Vestibular Systems
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Acceleration/Gravity
o Function: acceleration refers to changes in velocity. Gravity pulls objects towards
the ground.
o Question: how does the vestibular system detect changes in acceleration and
gravity, and why is it important for balance and spatial orientation?
 The vestibular system is in the inner ear. It has semicircular canals filled
with fluid. When you rotate your head, the fluid lags behind. This bending
of hair cells signals rotational movement.
 The vestibular system also has otolith organs and when your head
accelerates linearly, otoliths shift position. This bending of hair cells
signals linear acceleration and gravity.
 Detecting rotation helps maintain balance during turns and detecting linear
acceleration helps maintain posture and stability. Sensing gravity's pull
helps determine body's orientation in space and this spatial orientation is
vital for coordinated movements.
Semicircular Canals
o They are fluid filled structures in the inner ear that detect rotational movements of
the head.
o Question: explain how the structure and orientation of the semicircular canals
allow them to detect angular acceleration in different planes?
Otolith Organs
o (Utricle and saccule) detect linear acceleration and changed in head position
relative to gravity
Angular/Linear Acceleration
o Angular acceleration: changes in rotational speed or direction
o Linear acceleration: changes in linear speed or direction
o Question: how do the vestibular organs differentiate between angular and linear
acceleration, and how do these types of acceleration contribute to our sense of
movement and balance?
 It has 2 main organs: semicircular canals (angular acceleration) and otolith
organs (angular motion)
 Linear acceleration (forward/backwards and up/down) makes otoliths shift
position which bends hair cells and signals linear motion
 Angular helps sense rotation, turns and tilts
 These allow use to have coordination, and maintain equilibrium as we
move.
Yaw/Roll/Pitch
o Yaw: rotation around the Z axis (chin to shoulder)
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o Roll: rotation around the X axis (ear to ear)
o Pitch: rotation around the Y axis (forward and backward)
Somatogravic Illusion
o Occurs when the vestibular system misinterprets linear acceleration (such as
during rapid upward or downward motion) as changes in orientation. (plane
taking off)
o Question: how does the somatogravic illusion occur, and what are the potiental
consequences for pilots experiencing this illusion during flight travel?
Vision
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Visible Wavelengths
o The range of electromagnetic waves that the human eye can detect, corresponding
to different colors in the visible spectrum.
o Question: explain how the eye perceives different colors based on the
wavelengths of light and how this process is related to the functioning of cone
cells in the retina
Prism Experiment
o Demonstrates how white light can be separated into its component colors
(spectrum) through refraction
Iris, Pupil, Cornea, Fovea, Retina
o Iris: colored part of the eye that regulates the amount of light entering the eye by
adjusting the size of the pupil
 How does the iris control the size of the pupil in response to changes in
lighting conditions, and what role does this play in visual adaptation?
o Pupil: black circular opening in the center of the iris that allows light to enter the
eye and reach the retina
 Explain the role of the pupil in controlling the amount of light that enters
the eye and how it contributes to visual acuity and sensitivity
o Cornea: transparent outer layer of the eye that refracts light and helps focus it onto
the retina
 Question: explain the role of the cornea in the process of vision, including
its contribution to the eye’s ability to focus images on the retina
o Fovea: small central area of the retina responsible for sharp central vision and
high visual acuity
 Question: compare and contrast the functions of the fovea and peripheral
retina in visual perception detail their roles in different aspects of vision
o Retina: innermost layer of the eye that contains photoreceptor cells (rods and
cones) responsible for converting light into neural signals
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Question: describe the structure of the retina and the specific functions of
rods and cones in processing visual information under different lighting
conditions.
o Question: differentiate between the roles of the cornea and lens in focusing light
onto the retina. How do their functions complement each other, and what happens
when there are abnormalities or changes in these structures?
