes but everything would be very blurry

·      This is because they don’t have any cones at all, they only have rods

o   Very sensitive

o   Poor acuity / clearness

Dichromacy

·      Having only two receptors instead of three

·      Can be any of them that are missing:

o   Protanopia: impairment of the L cones

o   Deuteranopia: missing M cones

o   Tritanopia: missing S cones

·      What are these people seeing?

o   Unilateral dichromats

o   Deficiency in only one eye

o   Normal trichromatic (three cones) in one eye and the other eye has dichromacy (only two cones)

§  When diagnosing these deficiencies; use Ishihara plates

o   Red, green color blindness

Anomalous trichromats

·      Have three different types of cones but one of the cones sensitivity has shifted over a little so it overlaps with another

Sex linked conditions

·      Genes that produce photo pigments are located on the X chromosome

·      Genetic females could still have normal vision since they have one normal X chromosome and another infected X chromosome

·      Females could only really get it if they inherit both X chromosomes being infected

·      Males are more likely to get it because they only have one X chromosome so if they inherit it they will definitely have it

Color afterimages

·      Showing the opposites of the colors you’re going to see because the opposite of that color is what is still lingering

·      Opponent process theory of color

o   The way we perceive color isn’t made up of the three colors, its made up of colors that oppose each other

o   Dimensions of opposing colors combine to form our color perception

·      Hue cancelation studies

o   Added yellow light to try and cancel out the blue color

o   Can cancel out yellow with blue – vice versa

o   Can cancel out red with green – vice versa

§  Opposites don’t exactly match up with green and red

§  Red is the opposite of a light blue and green is opposite of a magenta

·      Different “theories” of color

o   Turns the trichromatic three cones (independent of each other) into the opponent process (blue vs yellow) which is what is then sent to your brain

§  How much yellow is there vs blue is what is sent to the brain

Impossible colors (not in textbook)

·      Some combinations that are just not physically possible in the real world because of the way the cones overlap and interact with each other

o   True cyan: S and M cones, with no L

§  Whenever you see cyan in the real world; the color is being desaturated / washed out some

How do you go from trichromatic to colors vs other color?

·      Has to do with receptive fields

o   Combining their information together that leads to one signal

o   Center surround fields

§  Have one kind of connection in the middle and a different on the outside

·      Inhibitory on outside

·      Excitatory on inside

o   Single opponent fields

§  Still has excitatory and inhibitory sections but on top of that, the signals are excited by different color factors

·      Center is excited by M cones (green)

·      Outside is excited by L cones (red)

§  (images)

·      Just one example of a single opponent field you can have

§  Turning a trichromatic signal into a continuum that’s green vs red

·      The “opponent” meaning

o   Double opponent fields

§  (images)

§  It would lead to no response at all because the signal from the one side is going to be completely signaled out by the color from the other side

§  Would get an inhibitory response if the red is against the green since the M is – in the red block so it would fire negatively

§  Would get an excitatory response if there is a boundary between the two colors; red and green

·      Responds strongly to the boundary between two colors

·      Does not respond to solid colors

§  (image) The boundary is being detected by our double opponent field which is why the white inside looks more orange than the white outside since it is lined with a boundary of orange vs purple

·      (don’t have to know the watercolor name)

·      Color constancy: Still able to recognize and detect the color itself, despite changes in environment or to it like the color of the light above

o   In example picture, can still tell that the color is red when there is a blue or green shade overtop of it but the red is actually a very dramatic change from the original red

o   We are compensating for the color of the lighting that we see in the picture

§  Mind is trying to compensate by subtracting out the blue light that is covering it which leads you to the original color; being red or yellow

§  Your mind perceives it as yellow even though it is actually a greyish

o   Real world situation: under different shades of white light in a room or during “golden hour” from the sunset or sunrise outside

§  Chromatic adaptation: similar to the ‘color after affect’ where ; you’re adapting to a color after looking at it for a while, and then after your receptors just don’t react as strongly as they did

·      Can also partly explain what’s happening in the images covered by a different color light

