Vision Flashcards
Which sense is arguably the most dominant? Give an example
Vision
Ex. In a movie theatre, the audio speakers are mounted somewhere else but you perceive the sound as coming from the actor’s mouths
Variations in amplitude (in the light hitting our eye) affect the perception of ______
Brightness
A greater amplitude results in a ______ picture
Brighter/ more intense
Variations in wavelength (in the light hitting our eye) affect the perception of ______
Colour
What is the range of the visible spectrum?
360- 750nm
True or false: all species share the same “visible” spectrum
False
Ex. bees can see light shorter than 360nm
Snakes can see light longer than 700nm, in infared spectrum. What is the purpose of this?
Able to see body heat, thus helps to find prey in the dark
Which physical light property affects our perception of saturation of colours?
Purity
What is “pure light”?
Light made up of a single wavelength; saturated colour
What is “desaturated” light?
Light that is a combo of many diff wavelengths
Is natural light desaturated or pure?
Usually in the middle
What is the cornea?
Transparent window in front of the eye
What is the sclera?
White part of the eye; a tougher membrane
Light first passes thru which part of the eye?
The cornea
After the cornea, through which structure does the light pass?
The pupil
What is the iris?
Coloured part of the eye; band of muscles controlled by the brain
What is the function of the iris?
Controls the size of the pupil
- not enough light reaching the retina –> pupils will dilate
- too much light –> pupil constricts
After the pupil, through which structure does the light pass?
The lens
What is the lens and what is its function?
Transparent structure/piece that can be altered by surrounding muscles and does the final focusing of light onto the retina at the back of the eye
True or false: images land on the retina normally
False
- lands upside down
- reversed from left to right
Describe the “accommodation” of the lens
Object = close
- lens gets fatter/rounder to produce a clear image
Object = far
- lens gets elongated to focus image on back of eye
After the lens, through which structure does the light pass?
Vitreous humour
After the vitreous humour, through which structure does the light pass?
Finally lands on the retina
What is the vitreous humour?
Clear, jelly like substance that comprises the main chamber inside the eyeball
What is the retina?
Paper thin neural tissue that lines the back of the eye
Network of neural cells arranged in three diff layers
Which structure is responsible for roughly 80% of the focusing of the eye?
The cornea
Which retinal layer are the photoreceptors located?
The farthest one to the back
What are photoreceptors?
Cells in the retina that are responsible for translating the physical stimulus of light into a neural signal that the brain can understand
Why is the retinal layer with the photoreceptors at the back, while the two transparent layers are at the front? (inside-out arrangement)
Photoreceptors get their nutrients from the retinal pigment epithelium (RPE) – a layer of cells at the very back of the eye
If the photoreceptors were located at the front of the retina, they would not have access to the RPE and would die
What are the two kinds of photoreceptors?
Rods
Cones
In which conditions are cones designed to operate?
High light intensities
Day vision
In which conditions are rods designed to operate?
Low light intensities; night vision
What kind of picture do cones provide us with?
Provide us with sensation of colour and sharpness of detail (visual acuity)
Cones become more concentrated towards the ______
Fovea
What is the fovea and what is its function?
Tiny spot in the middle of the retina that contains exclusively cones
Seeing images in detail; When we want to see something in great detail, we move our eyes so the image falls directly under the fovea
What kind of picture do rods provide us with?
No colour info and poor visual acuity
Where are the rods mainly located on the retina?
Increasing conc in the area surrounding the fovea
Why are rods very useful for peripheral vision?
The rods are in increasing conc in the area surrounding the fovea; makes peripheral vision more clear
Ex. trying to look at an object that’s far away in dim lighting
- -> staring directly = image focused on cone-rich fovea (doesn’t work well in dim environ)
- -> staring to side = you’re using your rods
Do humans have more cones or more rods?
Rods (125 million vs. 6 million)
What do bipolar cells do?
Relay the info from photoreceptors to ganglion cells
What do ganglion cells do?
Collect info from a larger segment of retina
Axons of these cells converge on one portion of the eye (optic disk)
Leave eye to join the optic nerve, which travels to the brain
Why is the optic disk considered our “blind spot”?
It is an exit hole in the eye for ganglion axons
Thus, contains no photoreceptors at all (and is therefore our blind spot)
At what point in the eye is the light converted into a neural signal
At the retina
What are horizontal and amacrine cells? What is their function?
Cells located in the retina that allows layers within the retina to communicate with each other
Allow info from adjacent photoreceptors to combine their info
- 130 mill rods and cones converge to travel along only 1 mill axons in the optic nerve
True or false: only neural processing happens in the retina
False
Some amount of visual processing is done before the signal is passed onto the brain (via the horizontal and amacrine cells)
True or false: the photoreceptors are divided into specific groups
True
Info from each groups converges into one signal that affects the ganglion cell down the line
Why is our visual acuity low for peripheral vision and so high for fovea vision?
Input from many codes and rods are combined into one ganglion cell; these groups get larger as we move towards the periphery of the eye
Vs.
In the fovea, each cone has a direct link with the brain –> a lot more detail is preserved
What is the “receptive field” [of a particular ganglion cell]?
Collection of rods and cones in the retina that, when stimulated, affects the firing of a particular ganglion cell
At what point in the eye do the axons of ganglion cells converge after collecting info from a larger segment of the retina?
