Vision Flashcards
(45 cards)
Observable spectrum
400 - 700
Which two parts are responsible for focusing on an object?
- Cornea (80% but fixed)
- Lens (20%, flexible)
What are Oculomotor cues for depth perception?
The position of our eyes and the state of the muscles controlling them, give us information about our distance to an object.
- > Convergence: inward/outward movement of eyes when adjusting for distance
- > Accommodation: change of lens shape
What are Monocular Cues for depth perception?
Cues using only one eye
- > Pictorial: information deducted from the 2d-image (like Occlusion, Relative size, Shadows, Texture gradient, familiar size, perspective convergence)
- > Movement-related: information based on movement (like motion parallax, Deletion, Accretion)
Motion Parallax
Far away objects seem to move slower than close-by objects.
Deletion, Accretion
Deletion -> Things being covered due to movement
Accretion -> Things becoming uncovered due to movement
Binocular Cues for depth perception
Cues that use both eyes
- Stereopsis (deducted from disparity)
Horopter
- Surface of zero disparity
- Sphere passing through point of focus
- Points on this imaginary surface have corresponding retinal points
Corresponding retinal points
When an object in our field of vision is represented on the same spot on our retina in both eyes, this object has “corresponding retinal points”. The disparity here is zero.
Disparity
When drawing lines from an object, through our pupils, to our retina, these lines don’t end up at corresponding points
Crossed/Uncrossed Disparity
- Crossed: Disparity that happens when an object is closer to us than our horopter
- Uncrossed: Disparity that happens when an object is further away than our horopter
Features of rods
- good for Night vision (light sensitive)
- 95% of our photoreceptors are rods
- many of them are grouped together on one ganglion cell
- most prominent in our periphery
Features of cones
- Color (wavelength) sensitive
- detailed vision
- make up 5% of receptors
- have their own ganglion cell
- centered around fovea
phototransduction cascade
receptor gets turned off by light -> bipolar cell gets turned on -> retinal ganglion cell -> optic nerve -> Brain
Receptive field
“Field” of photoreceptors connected to a single retinal ganglion cell
On- vs Off-Center receptive field
On: Fires when Center is lit and peripheral is dark
Off: Fires when Peripheral is lit and Center is dark
-> Refers to the ganglion cell’s response to its receptive field.
-> These properties of receptive fields help with contrast perception and also with detecting illumination differences, rather than average light falling on to the retina.
Lateral Inhibition
- Neighbouring cells inhibit each other through horizontal connections
- a strongly stimulated receptor inhibits surrounding receptors
- enhances contrast
Mach Bands
- Invented by Mach (Austrian)
- Stripes of different shades of grey
- we perceive them being more dark on the side that is next to the next brighter stripe due to lateral inhibition
Optic Disc
Blind spot in our visual field caused by the root of the optic nerve
-> Our brain tries to restore vision here by information from surrounding receptors and the other eye.
The two major transformations done in the eye
- From light stimulus into an image of the object
2. From the image/representation to an electrochemical signal
Fovea
Point of focus (+/- 5° from the Center)
Trichromatic Theory of Color Vision
- Young-Helmholz-Theory
- Derived from discovery that you need to mix at least 3 different wavelengths, to create every color.
- Vision depends on three different receptors
- we need at least 2 receptors to perceive color.
Opponent-Process Theory of Color Vision
- Works in co-existence with Trichromatic Theory
- States that color vision derives from opposing responses triggered by blue, red, Yello and green light.
Selective Reflection
Some objects don’t reflect every wavelength to the same amount. This results in the object having a certain “chromatic color”.