·      Lightness constancy:  accurately being able to detect the lightness of an object despite the brightness of light that is hitting it is changing

o   Black absorbs most of the light but not all of it

o   White reflects most light

o   Reflectance: amount of light being reflected by white vs black

o   Illumination: how much light is hitting the object in the first place

§  The factors of light (sun outside vs lights in a room) changes the amount of light being reflected off and is hitting your eye

·      Sun is much brighter than the lights in a room

·      (image)

·      The amount of light reflecting off of black when its being hit from the sun can be a lot higher units than the amount of white units that are bouncing off a white object when in dimmer, inside lighting

o   Depends on the amount of light hitting it

§  Ratio principal: lightness perception is based on the ratio between an objects light intensity and the light intensity of its surroundings

·      (image) ‘A’ and ‘B’ are actually the same color but they don’t look like the same color because of its surroundings and our mind making ‘B’ look lighter than it actually is since we see there is supposed to be a shadow over it

·      Reflectance edge: edge caused by a change in reflectance; a change in the actual color of the object

·      Illumination edge: edge in a scene where difference in brightness is caused by illumination ; objects color are both the same but more light is hotting one making it look brighter or darker

o   Dress example: The reason people can see it different ways is because of color constancy

§  When seeing blue and black; mind is compensating by subtracting out the bright yellow light from the background

§  When seeing yellow and white; mind is seeing it being under a shadow so you’re compensating and brightening the colors up

Lightness constancy

Identifying shadows

·      Penumbra: The fuzzy boarder around shadows edge

·      Meaningful shape:

·      Orientation of the surface: What direction is the surface pointing

Depth Perception

·      Inverse projection problem: makes depth perception harder

o   Makes a 2D picture eon your retina

o   Information you have on your eye is incomplete / ambiguous; can interpret it in any way

o   (man taking picture/ballerina

o   Hollow mask illusion: mask looks like it is sticking out on the hollow side, fooling your mind

·      No single solution

o   We rely on many different sources of information at once

§  Oculomotor cues: Cues that make use of the information using the muscles in your eyes

·      Paying attention to the tension in your eyes and using that to know how far or close something is

·      Can put strain on your eyes which helps you detect how close or far an object is

·      Convergence: eyes aren’t looking straight ahead; they’re focused in a little to both be looking at the same thing

o   The closer the object moves to you, the more your eyes turn in

·      Accommodation: when somethji8ng goes out of your eye it goes out of focus so you have to squeeze the lens to focus, making you tense up those eye muscles which you can detect

§  Monocular cues: can tell the depth even if you’re looking at it with one eye

·      Pictorial cues:

o   relative size: the farther away an object is from you, the smaller it is

o   relative height: the height in the picture, lower on the visual field= closer, higher up= farther away

§  for things that are above the horizon

§  the closer it is to the horizon, the farther away it is / farther from the horizon = closer to you & bigger in your vision

o   occlusion: “occluding your view” / “blocking your view” when something is covering another it is closer to you than what its blocking

o   perspective convergence: parallel lines come together as distance increases; they meet at the =

§  vanishing point: where all converging parallel lines come together at

o   familiar size: using knowledge of how big things actually are to figure out how far away they are

§  example: if a basketball and golf ball are both technically the same size on your visual field,

o   texture gradient: elements of patterns get smaller and more densely packed as they get farther

§  works on a big scale

o   atmospheric perspective: as stuff gets farther from you it looks hazier and lighter

§  from particles in the air and atmosphere

§  works on a big scale

o   shadows: changes your perception of where the object is moving or is placed in space

·      renaissance pictures use all of the cues and use them really well, making it look more realistic

§  Binocular cues:

·      Involves vision using both eyes

·      Stereoscopic vision: visual perception that uses information from both eyes

·      Binocular disparity: Slightly different picture in one eye vs the other

o   slight difference in the images seen by each eye due to their horizontal separation. This difference is crucial for depth perception and stereopsis, allowing the brain to interpret three-dimensional structures from two slightly different two-dimensional images

·      Corresponding Points: same location on each retina

·      Noncorresponding points: different locations on each retina

o   Finger on one retina is in different place on another retina, so appears as double image

o   Move along the = Horopter: the arc where everything is the same distance from one's eyes, all lead to = corresponding points- same location on both retinas

§  Everything on the horopter has corresponding points; The farther away from the horopter, the greater the absolute disparity

·      Absolute Disparity: difference in location off an objects image on the two retinas - how far off is the image on one retina compared to the other retina

Binocular Depth Perception:

§  Stereopsis: perception of depth that comes from binocular disparity

·      Perception of depth that is determines from point to point

§  Correspondence Problem: How do we figure out which points in each retinal image are in the same location in space?