Optic disc
True or false: the optic disc contains photoreceptors
False
It’s our blind spot
After the axons of ganglion cells have converged at the optic disc, on what structure do they leave the retina?
Optic nerve
Visual input from our right visual field is processed by our _______
Left hemisphere
Visual information from our left visual field is sent to __________
Both hemispheres
True or false: before reaching their respective hemispheres, the axons from the outer region of each retina have to cross over to the opposite hemisphere
False
The axons from the INNER (nasal) region of each retina have to cross over
The point at which the optic nerves from the eyes cross over to the opposite hemisphere is called the ________
Optic chiasm
Once info from each visual field arrives in their respective hemispheres, the optic nerve fibres split into two pathways. Most of the ganglion cell axons travel along the main pathway and synapse in the ________
Lateral geniculate nucleus (LGN)
What part of the brain does the LGN belong to?
The thalamus
After being processed at the LGN, where are visual signals sent to?
Primary visual cortex (occipital lobe)
What are two other names for the primary visual cortex?
V1
Striate cortex
What is the extrastriate cortex?
Areas in the occipital lobe outside of the striate cortex / V1
Describe how neurons converge their input as they travel down the visual system (through photoreceptors, ganglion cells, V1, LGN)
Many photoreceptors converge to a ganglion cell
Many ganglion cells converge to the receptive field of the LGN
The receptive field of many LGN cells converge to one V1 cell
Describe the topographical orientation in the visual cortex
Neighbouring regions in the retina project to neighbouring regions in the visual cortex
From the primary visual cortex, info is passed down to the _________
Extrastriate cortex
The information that gets passed down to the extrastriate cortex gets separated into two streams. What are they?
Ventral
Dorsal
What does the dorsal stream process?
“Where”
Where objects are, including their depth and motion in the field
The dorsal stream runs from the extrastriate cortex to the ________
Parietal lobe
What does the ventral stream process?
“What”
What the object is, including colour and form
The ventral stream runs from the extrastriate cortex to the ________
Temporal lobe
True or false: one neuron only responds to one specific attribute. All of the neurons firing together make up the picture
False
Neurons react most STRONGLY to a specific attribute. But it is possible to respond to more than one.
How did eyes start out (evolutionarily speaking)?
As a light-sensitive patch (i.e. jellyfish, worms)
What structure came after the light-sensitive patch?
Curved/cup eye (i.e. clams)
What is the advantage of having cup eyes over light-sensitive patches?
Allows the direction of light to be sensed (giving them a survival advantage)
What structure came after the cup eyes?
Crude lens (i.e. humans, monkeys)
What is the advantage of having crude lens over cup eyes?
Allows them to process visual input from different distances
Successively improved to allow better focusing and accommodation (i.e. with more transparent lens, etc.)
What are compound eyes (i.e. their structure)?
Made up of ommatidia (individual tubular units) that each point in a slightly different direction to gather the light that lay directly in front of it
Form a single image by putting together many sep signals
What kinds of animals have compound eyes?
Anthropods (crabs and insects)
What is the advantage of having compound eyes?
Can detect movements easily (but ONLY at close distances)
What are simple eyes (i.e. their structure)?
They have an eyeball, lens, and retina
Design varies depending on environment
What kinds of animals have simple eyes?
Vertebrates
Molluscs
What are the two functions of the eye?
Resolution (acuity)
Sensitivity (ability to get enough light)
True or false: If an animal has larger eyes, that means they have both high acuity and high night vision
False
Large eyes are better at both of these, but that does not mean that it automatically has both (i.e. humans have high acuity but poor night vision)
What are the advantages and disadvantages of laterally directed eyes?
Advantage:
- Large total view (don’t have to turn their heads)
Disadvantage:
- Two sep fields of view with little binocular overlap
- poor depth perception
- have to continuously scan their environment
What are the advantages and disadvantages of front directed eyes?
Advantage:
- more binocular overlap
- better depth perception
Disadvantage:
- narrow field of view
Are predators more likely to have front facing eyes or lateral facing eyes?
Front facing
Eyes are formed during the _______ month of pregnancy
Second
Eyes are capable of reacting to light in the _______ month of pregnancy
Sixth
What event is critical for the organized wiring of retinal cells? Why?
Random firing of retinal cells during the prenatal period
Det how neighbouring cells will be connected with each other
Why is our visual system the least developed sense at birth?
System req visual stimulation (isn’t possible before the baby is born and exposed to light)
What are newborn’s eyes like and how does that affect the image that they see?
- lens muscles are weak (can’t focus that well)
- pupil doesn’t react properly to changes in light (image is blurred)
By around _____ months, the infants ability to focus have improved to a level that is almost adult-like
Three
Do newborn’s retinas have a high or low density of retinal cells?
Low
Retinal cells in the fovea (in infants) don’t reach maturity until after ____ years of age
Four
At what age is the relevant brain development (for vision) fully developed?
Eleven years of age
Describe the pattern of visual acuity development
At birth:
- newborns can see something in 20 feet that an adult would’ve been able to at 600 ft
At six months:
- newborns can see something in 20 feet that an adult would’ve been able to at 100 ft
At one year:
- close to adult-like acuity
At 4-6 years of age:
- adult acuity
