vision Flashcards
What is Hue and intensity
Hue: dimension of colour determined by wavelength
Intensity: amount of energy in a wave, determined by amplitude (height)
Distance between peak and trough of light
Perceived as brightness of light
Intensity: brightness
What does a short wave mean for it’s colour and frequency?
high frequency (many)
blue colours
high pitched sounds
What does a log wave mean for it’s colour and frequency?
low frequency (few)
red colours
low pitched sounds
great amplitude (tall)
bright colours
loud sounds
Small amplitude (short wavelength)
dull colours soft sounds
The pupil
Area that allows light into eye
Adjustable Opening in centre of eye (black)
Lets light into eye so it can land on retina where light is converted to neural signals
Iris
Iris a ring of muscle that forms the coloured part of the eye around the pupil and controls the size of the pupil opening
Part of eye that gives eye colour
Lens
Changes in shape to bend lens a little bit to allow it to change focus on the retina
Focus
Fovea
Fovea area where object that centres visual field lands on retina
any time you focus image on something you rely on fovea
Location where optic nerve leaves the retina and goes back to the rest of the brain
This creates a blind spot
Retina
Part of your brain
Image presented on fovea is upside down
Accommodation: process in which lens changes shape
Lets you focus on near or far away objects
Retina: light sensitive inner surface of the eye containing receptor rods and cones plus layers of neurons that begin the processing of visual information
What are two different types of photo receptors
Rods: detect black white and grey stimuli
Number:120
More sensitive under: low light
Location in retina: More concentrated in peripheral retina
Outside fovea
Not colour sensitive
1 to one ration from cones to retinal ganglion cell
Allows for higher resolution processing
Why they are in high concentration in fovea
Good at detail
Cones:
Number: 6 million
Location: Near fovea (centre)
Fine detail and colour
Sensitive in: Well lite conditions
Vision in periphery is lower detail many rods sending same amount of information
Results in lower resolution
High convergence creates low visual equity
What it sacrifices in acuity, it makes up for sensitivity
Why they are better in the dark
How does sight work?
Light has to pass through other layers to get to photoreceptors then stimulus converted into neural impulse (transduction)
Once light is transduced into neural impulses that info in form of action potential travels back through layers in reverse order
Retinal ganglion cells send info back to other parts of brain
Horizontal vs amacrine cells
Horizontal cells go across streams of information processing
Amacrine do the same thing but at a different synapsis
Why is eye movement important?
Quick eye movements
We know when eyes moving vs world moving, cause brain controls for that
These bits of information are then integrated
Stabilize retinal image- see nothing
If you immobilize your eye completely, you can’t process or see any stimuli
Our visual system responds to change
What is transduction? What about visual transduction?
Transduction- conversion of one form of energy to another
Conversion of stimulus into neural impulse
Visual transduction- light energy to neural signals by visual receptors
Photopigments allows this
They are chemicals that absorb lights and cause changes to photo receptors
Diff photoreceptors have diff wavelengths
Pigment absorbs light
Absorption spectrum determines spectral sensitivity
Rhodopsin
What is it?
What happens when you see light?
Rhodopsin
The pigment found in rods
A G protein-linked receptor that responds to light in the dark
The darker it is, the more they fire:
- Cyclic GMP keeps Na+ channels open, causing the constant release of glutamate
When it’s lighter, those Na channels start to close:
- Visual transduction happens in photoreceptors
- Cyclic GMP deactivated Na+ channels close
- Rods hyperpolarize in response to light
- Activity is inhibited by the light
What is the retina-geniculate-striate pathway?
It is the primary visual pathway that transmits visual information from the retina to the primary visual cortex (V1) via the lateral geniculate nucleus (LGN) in the thalamus.
What percentage of retinal ganglion cell axons project to the LGN?
90% of retinal ganglion cell axons project to the LGN.
How is visual information from each eye processed in the brain?
Information from the left visual field of each eye is processed in the right LGN, while information from the right visual field is processed in the left LGN.
Where do most LGN neurons terminate in the primary visual cortex (V1)?
Most LGN neurons terminate in the lower part of cortical layer IV of V1.
Pathway from Eyes to Visual Cortex
- Visual Fields vs. Eyes
The visual fields, not the eyes, are contralateraly represented.
The left visual field is processed by the right hemisphere, and the right visual field is processed by the left hemisphere.
- Hemiretinas and Visual Information
Each eye is divided into two hemiretinas:
Nasal hemiretina (inner half, closer to the nose) (ones that coross over)
Temporal hemiretina (outer half, closer to the temples) stay ipsilateral
The left side of each hemiretina processes the left visual field, and the right side of each hemiretina processes the right visual field.
- Optic Chiasm and Crossing of Fibres
Nasal hemiretina fibres cross at the optic chiasm, sending information to the opposite lateral geniculate nucleus (LGN).
Temporal hemiretina fibres stay ipsilateral (same side) and do not cross.