·      Random Dot Stereograms: Two pictures presented to different eyes to give you a perception of depth

Stereopsis in the brain:

§  Disparity Selective Cells: Neurons that respond best to a particular degree of absolute disparity

·      Stimulating specific Neurons in monkeys

o   Stimulate a disparity selective cell, can change its perception of depth

·      Covering one eye of kitten, switching each day

o   Cats eyes did not develop disparity selective cells in the same way they normally would

§  Shows these cells are components that effect depth perception...

§  Different Species:

·      Eyes in front of head/face in predators: gives good depth perception, much wider range

·      Eyes on side of head in prey: both eyes cover both fields, less overlap - worse depth perception, much bigger FOV

Perceiving size

·      Visual angle: amount of the visual field (or the retina) that’s covered by a stimulus

o   Measure by angle because our eye is a sphere so the amount of your vision it is taking up is the visual angle

§  Example: holding your thumb up takes about 2 degrees of visual angle

o   Same amount of visual angle can be covering very different sizes

§  Visual angle on its own can’t tell you the size of something

§  But, if you know the visual angle and the distance, you can use those two pieces of information together to determine its size

Example: balloon is in the same spot and is taking up the same amount of space on both screens but the shadow shows the distance which helps you know the size

§  If you know the visual angle and the size of the object, then you can determine the distance

·      Example: know how big a basketball is

§  Size = visual angle x distance

·      Can use any two of these to find the other

§  Twice as far = ½ the visual angle

o   Emmerts law: size of afterimages judged by surroundings

§  Adapting the receptors on this part of your visual field, when you look at some4thing close to you compared to far away, its taking up the same part of your visual field but will look smaller or larger based off the distance

·      Size constancy: we can perceive things as being the same size even when their visual angle is changing at different distances

o   Mind makes things farther away smaller to compensate

§  Ponzo illusion: have objects along converging lines; when something is farther away it looks bigger to you

§  Shepard illusion: compensating for your depth perception; the two tables are the same shape

§  Muller-Lyer illusion: lines with arrows pointing inwards or outwards; perceive the line where its pointing outwards as longer compared to the line with arrows facing inward when they’re actually the same size

·      Conflicting cues theory: because one object is bigger overall then we are using that as an extra piece of information to judge how big the line is

·      Ames room: gets rid of any depth information that tells you that one side of the room is closer to you than the other

o   Tricks you into thinking two things are the same distance from you, making you think one is much bigger

·      Moon illusion: when you see the moon on the horizon or close to it, it looks much bigger than it does when it’s up in the sky even when it’s the same distance because it looks farther when it’s in the sky so it looks smaller in the sky than it does in the horizon

o   Takes up ½ degrees of visual angle when in the sky

o   Apparent distance theory: ?

o   Angular size contrast theory: when you’re seeing the moon directly ahead, there is nothing around it so you’re comparing it to the empty sky so it looks small but when it’s on the horizon you’re comparing it to the other things around it like the trees so it looks bigger

·      Development

o   When babies learn to develop familiar size cues

§  Played with toys of different sizes

§  5 months they don’t show the effect, just as likely to grab for either one

§  Couple months ~7 months later they learned how to use the distinction of familiar sizer and grabbed the bigger one first, thinking it was closer to them

o   Shadows:

§  Same age range of when they learned how to take advantage of the shadow information, thinking the one with deeper shadows was closer to them

Cutaneous perception

Made up of information that you can get from your skin and your body

·      Cutaneous senses: Completely different types of signals that pick up different types of information

o   Pressure

o   Vibration

o   Pain signals

o   Temperature

o   Itching

o   Proprioception

§  Knowledge of where your body is in space

o   Mechanoreceptors: receptors in the skin that respond to mechanical information (physical force & motion on your skin)

