Visual System and Perception Flashcards
How does the visual system work?
- Objects has energy(lights) that turns into nerve inpulses inside of the eye, and gets send to both of the hemispheres through the optic nerve
- The brain interpret the encodements from the receptors
Pupil
Control the light, or adjust the eyes to the light
Lens
Focus on objects to see something clearly, work with the retina
Retina
Has several receptors that are sensitive to light
Fovea
Has no rods but clusters of cones
- For accurate and precise vision
Does our eyes work like a camera?
- We dont snap pictures like a camera does, the analogy does not hold up
Transduction
Process of characteristics of stimulus to nerve impulses
Normal stimulus
- Electro magnetic energy, from the environment
- The visible spectrum for humans are between 350nm - 800nm
- Different electromagnetic waves are perceived as different types of colors in our brains (their wavelenghts)
Rods
- Sensitive to visible lights
- Black and white
- Prefer Dimlight
Dark adaptation
Process of when our eyes gets used to dim lights
- Rods not always activated
Cones
- Color receptors
- Sensitive to specific type of frequences of light
Cones can be specialised - Prefer bright lights
How does the visiual transduction work?
Bipolar cells (pathways) to the optic nerve, use of photopigments
- Many rods are connected to the same bipolar cells
- Some cones has “private lanes” in Fovea
Visual acuity
Ability to see fine details
Change blindness
Failure to notice changes in visual stimuli when those changes happen during a saccade
How does the eye move?
- Gets a sharp observation of only a small part of the environment
Our “full picture” is an illusion, the brain predicts and/or fill in missing information - Saccadic movements - rapid process, one point to another
- Fixations - pauses, takes in the info
Notices visual stimuli like change in color - Competing stimuli for attention, whats important to look at now?
Intentional blindness
Failure to see an object we are looking at directly if our attention is elsewher
- A phenomena
Trichromatic Theory - Basics
- Sensitive to different wavelenghts
- Cones have 3 different types
If all are active, we see white
Blue Green Red - Missing or malfunction of cones gives color blindness
Trichromatic Theory - Against
- Red-green blindness, but can still see yellow
- Cant explain after-images
After image
Certain color stimuli presented and then withdrawn
- Sees the stimuli in different colors
Opponent process theory
- Assumed 3 types of cones - 3 opposing systems
1 type - 2 different wavelenghts - We perceive a hue based on up to two colors at a time
- One color pair suppresses the other color
Green supresses Red, hence why we cant see those mixed - Explain after-images
What are the color pairs in opponent process theory?
- Green or red
- Blue or yellow
- Black or white
Dual process theory
- Three types of cones
Based on wavelenghts (Trichromatic) - receptor (early stage) - Signals from three color receptors combined before sent to the opponent cells (Opponent process) - brain (Later stage)
Combines input
Feature Detectors
Cell, specialised in visual stimuli
- Receive and integrate nerve impulses
Color, depth and movement
What is color constancy?
Color seems relatively constant under varying illumination conditions
- Depends on light frequencies and prior knowledge
- Banana - Grey color
How does depth perception work?
- The images in the retina is 2 dimensions
Length + Width - Brain creates a 3D image with help of
Monocular depth cues - Has more with 3D cues when it comes to images
Binocular depth cues
Monocular Depth cues
- There are 8 different types
Parallel lines
-Angle towards each other or to the middle
Texture - How it looks like on a distance
Shadows
Overlap
Size of the object - Distance judgements
Movements - Parallax - If we are moving, objects nearby moves faster than those futher away
Binocular depth
- Combines info from both eyes
Binocular disparity - Each eye sees a slightly different image
Image futher away from fixation points looks blurry
Oculo-motor depth cues
- Limited to on object
- Binocular vision
- Consists of accomodation and vergence
Holding a pen infront of you, eyes convergancing
Accomadation
Lens changes its shape in order to bring an object in focus on the retina
Vergeance
The process which the eyes move in equal and opposite directions of one another in order to fixate an object
Convergence
Result of vergeance, eyes turning inwards in order to focus on an object
How does perceptions of movement work?
- Complex process with info from several senses
- Identify or realize change of place of an object or body
- Getting info on speed and direction
How does visual perception work?
- It encodes the visual information and make a selection
- Active and rapid
Associative Agnosi
- Disrupts semantic access for object
Cant associate objects with meanings - Prior knowledge
- Can copy drawings but cant draw from memory or identify what they just drew
