Vision Flashcards
dog vision
- bad color vision
- can see green byt everything else is grayish
gecko vision
- have really nice color vision
- can see even better than use when it comes to certain things
Snail vision
- sees blobs
- tentacles are important for feeling the environment
bird vision
sharp colors and granularity
snake vision
night vision, reddish hue due to thermal vision
What wavelength is the visible spectrum
- around 400-700
- is the rainbow (far violet to far red and everything in between)
What is the color we see in terms of light?
- the color we see is the light being reflected back to use
- every other color is being absorbed
black vs. white color
- black absorbs all light and reflects none
- white reflects all light and absorbs none
How does a prism work?
- prism separates white light into the colors of the visible light spectrum
- similar to rainbow, when moisture in the air has sunlight (white light) bounce off, the light refracts
Each color in a rainbow corresponds to…
a different wavelength of electromagnetic spectrum
What are photons?
- Particles that form waves
- our vision is dependent on photons
What is brightness?
- number of photons emitted by a source
- more photons=brighter
What is color?
- frequency of photons (wavelength)
- red is longer wavelength/frequency than orange, etc
What is brightness for a pixel?
- for any particular pixel brightness is the number of photons per square unit space
What is color for a pixel?
- color is wavlength of photons
How are pixels brightness and color extracted/determined?
- extracted from comparing across nearby pixels (always in relation to something else/comparison)
- determined by edges, motion, and form
Optical features of the eye
What does the cornea do?
- refracts light
- the first surface that light hits
- covers the whole eye
Optical features of the eye
What is the pupil and what does it do?
- the pupil is an opening in the opaque disc called iris
- it controls light entering the eye
What controls eye movement?
- extraocular muscles control eye movement
- muscles located outside of eye field
What shape is lens for near focus?
globular
What shape is lens for far focus?
flatter
What is accommodation?
- process of focusing by changing the shape of the lens
- why we squint- it changes lense shape via ciliary muscles to make objects appear sharper
What do ciliary muscles in the eye do?
- adjust the focus
- by changing the shape of the pliable lens
What is binocular vision?
- the center region of the visual field
- what is seen by both eyes
Why is binocular vision helpful?
- it allows us to see depth
- animals w eyes on side of head cannot see depth well due to poor binocular vision
What is binocular depth perception correlated with?
positively correlated with the amount of visual field overlap (area seen w both eyes)
What do lateral portions of the retina monitor?
the medial portions of the visual field
Where does visual processing begin?
in the retina
What does the retina contain? Precisely where in the retina are these found?
- photoreceptor cells known as rods and cones
- found deep within the retina (buried under layers of other cells)
What does the ganglion cell layer form?
the optic nerve
what is the bipolar cell layer connected to?
- rods and cones as well as ganglion cell layer (in between the two)
What is targeted when light enters eye in pupil?
- the cells in the very back/last layer of the retina (the rods and cones)
Rods vs. Cones: system type
rods: scotopic system (low-light)
cones: photopic system (light)
Rods vs. Cones: photoreceptor type #
- rods: one type of photoreceptor
- cones: three different photoreceptors
Rods vs. Cones- more common where?
- rods: more common in peripheral parts of retina
- cones: more common in fovea (center of the retina)
Rods vs. Cones: sensitivity
- rods: very high sensitivity- respond during low light conidtions
- cones: low sensitivity- only active under brighter conditions
Rods vs. Cones: Wavelength
- rods: wavelength (frequency) insensitive
- cones: wavelength sensitive
When are rods saturated?
- in bright light (feeling blinded by sun)
What is the threshold for perception of color?
- 10E-5 lamberts (around the same as bright moonlight)
What does high acuity (keen) vision depend on?
high density of receptors
Where is the blind spot formed?
- where the optic nerve exits the retina because there are no photoreceptors present
What do horizontal cells do?
- allow communication between rods and cones- allows integration of information
What are amacrine cells and where are they found?
- found between bipolar cells- connect bipolar and ganglion cells
What is the relationship between amacrine and horizontal cells?
they have the same function/shape, but found in different layers of the retina
Transduction process (beginning)
- proteins in photoreceptors are light sensitive
- light colliding with rhodpsin (in case of rods) releases transducin (like a G-protein) that triggers intracellular effects
What is PDE?
- phosphodiesterase (a protein that breaks down cGMP)
Transduction pt 2 (intracellular effects)
- PDE is activated and breaks down cGMP
- since cGMP normally keeps Na+ channels open, receptor activation leads Na+ channels to close, leading to hyperpolarized
How does transduction work for cones?
- cones work as rods do, but their opsins are tuned to particular wavelengths
- meaning, there are some light stimuli they exhibit little response to
- there are three separate opsin proteins and three types of cones (blue, green, and red)
What are opsins? What are they tuned to?
- Opsins are proteins that are stimulated by light
- They are tuned to particular wavelengths
What causes color blindness?
a lack of red, green, or blue cones (one of them
What do photoreceptors contact?
bipolar cells, horizonal cells, and amacrine cells
What do bipolar cells do?
recieve input from photoreceptors and synapse on ganglion cells, whose axons form the optic nerve
What do off-center bipolar cells do?
- turning off light in the center of the field excites the cells
What do on-center bipolar cells do?
turning light on in the center of the field excited them
What do bipolar cells release and what does this do?
they release glutamate, which always depolarizes ganglion cells
What is the benefit of having multiple photoreceptors connect to one ganglion cell via bipolar cells?
