PSYCH 3310: Sensation and Precession

Why do we need color vision

Classification and identification of objects

organize visual perception

evolutionary advantage in finding safe food

color helps determine health of potential mate

Additive Color Mixture is

how screens work:

adding light wavelengths together creates new colors

when all primary colors are combined=white

Subtractive Color mixture is

how paint works:

removing wavelengths from white light so each new pigments reflect fewer wavelengths 

when all colors are combined = black

Digital Screens 

RGB elements activated by electrical charge causing them to glow 

by combining 3 colors into hue is created in one pixel.

Printer Carts

Pigment produces color using reflected light

Cyan, Yellow, Magenta and Black 

starts with white paper and ends black: color is added the result becomes darker

Gen Color Wheel

Primary: RYB- no other colors can be mixed to create them

Secondary: GOV- combine two primary colors

Tertiary:[R-O; R-V; Y-G; Y-O} combine primary and secondary

Hue

color in pure state position on color wheel, think genetic bar shown for color wavelength 

Intensity

How bright or dull color is (AKA saturation), think full to white color bar

Vaule

How light or dark color is

• Tint= white + hue

• Tone= gray + hue 

• Shade= black + hue 

• think three bars scale from how bright color is with three scales to white, gray and black

Three Steps of color

1. Detection

2. Discrimination

3. Appearance

Detection

Wavelengths of light must be detected in eyes

Discrimination

Must be able to tell the difference between one wavelength ( or mixture of wavelengths)

Appearance

assign perceived colors to lights and surfaces in the world and have those perceived colors be stable over tiem, regardless of different lighting conditions

Color Detection

S-Cones (“blue” cones) {PEAK 420}

M-Cones ('“green”cones) {PEAK 535}

L-Cones (“red” cones) {PEAK 565}

Photopic Vision

Occurs during day or bright light 

Increase color perception and sharpness

Requires use of central vision

Relies on both rods and cones photoreceptors 

Date based on photopic lumens

Mesopic Vision

Occurs during transitional light

Mixed color perception  

Most nighttime lighting is this 

relies on both rod and cones photoreceptors  

Scotopic Vision

Occurs at night or in dim light

decreases visual acuity 

causes loss of color perception 

requires use of peripheral vision 

relies heavily on rod photoreceptors 

Rods and the problem of univariance 

• Rods are excited by any wavelength of light 

• Respond best to different intensities of light

• One photoreceptors can’t differentiate between a change in wavelength and a change in intensity because it’s using the same photopigment. 

• Need to compare with other receptors for color vision 

• NEED cones for color discrimination 

Color Discrimination

Trichromacy: color of any light is defined in our visual system by relationships of outputs of three receptor types 

3 cones cause tri

Trichromacy with cones

• with 3 cones; can tell difference between lights of different wavelength based on combo of activity 

• under photopic conditions S-M-L are active  

• Different wavelength (chromatic light) elicit different responses to each cone type

Why isn’t 1 enough

Just having one cause ambiguous 

• CAN NOT tell a weak signal at the peak sensitivity from strong signal at an off-peak intensity 

Cone response 

Aborpiton spectrum x light intensity 

Special case of yellow (Under Metamers)

white light wavelengths are attempted

blue and similar light wavelength are absorbed

red, green and similar light wavelengths are reflected, the eye sees yellow

• Total stimulation of M cone is equal to TOTAL stimulation of L cones 

Introducing Metamers

• two lights can match if they evoke the same cone responses

• Many things in natural world have different spectral properties, but look the same to us 

  • Con: We can be tricked and think things look the same when they do not 

  • Pro: We can use this tot our advantage to have pixels create different perceptions

Defining Metamers

Metamers: Different mixtures of wavelength that look identical

• Generally, pair of stimuli that are perceived as identical in spite of physical differences 

Afterimages ( a part of Opponent-Process Theory )

Visual image seen after stimulus has been removed 

Negative afterimage: An afterimage whose polarity is opposite of the orginal stimulus

• Light stimuli produce dark negative afterimanges

• Colors are complementary:

  • Red= Green after images (vice-versa)

  • Blue= Yellow after images (vice-versa)

How can we a percept in absence of a stimulus

• Afterimanges occur due to fatigue and temporary desensitization of photoreceptor cells in retina after prolonged stimulation by bright or colored image.

• When you look away, these fatigued cells can not respond as effectively to new light, causing you to see a faint, residual image.

• Opponent photoreceptor are not fatigued so are more able to fire, thus changing the perception of color.