Light/Dark Adaptation
o Pupil changes size to limit amount of light admitted to the eye
o This is also affected by cognitive load and arousal
Rods/Cones/Bipolar/Retinal Ganglion Cells
o Rods: photoreceptor cells in the retina that are sensitive to low light levels and are
responsible for peripheral vision and night vision
 Question: explain how rods contribute to our ability to see in dimly lit
environments and why they are more sensitive to light compared to cones
o Cones: photoreceptor cells in the retina that are responsible for color vision
(trichromatic vision) and high visual acuity, especially in well-lit conditions
 Question: describe the 3 types of cones (red, green, blue) and their role in
color perception, including how they respond to different wavelengths of
light
o Bipolar Cells: neurons in the retina that receive input from photoreceptor cells
(rods & cones) and transmit visual information to ganglion cells
 Question: discuss the role of bipolar cells in visual processing and how
they contribute to the organization of visual signals before they reach the
optic nerve.
o Retinal Ganglion Cells: the output neurons of the retina that receive input from
bipolar cells and transmit visual information to the brain via the optic nerve.
Blindspot
o Small area on the retina where the optic nerve exits the eye, lacking photoreceptor
cells, and therefore not sensitive to light
o Question: how does that brain compensate for the blind spot in normal vision, and
what experiments can be conducted to demonstrate the existence of the blind
spot?
Top-Down/Bottom-Up
o Top-down: using prior knowledge and expectations to interpret sensory
information
o Bottom-up: analyzing sensory information from the environment without
preconceived notions
o Question: provide examples of top-down and bottom-up processing in visual
perception and explain how they influence our perception of objects and scenes
Accommodation
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o The ability of the eye to adjust the focus of the lens to see objects at different
distances (near and far) and gets worse with age
o Question: describe the process of accommodation in the eye, including the role of
ciliary muscles and changes in shape of the lens
Myopia/Hyperopia (eyeball or cornea changes shape)
o Myopia: nearsightedness where light does not reach fovea and does not reach the
focal point
o Hyperopia: far sightedness where light goes past the fovea and goes past the focal
point
o Question: describe the differences in the shape of the eyeball in myopia and
hyperopia, and explain how these conditions affect the focusing of light into the
retina
Lasik vs. Cataract
o Lasik: permanently changes the shape of the cornea
o Cataract: remove your eye’s natural lens and replace it with an intraocular lens
Phototransduction, Retinal, Rhodopsin, Isomerization
o Phototransduction:
 Starts with light contacting photoreceptors (rods and cones)
 In rods, the visual pigment is rhodopsin, which is looking for light photons
reflected to the back of the eye through the lens.
 Through rhodopsin we have retinal which is going to change its shape
when it makes contact with light (Isomerization)
 When this happens it causes the sodium channels to close
(hyperpolarization) which leads to reduction of action potentials.
 Ends with APs being sent through optic nerve
 However, in darkness, there are no photons of light making contact with
rhodopsin or retinal which means sodium channel is open and is
continuing to fire action potentials
o Retinal: light sensitives molecule that is bond to opsin proteins in photoreceptor
cells
o Rhodopsin: visual pigment found in rod cells, consisting of retinal bound to opsin
o Isomerization: the change in shape of retinal molecules when exposed to light.
Visual Convergence and Acuity
o Visual Convergence: merging of multiple input signal from photoreceptor cells
onto a single neuron in the visual pathway
o Acuity: the sharpness or clarity of vision, particularly in distinguishing fine
details.
o Question: explain how visual convergence and acuity are related and how they
contribute to our ability to perceive detailed images
Receptive Fields
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o Specific areas in space that a cell is responsive towards.
o They play a crucial role in processing visual information and detecting features
such as edges and movement
o Question: describe the concept of receptive fields in the visual system, including
how they vary across different types of neurons and their importance in visual
processing
On-Center/Off Center Bipolar
o On-center: turning on light excites the cell because it receives less glutamate,
which normally inhibits on-center bipolar cells
o Off-center: turning off light in the center of the field excites the cells because they
receive more glutamate and are depolarized
On-Center/Off Center Retinal Ganglion Cell (detecting contrast and edges)
o On-center: activated when light is focused on their center -- fire action potentials
in response to a bright stimulus surrounded by a ring of darkness
o Off-center: activated when light falls on their surrounding area - respond to dark
in center of receptive field
o Question: describe the response of on-center and off-center retinal ganglion cells
to light stimulation and how their properties contribute to visual processing
Cones (color)
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Perceived Color
o Subjective experience of color based on the brain’s interpretation of different
wavelengths of light.