- allows ganglion cells to monitor what they are “seeing” in a small patch of the visual field and put that information together
- ganglion cell can see larger area than one singular photoreceptor due to this integration
On-center/off-surround cell
- spot of light on center: bipolar cell depolarizes, ganglion cell has more action potentials
- spot of light in surround: bipolar cell hyperpolarizes, ganglion cell responds w less action potentials
- diffuse illumination of center and surround: doesn’t really affect ganglion cells
off-center/ on-surround cell
- spot of light on center: hyperpolarizes bipolar cell, decreases ganglion cell APs
- spot of light on-surround: bipolar cell depolarizes, increased action potentials
- diffused light: no real response in ganglion cells
What do ganglion cell axons form and where do they cross?
- ganglion cell axons form the optic nerve and cross at the optic chiasm
After passing the optic chiasm…
the axons are called the optic tract
Where do most optic tract axons synapse?
- on cells in the lateral geniculate nucleus (LGN)
- some axons go to the hypothalamus (suprachiasmatic nucleus)
optic chiasm details
- the optic nerves from each eye join at the optic chiasm
- some axons stay on the same side (ipsilateral) and some cross (contralateral)
- the goal is that all axons carrying information about the left visual field end up on the right and vice versa
What crosses and why? Nasal (medial) retina
- views the non-overlapping part of the visual field, so fibers from ganglion cells in this part cross over
Who crosses and why? temporal (lateral) retina
- views a shared part of the visual field
- so, those fibers stay ipsilateral
Lateral geniculate nucleus location and layers
- LGN located on thalamus
- has six main layers of cells
- different layers recieve input from different eyes (3 from left eye; 3 from right eye)
- layers 1-6 move dorsally (to the back of brain)
Magnocellular vs Parvocellular cells
- magnocellular; depth and motion (layers 1-2)
- parvocellular; fine detail, sensitive to color, high spatial resolutionc cells (3-6)
- have center-surround configurations
cells in LGN of thalamus
Where do LGN cells go
- axons of potsynaptic cells in the LGN form optic radiations and project to the occipital cortex (in the occipital lobe)
- first region is the primary visual cortex (V1)
How is the V1 organized?
- retinotopically
- meaning, cells that are near one another are likely to receive info via LGN neurons from ganglion cells that are nearby to one another on the retina
V1 Visual cortex neurons
- Each “simple cell” monitors/processes a small part of the contralateral visual field
- It responds to bars and edges present in that location (orientation matters)
- must already have “access” to the information of multiple LGN cells
What is ocular dominance column?
- vertical columns are arranged such that neurons in all layers respond to one eye
- “stripes of neurons in the visual cortex that respond preferentially to input from one eye or the other”
in V1
Orientation column explained
- vertical columns in which neurons in all layers respond rod shaped stimuli of a particular orientation
- individual cells in your V1 respond to only a particular line/edge, orientation
- organized regions of neurons that are excited by visual line stimuli of varying angles
What is the ventral pathway?
the “what” pathway
Ventral “what” pathway
V1 to V2
- v2 begins putting together information from multiple neurons in V1, building more complex representations of objects that depend upon multiple features and some “approximations”
Ventral “what pathway”
V2 to V4
- V4 neurons respond preferentially to complex radial and concentric stimuli
- they also exhibit wavelength (color) specific receptrive fields
Ventral “what” pathway
V4-IT (inferior temporal cortex)
- IT contains neurons that respond to complex shapes; with sensitivity to color and texture
- their receptrive field properties can be “shaped” by learning
- expert recognition vision (fusiform face area)
Which pathway is the dorsal pathway?
- the “where” pathway
dorsal “where” pathway
V1-V5 (medial temproal lobe)
- V5 (medial temporal lobe) contains neurons that encode percieved motion
Dorsal “where” pathway
Posterior parietal cortex
- neurons are tuned to spatial location of objects in space
- Visuomotor transformation : “the location (or spatial direction) of an object with respect to the initial position of the hand needs to be transformed into motor commands that move the arm toward the target”
What is serial processing
- as information is passed from one step to the next, more and more interesting information can be extracted from it
- ganglion cells detect spots—-V1 neurons detect edges—- V5 detects movemnt of edges…
When is the human binocular vision critical period?
3-8 months, extending longer if deprived
fancy word for lazy eye
amblyopia
How can amblyopia be treated?
- by correcting direction of deviated eye
- weakening dominant eye with a patch
- must happen before end of critical/sensitive period
What is balint’s syndrome? What causes it?
- a rare disorder associated w difficulties in visual and spatial coordination
- characterized by optic ataxia, oculomotor apraxia, and simultagnosia
- caused by bilateral lesions of the posterior and lateral occipital cortex
What is oculomotor apraxia?
difficulty voluntarily steering gaze
What is optic ataxia?
difficultry reaching using visual guidance
What is simultagnosia?
profound restriction of attention
prosopagnosia
- due to lesion in the fusiform gyrus
- inability to identify/perceive faces
- Ventral pathway (V1-V2-V4-IT)
IT is fusiform face area
What is object agnosia?
- inability to identify/percieve objects
- ventral pathway
- due to lesion in the fusiform gyrus
Hemi-spatial neglect
- inability to attend to one half of the visual field
- dorsal pathway: va-v5-posterior parietal cortex
- due to lesion in the posterior parietal cortex