§  Can involve pressure, movement, vibration, and stretching

§  Slowly adapting receptors (SA): respond to pressure stimuli

·      Example: Something is pressing on you for a second and then it goes away

·      These receptors are going to start firing when the pressure starts and then keeps firing the whole time something is touching you

§  Rapidly adapting receptors (RA): responds to changes in pressure stimuli

·      Start firing as soon as contact starts but almost instantly stops firing and then starts firing again when the pressure stops

·      Get used to the stimulus really quickly and fires again when there is another change in pressure / when the stimulus is taken away

·      Has squishy stuff around it:

o   Example of hand in a water balloon, you’d feel if someone’s hand was pressing down on the balloon and then wouldn’t feel it if they kept their hand there but then once they took their hand off you’d feel it and the water would move around

Near surface of skin:

§  Merkel receptors (SA1) = slowly adapting receptors 1

·      Good at picking up fine detail

§  Meissner corpuscles (RA1) = rapidly adapting receptors 1

·      Important at detecting motion on your skin

·      Useful at adjusting hand grips because pf the change

Deeper down in skin:

§  Ruffini Cylinders (SA2) = slowly adapting 2

·      Good for detecting stretching in your skin

§  Pacinian corpuscles (RA2 / PC) = rapidly adapting 2

·      Important for detecting vibration / a pressure that is coming and going quickly

·      Detect fine texture

Brain

·      Primary somatosensory cortex / receiving area / S1

o   Soma = body, so =  body senses

o   Homunculus= little man / map of human body inside of your head

§  The way it is like the body is that the responding areas are mapped out in the same order for the most part

·      But.. there are a few body parts in the cortex that are out of order

·      The size of each area is also not correlated to the bigger body parts

o   Cortical magnification:

§  The reason the body parts like hands have bigger areas in the brain than say the leg is because you have better perception in those parts of your body

o   Experience dependent plasticity:

§  Example: Monkeys trained for 3 months on task involving index finger

·      Results showed that there was a change in how much of the brain is designated to a certain body part just from their experience

o   Tactile acuity:

§  The level of small detail that you can pick up and be perceived through touch

Can measure this through:

§  Grating acuity: the participant would tell you if the lines of the grating were horizontal or vertical

§  Two point threshold: measuring with an “aesthesiometer” where you can adjust the two points where it ends up feeling like one point instead of 2 and can measure how close or far apart it has to be to still be able to tell its 2 points

·      Have really small two point threshold for fingers but compared to the arm the threshold number is much higher so it’s harder to detect if its two or one points

·      This relies on the Merkel receptors (SA1) because of the amount of these receptors in a certain space

o   These receptors are more spaced out in the arm then they are in the fingertip

·      Pinky and index finger have same number of Merkel receptors but your index finger has better acuity than the pinky because of the experience and use – like how it was in the monkey tactile acuity study

§  Receptive fields: separate receptor fields in parts of body that have good acuity like in the fingers but in body parts with less acuity like the arm the receptive fields are much bigger and overlap a lot

Texture

detecting repeating patterns of fine details

·      Pacinian corpuscles are good at picking up fine textures because they can detect vibrations

o   Example: when pressing down on fine parts of sandpaper, people couldn’t tell the difference in fine textures just by applying pressure

o   But could tell the difference with movement

o   This is because it is able to be transmitted through vibrations

·      Spatial cues: texture features that are large enough to detect with stationary pressure

·      Temporal cues: smaller texture features that are detected through movement

·      Texture example: turning off people’s ability to detect vibrations to see if they were still having the same results of telling the differences between different grids of sandpapers

o   When exposing them to 6 minutes of 250 Hz of vibration the PC cells adapted because they were overwhelmed which caused them to not be able to feel the vibrations anymore and not be able to tell the difference between the sandpapers

·      Haptic perception: perception based on exploring objects in the world through touch

Involves multiple systems:

o   Somatosensory system

o   Motor system: moving around to be able to feel different parts of the object to get the information you need

o   Cognitive system: doing trial and error, feeling different parts of the object coming up with ideas of what it could be

Exploratory procedures

§  Lateral motion: moving fingers across surface of something

§  Pressure: tell you about the density of object (hard like rock or soft like sponge)

§  Enclosure

§  Contour following: move fingers to find what shape is