Opponent- Color Theory

Some cells in LGN are Cone-Opponent Cells 

• Respond to RED-center/GREEN-surround and vice-versa for the first time

In primary visual cortex, Double-Opponent color cells are found for first time

• More complicated, combo properties of two colors opponents cells from LGN

From receptors to opponent process pairs

Blue- Yellow- excited by short-wave receptors and inhibited by medium and long-wave receptors 

Red-Green- excited by short-wave and long-wave receptor elements and its inhibited by medium wave elements

Greek names

Pro=Red

Deuter=Green

Tri=Blue

Color-Vision Demo

85 of male pop, .5% of female

Due to missing M or L cones

Achromatopsia

Only rods and no functioning cones

Very rae

only in white,gray and black tones

true color-blindness, poor visual acuity

very sensitive eye to bright light

Dichromatism: Only two CONES

Protanopia:

Deuteranopia

Tritanopia

Protanopia

see short-wavelength as blue

missing long-wavelength pigmen t

Neutral point = 492nm.

Above Neutral see yellow

Deuteranopia

see short-wavelength as blue

missing Medium wavelength pigment

Neutral point = 498nm.

Above Neutral see yellow

Tritanopia

see short-wavelength as blue

missing short-wavelength pigment

Neutral point = 570nm.

Above Neutral see red

Surface Reflectance

How much light an object reflects as function of wavelength 

fraction of incoming light that is reflected back

Color Constancy

visual system uses a lot of tricks to make sure things look the same color regardless of the illumination (light source) 

• Tendency of a surface to appear the same color under a wide range of illuminants 

  • To achieve this, must discount the illuminant and determine the surface color, regardless of how it appears

Chromatic Adpation

occurs when prolonged exposure to chromatic color leads to receptors: 

• “Adapting” when stimulus colors selectively bleaches a specific cone pigment 

• Decrease in sensitivity to color 

• Adaptation occurs to light sources to color constancy 

Pictorial Cue

sources of depth informations that can be shown in a 2D picture\

Cue approach to depth peprception

• Focuses on info in the Retinal imgiange that is correlated with depth in the scene 

• Occlusion 

• automatic through repeat exposure

Depth Cues

Info about the 3-d of visual space

• Pictorial or Oculomotor

Monocular Depth Cue

available even when the world is viewed with one eye alone

Binocular Depth Cue

relies on info from both eyes

Moving the eyes

Accommodation

Convergence 

Divergence

Accommodation

which the eye changes its focus ( len gets fatter as gaze is directed towards near objects)

Convergence

ability of two eyes to turn inward, often used to focus on nearer objects

Divergence

two eyes to turn outward, often used to focus on farther objects

Convergence Insufficiency

can make text look double when trying to read, some experience a “halo effect” instead of double vision.

Monocular Depth Cues

• Occlusion

• Relative Height

• Familiar and Relative Size

• Perspective Convergence

• Atmospheric Perspective

• Texture Gradient

• Shadows

• Motion Parallax

• Deletion and Accretion

Occlusion

cue to relative depth order in which; ex. one object obstructs the view of part of another object

Relative Height

Object touching the ground, those higher in the visual field to be father away. In the sky above the horizon, objects lower in the visual field appear to be farther away.

Relative Size

comparison of size between items without knowing the absolute size of either one. 

• we assume that smaller objects are farther away from us than larger objects.

Familiar Size

cue based on knowledge of the typical size of objects 

• typical size of an object, you can guess how fara way it is based on how small or large it appears. 

• cue of familiar size often works in conjuction within the cue of relative size

Linear perspective

lines are parallel in 3d will appear to converge in 2d images as they extend into the distance.

• Vanishing point: apparent point at which parallel lines receding in depth converge.

Atmospheric Perspective

Distant object look less sharp than nearer objects and sometimes have a blue tint 

Texture Gradient

number of similar objects are equally spaced throughout a scene, close-up elements have more detail and far away elements have less detail

Shadow

help brain infer distance, object location and 3D forms by indicating which objects are close, how they are oriented and their relationship to a light source.

Motion Parallax

images close to the observer faster across the visual field than images farther away.

• use information to calculate the distance of object in the environment. 

• head movement and any other relative movement between observers and object reveal motion parallax cues. 

Deletion and Accretion

Deletion occurs when an object moves behind another object moves behind another object.

Accretion occurs when the object reveals itself in the observers viewpoint. 

If the deleting and accretion happens quickly, then the object is registered as being closer to the blocking object. 

Deletion and accretion occurs slowly if the two objects are farther away.

