vision Flashcards
(39 cards)
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