- Pathway to the LGN
After the optic chiasm, visual information is directed to the LGN of the thalamus.
- Travel to the Primary Visual Cortex (V1)
From the LGN, visual information travels back to the primary visual cortex (V1) in the occipital lobe for processing.
Retina geniculate striate system
Retinotropic organization:
Q: What is retinotopic organization?
Q: How does the primary visual cortex (V1) handle high-acuity vision?
Q: What percentage of the primary visual cortex (V1) processes information from the fovea?
Q: What is retinotopic organization?
A: It is the mapping of visual information in the brain, where adjacent areas of the retina project to adjacent areas of the primary visual cortex (V1).
Q: How does the primary visual cortex (V1) handle high-acuity vision?
A: More cortical space is devoted to areas of high visual acuity, similar to how the somatosensory cortex disproportionately represents sensitive body parts.
Q: What percentage of the primary visual cortex (V1) processes information from the fovea?
A: About 25% of V1 is dedicated to processing input from the fovea, even though it occupies only a small portion of the retina.
The M and P Channels
Microcellular layers (M layers)
- Big cell bodies
- two bottom layers of LGN
- responsive to movement
Input from rodes
Parovocellular layers (P)
- Small cell bodies
top 4 lgn layers
- In charge of colour detail or still objects
Input from rodes
Contrast enhancement and match bands effect
Match bands are nonexsistent stripes that visual system creates to enhance contrast and make edges more pominent
- Its a consequence of lateral inhibition
Lateral inhibition
What is it?
How does it work?
Explain match bands example.
Lateral inhibition is a process in the visual system that enhances contrast, making edges and boundaries stand out more clearly. This is important for survival, such as detecting a predator against its background.
How It Works:
Each photoreceptor in the retina responds to light intensity.
The level of activity of a photoreceptor depends on:
How much light it receives (stimulus intensity).
How active its neighbouring photoreceptors are (lateral inhibition).
More active photoreceptors inhibit their neighbours, reducing their response and creating an effect where edges appear more distinct.
ex
Mach Bands – A Classic Example
When looking at a pattern with a bright area next to a dark area, the boundary between them appears more exaggerated than it actually is.
The bright side of the boundary looks even brighter, and the dark side looks even darker—this is contrast enhancement due to lateral inhibition.
Even though this exaggeration isn’t actually there, our visual system creates it to help us detect edges more effectively.
Receptive fields of visual neuron
The area of the visual field within which it is possible for a visual stimulus where it is possible for a visual stimulous to influence firing of a neuron
Three types of receptive fields of visual neuron
Receptive field of foveal areas smaller than those in periphery
Circular receptive field
Monocular
Centre surround organization
When do on centre cells respond most?What about off centre cells?
When light in centre
Light off centre
Neurons in receptive fields in striate cortex
neurons in v1
simple or coplex
Simple: receptive field are rectangular with on and off regions (location sensitive)
Orientation and location sensitive
- angle can determine if it responds
- monocular (impute from one eye only)
Complex: rectangular large receptive field responds best to particular stimulus anywhere in field
- No static on off regions
- orientation not location sensitive
- motion sensitive
-binocular
How do cells in V1 process information?
Cells with simpler receptive fields send information to cells with more complex receptive fields, allowing for hierarchical visual processing.
What are functional vertical columns in V1?
A: Vertical columns where all neurons share the same receptive field and ocular dominance (respond to input from the same eye).
What happens as you move horizontally across V1?
Ocular dominance columns shift, meaning that preference for input from the left and right eyes alternates in a striped pattern.
How is retinotopic organization maintained in V1?
Neurons preserve the spatial arrangement of visual input, so neighbouring areas of the retina are mapped to neighbouring areas of V1.
Trichromatic theory vs Opponent-process theory
- 3 types of receptors, each with diff spectral sensitivity
- 2 diff classes of cells encoding colour and another class encoding brightness
each encodes complementary
Q: What is color constancy?
: What does the Retinex theory state?
Q: What is color constancy?
A: The ability of the visual system to maintain consistent color perception despite changes in lighting and the wavelengths of light reflected.
Q: What does the Retinex theory state?
A: Color perception is based on the proportion of light of different wavelengths that a surface reflects, rather than the absolute wavelength.
Q: How does the Retinex theory explain color constancy?
A: The relative wavelengths reflected from an object remain constant in different lighting conditions, so color perception remains stable.
prosopagnosia
a neurological condition where individuals struggle to recognize faces, including those of familiar people, due to a problem with the brain’s ability to process facial information.
akinetopsia
motion blindness, is a rare neurological condition where individuals experience a selective loss of the ability to perceive visual motion, often seeing the world as a series of still images or freeze frames.
Blind sight
Blindsight is a rare ability that allows people to detect visual stimuli in areas of their visual field that they claim they can’t see. It’s a result of damage to the primary visual cortex in the brain.