o Depends on: (perceived color depends on the wavelength of light that an object
reflects)
 The wavelengths of light present
 Wavelengths the objects reflect
 Assumption about the wavelengths of light present (color consistency)
 Previously viewed colors (after-images)
 Language
 Top-down recalibration based on prior experience
Absorbance
o Ability of a substance (visual pigment (rhodopsin)) to absorb specific
wavelengths of light. It plays a role in determining the color of light that is
transmitted or reflected
Trichromatic Theory
o Proposes that color vision is based on the combined activity of 3 types of cone
cells in the retina, each sensitive to different wavelengths of light (red, green,
blue)
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o Question: discuss the mechanisms underlying the trichromatic theory of color
vision and how it explains our ability to perceive a wide spectrum of colors.
Population Coding
o The representation of sensory information (such as color perception) by the
combined activity of multiple neurons in the brain.
o Question: how does population coding contribute to the perception complex
visual stimuli, such as recognizing and discriminating between different colors?
Color Blindness (types)
o A condition where individuals have difficultly distinguishing certain colors
o Types:
 Red-green color blindness (protanopia and deuteranopia) and blue-yellow
colorblindness (tritanopia)
o Question: differentiate between the types of color blindness based on the specific
cone cells affected and the resulting color perception deficits. How does color
blindness support or challenge the trichromatic theory of color vision?
What causes color blindness?
o Genetics (1-12 men)
o Injury to the retina: retinal detachment
o Eye injuries caused by lasers
o Brain tumors – ones that affect the optic nerve or put pressure on the brain
o Radiation treatments
o Just gets worse because of age – often because of cataracts
Color Constancy
o Refers to the ability of the visual system to perceive colors consistently across
different lighting conditions, objects, and contexts.
o Question: explain how color consistency works in the visual system and provide
examples of situations where color consistency may be challenged.
Apparent Motion
o The perception of movement in a sequence of static images or stimuli, creating
the illusion of motion.
o Question: provide examples of apparent motion in everyday life and explain how
our visual system processes static stimuli to perceive motion
Rules of Apparent Motion
o Favors shortest path
o Stimuli must mimic timing and distance of real motion
o When we see matches what we expect based on our knowledge, experience, or
surrounding context, we are more likely to perceive motion even if the visual
input itself may not clearly indicate movement
o Side Note: Apparent motion highlights the role of top-down processing and how
our cognitive processes influence our perception of motion
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Point Like Walker
Flicker Fusion Threshold
o Frequency at which a blinking light appears stead. Depends on brightness, light
and dark adaptation, location of stimulus on retina. Max is about 120 frames per
second.
o Question: How does flicker fusion contribute to our perception of smooth motion
in movies or television, and what factors affect the threshold for flicker fusion?
Persistence of Vision
o An image persists for some time (1/30th of a second) after it's been removed
o Allows for illusions of a smooth moving picture (cartoons/flipbooks)
Dorsal Stream
o The “where” pathway and is responsible for processing visual information related
to spatial awareness, motion perception, and guiding actions
o Question: How does the dorsal stream contribute to tasks such as hand-eye
coordination and navigation in the environment?
Area V1 and MT
o Area V1: (Primary Visual Cortex) basic visual processing
o Area V5/MT: (Primary Motor Cortex) allows for motion coherence – is
specialized for processing motion information
o Question: how does the brain integrate motion signals from multiple sources to
perceive motion coherence, and what role does area MT play in the process.
Motion Coherence
o The perception of coherent motion when individual elements in a visual scene
move in a consistent direction
o Question: how does the brain integrate motion signals from multiple sources to
perceive motion coherence, and what role does area MT play in this process?
Motion Selection
o The ability to selectively attend to and process specific motion cues or patterns in
a complex visual scene
Saccadic Eye Movements
o Short, rapid eye movements that help re-focus tour gaze on to something else
(bringing objects of interest into the fovea)
o Question: Why don’t we see a blur when we’re moving our eyes all the time?
