Exam 3

Ace it again!!!

Functions of color vision

Functions of color vision

1. Classify

2. Organize

3. Survival

Isaac Newton proposed:

…white light is mixture of many colors

Prism

Object that separates different colors from white light

Visual Spectrum

Colors that humans can perceive; 400-700 nm

Blue: short wL

Green: medium wL

Yellow: medium/long wL

Red: long wL

Chromatic Colors

Light that reflects different wL’s (e.g., red, green, blue)

Selective Reflection

Some colors reflect more than others

Achromatic Colors

Light reflects equal wL’s

(e.g., white, black, & gray)

Selective transmission

Transparent objects (liquids, plastics, glass) allow wL’s to pass

Reflectance & Transmission Curves

Plot % of light reflected/transmitted to perceive specific wL’s

Describing wL’s based on mixing colors

1. Mixing paints

2. Mixing lights

Mixing Paints

Paint absorbs/takes away colors

• short, medium, long wL’s mixed together makes black

Subtractive Color Mixture

Paint from 2 mixed wL’s lose their colors

(e.g., blue (short) + yellow (long) = green (med)…blue & yellow no longer present

Mixing Lights

Short, medium, & long wL light shown together

• reflecting white light

(e.g., blue (short) + green (med) + red (long) = white)

Additive Color Mixture

Light from 2 different wL’s come together to make new color

(e.g., green (med) + red (long) = yellow (med, long)

Perceptual Dimensions of Color

Hue - color being assessed

Saturation - intensity & pureness of color

Desaturation - fading of a color

Value - brightness of the color

Theories of Color Theory

1. Trichromatic (Helmholtz, Young, Maxwell) -

Color vision based on 3 color receptors (red, green, and blue cones) combine to make colors

• Ex: Red and green cones activated together, we perceive yellow

2. Opponent-Process (Hering) -

Color perception relies on opposing pairs of colors (red vs. green, blue vs. yellow). Activation of 1 color suppresses the other

• Ex. Staring at a red object, then seeing brief green afterimage (cus of suppression of red cones)

Trichromatic Theory of Color Vision

Idea: Our perception of color is determined by 3 receptor mechanisms

Color Matching Experiment

Prompt: Adjust 3 wL’s in comparison field to match test field of 1 wL

Test & Comparison Field of Color Matching Experiment

Test Field - color of light experimenter wants observer to match

Comparison Field - observer manipulates lighting to match test field color

Results of Color Matching Experiment

Adjusting 3 wL’s - possible to match any colors in field

Adjusting 2 wL’s Only - can’t match all colors

Normal Vision - needs 3 receptors

Cones have which 3 pigments (colors)?

1. Short wL

2. Medium wL

3. Long wL

Visual Pigment Molecule

Where retinal bends from opsin to make light

Opsin

Protein structure differs representing the 3 diff. pigments

Metamerism

Colors of different wL’s create an identical color

• process of mixing

Metamers

Different wL’s come together to make similar color

• what we see when colors mix

Why are 3 Visual Pigments Necessary?

1 receptor (pigment)

• wL’s can’t be identified (shades of gray)

2 receptors = 2 pigments

• Can identify 2 wL (not just intensity of light)

3 receptors = 3 pigments

• Can identify 3 wL (perception of many colors)

Principle of Univariance

Receptors respond to light intensity (NOT different wL’s)

Opponent-Process Theory

Idea: One member of color pair suppresses other color

Phenomenological Method

An observation; describing what you see

Hering's Color Circle Experiment

People observed color circle & identified hue changes

Color differences seen as primary colors added in small amounts

(e.g., can’t have bluish yellow, but can have bluish red)

Primary Colors

Red, Green, Blue, Yellow

Unique Hues

(Don't mix/opposites)

1. Red/green

2. Blue/yellow

3. Black/white

Opponent Neurons

Location: Lateral Geniculate Nucleus (LGN)

• excitatory on one end of visible spectrum

• inhibitory on other end

How do the Trichromatic and Opponent-Process Theories work together?

Each describes physiological mechanisms in visual system

1. Trichromatic - explains cones in retina

2. Opponent-process - explains neural response from cones to brain

Color Deficiency

Partial loss of color perception

Color Blindness

Can’t see colors at all (only white, black, & gray; a monochromat)

Color Deficient-Dichromats

Some color can be observed

Types of Color Vision Deficiency

1. Monochromat

2. Dichromat

3. Anomalous trichromat

Monochromat

1 wL to see colors (gray, white, black)

Rare condition of color blindness

No cone functioning, only rods

Poor visual acuity & sensitive to bright light

Dichromat

2 wL’s to see color; some color

Males have it more than females

• They lack extra x chromosome (only need 1 x for normal vision)

Types of Dichromats

1. Protanopia

2. Deuteranopia

3. Tritanopia

Protanopia

Can't see red properly

May confuse with greens or browns

Deuteranopia

Can't see green properly

(difficulty distinguishing reds, greens, and browns)

Tritanopia

Can’t see blue properly

(may confuse blue and yellow)

Unilateral Dichromats

People w/ trichromatic vision in 1 eye & dichromatic vision in other

Ishihara Plates

Color vision test to diagnose people w/ color deficiencies

Anomalous Trichromat

3 wL’s, but colors are mixed

• colors perceived abnormally

Color Constancy

Perceive colors as constant under diff. lighting

Explanation for Blue/Black or Yellow/White Dress

Influenced by illumination of light/type of light

Lightness Constancy

Perceive achromatic colors (white, gray, black) as constant under diff. lighting

Depth Perception

How far/deep something is (visually)

