5.2 - How Do We See? Flashcards
Cornea
- where light first passes through
- thick outer layer of eye
Lens
- receives focused light from cornea
- bends light further inwards
- forms a picture on the retina
Retina
Inner surface of the back of the eyeball
Contains sensory receptors that transduce light into neural signals
Pupil
hole in the middle of the eye
small opening in front of the lens
Iris
Donut muscle that relaxes or contracts and makes the pupil smaller or bigger depending on the environment
What are the two types of receptor cells in the retina?
Rods and Cones
Rods
retinal cells that respond to low levels of light and result in black and white perception
- primarily for night vision
- don’t support colour vision
- poor at fine detail
Cones
retinal cells that respond to higher levels of light and result in colour perception
Fovea
centre of the retina where cones are densely packed
Ventral Stream of Processing “what stream”
- occipital lobe to temporal lobe
- specialized for perception and recognition of objects (ex. determining colours and shapes)
Dorsal Stream of Processing “where stream”
- occipital lobe to parietal lobe
- spacial perception (where an object is in relation to other objects)
Object Agnosia
- condition where someone is unable to identify objects (likely caused by damage to the “what” pathway)
Q: Does fovea have more rods or cones?
fovea only has cones
What is the most common form of colour blindness?
Red-green caused by a missing protein in green or red receptor
Myopia
- nearsighted
- eyeball slightly elongated
Hyperopia
- farsighted
- eyeball slightly shortened
Astigmatism
uneven curvature of the cornea that leads to distorted images
5.4
How is the colour of light determined?
The wavelength of the electromagnetic wave that reaches the eye
How does the trichromatic theory explain colour blindness?
Some people may be missing the photopigment that is sensitive to some of the wavelengths and therefore they can’t process that colour
Photopigments
protein molecules that become unstable and split apart when exposed to light
- absorb certain wavelengths
Opponent-Process Theory of colour perception
States that we perceive colours in opposing pairs (ex. red to green, yellow to blue, white to black)
- complimentary colours
- compliments the trichromatic theory
Hue of colour
colour on the spectrum
Saturation of colour
how colourful
Intensity of colour
how bright
Q: Are afterimages best explained by trichromatic or opposed-process theory?
Opponent-process theory because the idea is that when you look at an image in opposite colours, those colour receptors fatigue. When you look away, you will see the image again but with the opposing colours to the ones you were just looking at
Gestalt Principles - Proximity
we are likely to group these squares into 3 objects
Gestalt Principles - Similarity
grouping things on how closely they resemble each other (ex. we can see the ex because we group the 2 different shapes as an X and a background)
Gestalt Principles - Good Continuation
Seeing things as continuous even though in reality they are separate
Gestalt Principles - Closure
We tend to complete figures and shapes
Gestalt Principles - Common Fate
We tend to see things that move together as being part of the same group (ex. hidden bird made of lines that you can’t see unless the video plays and the lines move together)
Prosopagnosia
can’t recognize faces
Object constancy
Correctly perceiving objects as constant in their shape, size, colour, lightness, despite sensory data that could mislead perception
(ex. the space each angle of the car takes up on our retina is different but we know how big a car should be so they all look the same to us)
Size constancy
How far away an object is from us
Shape constancy
What angles we are seeing an object from
Colour constancy
Comparing the wavelengths from each object to the wavelengths from the background
Light constancy
How much light is being reflected from the object and its background
Fusiform Gyrus (FFA)
- in the temporal lobe
- responds most strongly to upright faces
- where face information is combined and processed
How do we recognize upside down faces?
Object recognition instead of facial recognition in the fusiform gyrus
Pareidolia
we are programmed to see faces and shapes even when they aren’t there (ex. seeing shapes in clouds)
Q: How do the Gestalt principles of proximity and similarity help explain why we see crowds instead of individuals
When we see people (similarity) close together (proximity) we group them together as one and perceive a crowd
Binocular depth cues
cues that arise from having 2 eyes (“bi” meaning two) (need to work together)
- Convergence
eyes turn inwards (cross-eyed) to view objects that are closer
- Divergence
eyes turn outwards to view objects further away
- Binocular Disparity and stereoscopic vision
the eyes have 2 slightly different views
- stereoscopic vision: (ex. viewfinders: 2 images, 1 in each eye, combined to make it seem 3D)
Monocular depth cues
cues available to each eye alone (“mono” meaning one)
- Occlusion
(a)
- in pictures, we know something is closer when it occludes (blocks) objects in the background
- Position relative to the horizon
(b)
- using horizon lines as reference
- Relative Size
(c)
- objects further away project a smaller retinal image
- Familiar Size
(d)
- assuming size because we know what size they should be (ex. cars)
- Texture Gradient
(f)
- pavement gets less visibly textured the further it gets from us
- Linear Perspective
(e)
- parallel lines converge in the distance creating a common point
Motion Parallax
- using motion as a depth cue (ex. when driving in a car the street signs pass you quickly but the tall buildings in the distance don’t seem to move - this helps create our sense of depth)
What two things does size perception rely on?
- size of retinal image
- distance from viewer (depth perception)
Stroboscopic movement (apparent motion)
illusion of movement when 2 or more slightly different pictures are played in succession and creates the illusion of movement
What do motion aftereffects provide evidence for?
that there are motion-sensitive neurons in the brain
Why do motion aftereffects occur?
when staring at something that is moving for long enough, the motion neurons will fatigue and get used to the motion so when you look away they’ll still be moving with the rhythm they adapted to
Q: How does the distance of an object affect the size of the retinal image it casts?
farther from viewer = smaller retinal image
