Vision Flashcards
What is light?
Discrete particles of energy, photons, or waves of electromagnetic energy
What do we perceive as wavelength?
Perception of colour
What do we perceive as amplitude?
Perception of brightness or intensity
What are the 3 achromatic colours?
Black = produced by lack of light
White = produced by an intense mixture of wavelengths in equal proportions
Grey = produced by a mixture of wavelengths in equal proportions at lower intensities
What are hues/colours?
Depend on wavelengths of light that a stimulus or object reflects into the eye
Most objects absorb different wavelengths and reflect the rest
What is the monocular visual field?
Visible to one eye
Contains one blind spot
How are monocular visual fields measured?
Using perimetry
What is the binocular visual field?
Area of overlap between monocular fields
What is seen by both eyes
What is the cornea?
Where light first enters the eye
Works with the lens to bend light onto the retina
Cannot change shape
What is the lens?
Focuses light onto the retina
Can move
How do we focus on a nearby object?
Less tension on ligaments holding lens in place
Holds lens in natural shape
Brings close objects into sharp focus
Loss common cause of presbyopia or hyperopia
How do we focus on a distant object?
Increase tension on ligaments holding the lens in place
Flattens the lens
Loss with myopia lens
Where is the site of transduction of light rays?
The retina
What are the 5 layers of cells in the retina?
Photoreceptors Horizontal cells Bipolar cells Amacrine cells Retinal ganglion cells
What are the photoreceptors?
Cones and rods
What do horizontal cells and amacrine cells do?
Lateral communication
What do retinal ganglion cells do?
Axons project on surface of retina
Make up optic nerve
What are 2 disadvantages to the retina inside-out design?
Light is distorted
Optic disk has no receptors
How do we fill in the blind spot?
Use info from receptors around the blind spot
Surface interpolation
What is the fovea?
Tiny indentation in the center of the retina
High acuity vision in the center
Densely packed cones and rod free
What type of vision requires good lighting?
The cone vision
What is the photopic system?
Provides high acuity coloured perception
What are S-cones?
Short wavelength Least abundant Blue High sensitivity Less concentrated in fovea
What are M-cones?
Medium wavelength
Green
What are L-cones?
Long-wavelength
Red
What is the trichromatic theory of colour vision?
3 different colour receptors
Any colour in visible spectrum can be matched by mixing together 3 different wavelengths of light in different proportions
Needs to have at least 3 wavelengths to match every colour
What vision is used in dimly lit conditions?
Rod vision
What is the scotopic visual system?
Lacks detail and colours
What is the convergence of the scotopic visual system?
Several hundred rods converge on one bipolar cell
Poor acuity
What happens if you lack rods?
Night blindness
What is the achromatic vision?
Shades of grey from black to white
Not colour sensitive
Do not detect red light
What is ON firing?
Detect light objects in the dark
What if OFF firing?
Detect dark objects in light environments
What are OFF firing bipolar cells
Depolarize when light is off
What are ON firing bipolar cells?
Depolarize when light is on
What cells are inhibited by glutamate?
ON firing cells
IPSP
What cells are excited by glutamate?
OFF firing cells
EPSP
Firing in ON center cells?
Light in center of receptive field increase firing
Light in periphery of receptive field = off firing inhibition
Firing in OFF center cells or ON surround?
Increase firing when light is on in the surrounding area of receptive field
Light in the center of the receptive field by decrease firing
What are horizontal cells responsible for?
Axoaxonic contact of photoreceptors
Acts as an interneuron
Enhances brightness contrast
What do ON center and OFF center cells respond best to?
Contrast
Most effective way to influence firing is to illuminate entire center and keep entire surround unilluminated
What is the geniculate striate pathway?
Retina to optic nerve to LGN to striate visual cortex
What is the SCN?
Control diurnal rhythms, RGC sensitive to blue light
What is the superior colliculus?
Reflexive eye and head movements
What is the pretectum?
Pupillary eye reflex
What is the LGN?
Receives input from the contralateral visual field
Disproportionately large foveal representation in striate cortex
What are the parvocellular layers?
Projections from small p RGC, more p cells than m cells
Project to top 4 layers of LGN
Responsive to colour, slow moving or stationary details, and fine pattern detail, small receptive field
Input primarily from cones
Project to bottom of striate layer 4 neurons
What are the magnocellular layers?
projections from big m RGC
Project to the bottom 2 layers of LGN
Responsive to movement, large receptive field
Input primarily from rods
Project to top part of striate layer 4 neurons
What is the striate cortex involved in?
The initial cortical processing of all visual information necessary for visual perception
What does damage to the striate cortex result in?
loss of vision in the contralesional hemifield
What is scotoma?
Damage in one hemisphere in V1
Area of blindness in the contralateral visual field of both eyes
What is an opponent-process theory?
2 different classes of cells encode colour and a third that encodes brightness Each class encodes 2 complementary perceptions
What is the secondary visual cortex?
Input mostly from V1
24 subsections
What is the association cortex?
Prestriate cortex and inferotemporal cortex
What is the dorsal stream?
Directs behavioural interaction with visual stimuli but not recognition of objects
Perception of where objects are
What is akinetopsia?
Inability to perceive fluid motion
Unilateral or bilateral MT damage in the dorsal stream
See the world in snapshots
Cannot appropriately control behaviour
What is the ventral stream?
Mediates conscious perception of objects
What is prosopagnosia?
Failure of face recognition
Can recognize other objects