Saccadic Suppression
o Reduced perceptual awareness
 A reduction in response in the retina
 Competition between what’s on the fovea versus everything else
 Not 100% sure
Covert Attention
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o Switching your attention without moving your eyes
 Enhanced detection abilities in the attended location
 Decreased perception of things outside the attended area – even for things
in your receptive field that you’re looking directly at.
o Question: how does covert attention help in tasks like listening to a conversation
in a noisy environment?
Selective Attention
o We choose what to take in and process and what to ignore
o Question: describe a situation where selective attention plays a role in task
performance. How can distractions affect selective attention?
Inattentional Blindness
o Occurs when individuals fail to notice unexpected stimuli or events in their visual
field due to their attention being focused elsewhere
o Question: what are some factors that can increase the likelihood of experiencing
inattentional blindness?
Posterior Parietal What/Where
o Integration of information from V1 with where things are in space (body position
and location of external objects)
o Input goes to prefrontal cortex
Unilateral Neglect & Treatments
o Patients can see but do not attend to areas in space – usually the left side.
o Treatments:
 Top-down treatment: training attentional intent – voluntary left gazing.
Requires that they are aware of the neglect
 Bottom-up treatment: wearing opaque glasses over the right side of the
lens which helps stimulate nerves, etc
Blindsight & Causes
o Ability individuals with blindness to detect and respond to visual stimuli despite
lacking awareness of having seen anything
o Damage to area V1 (Primary Visual Cortex)
o When V1 is damaged, people report that they cannot see – but it seems that they
are still processing visual stimuli
 Pupils reflex intact, retina intact, eyes intact
Priming
o Priming: exposure to one stimulus influences a response to another without
intention
o Masked Priming: exposure to some stimulus influences a response without
intention except the object that does the priming is not consciously seen
Application Questions:
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How would a person with color vision deficiency (color blindness) experience the
perception of colors differently compared to someone with normal color vision? Discuss
the underlying mechanisms and potential challenges in daily life.
Explain Population coding with respect to the trichromatic theory of color vision.
o We have 3 color photoreceptors that are sensitive to different wavelength rangges
of light that we perceive as different colors. The 3 cones are named for the
perceived color that they are most sensitive/active towards (blue-short), greenmedium, red-long). This also explains how population coding is used so we can
see beyond the 3 colors that the cones are most sensitive to. Since each cone has a
range of light it’s sensitive to, each produces a response of action potentials in
response to a specific range of frequencies. Since there is overlap in the ranges of
colors each cone is sensitive to, usually each cone is responding a specific amount
to any given wavelength. The combined activation of all 3 cones towards the
same wavelength of light leads to the perception of many colors and hues beyond
red, gree, and blue.
What is the difference between the functions of rods and cones in visual processing,
including their roles in different lighting conditions, color perception, and spatial
resolution. How do these photoreceptor cells work together to create a comprehensive
visual experience?
What would happen to the neural code if I were to see a patient who was no longer able
to produce retinal?
o There would be a steady neural code because sodium channels would be open,
and we would only see darkness because sodium channels would remain open.
How do receptive fields in the visual system contribute to tasks such as object
recognition, motion detection, and depth perception?
Differentiate between visual convergence and receptive fields in term of their roles in
processing visual information. How do these concepts work together to create a
comprehensive representation of the visual world?
What happens to the response of an on-center bipolar cell when light is focused on its
receptive field center vs when light is focused on its surrounding area? Explain the
mechanism behind these responses.
Explain how perceived color is influenced by the trichromatic theory. How does this
account for our ability to see a wide range of colors?
What makes objects absorb vs reflect certain wavelengths of light?
o When the frequency of light matches frequency at which electrons in the atoms of
the material vibrate, electrons absorb the energy of the light.
Somatosenstation
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Somatosensation
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o The perception of touch, pressure, temperature, and pain sensations from the skin
and internal organs
o Question: how does somatosensation contribute to our ability to interact with the
environment and experience sensations like warmth, pain, and texture?
