1. channel light to retina 2. house the retina

4) Visual Perception Flashcards by Ashley Wu

What is the goal of visual perception?

reconstruct 3D world from the 2D image that enters our eyes

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Perceptual constancy

Tendency to experience stable perception despite continually changing sensory input

Example of top down processing

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Describe the diff types of perceptual constancy

Shape
- we perceive objects maintain same shape even when it moves or turns

Colour
- we perceive same colour under different lighting

Size
- perceive same size when things are far away

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Distal vs Proximal Stimuli

Distal is stimuli that lie in the distance (outside of our body)

Proximal stimuli is what interacts with our senses

ex/
distal stimulus = printed page of a book
proximal = light energy reflected by the page that enters our eyes

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Perceptual Hypothesis

Infer which distal stimuli is responsible for proximal stimuli that we sense

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The guitar in a concert is an example of a ____ stimulus and the sound waves generated by the guitar that reaches our ears is considered the ____ stimulus

Distal
Proximal

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Gestalt Principles

Rules governing how we perceive things as unified wholes rather than individual parts

Proximity
We see closer objects as whole

Similarity
We see similar objects composing a whole more than dissimilar ones

Continuity
Perceive as whole even when objects block part of them

Closure
Brain fill in missing info

Symmetry
We see symmetrically arranged stuff as whole

Figure-ground
Focus on central figure and ignore background

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Depth Perception

ability to judge distance and 3D relations

appears in infancy

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Describe the binocular cues of depth perception

Retinal / Binocular Disparity
- Objects project images to slightly diff areas in each eye
- We see distant things similarly but close objects differently if we close one eye

Binocular Convergence
- Sense eyes converging towards each other when focusing on close things
- Brain knows how much eye is converging, can estimate distance

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Describe the monocular cues of depth perception

Motion Parallax
- Objects at diff distances look like they’re moving at a diff speed
- ex/ fence faster, cloud slower

Pictorial Depth Cues :

Linear perspective
Outlines converge as distance increases

Texture gradients
Texture less apparent if it’s far away

Interposition
Closer objects block our view of things behind it

Relative size
Distant objects look smaller than close ones

Height in plane
Distant objects appear higher, closer stuff appear lower

Light & shadow
Objects cast shadows, give us sense of 3D form

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Moon illusion is how moon looks small when we stare at it in night sky, but looks big when we see it on the horizon. What concepts are most likely related to this illusion?

Shape Constancy
Interposition
Size Constancy
Motion Parallax
Bottom up processing
Top down processing
Depth Cues

Depth Cues & Size Constancy

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Colour and intensity of light corresponds to

wavelength and amplitude

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functions of the eye

channel light to retina
house the retina

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Name the parts of the eye

Cornea
Contains transparent cells
Cornea starts to bend the light a little bit, iris controls light intake

Iris
Coloured ring of muscle around pupil
Regulate amount of light passing into eye by constricting & dilating (psychological too)

Pupil
Hole where light enters eye
Size controlled by iris (pupillary reflex)

Sclera
white part, maintains “ball” shape

Lens
Changes curvature to keep images in focus
Contains transparent cells

Retina
Neural tissue / membrane lining back of eye
Absorb light & process images
Convert light into neural activity

Fovea
Small spot at center of retina with only cones
Responsible for sharpness

Optic Nerve
Nerve (ganglion cells’ axons) that travels from retina to brain

Optic Disk
Hole in retina where optic nerve exits
No rods or sense receptors, Blind spot
Brain fills in info :O

Optic Chiasm
Point where half of the optic nerves from each eye cross over to opposite half of brain & half stays in same side
Both eyeballs get info from both fields, but most left visual field goes right (vice versa)

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Cornea

Contains transparent cells
Cornea starts to bend the light a little bit

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Iris

Coloured ring of muscle around pupil
Regulate amount of light passing into eye by constricting & dilating (psychological too)

Pupil

Hole where light enters eye
Size controlled by iris (pupillary reflex)

Sclera

white part
maintains “ball” shape

Lens

Changes curvature to keep images in focus
Contains transparent cells

Retina

Neural tissue / membrane lining back of eye
Absorb light & process images
Convert light into neural activity

Fovea

Small spot at center of retina with only cones
Responsible for sharpness

Optic Nerve

Nerve (ganglion cells’ axons) that travels from retina to brain

Optic Chiasm

Point where half of the optic nerves from each eye cross over to opposite half of brain & half stays in same side

Both eyeballs get info from both fields, but most left visual field goes right (vice versa)

Optic Disk

Hole in retina where optic nerve exits
No rods or sense receptors, Blind spot
Brain fills in info :O

Accommodation

Adjustment of the curve-ness of lens to alter visual focus for far or near objects

Myopia

Near sighted, can’t see far stuff well Bends light too much, image is sharpest before hitting retina

Hyperopia

Far sighted, can’t see near stuff well Bends light too little, image is sharpest after hitting retina

Presbyopia

Lens loses flexibility when we age

What is the pathway that light takes?

Cornea Pupil Lens Retina Optic Nerve Thalamus Visual cortex & structures in midbrain (for reflexes)

Cones

Visual receptors for daylight & color vision Detail / sharpness Most concentrated in fovea

Rods

Visual receptors for night & peripheral vision Basic shapes & forms More plentiful

Dark adaptation

Process where eyes become more sensitive to dark / dim light Takes a full 30 minutes Rods take longer to adapt

Light adaptation

process where eyes become less sensitive to bright lights

Receptive field

Collection of rods & cones Funnel signals to particular visual cell Affects firing of visual cell (horizontal / bipolar) when stimulated There’s a baseline level of firing even without simulation of light This is only causing one cell to fire

Describe the colour theories

Trichromatic Theory Colour vision is based on sensitivity three primary colours / types of cones Combination of red blue & green make other colours Additive = mixing lights Subtractive = mixing paint Opponent Process Theory Colour perception depends on receptors that make antagonistic responses to 3 pairs: Blue / Yellow Red / Green Black / White If one fires, the other is inhibited

Colour blindness

Can’t see some or all colours

Hubel & Wiesel

Curious about how we perceive shape & form Used cats, figure out what types of slits made visual cortex go crazy Feature Detectors Neurons that respond selectively to very specific features of complex stimuli

Feature Detectors

Neurons that respond selectively to very specific features of complex stimuli aka cell that detects lines & edges Each cell can detect a special specific orientation Combination of firing tells us where edges actually are Simple feature detector cell Respond best to lines of correct width, orientation, location Complex feature detector cell Respond best to lines moving in specific direction