4) Visual Perception Flashcards
What is the goal of visual perception?
reconstruct 3D world from the 2D image that enters our eyes
Perceptual constancy
Tendency to experience stable perception despite continually changing sensory input
Example of top down processing
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
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
Perceptual Hypothesis
Infer which distal stimuli is responsible for proximal stimuli that we sense
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
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
Depth Perception
ability to judge distance and 3D relations
appears in infancy
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
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
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
Colour and intensity of light corresponds to
wavelength and amplitude
functions of the eye
- channel light to retina
- house the retina
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)
Cornea
Contains transparent cells
Cornea starts to bend the light a little bit
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