Stereoscope

device for presenting one image to one eye and another image to the other eye

Binocular Disparity

differences in the images on the left and right retinas.

• Basis of stereoscopic vision

• Slightly different perspectives, viewpoints and occlusions

Stereopsis

depth information provided by binocular disparity

Corresponding Retinal Points

geometric concept stating that points on the retina of each eye where the monocular retinal images of single object are formed are at the same distance from the fovea in each eye

• Points on the retina that would overlap if the eyes were superimposed on each other.

Horopter

Imaginary sphere that passes through the point of focus

• objects on the horopter fall on corresponding points on the two retinas. 

• Objects that do not fall on noncorresponding points make disparate images.

Non corresponding Points

Objects that do not fall on the horopter fall on noncorresponding points 

• These points make disparate images. 

• Angle between these points is the absolute disparity 

• amount of disparity indicates how far an obhect is from the horopter 

• Relative Disparity is difference between the absolute disparity of two objects.

Free Fusion

technique of converging (crossing) or divergining (uncrossing) the eyes in order to view a stereogram without a stereoscope 

Stereoblindness

Inability to make use of binocular disparity as a depth cue.

Physiology of Depth Perception

• input from two eyes must converge onto the same cell 

• Many binocular neurons respond best when the retinal images are on corresponding points in the two retinas: Neural basis for the horopter 

• many binocular neurons respond best when similar images occupy slightly different positions on the retinas of two eyes

Infant Depth Perception

Binocular disparity (binocularly fixate) becomes functional early

Pictorial depth cues become functional later 

Depth from familiar size and cast shadows

Development of Binocular Vision and Stereopsis

Abnormal visual experince can disrupt binocular vison

Critical Period

Study of development, a period of time when the organism is particularly susceptible to development change

Strabismus

Misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye, and on the nonfoveal area of the other eye

Supression

In vison, the inhibition of an unwanted image

Type of Strabismus

Esotropia- one eye deviates inward

Exotropia- one eye deviates outward

Hypertropia- one eye deviates upward

Hypotropia- one eye deviates downward

Depth in other species

Frontal eyes- results in overlapping fields of view, are necessary fro binocular disparity 

Lateral eyes, which do not result in overlapping fields of view, provide a wider view ( predators) 

Locusts use motion parallax to judge distance.

Visual Angles

angle of an object relative to an observers eye

Depends on both the size of the simulus and distance from observers (as a person moves closer, the visual angle becomes larger)

Size Constancy

Perception that an objects size remains stable, regardless of its distance from observer

Size constancy & Emmerts Law

Perception of an objects size remains relatively constant.

Effect remains even ig the size of the retinal image changes  

Emmerts law- Retinal size of an afterimage remains constant. Perceived size will change depending on distance of projection, follows the size-distance scaling equation

Muller-Lyer illusion

Misapplied size-constancy scaling: works in 3-D is misapplied for 2-D object, Observers unconsciously perceive the fins are belonging to the outside and inside corners, outside corners would be closer and inside corners would be further away

Conflicting cues theory

perception of line length depends on actual length of vertical lines and overall length of figure, conflicting cues are integrated into a compromise perception of the length. 

Ames Room Illusion

made so that shape looks like a normal room when viewed from a particular observation points, right corner is twice as far from the observer as the left corner.

Optic Flow

appearance of objects as the observer moves past them

Gradient of flow- difference in flow as a function of distance from the observer 

Focus of expansion- point in distance where there is no flow

Walking- Visual direction strategy

Observers keep their body pointed towards a target

• walkers correct when traget drifts to left or right

Landmark Navigation

taking routes that require making turns

landmarks are objects on the route that serves as cues to indicate where to turn

Hippocampus: Place cells

Neurons in the hippocampus that fire when an animal occupies a specific location in its environment known as PLACE FEILD

Selective firing creates an internal, neural representation of space, forming the basis of a cognitive map that is essential for spatial memory and navigation.

Entorhinal Cortex: GRIND CELLS

Neurons in the entorhinal cortex that fires in a HEXAGONAL periodic grind pattern as an animal navigates 

Provides that brain with a coordinate system for spatial navigation and creating a congitive map of its environment 

Essential for understanding an animals position, distance and direction in space 

Internally generated grid

Naigation and Neuroplasticity

significantly larger Posterior Hippocampus; as they have more experience navigating the city= demos neuroplasticity

Egocentric Navigation

“first-person” or body-centered frame of reference, with locations defined in relation to ones own position and heading

Allocentric Navigation

“third-person” or world-centered frame of reference to create an internal cognitive map of environment.