• happens automatically through repeated exposure of cues

Cues to Signal Depth

1. Oculomotor

2. Monocular

3. Binocular

Oculomotor

Cues based on sensing position of eyes via eye muscles tension

Convergence

Inward movement of eyes when focusing on nearby objects

Accommodation

Lens shape changes focusing on objects at different distances

Lenses flatten - far away

Lenses thicken - nearby

Monocular

Cues available in 1 eye:

• Pictorial

• Movement-based

Pictorial Cues

Depth cues from 2D images from 1 eye (8 total)

Pictorial Cue #1. Occlusion

When one objects hides/partially hides from another object

Pictorial Cue #2. Relative Height

Objects closer to base of horizon seem more distant, objects away from base seem closer

Pictorial Cue #3. Relative Size

Equal size objects, closer one looks bigger, far away one looks smaller

Pictorial Cue #4. Familiar Size

Judging distance according to prior knowledge

Pictorial Cue #5. Perspective Convergence

Parallel lines appear to come together in the distance

Pictorial Cue #6. Atmospheric Perspective

Distant objects appear less sharp than nearer objects

Pictorial Cue #7. Texture gradient

Elements in a scene seem more closely packed when distance increases

Pictorial Cue #8. Shadows

Decrease in light intensity (blockage of light)

Movement-Based Cues

Sources of depth info from an observer's movement

1. Motion Parallax

2. Deletion & Accretion

Motion Parallax

In direction of movement:

Close objects move fast

Far objects move slow

(e.g., Looking out car window & observing)

Deletion & Accretion

Object distance perception based on covering/uncovering objects as observer moves

Deletion - covering object

Accretion - uncovering object

Binocular

Cues depending on 2 eyes

Stereoscopic Depth Perception

Awareness of depth through input from both eyes

Difference Between 2D & 3D Image

2D - Both eyes receive same info

• flat images

• relying on monocular cues (pictorial) for both eyes

3D - Both eyes receive different info

• images positioned in diff. viewpoints for 3D experience

Strabismus

Eye misalignment; 1 eye is suppressed causing an individual to use one eye to avoid double vision

• People rely on monocular instead of binocular cues

Binocular Disparity

Difference in images from left & right eyes

Corresponding Retinal Points

Points on retina where image overlap (same)

Horopter

Imaginary sphere that passes through point of focus

Noncorresponding Retinal Points

Objects that don’t fall on horopter

• makes diff. images in both eyes

Absolute Disparity

Objects deviate from falling on corresponding retinal points

Angle of Disparity

Amount of absolute disparity indicates how far an object is from horopter; POV

Relative Disparity

Diff. between absolute disparity of 2 objects, switching both angles

Crossed Disparity

When you focus your horopter far away

• close object in front of you creates crossed disparity

• close object is doubled

Uncrossed Disparity

When you focus your horopter close up

• far object creates uncrossed disparity

• far object is doubled

Stereopsis

Ability to perceive depth through binocular disparity (diff. in viewpoint for both eyes)

• 3D movies: slightly different positions of an image in left-eye and right-eye are superimposed (placed over each other) on a screen

Correspondence Problem

How does visual system match images from both eyes when both are shown diff. viewpoints in 3D?

• Our visual system can detect specific features/parts of an object from both eyes together to form a single 3D object

Binocular Depth Cells/Disparity-Selective Cells

Specialized neurons that respond to binocular disparity; located in primary visual cortex

• Respond to absolute disparity (when your left and right eyes create different images and not a single image)

Perceiving Size

Depth & size perception are interrelated

Holway and Boring Experiment

Observers presented 2 light circles at intersection of 2 hallways

Right hallway - luminous test circle placed 10-120 ft away

Left hallway - luminous comparison circle 10 ft away

Visual Angle

Angle of an object relative to observer's eye

• depends on size & distance from observer

Results of Holway and Boring Experiment

Part 1 - Depth cues (binocular disparity, motion parallax, shading) were given to observer

Result - Judgments of circle size were based on physical size cus they had cues of distance

Part 2 - No depth cues were given instead were eliminated

Result - Judgments of circle size were similar based on size of retinal images w/o cuing of distance

Size Constancy

Perception of an object's size remains relatively the same even when we view object at different distances

Visual Illusions

Our size perception can be tricked by different visual illusions

Müller-Lyer Illusion

Misperceiving 2 lines w/ equal lengths as different due to fins connected to the lines

Explanations for Müller-Lyer Illusion

Misapplied Size Constancy Scaling - We view 2D as though it’s 3D

Conflicting Cues Theory - Our misperception of line length is caused by conflicting info: actual length of lines & overall length of figure

Ponzo Illusion

2 same sized objects placed over different areas of railroad track in picture

Far object appears larger than closer object although both are same size

Explanation for Ponzo Illusion

Misapplied size-constancy scaling

Ames Room

2 people of equal size appear very different in size in a room

One appears like a giant over the other

Explanations for Ames Room

Size-distance scaling - Distance is the same for both people but not the size

Relative size - One person is taking up more space than the other in same distance

Moon Illusion

Moon appears larger on horizon than when it is higher in the sky

Explanations for Moon Illusion

Apparent-distance theory - Horizon moon is surrounded by depth cues while moon higher in the sky has none

Angular size-contrast theory - The moon appears smaller when surrounded by larger objects

Sound is Defined in 2 Ways

1. Physical

2. Perceptual

Physical Sound

What a person senses during hearing through pressure changes occurring in ears