Proprioception
o (or kinesthesia) is the sense through which we perceive the position and
movement of our body, including our sense of equilibrium and balance, senses
that depend on the notion of force.
Cutaneous Senses
o Pain, mechanical touch, and temperature
Primary Somatosensory Cortex (S1)
o Cortex codes for the physical space of the body
o Adjacent regions of cortex represent adjacent regions of the body
o Regions with good acuity (small receptive fields) undergo LESS summation in S1
Neurons
Cortical Plasticity: Phantom Limb Syndrome
o Perception of a limb that is not present
 Relation to S1: after limb amputation, the sensory inputs that used to come
from the missing limb are no longer present. This absence of input can
lead to cortical reorganization in S1. The neurons in S1 that previously
responded to stimuli from the missing limb may start to respond to inputs
from nearby areas or adjacent body parts.
 Treatments for PLS: Mirror therapy for example aims to rewire the brain’s
perception of the missing limb by engaging cortical plasticity.
 Cortical plasticity in monkeys to use certain fingers – The regions devoted
to trained fingers have a larger region after training.
Receptive Fields & Acuity
o Receptive fields: The area on the skin that, when stimulated, influences the firing
rate of a cortical neuron
o Acuity: ability to discriminate fine details in touch or sensory perception
 good acuity has the smallest receptive fields because there is less
summation – larger summation on larger parts of body such as forearm
compared to finger tip.
Homunculus
o Visual representation of the somatosensory cortex, with body parts scaled
according to their sensory importance and representation in the cortex.
o Most sensitive areas have a larger representation
 Ex: lips, ears, hands
Some more practice questions
1. During the pandemic, there has been discussion around "zoom fatigue" or "zoom burnout",
especially in school settings. Students, faculty, and staff have reported difficulty directing
attention like they normally do in a face-to-face scenario. Based on our lectures on attention
and awareness, what is one hypothesis that might be able to explain this "zoom" related
phenomenon?
2. In a class example, students stared at a blue screen which was then switched to a white screen.
Some students reported the perception of an orange hue upon presentation of a white screen.
Please explain this perceptual phenomenon of seeing an orange hue and why it occurs. Draw a
graph(s) that depicts the responses of cones within this phenomenon to support your answer.
a. The eye has cone cells that detect color: S cone (blue), M cone (green, and L cone
(red). When you stare at blue light, the S cone gets fatigued and responds less.
When you switch to white light, all cone types respond, but this fatigued S cone
respond weakly. The M and L cones respond normally which creates an
imbalance that creates an orange perception. Orange is red and green with less
blue.
b.
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c.
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L
d. Intensity|
M
e.
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f.
| S
g.
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h.
+-------------------->
i.
Blue White
j.
Time
3. How does the photo-transduction process in the retina contribute to our ability to perceive and
distinguish different colors? Discuss the role of cone cells and their visual pigments in color
vision
a. The retina has rods (detect light/dark) and cones (color). There are 3 types of
cones: S (blue), M (green), L (red) that are sensitive to different wavelengths of
light. Different wavelengths of light activate these cone types in different
combinations. The brain interprets the mix of activation among the red, green,
and blue cones which helps perceive color.
4. Differentiate between the mechanisms of vision correction in LASIK surgery and cataract
surgery. How do these procedures target different aspects of vision problems?
a. Lasik corrects refractive errors and reshapes the cornea to improve how light
focuses on the retina. it helps correct nearsighted (myopia), farsighted
(hyperopia) and astigmatism.
b. Cataract surgery treats clouding of the eye’s natural lens by removing the lens
and replacing it with an intraocular lens.
c. Lasik targets cornea for refractive corrections and cataract replaces the entire
lens when it degrades (with age)
5. What is the primary visual pigment found in rod cells, and how does its activation lead to the
generation of neural signals in response to light stimulation?
a. Rods contain rhodopsin that consists of opsin bound to retinal. When rhodopsin
absorbs light, it changes its shape (isomerization). This causes sodium levels to
decrease and close their gates. This causes the rod to become hyperpolarized in
response to light. The level of hyperpolarization is proportional to the amount of
light absorbed by rhodopsin. The hyperpolarization signal from rods then gets
transmitted to other neurons for further visual processing which is how rod
activation by rhodopsin initiates the neural encoding of light.
