Vision Flashcards
How does light travel through the eye?
Cornea –> pupil –> lens
What is the cornea?
A clear hard covering that protects the lens
What is the pupil?
An opening in the iris in which light enters the eye
What is the lens?
The structure behind the pupil that bends light rays to focus images on the retina and allow larger area of visual space in the small eye area
What is the iris and it’s function?
- A muscle that makes up the colored part of the eye
- adjusts pupil to control the amount of light that enters
the eye
What is the retina?
- The thin layer of tissue that lines the back of the eye
- The lens bends light rays to focus light on the retina
What is the process of Accommodation?
The process by which muscles control the shape of the lens to adjust it to view objects at different distances
What are the cells in the retina called?
Photoreceptors called rods and cones
What is the purpose of photoreceptors?
These convert light energy to neural impulses
Explain the pathway of light through the eye in terms of cells
Ganglion cells –> amacrine cells –> bilayer cells –> horizontal cells –> photoreceptor layer (rods and cones)
What are rods?
- One of two photoreceptors
- Located on the outer periphery of the retina
- used in vision at night
- very sensitive to light
- become “bleached” in the morning when sudden bright light hits the eye
- more numerous
- protein contained in these cells called rhodopsin
What are cones?
- One of two photoreceptors
- responsible for our colour vision
3 photosins: short (blue), medium (green), long (red) - function well in bright light
- give our vision sharpness and detail
- best in bright light
- less numerous
- protein contained in these cells called photopsins
What is the fovea?
- A spot in the back of the retina that contains the highest concentration of cones
- Because of this high concentration of cones, when ligh hits the fovea, the clearest image we can see is produced
Explain the difference in photoreceptors in humans and dogs and how this affects our vision
While both dogs and humans have more rods than cones, dogs have less cone cells than rod cells compared to humans
This explains why dogs have better night vision that humans ( the more rod cells ) and why they have poor detailed vision and poorer colour vision (less cones than humans)
what are the theories of the perception of colour?
The trichromatic colour theory
- colour is perceived by mixing wavelengths of light
The opponent process theory
- cones are linked together in opposing colour pairs
and so when one fires, the other cannot
Define the optic nerve and explain its function
Structure made from the axons of ganglion cells that transmits signals from the eye to the brain
Define and explain the optic disk
- The small area that contains no photoreceptors where the optic nerve exits the eye
- Forms a blind spot on the retina
What are the factors in motion perception?
- size of the background
- size of the object
Explain the visual pathways in human vision
- The left side of the retina in each eye senses the right visual field
- The right side of the retina in each eye senses the left visual field
- The two strands from each of the two optic nerves for the right and left side of the retinas meet at a point called the OPTIC CHIASM where the opposite strand crosses over. This leaves us with both right side strands of the optics nerves together and both left side strands of the optic nerves together. The right side and left side strands then continue to the thalamus where signals are then sent to the primary visual cortex in the occipital lobe
What is a respective field in terms of vision?
The area of visual space that stimulates specific neurons
What are feature detectors in terms of vision?
Neurons in the visual cortex that analyze retinal images and respond to certain aspects of shapes (angles, movement, ect)
What is apparent motion?
When you think something is moving when in reality nothing is actually moving
Motion blindness - Akinetopsia
What is depth perception?
The ability to distinguish what is near or far and see objects in three dimensions
What are binocular depth cues?
- Cues that depend on both eyes
- binocular disparity
- convergence
What is convergence?
- binocular depth cue
- determining the distance of an object by messages of how much the muscles contract to focus on an object
What is binocular disparity?
- binocular depth cue
- creates depth by using the difference in what one eye sees versus the other
What are monocular depth cues?
- motion parallax
- detailing of an object
- cues that only require one eye
What is motion parallax?
comparing sizes of objects in the visual to determine distances objects/ depth
How can detailing of an object be of use when determining depth?
The farther away an object is, the fewer details we can see
Details could be: texture, shading, ect
What is perceptual constancy?
- The ability of the brain to preserve perception of objects in spite of changes in the retinal image
- using shape and size constancy
- example of this is the Ames room
Gestalt Laws of Perception
The tendency to group things together by:
- similarity
- continuity
- proximity
- closure ( holes in a perceived triangle)
- figure
- ground
Visual areas of the cortex
- postier parietal cortex
- prestriate cortex
- primary visual (striate) cortex
- inferotemporal cortex
Dorsal and Ventral streams
Ventral stream
- What? pathway
- moves from occipital lobe to temporal lobe
- identifies objects by looking at size, shape, orientation
Dorsal stream
- Where? pathway
- Moves from the occipital lobe to the parietal lobe
- locates objects relative to yourself
Explain the vegetable face man experiment and what was found as a result of this experiment
Experiment with participants being split-brain patients
- the right hemisphere saw a face
- the left hemisphere saw vegetables
This gave evidence for:
right hemisphere is the face processor
left hemisphere is the object processor
What are feature detectors?
Neurons in the visual cortex that analyze retinal images and responds to certain aspect of shapes such as angles movement and more
What is a simple cell in terms of vision?
- A cell that only responds to visual stimuli that are still or are in the middle of the respective visual fields
- can only respond to very specific things they are programmed to do
What are complex cells in terms of vision?
- Cells that can respond to visual stimuli in different parts of its respective field
- can respond to multiple things
