Chapter 2 Flashcards
Additive Color Mixing
Mixing that happens when lights of different wavelengths are perceived by the eye
- Red, Green, Blue
Subtractive Color Mixing
Physical process of color mixing that happens within the stimulus (paint)
- Red, Yellow, Blue
Visible Lights
- wavelengths of light are either absorbed or reflected (what we see)
- White reflects all colors of light
- Black absorbs all colors of light
Ex: Red/Blue absorbs, Green reflects
Sclera
White of the eye
Eye muscle
1 of 6 surrounding muscles to help rotate the eye in all directions
Iris
Colored area containing muscles that control the pupil
Pupil
Opening at the center of the iris that lets light in
- Light reflected from objects)
Lens
Transparent disk that focuses light rays for near or distant vision (20% of light is focused)
Cornea
Curved, transparent dome that bends incoming light (80% of light is focused)
Retina
Innermost layer of the eye, where incoming light is converted into nerve impulses
- 120 million rods
- 6 million cones
Fovea
Part of the retina where incoming light rays are most sharply focused
- Size of 12pt font “o”
- Contains only cones (50,000 or 1%)
Optic Nerve
Transmits impulses from the retina to the rest of the brain
Blind Spot
Place where the optic nerve leaves the eye (No receptors)
How to find your Blind Spots
- Fills in the space where the image disappears
Macula
fovea and small area surrounding fovea
Macular Degeneration
- age related
- fovea is destroyed because the cones are breaking down
- blurry on what you are trying to focus on
Retinitis Pigmentosa
- genetic disease
- attacks the rods (dark spots indicate damaged rods)
- can lead to blindness
Focusing Light on Receptors
- upside down and backwards
Accommodation
- process occurs unconsciously
- change in shape of the lens
- muscles at front of the eye tighten/contract –> increases the curvature of the lens and gets THICKER
- eye is constantly adjusting based on distances
Myopia
corneas too steep or eyes too long
(Nearsightedness)
- visual focus at the front of retina
Hyperopia
corneas too flat or eyes too short
(Farsightedness)
- visual is behind retina
How do we get it corrected?
- brain converts raw date and makes sense of it
- occipital lobe
- doesn’t rotate image back in place
- takes account location cues based on head orientation
- newborns may see inverted
- Corpus callosum –> linking left and right hemispheres
Pathway to the brain (Left)
- left visual signal
- right side of retina along the optic nerve
- right thalamus
- right visual cortex (occipital lobe)
Pathway to the brain (Right)
- right visual field
- left sides of retinas along optic nerve
- left thalamus
- left visual field (occipital lobe)
Visual Transduction
- light into electricity
- 2 visual pigment molecules (opsin and retinal)
- occurs when retinal absorbs light
Opsin
a large protein
Retinal
light sensitive molecule
- changes shape from bent to straight “isomerization”
Visual Pigment Bleaching
- original color is dark
- when bleached it is not useful for vision
- ## retinal needs to become bent and reattach the opsin for transduction (visual pigment regeneration)
Dark Adaptation
- cones adapt in 3-4 mins (sharp/focus/color)
- rods adapt in 20-30 mins (low light–> shape & form)
Color Perception: Trichromatic Color Theory
- 3 kinds of cones
- each sensitive to various wavelengths
- Blue (short), Green (medium), Red (long)
– Helps understand color blindness
Trichromats
Human, monkey, apes
Dichromats
Dogs, most humans that have color blindness
Monochromats
rare, no color vision, only 1 type of cone
Opponent Process Theory
- neurons have an excitatory and inhibitory response to various wavelengths
- Opponents:
— Red/Green, Yellow/Blue, White/Black
Afterimage
- Eyes adapt to colors when the specific cones for those colors receive the light and fire
- if the color isn’t there, the neurons will not fire
- Absolute refractory
- Result is perception of opposite color
Absolute Refractory
when you remove stimulus you have fatigued cells
- ones that aren’t overworked will fire, fatigued won’t fire
3 Parts to Visual Pathway
Parts of a Neuron
- nerve fiber
- synapse
- cell body
- dendrite
- axon/nerve fiber
- mylin
Action Potentials
- electrical signals that take place in a neuron
(know how to label an action potential pathway)
Know the cellular level of a action potential!
:)
Features of Action Potentials
- Propagated Response
- Refractory Period
- Spontaneous Activity
Propagated Response
When triggered, continues down axon at the same strength
Refractory period
~ 1 ms recovery time
- when one nerve impulse occurs and another can be generated
Spontaneous Activity
baseline firing
- AP occur in absence of stimuli from environment
How to Change rate of firing
- Changing stimulus intensity changes, NOT size of AP
- max 500-800 impulses per sec
Responses at Receptor Sites
Excitatory and Inhibitory
Excitatory response
- closer to positive
- increase chance of AP
- Depolarization (more positively charged)
Inhibitory Response
- closer to negative
- decreases chance of AP
- Hyperpolarization (becoming negatively charged)
A Response Depends on…
- type of neurotransmitter released
- properties of the receptor site (receiving neuron)
Glutamate
- Primary Excitatory NT
- Receptor Sites: NMDA, AMPA, Kainate
- Na+ ions flow into cell
- Depolarization
GABA
- Primary Inhibitory NT
- GABAa: Ion channel opens
– Cl- ions flow into cell - GABAb: Protein –> Ion channel opens
– K+ ions leave cell - Hyperpolarization
Each Eye Contains
- 126 million receptors (120 rods, 6 cones)
- 1 million ganglion cells (per eye)
- ratio for rods to ganglion (120:1)
- ratio for cones to ganglion (6:1)
- cones in fovea are 1:1 ratio
Convergence
- when a number of neurons synapse onto a single neuron
- signals form rods converge MORE and cones converge LESS
resulting in rods being more sensitive to light and cones having better detailed vision (acuity)
SHORT ANSWER Question
Convergence Summary
- High convergence: high sensitivity and low acuity (ROD)
- Low convergence: low sensitivity and high acuity (CONE)
Testing Visual Acuity
- reading symbols on an eye chart
- babies need specialized methods
— Preferential Looking (PL) Technique
— Visual Evoked Potential (VEP)
