Vision Flashcards
What are the 2 principles of vision?
- Perception is dynamic - we perceive change
- we perceive constancies in a changing environment
What is the electromagnetic radiation continuum?
- is generated when an atom emits a “particle” called a photon
- the energy of photons determines their wavelength
- different wavelengths give rise to the perception of different colours
True or false: the human eye is only capable of detecting light within a narrow range of wavelengths
True
What is the effect of a short wavelength?
Ultraviolet light
(Gamma rays, X rays)
What is the effect of a long wavelength?
Infrared light
(radar, radio)
Where is the Retina positioned in the eye?
Above the line of sight and Fovea at the back of the eye
What is Saccades?
Our eyes are constantly moving
- if an image stays stable it disappears on the retina (the photoreceptors stop firing) and the brain fills in the missing spaces
Describe the stationary blind spot
We have a stationary blind spot where the optic nerve enters the eye and we are unaware of it
What controls the shape of the lens to accommodate near or far targets?
the ciliary muscles
To focus on a far target what happens to the lens?
Lens flattens
To focus on a near target what happens to the lens?
Lens rounds
What are the properties of cones?
- fast dark adaptation
- low dark sensitivity
- “yellow” sensitive
- high acuity
(fovea and periphery)(6 million)
What are the properties of Rods?
- slow dark adaptation
- high dark sensitivity
- “green” sensitive
- low acuity
(Mainly peripheral vision) (120 million)
What is the Duplex retina theory?
Schultze proposed that the rods and cones form two separate visual fields; Photopic and Scotopic
What is the Photopic visual field in the Duplex Retina theory?
Bright light vision via cones
- “day blind” without cones
What is the Scotopic visual field in the Duplex Retina theory?
Dim light vision via rods
- “night blind” without rods
What cells do Receptor cells synapse with?
Bipolar cells
What cells do bipolar cells synapse with?
ganglion cells
What do Horizontal cells do?
connect different receptor or bipolar cells
What do Amacrine cells do?
connect different bipolar or different ganglion cells
What do connecting cells (horizontal and amacrine) allow for?
events at one location to influence events at another
On average how many receptors connect to 1 ganglion cell?
126
What is the function of ganglion cells?
like a lens on part of the visual field - captures image over an area of the retina - receptive field
- enhance the image in its local area
What is the function of receptors?
points of light
What is the process of lateral inhibition?
- attached receptor cell when stimulated caused rapid rate firing (large response) from ganglion cells
- in stimulating an adjoining receptor which did not itself excite the monitored ganglion cell, output of the ganglion cell was reduced
- RICH GETS RICHER SCHEME
What are the two types of connections that ganglion cells have within their receptive field?
excitatory and inhibitory
What is an excitatory connection that ganglion cells have within their receptive field?
Some ganglion cells can be excited by light inside the receptive field
What is an inhibitory connection that ganglion cells have within their receptive field?
Inhibited by light outside the receptive field
What occurs in centre-surround receptive fields?
illumination of center is inhibitory while illumination of the surround is excitatory
In centre-surround receptive fields, what occurs in relation to retinal ganglion cells?
The retinal ganglions cells can act as edge detectors, integrate patterns of lightness over an area and Indicate whether that pattern of lightness within an area is different to that in an adjacent area (an edge)
What cells do exhibit centre-surround antagonism?
X cells or Y cells
What cells do not exhibit centre-surround antagonism?
W cells
What two visual channels are the X and Y cells associated with?
Pravocellular and magnocellular systems
What are the characteristics of the Parvocellular system?
(size, response, RF size, RF type, RF distribution, movement, speed of nerve, transmission, function)
Size: small
Response: sustained
RF size: small
RF Types: X
RF distribution: foveal
Movement: poor
Speed of nerve: slow
Transmission: detail
Function: space and colour
What are the characteristics of the Magnocellular system?
(size, response, RF size, RF type, RF distribution, movement, speed of nerve, transmission, function)
Size: large
Response: transient
RF size: large
RF Types: Y
RF distribution: peripherial
Movement: good
Speed of nerve: fast
Transmission: motion
Function: depth and time
What is the function of the Tectopulvinar system?
- localisation of objects in space
- guidance of eye movements
- gross pattern perception
Some optic tract fibres project to the superior colliculi and then on to the pulvinar and lateral posterior nuclei.
What does a Lateral Geniculate Nucleus do?
receive input from the visual cortex (back projections) allowing feedback based on previously processed information
What are the structures located in the thalamic region called?
The Tectum
Cells in the superior colliculi have receptive fields on the retina and receive their input from…
magno (or magno-like) retinal ganglion cells
Without a Lateral Geniculate Nucleus, what occurs?
patterns are unable to be recognised
Without the superior colliculi, what occurs?
able to recognise patterns but unable to accurately approach them
What are the two seperarte pathways in the Tectopulvinar System and what do they do?
Focal system for recognition
Ambient system for localisation
What is Blindsight?
(Weiskrantz, 1977, 1992)
some people with damage to the focal system can still react to visual stimuli (e.g. point to them) although they claim that they cannot see them
How does the Lateral Geniculate Nucleus project?
project to the primary visual cortex in the occipital lobe at the rear of the brain
Describe where the lobes and pathways of the visual cortex are positioned in the brain?
The parietal lobe is at the top rear
The where pathway is below the parietal lobe extending from the primary visual cortex
The occipital lobe is below the where pathway at the rear
The Primary Visual Cortex is at the bottom rear of the brain
The what pathway extend from the PVC towards the temporal lobe
The temporal lobe is at the bottom of the brain towards at the front of the bottom section of the brain (before the dip)
What do the simple cortical cells respond to?
bars of a particular orientation
What do the complex cortical cells often respond to?
a correctly oriented bar moving across the entire receptive field. Some cells are even direction sensitive
What do Hypercomplex cortical cells fire to?
only to moving lines of a particular length or moving corners or angles.
What do cortical cells act as?
feature detectors
What is the dorsal pathway?
Where
- travels up to the parietal lobe and is concerned with motion perception and spatial awareness
What is the ventral system?
What
- travels to the temporal lobe and is concerned with object recognition
Describe how adaptation occurs in the visual system.
the system slowly stops responding to constant stimuli
stopping a stimulus can result in an aftereffect (e.g. colour or motion aftereffect)
adapting to constant stimulation helps the system stabalise