6. How does the photo-transduction process in the retina relate to common vision disorders such
as retinitis pigmentosa? Explain how disruptions in this process can impact vision.
a. Retinitis pigmentosa is the most common form of RP and is a rod-cone
dystrophy, in which the first symptom is night blindness, followed by progressive
loss in the peripheral visual field in daylight and eventually leading to blindness.
When a rod deteriorates, the retina loses its ability to transduce light through
photo-transduction which impairs vision through defects in visual pigments,
signaling through the process and ion channels.
7. What is the main difference between color consistency and color perception? Provide examples
to illustrate each concept.
a. Color consistency is a measure of how a color appears under different
conditions, while color perception is the experience of how an individual
perceives and interprets color, which varies.
b. Color consistency ex: high-quality paint is considered good if it appears the same
shade of red under daylight and light bulbs.
c. Color perception ex: color blindness where individuals have a deficiency in
perceiving certain colors due to lack of a specific cone. Their color perception is
different from those with normal color vision, even though the colors themselves
remain consistent.
8. What distinguishes area MT from Area V1 in terms of their specialization and processing of
visual information? Provide examples to illustrate their functions
a. V1:
i. Processes basic visual features such as colors, lines, edges, depth
ii. Small receptive fields
iii. EX: detect the presence of a line or edge in visual field
b. MT:
i. Higher in visual processing
ii. Motion signals and patterns of motion – direction, speed, and coherent
motion
iii. Larger receptive fields
iv. Ex: Direction and speed of a moving car across visual field
9. If posterior parietal cortex is lesioned, patients may exhibit:
a. Abnormal pupillary reflex
b. Unconscious ability to perceive objects in space
c.
Unilateral neglect
d. Inattentional Blindness
10. If primary visual cortex is lesioned, patients may exhibit:
a.
Abnormal pupillary reflex
b. Inattentional Blindness
c. Awareness of sight
d. Blindsight
11. In Phototransduction, the process in which retinal changes its shape is called _____________.
This process allows for indirect _____________.
a. Depolarization; Isomerization
b. Isomerization; Depolarization
c. Isomerization; Hyperpolarization
d. Hyperpolarization; Isomerization
How does Light/Dark adaptation differ from Focal Adaptation (focusing on the fovea)? Make
sure to explain the regions of the eye involved and the role that each form of adaption plays in
vision. -- Light/dark adaptation affects the entire retina, adjusting overall sensitivity to light
levels, while focal adaptation specifically tunes the fovea's sensitivity and acuity for central
visual tasks like reading or recognizing fine details.
7. Cats do not have a fovea! What role does the fovea play in visual perception and how does the
lack of a fovea in the cat impact their visual perception-- The fovea is a part of the eye that is
responsible for sharp central vision and detailed perception of colors and shapes. Cats, lacking a
fovea, may have reduced ability to see fine details and may rely more on motion and peripheral
vision for hunting and navigating their environment.
12. What cellular connections form the receptive field of a retinal ganglion cell? Make sure to
define a receptive field in your answer.
a. A recpetive field is the region of sensory space in which the presence of a
stimulus will alter the firing rate of a particular neuron. The receptive field of a
RGC is formed by the connections it receives from bipolar cells, which in turn
receive input from photoreceptors (rods and cones) in the retina. Specifically,
photorecptors (rods and cones) transduce light signals into electrical signals.
Bipolar cells receive EPSPs from photoreceptors within the center of their
receptive field. They increase their firing rates for light in their receptive field
center, but decrease firing in the surround. This allows them to detect contrasts
and edretinges.
\
How does top-down attentional control differ from bottom-up attentional control?
-- rods hyperpolarize (stop releasing glutamate) to levels of light
-- Cones hyperpolarize (stop relasing glutamate) to different colors (specific wavelengths)